JP7632269B2 - Gas engine control device and program - Google Patents

Description

The disclosure in this specification relates to a control device and a program for a gas engine.

In gas engines that use gas fuels such as compressed natural gas (CNG) and hydrogen, a technique for injecting gas fuel from a fuel injection valve into the combustion chamber is known in which the gas fuel is injected during the intake stroke and the compression stroke (see, for example, Patent Document 1). In this case, the filling efficiency of the combustion chamber can be increased by injecting the gas fuel during the compression stroke as much as possible.

Patent No. 4196733

However, if gas fuel is injected as early as possible during the compression stroke, the time for mixture formation is reduced, raising concerns that the homogeneity of the mixture in the combustion chamber may decrease. Also, one possible cause of the decrease in homogeneity of the mixture in the combustion chamber is the in-cylinder flow caused by the inflow of fresh air into the combustion chamber. If the homogeneity of the mixture decreases, there are concerns that it may lead to a decrease in thermal efficiency due to increased unburned losses and a worsening of exhaust emissions. Therefore, technology to improve the homogeneity of the mixture is desirable.

The present invention has been made in consideration of the above circumstances, and aims to provide a control device and program for a gas engine that can improve the homogeneity of the mixture in the combustion chamber.

In order to solve the above problems, the control device for a gas engine according to the present invention comprises:
The present invention is applied to a gas engine including a piston that reciprocates in a cylinder and a fuel injection valve that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber, the gas fuel injected from the fuel injection valve being combusted in the combustion chamber,
a calculation unit that calculates a homogeneity indicating a degree of homogeneity of a mixture of air and the gas fuel injected from the fuel injection valve in the combustion chamber as a homogeneity estimated value;
a control unit that controls at least one of a fuel injection timing and a fuel pressure of the fuel injection valve based on the homogeneity estimation value calculated by the calculation unit;
The present invention is characterized by comprising:

In a gas engine, the combustion state varies depending on the homogeneity of the mixture of gas fuel and air in the combustion chamber. The homogeneity of the mixture also varies depending on injection conditions such as fuel injection timing and fuel pressure. Focusing on this point, the homogeneity indicating the degree of homogeneity of the mixture of gas fuel and air injected from a fuel injection valve in the combustion chamber is calculated as a homogeneity estimate value, and at least one of the fuel injection timing and fuel pressure of the fuel injection valve is controlled based on the homogeneity estimate value. In this case, by controlling the fuel injection timing and fuel pressure, the degree of swirl and the mixing time of the gas fuel injected from the fuel injection valve into the combustion chamber when it swirls up from the top surface of the piston are appropriately changed, and the homogeneity in the combustion chamber can be optimized. This allows the gas fuel to be burned appropriately in the gas engine.

The homogeneity of the mixture also depends on the variation in the mixture within the combustion chamber, and the smaller the variation in the mixture within the combustion chamber, the higher the homogeneity. The homogeneity of the mixture also depends on the variation in the concentration distribution of the gas fuel within the combustion chamber, and the smaller the variation in the concentration distribution within the combustion chamber, the higher the homogeneity.

Another invention relating to a gas engine control device is:
The present invention is applied to a gas engine including a piston that reciprocates in a cylinder and a fuel injection valve that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber, the gas fuel injected from the fuel injection valve being combusted in the combustion chamber,
a homogeneity determination unit that determines whether the interior of the combustion chamber is in a predetermined low homogeneity state, which is a state in which a homogeneity indicating a degree of homogeneity of a mixture of air and the gas fuel injected from the fuel injection valve is reduced;
a control unit that controls at least one of a fuel injection timing and a fuel pressure of the fuel injection valve in order to increase the degree of homogeneity when it is determined that the low homogeneity state has occurred;
The present invention is characterized by comprising:

In the above configuration, it is determined whether the inside of the combustion chamber will enter a predetermined low homogeneity state in which the degree of homogeneity of the mixture of gas fuel injected from the fuel injection valve and air decreases, and if it is determined that the low homogeneity state will occur, at least one of the fuel injection timing and fuel pressure of the fuel injection valve is controlled to increase the homogeneity. In this case, by controlling the fuel injection timing and fuel pressure, the degree of swirl and mixing time of the gas fuel injected from the fuel injection valve into the combustion chamber when it swirls up from the top surface of the piston are appropriately changed, and the homogeneity in the combustion chamber can be optimized. This allows the gas fuel to be burned appropriately in the gas engine.

In addition, the invention relating to the fuel injection valve is as follows:
A fuel injection valve for gas fuel that is used in a four-stroke reciprocating engine having a piston that reciprocates in a cylinder and that directly injects gas fuel into a combustion chamber, comprising:
the engine has an intake port and an exhaust port, and generates an in-cylinder flow including a vertical swirl component in the combustion chamber by air flowing in from the intake port during an intake stroke;
The tip of the injection valve is provided with an injection part for injecting gas fuel,
the injection portion has a plurality of injection holes, and the plurality of injection holes are provided so as to inject fuel in a direction away from a central axis of the injection valve,
The present invention is characterized in that the state of the jet of gas fuel injected from each of the nozzle holes is determined according to the positions of the intake port and the exhaust port and the direction of injection of the gas fuel from each of the nozzle holes so that the penetration force of the jet of gas fuel injected from each of the nozzle holes in the combustion chamber is equal to each other.

When gas fuels such as CNG or hydrogen are used in engines, the efficiency of filling the combustion chamber can be increased by injecting the gas fuel during the compression stroke as much as possible. However, by injecting during the compression stroke, the time for mixture formation is reduced, which raises concerns about reduced homogeneity. In addition, when fresh air flows into the combustion chamber from the intake port during the intake stroke, different types of in-cylinder flows occur in the intake port side area and the exhaust port side area in the combustion chamber, which may also result in reduced homogeneity. Specifically, in the combustion chamber, a vertical swirl component of in-cylinder flow occurs downward (from the head side to the top of the piston) in the exhaust port side area, and a vertical swirl component of in-cylinder flow occurs upward (from the top of the piston to the head side) in the intake port side area, which may cause variations in the homogeneity of the mixture in the combustion chamber.

In this regard, in the above configuration, multiple nozzle holes are provided in the injection section at the tip of the injection valve so that fuel is injected in a direction away from the central axis of the injection valve, making it possible to inject gas fuel in a highly dispersed state. In addition, the state of the gas fuel jet injected from each nozzle hole is determined according to the positions of the intake port and exhaust port and the direction of gas fuel injection from each nozzle hole, so that the penetration force of the gas fuel jets injected from each nozzle hole in the combustion chamber is equal to each other regardless of the in-cylinder flow occurring in the combustion chamber. As a result, it is possible to improve the homogeneity of the mixture in the combustion chamber.

Another invention relating to a fuel injection valve is:
A fuel injection valve for gas fuel used in a four-stroke reciprocating engine having a piston that reciprocates in a cylinder, the fuel injection valve being disposed at a position offset to an intake side or an exhaust side in a combustion chamber and directly injecting gas fuel into the combustion chamber,
The engine has an intake port and an exhaust port, and generates an in-cylinder flow including a vertical swirl component in the combustion chamber by air flowing in from the intake port during an intake stroke, and an ignition plug is provided at a position that is a center of an upper surface of the combustion chamber,
The tip of the injection valve is provided with an injection part for injecting gas fuel,
the injection portion has a plurality of injection holes, and the plurality of injection holes are provided so as to inject fuel in a direction away from a central axis of the injection valve,
when the inside of the combustion chamber is divided into two regions, an area on the exhaust port side being a first region and an area on the intake port side being a second region, the plurality of injection holes include a first injection hole which injects gas fuel toward the first region side of the first region side and a second injection hole which injects gas fuel toward the second region side,
The first and second nozzle holes have different injection energy states of the gas fuel injected, the injection energy of the gas fuel injected from the first nozzle hole is stronger than the injection energy of the gas fuel injected from the second nozzle hole, and the penetration force of the jets of gas fuel injected from the first and second nozzle holes in the combustion chamber is proportional to the travel distance of the gas fuel from each nozzle hole to the spark plug.

In a fuel injection valve arranged at an offset position toward the intake side or exhaust side in the combustion chamber, in order to improve the homogeneity of the mixture, it is desirable to consider that the jet from each nozzle hole is affected by the flow in the cylinder, and that the time required for the jet from each nozzle hole to reach the ignition plug differs after it hits the upper surface of the piston and rolls up. In this regard, the injection energy of the gas fuel injected from the first nozzle hole is made stronger than the injection energy of the gas fuel injected from the second nozzle hole, and the penetration force of the jet of gas fuel injected from the first nozzle hole and the second nozzle hole in the combustion chamber is made proportional to the travel distance of the gas fuel from each nozzle hole to the ignition plug. In this way, it is possible to improve the homogeneity of the mixture in the combustion chamber while considering that the jet from each nozzle hole is affected by the flow in the cylinder and that the time required for the jet from each nozzle hole to reach the ignition plug differs.

FIG. 1 is a diagram showing an overview of an engine system. FIG. 2 is a diagram showing the arrangement of openings, fuel injection valves, and the like in a cylinder head. FIG. 4 is a flowchart showing a procedure of fuel injection control. FIG. 4 is a diagram for explaining a flow inside a cylinder. 4 is a diagram for explaining the effect of an in-cylinder flow on a jet of gas fuel; FIG. 4 is a diagram for explaining the configuration of each nozzle hole. 13 is a diagram showing a state in which the penetration force of the jet of gas fuel is equal regardless of the flow inside the cylinder. FIG. FIG. 4 is a diagram for explaining the configuration of each nozzle hole. FIG. 6 is a diagram for explaining the configuration of each injection hole in a modified example of the first embodiment. 13A and 13B are diagrams for explaining the influence of an in-cylinder flow on a jet of gas fuel in the second embodiment. FIG. 4 is a diagram for explaining the configuration of each nozzle hole. FIG. 13 is a diagram showing the trajectory of a jet in a combustion chamber in the third embodiment. 4 is a diagram for explaining the effect of an in-cylinder flow on a jet of gas fuel; 13 is a diagram showing a state in which the penetration force of the jet of gas fuel is equal regardless of the flow inside the cylinder. FIG. FIG. 13 is a configuration diagram of a control system according to a fourth embodiment. FIG. 13 is a block diagram for explaining a method for calculating a homogeneity estimate value. FIG. 13 is a relationship diagram for calculating a homogeneity estimate value. FIG. 13 is a relationship diagram for calculating a homogeneity estimate value. FIG. 13 is a relationship diagram for calculating a homogeneity estimate value. 4 is a flowchart showing a procedure of fuel injection control. 4 is a time chart for explaining fuel injection timing. FIG. 4 is a diagram showing the relationship between the injection start timing and the filling efficiency. FIG. 13 is a diagram showing an estimated homogeneity value corresponding to the injection start timing. 13 is a flowchart showing a procedure of fuel injection control in the fifth embodiment. FIG. 4 is a diagram showing an estimated homogeneity value corresponding to fuel pressure. 13 is a flowchart showing a procedure of fuel injection control in the sixth embodiment. FIG. 13 is a diagram showing an estimated homogeneity value corresponding to the injection start timing. 13 is a flowchart showing a procedure of fuel injection control in the seventh embodiment. 10 is a flowchart showing a procedure of fuel injection control in a modified example. FIG. 10 is a diagram for explaining a form of fuel injection in a modified example.

First Embodiment
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a gas engine that uses hydrogen or CNG as a gas fuel is used as an engine in an on-board engine system. An overall schematic diagram of this system is shown in FIG.

In the engine system shown in FIG. 1, the engine 10 is a four-stroke, direct-injection, multi-cylinder engine with one combustion cycle consisting of an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. The engine 10 has a cylinder block 11 and a cylinder head 12, and a piston 13 is housed in each cylinder 11a formed in the cylinder block 11. A combustion chamber 14 is defined by the cylinder inner wall, the cylinder head 12, and the piston 13. The cylinder head 12 is formed with an intake port 15 and an exhaust port 16 that open into the combustion chamber 14. The intake port 15 and the exhaust port 16 are opened and closed by an intake valve 21 and an exhaust valve 22, respectively, which are driven by a cam (not shown). An intake pipe 23 for drawing in outside air is connected to the intake port 15, and an exhaust pipe 24 for discharging exhaust gas is connected to the exhaust port 16.

The intake pipe 23 is provided with a surge tank 25, which is provided with an intake pressure sensor 26 that detects the pressure inside the intake pipe. A throttle valve 27 is provided upstream of the surge tank 25 in the intake pipe 23. The exhaust pipe 24 is provided with a catalyst such as a three-way catalyst for purifying CO, HC, NOx, etc. in the exhaust.

A fuel injection valve 31 and an ignition plug 32 are attached to the cylinder head 12 for each cylinder 11a. The fuel injection valve 31 injects fuel supplied from a fuel supply device 40 directly into the combustion chamber 14. In the combustion chamber 14, the fuel injected from the fuel injection valve 31 is ignited by spark discharge from the ignition plug 32 and is used for combustion.

Figure 2 is a diagram showing the arrangement of openings, fuel injection valves 31, etc. in the cylinder head 12. The cylinder head 12 is provided with two intake ports 15a as openings on the combustion chamber 14 side of the intake port 15, and two exhaust ports 16a as openings on the combustion chamber 14 side of the exhaust port 16. In other words, the cylinder head 12 is provided with four openings that lead to the combustion chamber 14. The fuel injection valve 31 and the spark plug 32 are provided in the center of the top surface of the combustion chamber 14.

Returning to the explanation of FIG. 1, the fuel injection valve 31 is connected to a fuel container 36 via a fuel pipe 35. Gas fuel is stored in the fuel container 36 under high pressure. The fuel pipe 35 is provided with an adjustment valve 37, such as a pressure reducing valve, a main stop valve, and a shutoff valve, that adjusts the fuel supply from the fuel container 36, and a fuel pressure regulator 33 that adjusts the pressure (fuel pressure) of the gas fuel supplied to the fuel injection valve 31. The pressure reducing valve reduces the fuel pressure to a predetermined set pressure (e.g., 3.0 MPa) when the gas fuel supplied from the fuel container 36 becomes abnormally high pressure. The main stop valve and the shutoff valve allow and shut off the flow of gas fuel in the fuel pipe 35. The fuel pressure regulator 33 adjusts the fuel pressure, for example, within a range of 1 to 3 MPa.

As is well known, the ECU 80 is an electronic control device mainly composed of a microcomputer including a CPU, ROM, RAM, etc., and performs various controls of the engine 10 according to the engine operating state at each time by executing various control programs stored in the ROM. Specifically, the ECU 80 inputs various detection signals from the intake pressure sensor 26 and a rotation speed sensor (not shown), etc., and controls the operation of the fuel injection valve 31 and the spark plug 32 based on the detection signals.

Next, the configuration of the fuel injection valve 31 will be described. Figure 3 is a cross-sectional view of the fuel injection valve 31.

As shown in FIG. 3, the fuel injection valve 31 has a first needle 41, a second needle 42, and a body 43 that houses the needles 41, 42. A movable core 44 is fixed to the first needle 41, and the first needle 41 and the movable core 44 are biased downward in the figure by a spring 45. In this case, the first needle 41 is biased in a direction to abut against a first valve seat 43a formed in the body 43, that is, in a direction to block the fuel passage 46 in the body 43 by the first needle 41. The fuel injection valve 31 also has a solenoid coil 48, and when the solenoid coil 48 is energized, the first needle 41 and the movable core 44 can move upward in the figure against the biasing force of the spring 45.

A cylindrical tube 51 is fixed to the tip of the body 43, and the second needle 42 is housed in the body 43 between the first needle 41 and the tube 51. The second needle 42 is biased by a spring 52 toward the upper side of the figure, that is, in a direction in which it abuts against a second valve seat 43b formed on the body 43. The first needle 41 and the second needle 42 are provided spaced apart from each other in the axial direction, and an intermediate chamber 53 is formed between the needles 41, 42.

A cap 61 is attached to the tip of the body 43 at a position that blocks the passage 51a inside the cylinder 51, as an injection part. The cap 61 has a bulging part 61a that bulges out in a substantially hemispherical shape, and multiple injection holes 62 are provided in the bulging part 61a. This gives the fuel injection valve 31 a multi-hole structure. Each injection hole 62 is provided so that fuel is injected in a direction away from the central axis J of the fuel injection valve 31, that is, so that fuel is injected in a radial direction.

When the solenoid coil 48 is not energized, the first needle 41 is seated on the first valve seat 43a and the fuel passage 46 is blocked. The second needle 42 is held in a seated state on the second valve seat 43b. As a result, the fuel injection valve 31 is held in a state where fuel injection is stopped. On the other hand, when the solenoid coil 48 is energized, the first needle 41 is lifted off the first valve seat 43a and fuel flows into the intermediate chamber 53. In this case, the pressure of the fuel that has flowed into the intermediate chamber 53 causes the second needle 42 to move downward in the figure, so that the second needle 42 is lifted off the second valve seat 43b and fuel flows downstream of the second needle 42. As a result, fuel is injected from the nozzle hole 62 of the cap 61.

Here, an overview of the fuel injection control performed by the ECU 80 will be explained using the flowchart in Figure 4.

In FIG. 4, in step S11, the fuel injection amount is determined based on the engine speed and the required torque using the injection amount map. In step S12, the injection period (the period during which the fuel injection valve 31 is energized) is determined based on the fuel injection amount and the pressure of the gas fuel supplied to the fuel injection valve 31. In step S13, the injection start time is determined. At this time, the injection start time is set to a more advanced time within the range where the filling efficiency is equal to or greater than a predetermined value, taking into account the sensitivity of the filling efficiency to the injection start time. In step S14, the injection end time is determined. At this time, the injection end time is determined based on the injection period and injection start time determined in steps S12 and S13 within a range within a predetermined upper limit injection end time. The upper limit injection end time is the most retarded injection end time determined from the limit at which injection is possible with respect to the rise in cylinder pressure during the compression stroke, and is preferably set based on the cylinder pressure and injection pressure.

Then, in step S15, it is determined whether the actual injection amount actually injected from the fuel injection valve 31 matches the fuel injection amount (target injection amount) calculated in step S11. Specifically, the actual injection amount is calculated based on the detection value of the A/F sensor provided in the exhaust pipe 24 and the measurement value of the fuel flow meter provided in the fuel pipe 35, and it is determined whether the actual injection amount matches the target injection amount depending on whether the difference between the actual injection amount and the target injection amount is equal to or less than a predetermined value. At this time, if the actual injection amount matches the target injection amount, the process proceeds to step S20. On the other hand, if the actual injection amount does not match the target injection amount, the process proceeds to step S16, where the injection timing is reset.

In step S16, a correction value for the injection end timing is calculated to resolve a state in which the actual injection amount is insufficient relative to the target injection amount, or a state in which the actual injection amount exceeds the target injection amount. Specifically, a correction value for correcting the injection end timing to the retard or advance side is calculated based on the difference between the actual injection amount and the target injection amount. At this time, the larger the difference between the actual injection amount and the target injection amount, the larger the correction value that is calculated. The correction value may also be calculated based on the fuel pressure, and the higher the fuel pressure, the smaller the correction value. The correction value may be a predetermined fixed value.

In step S17, it is determined whether the injection end time corrected using the correction value calculated in step S16 exceeds the upper limit injection end time. If the corrected injection end time exceeds the upper limit injection end time, the process proceeds to step S18, where the upper limit injection end time is set as the injection end time for the current fuel injection. If the corrected injection end time does not exceed the upper limit injection end time, the process proceeds to step S19, where the corrected injection end time is set as the injection end time for the current fuel injection.

In step S20, the fuel injection valve 31 is energized based on the injection start and end times determined as described above, and fuel injection is performed.

In a gas engine that uses gas fuel as fuel, it is desirable to inject fuel during the compression stroke as much as possible to increase the filling efficiency in the combustion chamber 14. However, when fuel is injected during the compression stroke, it is considered that the homogeneity may decrease due to the shortening of the time for mixture formation and the inflow of fresh air during the intake stroke, which causes in-cylinder flow. Therefore, in the fuel injection valve 31 of this embodiment, the state of the jet of gas fuel injected from each injection hole 62 is determined according to the positions of the intake port 15 and the exhaust port 16 and the direction of injection of gas fuel from each injection hole 62, and this makes the penetration force of the jet of gas fuel injected from each injection hole 62 in the combustion chamber 14 equal to each other, thereby making it possible to improve the homogeneity of the mixture. Below, the in-cylinder flow in the combustion chamber 14 and the new configuration of the fuel injection valve 31 that takes the in-cylinder flow into consideration will be described in detail. Note that the penetration force of the jet means the force that takes into account the influence of external disturbances (in-cylinder flow).

First, the flow inside the cylinder will be explained with reference to Figure 5. In the following explanation, the combustion chamber 14 is divided into two, with the area on the exhaust port 16 side being the first area R1 and the area on the intake port 15 side being the second area R2.

As shown in FIG. 5(a), during the intake stroke, fresh air flows from the intake port 15 into the combustion chamber 14 as the intake valve 21 opens. At this time, the fresh air flows from the intake port 15 into the combustion chamber 14 through the gap created by the open intake valve 21 as the piston 13 moves downward, and flows downward in the figure along the inner wall of the first region R1 of the combustion chamber 14.

Also, as shown in FIG. 5(b), during the compression stroke, the upward movement of the piston 13 with the intake valve 21 and exhaust valve 22 closed causes the in-cylinder flow that occurs during the intake stroke to move downward in the figure to be pushed up by the upper surface of the piston, generating a vertically swirling in-cylinder flow. Note that FIG. 5 only shows the vertically swirling component of the in-cylinder flow, but the in-cylinder flow also includes a horizontally swirling component, that is, a swirling component in the circumferential direction of the cylinder.

Next, the effect of the in-cylinder flow on the gas fuel jet will be specifically described. Figure 6(a) shows the effect of the in-cylinder flow on the gas fuel jet in the first half of the compression stroke, and Figure 6(b) shows the effect of the in-cylinder flow on mixture formation in the second half of the compression stroke. Note that Figures 6(a) and (b) assume that the fuel injection valve 31 has multiple injection holes 62 all of the same shape, and that fuel is injected radially from each injection hole 62.

6A, the gas fuel is injected from each nozzle hole 62 of the fuel injection valve 31 in a radial direction, thereby dispersing the gas fuel in the combustion chamber 14. However, the high dispersion of the gas fuel reduces the penetration force of the jet in each nozzle hole 62, and the jet is further affected by the flow in the cylinder, resulting in a difference in the penetration force of the jet in the first region R1 and the second region R2. In detail, in the combustion chamber 14, a vertical swirling component of the flow in the cylinder occurs downward (from the head side to the piston top side) in the first region R1, and an upward (from the piston top side to the head side) in the second region R2. Therefore, the penetration force of the jet is weakened in the first region R1, while the penetration force of the jet is strengthened in the second region R2, resulting in an unbalanced roll-up of each jet after the piston collision.

As a result, as shown in FIG. 6(b), there is variation in the homogeneity of the mixture when it is formed in the combustion chamber 14.

In this embodiment, the injection energy of the gas fuel injected from each nozzle hole 62 is appropriately set taking into account the in-cylinder flow occurring in the combustion chamber 14, and the specific configuration is described in FIG. 7.

7, (a) is a diagram showing the arrangement of each nozzle hole 62 in the cap 61 at the tip of the injection valve, and (b) is a vertical cross-sectional view of the cap 61. In each of these figures, the cap 61 has four nozzle holes 62 arranged evenly in the circumferential direction, and among these nozzle holes 62, the nozzle hole 62 that injects gas fuel toward the first region R1 in the combustion chamber 14 is called the first nozzle hole 62A, and the nozzle hole 62 that injects gas fuel toward the second region R2 is called the second nozzle hole 62B. In addition, the nozzle hole 62 other than the first nozzle hole 62A and the second nozzle hole 62B is called the third nozzle hole 62C. Note that the opening shape of each nozzle hole 62 in the direction perpendicular to the axial direction is a perfect circle. However, the opening shape of each nozzle hole 62 may be an ellipse that is long in the radial direction of the injection valve tip, or an ellipse that is long in the circumferential direction.

In the configuration shown in FIG. 7, the first nozzle hole 62A and the second nozzle hole 62B each have a uniform opening area from the inlet side to the outlet side, and the opening area relationship is such that the opening area of the first nozzle hole 62A is greater than the opening area of the second nozzle hole 62B. As a result, the first nozzle hole 62A has a larger injection amount per unit time than the second nozzle hole 62B. In this case, since the injection energy of the gas fuel injected from each nozzle hole 62 is proportional to the mass and the square of the speed of the object, the injection energy of the gas fuel injected from the first nozzle hole 62A is stronger than the injection energy of the gas fuel injected from the second nozzle hole 62B.

The third nozzle hole 62C is a nozzle hole 62 for injecting fuel in a direction along the boundary between the first region R1 and the second region R2 in the combustion chamber 14. The third nozzle hole 62C has a uniform opening area from the inlet side to the outlet side, and the relationship of the opening areas is opening area of the first nozzle hole 62A > opening area of the third nozzle hole 62C > opening area of the second nozzle hole 62B. As a result, the injection energy of the gas fuel injected from the third nozzle hole 62C is weaker than the injection energy of the gas fuel injected from the first nozzle hole 62A, and stronger than the injection energy of the gas fuel injected from the second nozzle hole 62B.

The fuel injection valve 31 is assembled in the cylinder head 12 of the engine 10 so that the first nozzle hole 62A injects gas fuel toward the first region R1 on the exhaust port 16 side, the second nozzle hole 62B injects gas fuel toward the second region R2 on the intake port 15 side, and the third nozzle hole 62C injects gas fuel in a direction along the boundary between the first region R1 and the second region R2.

According to the fuel injection valve 31 having the configuration shown in FIG. 7, as shown in FIGS. 8(a) and (b), the penetration force of the jets of gas fuel injected from each nozzle hole 62 in the combustion chamber 14 is equal to each other, making it possible to form a highly homogeneous mixture. In this case, by increasing the injection energy of the first nozzle hole 62A and decreasing the injection energy of the second nozzle hole 62B, the penetration force F1 of the jet from the first nozzle hole 62A and the penetration force F2 of the jet from the second nozzle hole 62B are equal.

The configuration of each nozzle hole 62 can be changed from that shown in FIG. 7 to that shown in FIG. 9. In the configuration shown in FIG. 9, there are four nozzle holes, and the first nozzle hole 62A injects gas fuel toward the first region R1, the second nozzle hole 62B injects gas fuel toward the second region R2, and the third nozzle hole 62C injects gas fuel in a direction along the boundary between the regions R1 and R2.

In the configuration shown in FIG. 9, the first nozzle hole 62A and the second nozzle hole 62B each have a tapered structure, and the first nozzle hole 62A is an inverse tapered type that is narrowed from the inlet side to the outlet side, and the second nozzle hole 62B is a tapered type that is widened from the inlet side to the outlet side. As a result, the injection speed of the gas fuel is higher in the first nozzle hole 62A than in the second nozzle hole 62B. In this case, since the injection energy of the gas fuel injected from each nozzle hole 62 is proportional to the mass and the square of the speed of the object, the injection energy of the gas fuel injected from the first nozzle hole 62A is stronger than the injection energy of the gas fuel injected from the second nozzle hole 62B.

The third nozzle hole 62C has a non-tapered structure in which the opening area is uniform from the inlet side to the outlet side, so that the injection energy of the gas fuel injected from the third nozzle hole 62C is weaker than the injection energy of the gas fuel injected from the first nozzle hole 62A and is stronger than the injection energy of the gas fuel injected from the second nozzle hole 62B.
is.

In the configuration shown in FIG. 9, as shown by the dashed line, it is preferable that the opening areas of the first injection hole 62A and the second injection hole 62B are equal at the intermediate position of 1/2 in the thickness direction of the cap 61 (bulge portion 61a). It is preferable that the opening areas of each injection hole 62A, 62B at this intermediate position are the same as the opening area of the third injection hole 62C. However, it is also possible to configure the opening areas of the outlet side of the first injection hole 62A and the second injection hole 62B to be equal to each other.

Even in the fuel injection valve 31 having the configuration shown in Figure 9, as shown in Figures 8(a) and (b), the penetration force of the gas fuel jets injected from each nozzle hole 62 in the combustion chamber 14 can be made equal to each other, making it possible to form a highly homogeneous mixture.

The present embodiment described above provides the following excellent effects:

The cap 61 (injection part) at the tip of the injection valve is provided with multiple injection holes 62 so that fuel is injected in a direction away from the injection valve central axis J, making it possible to inject gas fuel in a highly dispersed state. In addition, the state of the gas fuel jet injected from each injection hole 62 is determined according to the positions of the intake port 15 and exhaust port 16 and the direction of gas fuel injection from each injection hole 62, so that the penetration force of the gas fuel jet injected from each injection hole 62 in the combustion chamber 14 is equal to each other regardless of the in-cylinder flow occurring in the combustion chamber 14. This makes it possible to improve the homogeneity of the mixture in the combustion chamber 14, and thus suppresses the decrease in thermal efficiency and the deterioration of exhaust emissions due to an increase in unburned loss.

In the first nozzle hole 62A that injects gas fuel toward the first region R1 on the exhaust port 16 side, the momentum of the jet is attenuated by the vertical swirl component of the in-cylinder flow, while in the second nozzle hole 62B that injects gas fuel toward the second region R2 on the intake port 15 side, the momentum of the jet is amplified by the vertical swirl component of the in-cylinder flow. Taking this into consideration, the injection energy of the gas fuel injected from the first nozzle hole 62A is made stronger than the injection energy of the gas fuel injected from the second nozzle hole 62B. This makes it possible to improve the homogeneity of the mixture.

The injection energy of the gas fuel injected from the first nozzle hole 62A is made stronger than that of the gas fuel injected from the third nozzle hole 62C, while the injection energy of the gas fuel injected from the second nozzle hole 62B is made weaker than that of the gas fuel injected from the third nozzle hole 62C. This makes it possible to appropriately set the injection energy of the jet from each of the nozzle holes 62A to 62C while improving the high dispersion by making the cap 61 more porous.

When hydrogen is used as the gas fuel, its density is smaller than that of CNG, and the injection energy of the jet is smaller, so it is thought to be more susceptible to the effects of in-cylinder flow. In this regard, even when hydrogen is used as the gas fuel, it is possible to improve the homogeneity of the mixture in the combustion chamber 14.

(Modification of the first embodiment)
The nozzle holes 62 may be configured as shown in Figures 10(a) to 10(d), which show the arrangement of the nozzle holes 62 in a cap 61 at the tip of the injection valve.

In the configuration shown in FIG. 10(a), the first nozzle hole 62A of the first to third nozzle holes 62A to 62C has a larger opening area than the other nozzle holes 62B and 62C, thereby increasing the injection energy. The first nozzle hole 62A can also be made inverted tapered to increase the injection speed and increase the injection energy. It is preferable that the nozzle holes 62B and 62C both have a non-tapered structure and have the same injection energy.

In the configuration shown in FIG. 10(b), the second nozzle hole 62B of the first to third nozzle holes 62A to 62C has a smaller opening area than the other nozzle holes 62A, 62C, thereby weakening the injection energy. The second nozzle hole 62B can also be tapered to reduce the injection speed and weaken the injection energy. Note that both nozzle holes 62A, 62C have a non-tapered structure and preferably have the same injection energy.

In the configuration shown in FIG. 10(c), there are six nozzle holes, with two each of the first nozzle hole 62A, the second nozzle hole 62B, and the third nozzle hole 62C. As described above, the injection energy of each of these nozzle holes 62A to 62C is as follows: injection energy of first nozzle hole 62A > injection energy of third nozzle hole 62C > injection energy of second nozzle hole 62B.

In the configuration shown in FIG. 10(d), a first nozzle hole 62A and a second nozzle hole 62B are provided as the multiple nozzle holes 62. The number of each of these nozzle holes 62A and 62B may be, for example, one each, but it is also possible to provide two or more of each. The injection energy of each of these injection holes 62A and 62B is set so that the injection energy of the first nozzle hole 62A is greater than the injection energy of the second nozzle hole 62B.

Second Embodiment
Next, the second embodiment will be described, focusing on the differences from the first embodiment. In this embodiment, the direction of the vertical swirling component of the in-cylinder flow is different between the first region R1 on the exhaust port 16 side and the second region R2 on the intake port 15 side in the combustion chamber 14, but at the boundary between these regions R1 and R2, the difference in the vertical swirling component of the in-cylinder flow in the direction along the boundary is small. This will be described with reference to FIG. 11.

Figure 11(a) is a perspective view showing the configuration of cylinder 11a, in which a vertical section passing through the center position between two intake ports 15a and the center position between two exhaust ports 16a is cross section A1, and a vertical section dividing the intake side and exhaust side and perpendicular to cross section A1 is cross section A2. Figure 11(b) shows the in-cylinder flow at cross section A1, and Figure 11(c) shows the in-cylinder flow at cross section A2.

As shown in FIG. 11(b), it is assumed that fuel injection is performed at the location corresponding to cross section A1 as shown in B1 and B2. In this case, B1 and B2 are affected by the vertical swirl of the in-cylinder flow, one of which is attenuated and the other is strengthened. In contrast, as shown in FIG. 11(c), when fuel injection is performed at the location corresponding to cross section A2 as shown in C1 and C2, the influence of the vertical swirl of the in-cylinder flow on C1 and C2 is approximately the same. In other words, cross section A2 is a vertical cross section perpendicular to cross section A1, and the direction in which cross section A2 extends is along the boundary between the first region R1 and the second region R2. Therefore, unlike cross section A1, cross section A2 does not affect C1 and C2 due to the in-cylinder flow with vertical swirls in different directions.

In this embodiment, as shown in FIG. 12, the cap 61 is configured to have only injection holes 62 that inject gas fuel in a direction along the boundary between the first region R1 and the second region R2. As a result, gas fuel is injected from each injection hole 62 in the form shown in FIG. 11(c). In this embodiment, the injection energy of the gas fuel injected from each injection hole 62 is equal to each other. The configuration of this embodiment makes it possible to suppress variations in the homogeneity of the mixture caused by the flow inside the cylinder.

In addition, multiple injection holes 62 for injecting gas fuel may be provided on each of the left and right sides of FIG. 11(c). The injection holes 62 may have either a non-tapered structure or a tapered structure. If they have a tapered structure, they may be either an inverted tapered type or a tapered type.

Third Embodiment
Next, the third embodiment will be described, focusing on the differences from the first embodiment. In the first embodiment, the fuel injection valve 31 is provided at the center of the top surface of the combustion chamber 14, but in this embodiment, the fuel injection valve 31 is provided at a position offset from the center of the top surface of the combustion chamber 14 toward the intake side.

Figure 13 is a diagram showing the trajectory of the jet in the combustion chamber 14. In Figure 13, the left side of the figure is the intake side, and the right side is the exhaust side. The spark plug 32 is provided at the center of the top surface of the combustion chamber 14, and the fuel injection valve 31 (cap 61) is provided at a position offset to the intake side. In this configuration, in addition to the fact that the jet from each nozzle hole 62 is affected by the flow inside the cylinder, it is considered that the travel distance from the jet from each nozzle hole 62 to the spark plug 32 after it collides with the top surface of the piston and rolls up is different. The travel distance is, in detail, the distance that the jet travels via the top surface of the piston, along the inner wall of the cylinder and the cylinder head 12, to the position of the spark plug 32. In FIG. 13, the trajectory of the jet from the first nozzle hole 62A is T1, and the trajectory of the jet from the second nozzle hole 62B is T2. Comparing these trajectories T1 and T2, it can be seen that the gas fuel travels a longer distance to the spark plug 32 from the first nozzle hole 62A than from the second nozzle hole 62B. These factors raise concerns about a decrease in the homogeneity of the mixture.

Figure 14(a) shows the effect of the in-cylinder flow on the gas fuel jet in the first half of the compression stroke, and Figure 14(b) shows the effect of the in-cylinder flow on the mixture formation in the second half of the compression stroke. Note that Figures 14(a) and (b) assume that the fuel injection valve 31 has multiple injection holes 62 all of the same shape, and that fuel is injected from each injection hole 62 toward the first region R1, which is the region on the exhaust port 16 side, and the second region R2, which is the region on the intake port 15 side.

As shown in FIG. 14(a), in the combustion chamber 14, due to the influence of the in-cylinder flow as described above, there is a difference in the penetration force of the jets in the first region R1 and the second region R2, and the roll-up of each jet after the piston collision becomes unbalanced. Therefore, as shown in FIG. 14(b), there is variation in the homogeneity of the mixture when it is formed in the combustion chamber 14.

In this embodiment, the injection energy of the gas fuel injected from each nozzle hole 62 is appropriately set taking into account the in-cylinder flow occurring in the combustion chamber 14, and the specific configuration is similar to the configuration shown in Figure 7 or Figure 9 described above.

That is, the first nozzle hole 62A and the second nozzle hole 62B provided in the cap 61 have different opening areas or different taper structures, so that the injection energy of the gas fuel injected from the first nozzle hole 62A is stronger than the injection energy of the gas fuel injected from the second nozzle hole 62B. In addition, in terms of the configuration including the third nozzle hole 62C, the relationship of the injection energy of the gas fuel injected from each of the nozzle holes 62A to 62C is injection energy of the first nozzle hole 62A > injection energy of the third nozzle hole 62C > injection energy of the second nozzle hole 62B.

Comparing the jet from the first nozzle hole 62A and the jet from the second nozzle hole 62B, the distance traveled by each jet after colliding with the upper surface of the piston and rolling up to reach the ignition plug 32 is different. Therefore, in this embodiment, the injection energy of each nozzle hole 62A, 62B is determined taking into consideration the difference in the travel distance of the gas fuel from each nozzle hole 62A, 62B to the ignition plug 32. In this case, it is preferable that the injection energy of each nozzle hole 62A, 62B is determined so that the penetration force of the jet from each nozzle hole 62A, 62B is proportional to the travel distance of the gas fuel from each nozzle hole 62A, 62B to the ignition plug 32.

According to the fuel injection valve 31 of this embodiment, as shown in Figures 15(a) and (b), the injection energy of the first injection hole 62A is made stronger and the injection energy of the second injection hole 62B is made weaker, so that the penetration force F1 of the jet from the first injection hole 62A and the penetration force F2 of the jet from the second injection hole 62B are adjusted. In this case, the gas fuel travels a longer distance to the ignition plug 32 from the first injection hole 62A than from the second injection hole 62B, so the penetration force F1 of the jet from the first injection hole 62A is stronger than the penetration force F2 of the jet from the second injection hole 62B. This makes it possible to form a highly homogeneous mixture in the combustion chamber 14.

As a modified example of the third embodiment, the fuel injection valve 31 (cap 61) may be provided in the combustion chamber 14 at a position offset from the center of the upper surface toward the exhaust side. In this case, the injection energy of each injection hole 62A, 62B may be determined based on the fact that the travel distance of the gas fuel to the ignition plug 32 is shorter for the first injection hole 62A than for the second injection hole 62B, while taking into account the influence of the flow inside the cylinder as described above.

(Modifications of the First to Third Embodiments)
The above embodiment may be modified, for example, as follows.

- In the above embodiment, the fuel injection valve 31 is configured such that the first needle 41 and the second needle 42 are arranged axially side by side in the body 43, but is not limited to this configuration. For example, a single needle may be provided in the body 43, and when the needle opens, the fuel passage 46 in the body 43 opens and gas fuel is injected from each nozzle hole 62.

- In the above embodiment, the engine 10 is configured to generate an in-cylinder flow in the combustion chamber 14 that includes a lateral swirl component and a vertical swirl component, but the engine 10 may be configured so that no lateral swirl component is generated, or if any is generated, it is very small.

Fourth Embodiment
In this embodiment, fuel injection control is performed to increase the homogeneity of the mixture of gas fuel and air injected from the fuel injection valve 31 into the combustion chamber 14. That is, this embodiment is made with attention paid to the fact that the combustion state varies depending on the homogeneity of the mixture of gas fuel and air in the combustion chamber 14 of the engine 10, and the homogeneity of the mixture of gas fuel and air injected from the fuel injection valve 31 into the combustion chamber 14 is calculated as a homogeneity estimation value X, and the fuel injection timing of the fuel injection valve 31 is controlled based on the homogeneity estimation value X. In this embodiment, the engine system shown in FIG. 1 is used. Although not shown in FIG. 1, the engine system may have a turbocharger such as a turbocharger or a supercharger, or a variable valve mechanism that adjusts the opening and closing timing of the intake and exhaust valves.

Figure 16 is a diagram showing the configuration of the control system in this embodiment. Detection signals are sequentially input to the ECU 80 from various sensors including a rotation speed sensor 71, an air flow sensor 72, a fuel pressure sensor 73, and an in-cylinder pressure sensor 74. The rotation speed sensor 71 detects the engine rotation speed NE, and the air flow sensor 72 detects the intake air amount Qin as the engine load. The fuel pressure sensor 73 is provided in the fuel piping 35 between the fuel pressure regulator 33 and the fuel injection valve 31, and detects the fuel pressure Pf, which is the pressure of the fuel supplied to the fuel injection valve 31. The in-cylinder pressure sensor 74 is provided in the cylinder head 12, and detects the in-cylinder pressure Pc, which is the pressure inside the combustion chamber 14.

The ECU 80 controls the operation of the fuel injection valve 31, the spark plug 32, and the fuel pressure regulator 33 based on the detection signals of the above sensors. As fuel injection control, the ECU 80 calculates the fuel injection amount Qf based on the engine speed NE and the engine load (required torque or intake amount Qin), calculates the injection period Td of the fuel injection valve 31 based on the fuel injection amount Qf and the fuel pressure Pf, and performs fuel injection by the fuel injection valve 31 based on the injection period Td. In this embodiment, fuel injection is mainly performed during the compression stroke. The start of the injection period Td is the injection start time SOI, and the end of the injection period Td is the injection end time EOI. The injection start time SOI and the injection end time EOI each correspond to the "fuel injection timing".

The ECU 80 also controls the fuel pressure using the fuel pressure regulator 33 by setting a target fuel pressure Ptg based on the engine speed NE and the engine load, and performs fuel pressure feedback control so that the fuel pressure Pf (actual fuel pressure) detected by the fuel pressure sensor 73 matches the target fuel pressure Ptg. In this case, the fuel pressure Pf is controlled within a range of 1 to 3 MPa, for example.

In this embodiment, the fuel injection valve 31 has the configuration shown in FIG. 3, and the fuel injection valve 31 has a porous structure with multiple injection holes 62 at its tip. The number of injection holes 62 is, for example, four, and each injection hole 62 has the same size. Each injection hole 62 is arranged so that fuel is injected in a direction away from the central axis J of the fuel injection valve 31, i.e., radially, and toward the top surface of the piston.

According to the findings of the present inventors, the main factors that contribute to the homogeneity of the mixture in a gas engine include the jet penetration, which is the penetration (penetration force) of the gas fuel immediately after fuel injection by the fuel injection valve 31, the jet roll-up when the gas fuel rolls up from the top surface of the piston in the combustion chamber 14, and the mixing time of the gas fuel and air in the combustion chamber 14. The jet penetration is a contributing factor to the homogeneity in the period from the start of injection to the arrival of the gas fuel at the top surface of the piston when the compression stroke injection is performed by the fuel injection valve 31. The jet roll-up indicates the degree of roll-up when the gas fuel rolls up along the inner wall of the cylinder after reaching the top surface of the piston, and is a contributing factor to the homogeneity in the period from the arrival of the top surface of the piston to the end of fuel injection. The mixing time is a contributing factor to the homogeneity in the period from the end of fuel injection to the ignition timing (or TDC).

In this embodiment, the ECU 80 calculates estimated values for each of the three elements that contribute to the homogeneity of the mixture, namely, jet penetration, jet roll-up, and mixing time (jet penetration estimated value A, roll-up estimated value B, and mixing time estimated value C), and calculates a homogeneity estimated value X based on each of these estimated values. The ECU 80 then controls the fuel injection timing of the fuel injection valve 31 based on the homogeneity estimated value X.

The calculation method of the homogeneity estimation value X is explained with reference to FIG. 17. FIG. 17 is a functional block diagram related to the calculation of the homogeneity estimation value X performed by the ECU 80. As shown in FIG. 17, the ECU 80 has a first calculation unit M1 that calculates the jet penetration estimation value A, a second calculation unit M2 that calculates the roll-up estimation value B, and a third calculation unit M3 that calculates the mixing time estimation value C, and calculates the homogeneity estimation value X by adding up these respective estimation values A, B, and C (X=A+B+C).

The first calculation unit M1 calculates an estimated jet penetration value A based on a jet volume a1 indicating the size of the jet of gas fuel in the combustion chamber 14 (in the cylinder) and an in-cylinder volume a2 at the start of fuel injection. Specifically, the estimated jet penetration value A is calculated by the following formula 1.
A=k1×(a1/a2) (Formula 1)
In Equation 2, k1 is a predetermined coefficient (the same applies to k2 to k8 below).

The jet volume a1 is calculated based on the fuel pressure Pf and the fuel injection amount Qf as parameters. For example, the jet volume a1 is calculated from the fuel pressure Pf and the fuel injection amount Qf based on the relationship shown in FIG. 18(a). The jet volume a1 is calculated to be a larger value the greater at least one of the fuel pressure Pf and the fuel injection amount Qf is.

The in-cylinder volume a2 is calculated from the injection start timing SOI, for example, based on the relationship shown in FIG. 18(b). The in-cylinder volume a2 is calculated to be a larger value as the injection start timing SOI advances relative to TDC.

The estimated jet penetration value A indicates the size of the jet in the combustion chamber 14, i.e., the proportion of the in-cylinder volume that the jet occupies, and is calculated to be a larger value the higher the fuel pressure Pf (the larger the numerator term in the above formula 1) or the more retarded the injection start timing SOI is toward TDC (the smaller the denominator term in the above formula 1).

The second calculation unit M2 calculates the roll-up estimated value B by adding a jet term b1, which is a term related to the state of the jet that contributes to the roll-up of the jet, and an in-cylinder environment term b2, which is a term related to the environment inside the cylinder that contributes to the roll-up of the jet. Specifically, the second calculation unit M2 calculates the roll-up estimated value B by the following formula 2.
B=b1+b2 (Formula 2)
In other words, since the degree of jet curl can change depending on the state of the jet itself and can also change depending on the in-cylinder environment, the jet term b1 and the in-cylinder environment term b2 are calculated separately, and these terms are added together to calculate the curl-up estimated value B.

The jet term b1 is
A jet velocity contribution b11 indicating the contribution of the jet velocity to the jet roll-up;
- Extrusion contribution b12 indicating the contribution of the jet extrusion to the jet roll-up;
Based on this, it is calculated by the following formula 3.
b1=k2×b11+k3×b12 (Formula 3)
The jet velocity contribution ratio b11 is calculated from the fuel pressure Pf based on the relationship shown in Fig. 19A, for example. The jet velocity contribution ratio b11 is calculated to be a larger value as the fuel pressure Pf increases, because the jet velocity increases as the fuel pressure Pf increases.

The pushing contribution b12 is calculated based on the injection period Td, for example, based on the relationship shown in FIG. 19(b). The pushing contribution b12 is calculated to be a larger value as the injection period Td becomes longer.

Moreover, the in-cylinder environment term b2 is expressed as follows:
A travel distance contribution b21 indicating the contribution of the jet travel distance to the jet roll-up;
- A degree of contribution of the in-cylinder flow to the jet roll-up b22;
Piston up contribution b23 indicating the contribution of the piston up speed to the jet roll-up;
- A degree of contribution of the in-cylinder pressure b24 indicating the degree of contribution of the in-cylinder pressure at the time of fuel injection to the jet roll-up;
Based on this, it is calculated by the following formula 4.
b2=k4×b21+k5×b22+k6×b23+k7×b24 (Formula 4)
The jet travel distance in the combustion chamber 14 is the distance required for the jet to travel through the upper surface of the piston and the inner wall of the cylinder to reach the position of the spark plug 32, and the shorter the jet travel distance, the stronger the momentum of the jet, and therefore the greater the contribution to homogeneity. The jet travel distance varies depending on the injection start timing SOI, and the closer the injection start timing SOI is to TDC (the more retarded the timing is), the shorter the jet travel distance. The travel distance contribution b21 is calculated from the injection start timing SOI, for example, based on the relationship shown in Figure 20(a). The closer the injection start timing SOI is to TDC (the more retarded the timing is), the greater the travel distance contribution b21 is calculated to be.

The in-cylinder flow contribution b22 is calculated according to the strength of the in-cylinder flow, for example, based on the relationship shown in FIG. 20(b). The in-cylinder flow varies according to the engine rotation state and engine load, and the degree of strength of the in-cylinder flow is determined, for example, based on the engine rotation speed NE and the intake air amount Qin. In this case, the stronger the flow, the higher the engine rotation speed NE or the greater the intake air amount Qin. In addition, if the fuel injection valve 31 has a porous structure, it is considered that the weaker the in-cylinder flow, the greater the contribution of the homogeneity, and the stronger the in-cylinder flow, the smaller the contribution of the homogeneity. Taking these factors into consideration, the in-cylinder flow contribution b22 is calculated to be a larger value the weaker the in-cylinder flow, and a smaller value the stronger the in-cylinder flow.

When the fuel injection valve 31 has one nozzle hole, i.e., a single hole, the in-cylinder flow contribution b22 is calculated as a constant value regardless of the strength of the in-cylinder flow.

When the piston 13 moves upward during the compression stroke, the greater the piston rising speed, the greater the contribution of homogeneity. Also, the higher the engine speed NE, the greater the piston rising speed. Taking these factors into consideration, the piston up contribution b23 is calculated from the engine speed NE, for example, based on the relationship in FIG. 20(c). The higher the engine speed NE, the greater the piston up contribution b23 is calculated to be.

The in-cylinder pressure contribution b24 is calculated from the in-cylinder pressure Pc, for example, based on the relationship in FIG. 20(d). The higher the in-cylinder pressure Pc, the shorter the distance the jet can travel, so the in-cylinder pressure contribution b24 is calculated as a smaller value. The in-cylinder pressure Pc used here is the pressure inside the combustion chamber 14 during fuel injection, and is detected by the in-cylinder pressure sensor 74. However, if the configuration does not include the in-cylinder pressure sensor 74, the in-cylinder pressure Pc can be estimated from the intake air volume Pin, the intake temperature, the closing timing of the intake valve 21, etc.

The third calculation unit M3 calculates a mixing time estimate C based on the ignition timing IG, the injection end timing EOI, and the engine speed NE, using the following equation 5.
C=((IG[CA]-EOI[CA])×60[sec])/(NE[rpm]×360[CA]) (Formula 5)
The more advanced the injection end timing EOI is, the larger the calculated mixing time estimate C. In addition, in Equation 5, it is also possible to calculate the mixing time estimate C by using the angle period from the injection end timing EOI to TDC instead of the angle period from the injection end timing EOI to the ignition timing IG.

The ECU 80 controls the fuel injection timing of the fuel injection valve 31 based on the homogeneity estimation value X calculated as described above. In this case, the ECU 80 sets the fuel injection timing at which the homogeneity estimation value X becomes greater than a predetermined threshold as a command value for fuel injection control of the fuel injection valve 31, and causes the fuel injection valve 31 to inject fuel based on that fuel injection timing.

The fuel injection control based on the homogeneity estimation value X will be explained using the flowchart shown in FIG. 21. This process is repeatedly performed by the ECU 80 at a predetermined interval.

In step S21, various information such as operating conditions and sensor detection signals are acquired. Specifically, the engine speed NE, engine load information (required torque, etc.), fuel pressure Pf, and in-cylinder pressure Pc are acquired.

In step S22, the fuel injection amount Qf is determined based on the engine speed NE and the required torque using an injection amount map. In step S23, the injection period Td is determined based on the fuel injection amount Qf and the fuel pressure Pf.

In step S24, the SOI setting range within which the injection start timing SOI can be set is determined. This SOI setting range is explained using the time chart in FIG. 22. In FIG. 22, the advance limit (most advanced timing) for the injection start timing SOI is set to the lower limit injection start timing SOImin, and the retard limit (most retarded timing) is set to the upper limit injection start timing SOImax, and the injection start timing SOI of the fuel injection valve 31 is set within the SOI setting range from SOImin to SOImax. In FIG. 22, "IVC" is the closing timing of the intake valve 21.

Here, the efficiency of gas fuel filling the combustion chamber 14 varies depending on the injection start timing SOI, and it is considered that the filling efficiency with respect to the injection start timing SOI has the relationship shown in Figure 23. In this case, based on the relationship in Figure 23, the injection start timing SOI that is more advanced within the range in which the filling efficiency is equal to or greater than a predetermined value is set as the lower limit injection start timing SOImin.

In addition, in FIG. 22, the retard limit (most retarded timing) of the injection end timing EOI is set to the upper limit injection end timing EOImax, and the upper limit injection start timing SOImax is set based on the upper limit injection end timing EOImax and the injection period Td. The upper limit injection end timing EOImax is the most retarded injection end timing determined from the limit at which injection is possible with respect to the increase in the in-cylinder pressure during the compression stroke, and may be calculated from the fuel pressure Pf and the in-cylinder pressure Pc. However, the upper limit injection end timing EOImax may be determined as a fixed value.

The method for setting the lower injection start timing SOImin, which is the advance limit of the injection start timing SOI, and the upper injection start timing SOImax, which is the retard limit, is not limited to the above method. For example, SOImin and SOImax can also be set to predetermined fixed values.

In step S25, homogeneity estimates X corresponding to multiple injection start timings SOI are calculated within the SOI setting range (SOImin to SOImax). That is, multiple (n) candidate values for the injection start timing SOI within the SOI setting range are defined as SOI candidate values T1 to Tn, and homogeneity estimates X are calculated for each of the SOI candidate values T1 to Tn using the calculation method of FIG. 17. The number of SOI candidate values T1 to Tn is arbitrary, but it is preferable that the SOI candidate values T1 to Tn are defined in increments of 10 [CA] within the SOI setting range (SOImin to SOImax), for example.

In step S26, it is determined whether any of the homogeneity estimation values X calculated in step S25, i.e., the homogeneity estimation values X corresponding to the SOI candidate values T1 to Tn, is equal to or greater than the target value Xtg. The target value Xtg is a threshold value for determining whether the mixture in the combustion chamber 14 is in a low homogeneity state.

If the homogeneity estimate X includes any value that is equal to or greater than the target value Xtg, the process proceeds to step S27, where the most advanced injection start timing SOI among the SOI candidate values T1 to Tn at which the homogeneity estimate X is equal to or greater than the target value Xtg is set as the control command value for the injection start timing SOI. If the homogeneity estimate X does not include any value that is equal to or greater than the target value Xtg, the process proceeds to step S28, where the injection start timing SOI corresponding to the largest homogeneity estimate X among the homogeneity estimate values X is set as the control command value for the injection start timing SOI.

Using Figures 24(a) and (b), a supplementary explanation is given of the process of setting the injection start timing SOI from multiple homogeneity estimate values X for each SOI candidate value T1 to Tn. In Figure 24(a), the homogeneity estimate values X for each SOI candidate value T1 to Tn include those that are equal to or greater than the target value Xtg. In this case, the most advanced SOI candidate value T1 (lower limit injection start timing SOImin) among the SOI candidate values T1 to Tn corresponding to the homogeneity estimate value X equal to or greater than the target value Xtg is set as the control command value for the injection start timing SOI. By setting the injection start timing SOI on the most advanced side under the condition that the homogeneity estimate value X is equal to or greater than the target value Xtg, it is possible to improve thermal efficiency by increasing the in-cylinder pressure during adiabatic compression.

In addition, in FIG. 24(b), the homogeneity estimation value X for each of the SOI candidate values T1 to Tn does not include any that is equal to or greater than the target value Xtg. In other words, all of the homogeneity estimation values X are less than the target value Xtg. In this case, the SOI candidate value Tx corresponding to the largest homogeneity estimation value X among the homogeneity estimation values X is set as the control command value for the injection start timing SOI.

In step S29, the injection end timing EOI of the fuel injection control is determined based on the injection start timing SOI and the injection period Td set in steps S27 and S28.

Then, in steps S30 to S35, fuel injection is performed while making an appropriate correction according to whether or not there is an excess or deficiency in the fuel injection amount. That is, it is determined whether or not the actual injection amount actually injected from the fuel injection valve 31 matches the target injection amount (fuel injection amount Qf), and if the actual injection amount matches the target injection amount, fuel injection from the fuel injection valve 31 is performed based on the injection start timing SOI and injection end timing EOI determined as described above (step S35). If the actual injection amount does not match the target injection amount, fuel injection is performed after resetting the injection timing (steps S31 to S35). Note that the processing of steps S30 to S35 is the same as the processing of steps S15 to S20 in FIG. 4 in the first embodiment, and detailed explanations are omitted here.

The present embodiment described above provides the following excellent effects:

The homogeneity of the mixture in the combustion chamber 14 is calculated as a homogeneity estimate value X, and the fuel injection timing of the fuel injection valve 31 is controlled based on the homogeneity estimate value X. In this case, by controlling the fuel injection timing, the degree of swirl of the gas fuel injected from the fuel injection valve 31 into the combustion chamber 14 when it swirls up from the top surface of the piston and the mixing time are appropriately changed, and the homogeneity in the combustion chamber 14 can be optimized. This allows the gas fuel to be burned appropriately in the gas engine.

As a command value for fuel injection control of the fuel injection valve 31, the injection start time SOI (fuel injection time) at which the homogeneity estimate value X becomes greater than the target value Xtg is set, and fuel injection by the fuel injection valve 31 is performed based on the injection start time SOI. By such fuel injection control, the desired homogeneity can be achieved in the combustion chamber 14.

A number of SOI candidate values T1 to Tn are set as candidate values for the injection start timing SOI, a homogeneity estimate value X is calculated for each of the SOI candidate values T1 to Tn, and the injection start timing SOI is set as a control command value based on the SOI candidate value corresponding to the homogeneity estimate value X that is greater than the target value Xtg among the homogeneity estimate values X. In this case, it is possible to properly grasp the injection start timing SOI that enables improvement in homogeneity while taking into account the effect that changing the injection start timing SOI has on the homogeneity.

A number of SOI candidate values T1 to Tn are determined within an SOI setting range between the advance limit (SOImin) and retard limit (SOImax) of the injection start timing SOI, and a homogeneity estimate value X is calculated for each of the SOI candidate values T1 to Tn. The injection start timing SOI is set as a control command value based on the SOI candidate value that corresponds to the homogeneity estimate value X that is greater than the target value Xtg and is the most advanced within the SOI setting range. In this case, the homogeneity estimate value X is set to be equal to or greater than the target value Xtg, and the injection start timing SOI is set to be the most advanced, thereby improving thermal efficiency by increasing the cylinder pressure during adiabatic compression.

When all of the homogeneity estimate values X calculated for the SOI candidate values T1 to Tn are smaller than the target value Xtg, the fuel injection timing is set as a control command value based on the SOI candidate value corresponding to the largest homogeneity estimate value X among those homogeneity estimate values X. In this case, even if the desired homogeneity level is not reached, the best homogeneity can be achieved under the circumstances.

The main factors that contribute to the homogeneity of the mixture in a gas engine are considered to include the jet penetration, which is the penetration (penetration force) of the gas fuel immediately after fuel injection by the fuel injection valve 31, the jet roll-up when the gas fuel rolls up from the top surface of the piston in the combustion chamber 14, and the mixing time of the gas fuel and air in the combustion chamber 14. In addition, each of these factors varies depending on at least the fuel injection timing of the fuel injection valve 31 (injection start timing SOI, injection end timing EOI). Taking this into consideration, the homogeneity estimate value X is calculated based on the jet penetration estimate value A, the roll-up estimate value B, and the mixing time estimate value C. This allows the homogeneity estimate value X to be calculated appropriately, and ultimately optimizes the fuel injection control.

The homogeneity of the mixture in the combustion chamber 14 is considered to vary depending on the fuel injection timing of the fuel injection valve 31 (injection start timing SOI, injection end timing EOI), the fuel pressure Pf, the engine speed NE, the engine load (intake amount), and the cylinder pressure Pc. In this regard, the homogeneity estimate value X is calculated based on the fuel injection timing of the fuel injection valve 31 (injection start timing SOI, injection end timing EOI), the fuel pressure Pf, the engine speed NE, the engine load (intake amount), and the cylinder pressure Pc, so that the homogeneity of the mixture can be properly grasped.

Fifth Embodiment
In this embodiment, the pressure of the fuel injected from the fuel injection valve 31 (fuel pressure) is controlled based on the homogeneity estimation value X, and the details thereof will be described below. Note that the calculation of the homogeneity estimation value X is similar to the configuration of the fourth embodiment.

The fuel injection control based on the homogeneity estimation value X will be explained using the flowchart shown in FIG. 25. This process is repeatedly performed by the ECU 80 at a predetermined interval.

In step S41, various information such as operating conditions and sensor detection signals are acquired. Specifically, the engine speed NE, engine load information (required torque, etc.), fuel pressure Pf, and in-cylinder pressure Pc are acquired.

In step S42, the fuel injection amount Qf is determined based on the engine speed NE and the required torque using an injection amount map. In step S43, the injection start timing SOI is determined. In this case, for example, based on the relationship in FIG. 23, the injection start timing SOI is determined to be more advanced within the range where the filling efficiency is equal to or greater than a predetermined value.

In step S44, the injection end timing EOI corresponding to multiple fuel pressures Pf within the fuel pressure setting range from a predetermined lower limit fuel pressure Pmin to an upper limit fuel pressure Pmax is calculated. That is, multiple (n) candidate values of the fuel pressure Pf within the fuel pressure setting range are set as fuel pressure candidate values P1 to Pn, and the injection end timing EOI is calculated for each of the fuel pressure candidate values P1 to Pn. For example, the lower limit fuel pressure Pmin is 1.0 [MPa], and the upper limit fuel pressure Pmax is 3.0 [MPa]. The number of fuel pressure candidate values P1 to Pn is arbitrary, but it is preferable that the fuel pressure candidate values P1 to Pn are set in increments of 0.1 to 0.5 [MPa] within the fuel pressure setting range (Pmin to Pmax). The injection end timing EOI is calculated as a value on the more advanced side as the fuel pressure Pf is higher.

For each fuel pressure candidate value P1 to Pn within the fuel pressure setting range, an upper limit injection end timing EOImax, which is the retard limit (most retarded timing) of the injection end timing EOI, is determined, and the injection end timing EOI is calculated so that it is more advanced than the upper limit injection end timing EOImax. The upper limit injection end timing EOImax is the most retarded injection end timing EOI determined from the limit at which injection is possible in response to the rise in in-cylinder pressure during the compression stroke, and is preferably set to the more retarded side the higher the fuel pressure Pf. The upper limit injection end timing EOImax can also be determined based on the fuel pressure Pf and the in-cylinder pressure Pc.

In step S45, within the fuel pressure setting range (Pmin to Pmax), the homogeneity estimation value X is calculated for each fuel pressure candidate value P1 to Pn using the calculation method in FIG. 17. At this time, for each fuel pressure candidate value P1 to Pn, the homogeneity estimation value X is calculated using the injection start timing SOI and injection end timing EOI calculated in steps S43 and S44.

In step S46, it is determined whether any of the homogeneity estimation values X calculated in step S45, i.e., the homogeneity estimation values X corresponding to the multiple fuel pressure candidate values P1 to Pn, is equal to or greater than the target value Xtg. The target value Xtg is a threshold value for determining whether the mixture in the combustion chamber 14 is in a low homogeneity state.

If the homogeneity estimation value X includes any value that is equal to or greater than the target value Xtg, the process proceeds to step S47, where the lowest fuel pressure Pf among the fuel pressure candidate values P1 to Pn at which the homogeneity estimation value X is equal to or greater than the target value Xtg is set as the control command value for the fuel pressure Pf. If the homogeneity estimation value X does not include any value that is equal to or greater than the target value Xtg, the process proceeds to step S48, where the fuel pressure Pf corresponding to the maximum homogeneity estimation value X among the homogeneity estimation values X is set as the control command value for the fuel pressure Pf.

Using Figures 26(a) and (b), a supplementary explanation is given of the process of setting the fuel pressure Pf from multiple homogeneity estimation values X for each fuel pressure candidate value P1 to Pn. In Figure 26(a), the homogeneity estimation value X for each fuel pressure candidate value P1 to Pn includes values that are equal to or greater than the target value Xtg. In this case, the lowest fuel pressure candidate value P3 among the fuel pressure candidate values P1 to Pn that correspond to the homogeneity estimation value X equal to or greater than the target value Xtg is set as the control command value for the fuel pressure Pf. By setting the lowest fuel pressure Pf under the condition that the homogeneity estimation value X is equal to or greater than the target value Xtg, it is possible to improve homogeneity while saving energy.

In addition, in FIG. 26(b), the homogeneity estimation value X for each of the fuel pressure candidate values P1 to Pn does not include any value that is equal to or greater than the target value Xtg. In other words, all of the homogeneity estimation values X are less than the target value Xtg. In this case, the fuel pressure candidate value Px that maximizes the homogeneity estimation value X is set as the control command value for the fuel pressure Pf.

In step S49, the injection end timing EOI of the fuel injection control is determined based on the fuel injection amount Qf determined in step S42, the injection start timing SOI determined in step S43, and the fuel pressure Pf set in steps S47 and S48.

Then, in steps S30 to S35, as explained in FIG. 21, it is determined whether the actual injection amount of the fuel injection valve 31 matches the target injection amount. If the actual injection amount matches the target injection amount, fuel injection from the fuel injection valve 31 is performed based on the injection start timing SOI and injection end timing EOI determined as described above (step S35). If the actual injection amount does not match the target injection amount, fuel injection is performed after resetting the injection timing (steps S31 to S35).

In this embodiment, multiple fuel pressure candidate values P1 to Pn are determined, a homogeneity estimate value X is calculated for each of the fuel pressure candidate values P1 to Pn, and the fuel pressure Pf is set as a control command value based on the fuel pressure candidate value corresponding to the homogeneity estimate value X that is greater than the target value Xtg. This makes it possible to perform fuel injection control using an appropriate fuel pressure Pf to ensure homogeneity.

When all of the homogeneity estimation values X calculated for each of the fuel pressure candidate values P1 to Pn are smaller than the target value Xtg, the fuel pressure Pf is set as the control command value based on the fuel pressure candidate value corresponding to the largest homogeneity estimation value X among those homogeneity estimation values X. In this case, even if the desired homogeneity level is not reached, the best homogeneity can be achieved under the circumstances.

Sixth Embodiment
In this embodiment, the fuel injection timing and fuel pressure of the fuel injection valve 31 are controlled based on the homogeneity estimation value X. The details of this control will be described below. Note that the calculation of the homogeneity estimation value X is similar to the configuration of the fourth embodiment.

The fuel injection control based on the homogeneity estimation value X will be explained using the flowchart shown in FIG. 27. This process is repeatedly performed by the ECU 80 at a predetermined interval.

In step S51, various information such as operating conditions and sensor detection signals are acquired. Specifically, the engine speed NE, engine load information (required torque, etc.), fuel pressure Pf, and in-cylinder pressure Pc are acquired.

In step S52, the fuel injection amount Qf is determined based on the engine speed NE and the required torque using an injection amount map. In step S53, the fuel pressure Pf is set to the lower limit fuel pressure Pmin (e.g., 1.0 MPa) in this system.

In step S54, the SOI setting range within which the injection start timing SOI can be set is determined. As shown in FIG. 22 described above, this SOI setting range is set in the range from the lower limit injection start timing SOImin, which is the advance limit (most advanced timing) of the injection start timing SOI, to the upper limit injection start timing SOImax, which is the retard limit (most retarded timing) of the injection start timing SOI.

In step S55, homogeneity estimates X corresponding to multiple injection start timings SOI are calculated within the SOI setting range (SOImin to SOImax). That is, multiple (n) candidate values for the injection start timing SOI within the SOI setting range are defined as SOI candidate values T1 to Tn, and homogeneity estimates X are calculated for each of the SOI candidate values T1 to Tn using the calculation method of FIG. 17. The number of SOI candidate values T1 to Tn is arbitrary, but it is preferable that the SOI candidate values T1 to Tn are defined in increments of 10 [CA] within the SOI setting range (SOImin to SOImax), for example.

In step S56, it is determined whether any of the homogeneity estimation values X calculated in step S55, i.e., the homogeneity estimation values X corresponding to the SOI candidate values T1 to Tn, is equal to or greater than the target value Xtg. The target value Xtg is a threshold value for determining whether the mixture in the combustion chamber 14 is in a low homogeneity state.

If any of the homogeneity estimates X is equal to or greater than the target value Xtg, the process proceeds to step S57, where the most advanced injection start timing SOI among the SOI candidate values T1 to Tn at which the homogeneity estimate X is equal to or greater than the target value Xtg is set as the control command value for the injection start timing SOI. In addition, the fuel pressure Pf used in calculating the current homogeneity estimate X is set as the control command value for the fuel pressure Pf.

If the homogeneity estimation value X does not include any value that is equal to or greater than the target value Xtg, the process proceeds to step S58, where it is determined whether the fuel pressure Pf used to calculate the homogeneity estimation value X this time is the upper limit fuel pressure Pmax (e.g., 3.0 MPa). If Pf<Pmax, the process proceeds to step S59, where the fuel pressure Pf is increased by a predetermined value.

Then, returning to step S55, the fuel pressure Pf changed to the increasing side is used to calculate homogeneity estimates X for multiple SOI candidate values T1 to Tn within the SOI setting range (SOImin to SOImax), and it is determined whether any of the homogeneity estimates X is equal to or greater than the target value Xtg (steps S55 and S56). If any of the homogeneity estimates X is equal to or greater than the target value Xtg, the process proceeds to step S57, whereas if no of the homogeneity estimates X is equal to or greater than the target value Xtg, the process proceeds to step S58. According to steps S58 to S60, the fuel pressure Pf is increased by a predetermined value until Pf=Pmax.

When Pf=Pmax, the process proceeds to step S60, where the injection start timing SOI corresponding to the largest homogeneity estimation value X among the homogeneity estimation values X calculated using the upper fuel pressure limit Pmax is set as the control command value for the injection start timing SOI. In addition, the upper fuel pressure limit Pmax is set as the control command value for the fuel pressure Pf.

The process of setting the injection start timing SOI performed in steps S55 to S60 will be further explained using Figures 28(a) to (c). In Figure 28(a), the homogeneity estimate value X for each SOI candidate value T1 to Tn includes values that are equal to or greater than the target value Xtg. In this case, the most advanced SOI candidate value T1 (lower limit injection start timing SOImin) among the SOI candidate values T1 to Tn corresponding to the homogeneity estimate value X equal to or greater than the target value Xtg is set as the control command value for the injection start timing SOI.

In addition, in FIG. 28(b), the homogeneity estimation value X for each SOI candidate value T1 to Tn does not include any homogeneity estimation value X that is equal to or greater than the target value Xtg. In other words, all homogeneity estimation values X are less than the target value Xtg. In this case, the fuel pressure Pf is increased by a predetermined value within the fuel pressure range where Pf<Pmax, and the homogeneity estimation value X is calculated for each of the SOI candidate values T1 to Tn within the SOI setting range, and the homogeneity estimation value X and the target value Xtg are compared. The homogeneity estimation value X increases with an increase in the fuel pressure Pf. As a result, as shown in FIG. 28(c), when the homogeneity estimation value X includes any that is equal to or greater than the target value Xtg, the SOI candidate value Tx corresponding to that homogeneity estimation value X (the homogeneity estimation value X that is equal to or greater than Xtg) is set as the control command value for the injection start timing SOI.

Then, in step S61, the injection end timing EOI of the fuel injection control is determined based on the injection start timing SOI set in steps S57 and S60 and the injection period Td calculated from the fuel injection amount Qf and the fuel pressure Pf.

Then, in steps S30 to S35, it is determined whether the actual injection amount of the fuel injection valve 31 matches the target injection amount. If the actual injection amount matches the target injection amount, the fuel injection valve 31 injects fuel based on the injection start timing SOI and injection end timing EOI determined as described above (step S35). If the actual injection amount does not match the target injection amount, the injection timing is reset and then fuel injection is performed (steps S31 to S35). Note that the processing of steps S30 to S35 is the same as the processing of steps S15 to S20 in FIG. 4 in the first embodiment, and detailed description will be omitted here.

In this embodiment, if the homogeneity estimate value X calculated for each SOI candidate value T1 to Tn is all smaller than the target value Xtg, the fuel pressure Pf is increased and the homogeneity estimate value X is calculated again, and the fuel injection timing and fuel pressure Pf at which the homogeneity estimate value X is greater than the target value Xtg are set as the control command values. In this case, even in a situation where the desired homogeneity level cannot be achieved by adjusting the injection start timing SOI alone, the desired homogeneity level can be achieved by additionally adjusting the fuel pressure Pf.

Seventh Embodiment
In this embodiment, a determination is made as to whether the interior of the combustion chamber 14 will enter a predetermined low-homogeneity state in which the homogeneity of the mixture decreases, and if it is determined that the low-homogeneity state will occur, control is performed on the fuel injection timing of the fuel injection valve 31 in order to increase the homogeneity of the mixture.

Factors that may reduce the homogeneity of the mixture include insufficient swirling of the gas fuel in the combustion chamber 14 and insufficient mixing time after the injection of the gas fuel. Of these factors, insufficient swirling is caused, for example, by the injection start time SOI being too early, whereas insufficient mixing time is caused, for example, by the injection start time SOI being too late. In other words, the above two factors are in a trade-off relationship. Therefore, in this embodiment, the fuel injection timing is controlled based on the factors that cause the low homogeneity state.

The fuel injection control based on the homogeneity estimation value X will be explained using the flowchart shown in FIG. 29. This process is repeatedly performed by the ECU 80 at a predetermined interval.

In step S71, a predetermined map or table is used to determine the fuel injection amount Qf, the injection period Td, the injection start timing SOI, and the injection end timing EOI. In the following step S72, the homogeneity estimate value X is calculated using the calculation method of FIG. 17. At this time, the homogeneity estimate value X is calculated by adding the jet penetration estimate value A, the roll-up estimate value B, and the mixing time estimate value C.

In step S73, it is determined whether the homogeneity estimation value X is lower than a predetermined threshold value Th1, indicating a low homogeneity state. If the homogeneity estimation value X is higher than the threshold value Th1 and the homogeneity state is not low, the process proceeds to step S77, where fuel injection is performed by the fuel injection valve 31 based on the injection conditions calculated in step S71.

If the state is low homogeneity, the process proceeds to step S74, where it is determined whether the cause of the decrease in homogeneity is a first cause caused by insufficient rolling up of the gas fuel injected from the fuel injection valve 31 when it rolls up from the top surface of the piston, or a second cause caused by insufficient mixing time for mixture formation after the injection of the gas fuel from the fuel injection valve 31. Specifically, it is determined whether the roll-up estimated value B is smaller than a predetermined threshold value Th2, and if the roll-up estimated value B is smaller than the threshold value Th2, it is determined that the first cause is caused by insufficient rolling up, and if the roll-up estimated value B is not smaller than the threshold value Th2, it is determined that the second cause is caused by insufficient mixing time.

In step S74, instead of the process of determining whether the roll-up estimated value B is smaller than the threshold value Th2, it is also possible to perform a process of determining whether the mixing time estimated value C is smaller than the threshold value Th3. In this case, if the mixing time estimated value C is smaller than the threshold value Th3, it is determined that the cause of the decrease in homogeneity is the second cause, and if the mixing time estimated value C is not smaller than the threshold value Th3, it is determined that the cause of the decrease in homogeneity is the first cause.

If it is determined that the cause of the decrease in homogeneity is the first cause, the process proceeds to step S75, where the injection start time SOI and the injection end time EOI are each shifted to the retard side by a predetermined value in order to retard the fuel injection timing. If it is determined that the cause of the decrease in homogeneity is the second cause, the process proceeds to step S76, where the injection start time SOI and the injection end time EOI are each shifted to the advance side by a predetermined value in order to advance the fuel injection timing. This increases the homogeneity of the mixture.

Then, in step S77, fuel injection is performed by the fuel injection valve 31 based on the injection conditions calculated in steps S71, S75, and S76.

The present embodiment described above provides the following excellent effects:

When it is determined that the inside of the combustion chamber 14 is in a predetermined low homogeneity state, the fuel injection timing of the fuel injection valve 31 is controlled to increase the homogeneity of the mixture. In this case, by controlling the fuel injection timing of the fuel injection valve 31, the degree of swirl of the gas fuel injected from the fuel injection valve 31 into the combustion chamber 14 when it swirls up from the top surface of the piston and the mixing time can be adjusted, and thus the homogeneity of the mixture can be increased.

If the cause of the decrease in homogeneity of the mixture is the first cause (a cause due to insufficient gas fuel swirl), the fuel injection timing of the fuel injection valve 31 is retarded, and if the cause is the second cause (a cause due to insufficient gas fuel mixing time), the fuel injection timing of the fuel injection valve 31 is advanced. This makes it possible to appropriately control the improvement of homogeneity while taking into account the cause of the decrease in homogeneity.

The fuel injection timing of the fuel injection valve 31 (injection start timing SOI, injection end timing EOI) is used as a parameter to calculate the wind-up estimate B and the mixing time estimate C, and the homogeneity estimate X is calculated based on these estimates B and C. In this configuration, it is determined whether the cause of the decrease in homogeneity is the first cause or the second cause based on the wind-up estimate B or the mixing time estimate C. This makes it possible to properly determine whether the cause of the decrease in homogeneity of the mixture is the first cause or the second cause, and thus to properly retard or advance the fuel injection timing.

(Modifications of the fourth to seventh embodiments)
The method of calculating the homogeneity estimation value X can be changed from the method shown in Fig. 17. For example, in the above embodiment, the jet penetration estimation value A is calculated using the fuel pressure Pf, the fuel injection amount Qf, and the injection start timing SOI as parameters, but instead, the jet penetration estimation value A may be calculated using the fuel pressure Pf and the injection start timing SOI as parameters.

In the above embodiment, the estimated wind-up value B is calculated using the parameters fuel pressure Pf, injection period Td, injection start timing SOI, in-cylinder flow, engine speed NE, and in-cylinder pressure Pc (Figures 19(a) and (b), and 20(a) to (d)). However, the estimated wind-up value B may be calculated using at least the parameters fuel pressure Pf, injection period Td, injection start timing SOI, and in-cylinder flow (Figures 19(a) and (b), and 20(a) and (b)).

In the above embodiment, the mixing time estimate C is calculated based on the angle period from the injection end time EOI to the ignition time IG (or the angle period from the injection end time EOI to the TDC) and the engine speed NE, but the mixing time estimate C may be calculated using at least the injection end time EOI and the engine speed NE as parameters.

The homogeneity estimate X can also be calculated using at least one of the fuel injection timing (SOI, EOI) of the fuel injection valve 31, the fuel pressure Pf, the engine speed NE, and the engine load (Pin).

In addition, instead of calculating the homogeneity estimate value X by adding the jet penetration estimate value A, the roll-up estimate value B, and the mixing time estimate value C, the homogeneity estimate value X may be calculated by adding the roll-up estimate value B and the mixing time estimate value C. The homogeneity estimate value X may be calculated using at least one of the jet penetration estimate value A, the roll-up estimate value B, and the mixing time estimate value C.

- As a modification of the fourth embodiment, the ECU 80 may be configured to perform the fuel injection control shown in FIG. 30. The flowchart in FIG. 30 is a partial modification of the flowchart in FIG. 21, in which the processing of step S81 is performed instead of steps S26 to S28.

Specifically, in step S25 of FIG. 30, the ECU 80 calculates homogeneity estimate values X corresponding to multiple injection start timings SOI within the SOI setting range (SOImin to SOImax), and then proceeds to step S81, where the ECU 80 sets the injection start timing SOI corresponding to the largest homogeneity estimate value X among the homogeneity estimate values X as the control command value for the injection start timing SOI. Then, the ECU 80 determines the injection end timing EOI based on the injection start timing SOI and the injection period Td (step S29).

In the above configuration, multiple SOI candidate values are determined within the SOI setting range (settable range), a homogeneity estimate value X is calculated for each of the SOI candidate values, and the fuel injection timing is set as a control command value based on the SOI candidate value corresponding to the largest homogeneity estimate value X among the homogeneity estimate values X. This fuel injection control makes it possible to achieve the desired homogeneity in the combustion chamber 14.

- In the seventh embodiment shown in FIG. 29, if it is determined that the mixture is in a low homogeneity state (if step S73 is YES), it is also possible to implement control to increase the fuel pressure Pf. Even with this configuration, the homogeneity of the mixture can be increased.

- In the process of FIG. 29 of the seventh embodiment, the homogeneity estimation value X is calculated, and whether or not the homogeneity state is low is determined based on the homogeneity estimation value X (steps S72, S73), but this may be modified as follows. It may be determined whether or not the engine operating region is in a high-speed, medium-load region, and the low homogeneity state may be determined based on whether or not the engine operating region is in the high-speed, medium-load region. Alternatively, it may be determined that the low homogeneity state is low based on the engine operating state being in a transient state, or based on a decrease in the gas fuel in the fuel container 36.

When the engine is in the high-speed, medium-load range, the mixing time between the gas fuel and the air is short, and the jet roll is reduced, so it is determined to be in a low-homogeneity state. When the engine is in a transient state, the jet roll may be reduced due to a delayed response in the intake volume, so it is determined to be in a low-homogeneity state. In particular, in a deceleration transient state, it is believed that the jet roll is reduced due to an increase in in-cylinder pressure caused by a delayed response in the intake volume. In addition, when the gas fuel in the fuel container 36 is reduced to a predetermined level or less, the jet roll may be reduced due to a drop in fuel pressure, so it is determined to be in a low-homogeneity state.

- The fuel injection valve 31 applied to the fourth to seventh embodiments has a multi-hole structure with multiple injection holes 62, and each injection hole 62 has the same size, but this may be changed. For example, each injection hole 62 may have the shape described in Figures 2, 7, 9, 10, and 12. In addition, the fuel injection valve 31 may have a single-hole structure with a single injection hole 62.

- In the above embodiment, the engine 10 is configured such that gas fuel is injected radially from each nozzle hole 62 provided at the tip (cap 61) of the fuel injection valve 31 toward the top surface of the piston (see FIG. 8), but this may be changed. Specifically, as shown in FIG. 31, the gas fuel is injected toward the cylinder wall surface from the nozzle hole 62 provided at the tip (cap 61) of the fuel injection valve 31. In this case, the injection direction is only one direction in the cylinder plan view, and the fuel injection in that direction forms a tumble flow as a jet of gas fuel in the combustion chamber 14. In other words, the gas fuel injected from the fuel injection valve 31 reaches the top surface of the piston from the cylinder wall surface, and further forms a vertical swirling flow by rolling up from the top surface of the piston. In this case, the collapse of the tumble flow due to the piston rising increases the turbulence, promoting the diffusion of the gas fuel. In addition, the tumble ratio, which indicates the strength of the tumble flow, can be improved by retarding the injection start timing or increasing the fuel pressure. This can improve turbulence when the tumble flow collapses, and promotes the diffusion of the gas fuel, improving homogeneity.

The direction of fuel injection is arbitrary, and may be, for example, from the intake port side to the exhaust port side, from the exhaust port side to the intake port side, or perpendicular to the direction in which the intake port and exhaust port are aligned.

Even in the engine 10 configured as shown in FIG. 31, the ECU 80 may calculate the homogeneity of the mixture in the combustion chamber 14 as a homogeneity estimate value X, and control at least one of the fuel injection timing and the fuel pressure of the fuel injection valve 31 based on the homogeneity estimate value X (see the fourth to sixth embodiments). In this case, particularly, for the gas fuel injected from the nozzle hole 62 of the fuel injection valve 31 toward the cylinder wall surface during the engine compression stroke, a roll-up estimate value B is calculated that indicates the degree of jet roll-up when the gas fuel passes through the cylinder wall surface and rolls up from the top surface of the piston. Then, a homogeneity estimate value X including the roll-up estimate value B is calculated, and fuel injection control is performed based on the homogeneity estimate value X.

In addition, in the engine 10 configured as shown in FIG. 31, it is preferable to determine whether the inside of the combustion chamber 14 is in a predetermined low homogeneity state, and if it is determined that the inside of the combustion chamber 14 is in a low homogeneity state, control of the fuel injection timing of the fuel injection valve 31 is performed to increase the homogeneity of the mixture (see the seventh embodiment).

The control unit and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control unit and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described in the present disclosure may be realized by one or more dedicated computers configured by combining a processor and a memory programmed to execute one or more functions with a processor configured with one or more hardware logic circuits. In addition, the computer program may be stored in a computer-readable non-transient tangible recording medium as instructions executed by the computer.

10...engine, 13...piston, 14...combustion chamber, 15...intake port, 16...exhaust port, 31...fuel injector, 32...spark plug, 61...cap, 62...nozzle hole, 80...ECU.

Claims (22)

The present invention is applied to a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), and the gas fuel injected from the fuel injection valve is combusted in the combustion chamber,
a calculation unit that calculates a homogeneity indicating a degree of homogeneity of a mixture of air and the gas fuel injected from the fuel injection valve in the combustion chamber as a homogeneity estimated value;
a setting unit that sets, as a command value for fuel injection control of the fuel injection valve, at least one of a fuel injection timing and a fuel pressure at which the homogeneity estimation value calculated by the calculation unit becomes greater than a predetermined threshold value;
a control unit that causes the fuel injection valve to inject fuel based on at least one of the fuel injection timing and the fuel pressure as the command value set by the setting unit ; and
Equipped with
the calculation unit calculates the homogeneity estimation value by using a fuel injection timing of the fuel injection valve as a parameter,
The control device (80) for a gas engine, wherein the setting unit determines a plurality of candidate values for the fuel injection timing, calculates the homogeneity estimation value for each of the candidate values using the calculation unit, and sets the fuel injection timing as the command value based on the candidate value corresponding to the homogeneity estimation value that is greater than the threshold value among the calculated homogeneity estimation values. 2. The control device for a gas engine according to claim 1, wherein the setting unit sets the injection start timing as the fuel injection timing, determines the plurality of candidate values within a settable range between an advance limit and a retard limit of the injection start timing, calculates the homogeneity estimation value for each of the candidate values by the calculation unit, and sets the fuel injection timing as the command value based on the candidate value that corresponds to a homogeneity estimation value that is greater than the threshold value and is the most advanced within the settable range among the calculated homogeneity estimation values. 3. The gas engine control device according to claim 2, wherein when the homogeneity estimation values calculated for the respective candidate values are all smaller than the threshold value, the setting unit sets the fuel injection timing as the command value based on the candidate value corresponding to the largest homogeneity estimation value among the homogeneity estimation values . the calculation unit calculates the homogeneity estimation value by using a fuel injection timing of the fuel injection valve and a fuel pressure as parameters,
3. The gas engine control device according to claim 2, wherein, when the homogeneity estimation values calculated for the candidate values are all smaller than the threshold value, the setting unit changes the fuel pressure to a high pressure, and calculates the homogeneity estimation value again using the calculation unit, and sets, as the command value, a fuel injection timing and a fuel pressure at which the homogeneity estimation value becomes larger than the threshold value . The present invention is applied to a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), and the gas fuel injected from the fuel injection valve is combusted in the combustion chamber,
a calculation unit that calculates a homogeneity indicating a degree of homogeneity of a mixture of air and the gas fuel injected from the fuel injection valve in the combustion chamber as a homogeneity estimated value;
a setting unit that sets, as a command value for fuel injection control of the fuel injection valve, at least one of a fuel injection timing and a fuel pressure at which the homogeneity estimation value calculated by the calculation unit becomes greater than a predetermined threshold value;
a control unit that causes the fuel injection valve to inject fuel based on at least one of the fuel injection timing and the fuel pressure as the command value set by the setting unit ; and
Equipped with
the calculation unit calculates the homogeneity estimation value by using a fuel pressure as a parameter,
The control device (80) for a gas engine, wherein the setting unit determines a plurality of candidate values for fuel pressure, calculates the homogeneity estimation value for each of the candidate values using the calculation unit, and sets the fuel pressure as the command value based on the candidate value corresponding to a homogeneity estimation value that is greater than the threshold value among the calculated homogeneity estimation values. 6. The gas engine control device according to claim 5, wherein when the homogeneity estimation values calculated for the respective candidate values are all smaller than the threshold value, the setting unit sets the fuel pressure as the command value based on the candidate value corresponding to a largest homogeneity estimation value among the homogeneity estimation values . The present invention is applied to a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), and the gas fuel injected from the fuel injection valve is combusted in the combustion chamber,
a calculation unit that calculates a homogeneity indicating a degree of homogeneity of a mixture of air and the gas fuel injected from the fuel injection valve in the combustion chamber as a homogeneity estimated value;
a control unit that controls at least one of a fuel injection timing and a fuel pressure of the fuel injection valve based on the homogeneity estimation value calculated by the calculation unit;
Equipped with
the calculation unit calculates the homogeneity estimation value by using an injection start timing of the fuel injection valve as a parameter,
A control device (80) for a gas engine, comprising: a setting unit that determines a plurality of candidate values for the injection start timing within a settable range between an advance limit and a retard limit of the injection start timing, calculates the homogeneity estimation value for each of the candidate values by the calculation unit, and sets the fuel injection timing as a control command value of the control unit based on the candidate value corresponding to the largest homogeneity estimation value among the calculated homogeneity estimation values. The control device for a gas engine according to any one of claims 1 to 7, wherein the calculation unit uses the fuel injection timing of the fuel injection valve as a parameter to calculate a jet penetration estimate value indicating the size of the jet of gas fuel injected from the fuel injection valve, a roll-up estimate value indicating the size of the roll-up of the gas fuel injected from the fuel injection valve when it is rolled up from the top surface of the piston, and a mixing time estimate value indicating a mixing time during which mixture formation is performed after the injection of the gas fuel from the fuel injection valve, and calculates the homogeneity estimate value based on the roll-up estimate value, the mixing time estimate value, and the jet penetration estimate value. 8. The control device for a gas engine according to claim 1 , wherein the calculation unit calculates the homogeneity estimation value using a fuel injection timing of the fuel injection valve, a fuel pressure, an engine rotation speed, and an engine load as parameters. The present invention is applied to a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), and the gas fuel injected from the fuel injection valve is combusted in the combustion chamber,
a calculation unit that calculates a homogeneity indicating a degree of homogeneity of a mixture of air and the gas fuel injected from the fuel injection valve in the combustion chamber as a homogeneity estimated value;
a control unit that controls at least one of a fuel injection timing and a fuel pressure of the fuel injection valve based on the homogeneity estimation value calculated by the calculation unit;
Equipped with
The calculation unit uses the fuel injection timing of the fuel injection valve as a parameter to calculate a jet penetration estimate value indicating the size of the jet of gas fuel injected from the fuel injection valve, a roll-up estimate value indicating the size of the roll-up of the gas fuel injected from the fuel injection valve when it rolls up from the top surface of the piston, and a mixing time estimate value indicating the mixing time during which mixture formation is performed after the injection of the gas fuel from the fuel injection valve, and calculates the homogeneity estimate value based on the roll-up estimate value, the mixing time estimate value, and the jet penetration estimate value . The present invention is applied to a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), and the gas fuel injected from the fuel injection valve is combusted in the combustion chamber,
a calculation unit that calculates a homogeneity indicating a degree of homogeneity of a mixture of air and the gas fuel injected from the fuel injection valve in the combustion chamber as a homogeneity estimated value;
a control unit that controls at least one of a fuel injection timing and a fuel pressure of the fuel injection valve based on the homogeneity estimation value calculated by the calculation unit;
Equipped with
A control device (80) for a gas engine , wherein the calculation unit calculates the homogeneity estimation value using a fuel injection timing of the fuel injection valve, a fuel pressure, an engine rotation speed, and an engine load as parameters. The present invention is applied to a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), and the gas fuel injected from the fuel injection valve is combusted in the combustion chamber,
a calculation unit that uses a fuel injection timing of the fuel injection valve as a parameter to calculate a jet penetration estimate value indicating a size of a jet of gas fuel injected from the fuel injection valve, a roll-up estimate value indicating a size of the roll-up of the gas fuel injected from the fuel injection valve when the gas fuel injected from the fuel injection valve rolls up from an upper surface of a piston, and a mixing time estimate value indicating a mixing time during which a mixture is formed after the injection of the gas fuel from the fuel injection valve, and calculates a homogeneity estimate value indicating a degree of homogeneity of a mixture of the gas fuel injected from the fuel injection valve and air in the combustion chamber based on the roll-up estimate value, the mixing time estimate value, and the jet penetration estimate value;
a homogeneity determination unit that determines whether or not the interior of the combustion chamber is in a predetermined low homogeneity state , in which the homogeneity is reduced, based on the homogeneity estimated value calculated by the calculation unit ; and
a control unit that controls at least one of a fuel injection timing and a fuel pressure of the fuel injection valve in order to increase the degree of homogeneity when it is determined that the low homogeneity state has occurred;
A control device (80) for a gas engine comprising: The present invention is applied to a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), and the gas fuel injected from the fuel injection valve is combusted in the combustion chamber,
a calculation unit that calculates a homogeneity indicating a degree of homogeneity of a mixture of air and gas fuel injected from the fuel injection valve in the combustion chamber as a homogeneity estimated value by using a fuel injection timing of the fuel injection valve, a fuel pressure, an engine rotation speed, and an engine load as parameters;
a homogeneity determination unit that determines whether or not the interior of the combustion chamber is in a predetermined low homogeneity state , in which the homogeneity is reduced, based on the homogeneity estimated value calculated by the calculation unit ; and
a control unit that controls at least one of a fuel injection timing and a fuel pressure of the fuel injection valve in order to increase the degree of homogeneity when it is determined that the low homogeneity state has occurred;
A control device (80) for a gas engine comprising: the homogeneity determining unit, when it is determined that the low homogeneity state has occurred, determines whether the cause of the decrease in homogeneity is a first cause caused by insufficient rolling up of the gas fuel injected from the fuel injection valve when the gas fuel is rolled up from an upper surface of the piston, or a second cause caused by insufficient mixing time for mixture formation after the injection of the gas fuel from the fuel injection valve,
The control unit is
If the cause of the decrease in homogeneity is the first cause, retarding the fuel injection timing of the fuel injection valve,
14. The control device for a gas engine according to claim 12, further comprising: advancing a fuel injection timing of the fuel injection valve when the cause of the decrease in homogeneity is the second cause. a calculation unit that calculates either a roll-up estimated value indicating a magnitude of roll-up when the gas fuel injected from the fuel injection valve rolls up from an upper surface of a piston, or a mixing time estimated value indicating a mixing time during which an air-fuel mixture is formed after the injection of the gas fuel from the fuel injection valve, based on a fuel injection timing of the fuel injection valve,
15. The gas engine control device according to claim 14, wherein the homogeneity determination unit, when it is determined that the low homogeneity state will occur, determines whether the cause of the decrease in homogeneity is the first cause or the second cause based on the estimated wind-up value or the estimated mixing time value. A program executed by a processor in a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), the gas fuel injected from the fuel injection valve being combusted in the combustion chamber,
a calculation process of calculating a homogeneity indicating a degree of homogeneity of a mixture of air and the gas fuel injected from the fuel injection valve in the combustion chamber as a homogeneity estimation value;
a setting process for setting at least one of a fuel injection timing and a fuel pressure, at which the homogeneity estimation value calculated by the calculation process becomes greater than a predetermined threshold value, as a command value for fuel injection control of the fuel injection valve;
a control process for causing the fuel injection valve to inject fuel based on at least one of the fuel injection timing and the fuel pressure as the command value set by the setting process;
Including,
the calculation process calculates the homogeneity estimation value using a fuel injection timing of the fuel injection valve as a parameter,
the setting process determines a plurality of candidate values for the fuel injection timing, calculates the homogeneity estimation value for each of the candidate values by the calculation process, and sets the fuel injection timing as the command value based on the candidate value corresponding to the homogeneity estimation value larger than the threshold value among the calculated homogeneity estimation values. A program executed by a processor in a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), the gas fuel injected from the fuel injection valve being combusted in the combustion chamber,
a calculation process of calculating a homogeneity indicating a degree of homogeneity of a mixture of air and the gas fuel injected from the fuel injection valve in the combustion chamber as a homogeneity estimation value;
a setting process for setting at least one of a fuel injection timing and a fuel pressure, at which the homogeneity estimation value calculated by the calculation process becomes greater than a predetermined threshold value, as a command value for fuel injection control of the fuel injection valve;
a control process for causing the fuel injection valve to inject fuel based on at least one of the fuel injection timing and the fuel pressure as the command value set by the setting process; and
Including,
the calculation process calculates the homogeneity estimation value using a fuel pressure as a parameter,
the setting process determines a plurality of candidate values for fuel pressure, the calculation process calculates the homogeneity estimation value for each of the candidate values, and the fuel pressure as the command value is set based on the candidate value corresponding to the homogeneity estimation value larger than the threshold value among the calculated homogeneity estimation values. A program executed by a processor in a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), the gas fuel injected from the fuel injection valve being combusted in the combustion chamber,
a calculation process of calculating a homogeneity indicating a degree of homogeneity of a mixture of air and the gas fuel injected from the fuel injection valve in the combustion chamber as a homogeneity estimation value;
a control process for controlling at least one of a fuel injection timing and a fuel pressure of the fuel injection valve based on the homogeneity estimation value calculated by the calculation process;
Including,
the calculation process calculates the homogeneity estimation value using an injection start timing of the fuel injection valve as a parameter,
a setting process for determining a plurality of candidate values for the injection start timing within a settable range between an advance limit and a retard limit of the injection start timing, calculating the homogeneity estimation value for each of the candidate values by the calculation process, and setting the fuel injection timing as a control command value of the control process based on the candidate value corresponding to the largest homogeneity estimation value among the calculated homogeneity estimation values. A program executed by a processor in a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), the gas fuel injected from the fuel injection valve being combusted in the combustion chamber,
a calculation process of calculating a homogeneity indicating a degree of homogeneity of a mixture of air and the gas fuel injected from the fuel injection valve in the combustion chamber as a homogeneity estimation value;
a control process for controlling at least one of a fuel injection timing and a fuel pressure of the fuel injection valve based on the homogeneity estimation value calculated by the calculation process;
Including,
The program in the calculation process calculates, using a fuel injection timing of the fuel injection valve as a parameter, a jet penetration estimate value indicating the size of the jet of gas fuel injected from the fuel injection valve, a roll-up estimate value indicating the size of the roll-up of the gas fuel injected from the fuel injection valve when it is rolled up from the top surface of the piston, and a mixing time estimate value indicating a mixing time during which a mixture is formed after the injection of the gas fuel from the fuel injection valve, and calculates the homogeneity estimate value based on the roll-up estimate value, the mixing time estimate value, and the jet penetration estimate value. A program executed by a processor in a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), the gas fuel injected from the fuel injection valve being combusted in the combustion chamber,
a calculation process of calculating a homogeneity indicating a degree of homogeneity of a mixture of air and the gas fuel injected from the fuel injection valve in the combustion chamber as a homogeneity estimation value;
a control process for controlling at least one of a fuel injection timing and a fuel pressure of the fuel injection valve based on the homogeneity estimation value calculated by the calculation process;
Including,
a program for calculating the homogeneity estimation value using a fuel injection timing of the fuel injection valve, a fuel pressure, an engine rotation speed, and an engine load as parameters in the calculation process. A program executed by a processor in a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), the gas fuel injected from the fuel injection valve being combusted in the combustion chamber,
a calculation process for calculating, using a fuel injection timing of the fuel injection valve as a parameter, a jet penetration estimate value indicating a size of a jet of gas fuel injected from the fuel injection valve, a roll-up estimate value indicating a size of the roll-up of the gas fuel injected from the fuel injection valve when the gas fuel injected from the fuel injection valve rolls up from an upper surface of a piston, and a mixing time estimate value indicating a mixing time during which a mixture is formed after the injection of the gas fuel from the fuel injection valve, and calculating a homogeneity indicating a degree of homogeneity of a mixture of the gas fuel injected from the fuel injection valve and air in the combustion chamber as a homogeneity estimate value based on the roll-up estimate value, the mixing time estimate value, and the jet penetration estimate value;
a homogeneity determination process for determining whether or not the interior of the combustion chamber is in a predetermined low homogeneity state, in which the homogeneity is reduced, based on the homogeneity estimated value calculated by the calculation process;
a control process for controlling at least one of a fuel injection timing and a fuel pressure of the fuel injection valve in order to increase the degree of homogeneity when it is determined that the low homogeneity state has occurred;
Including, the program. A program executed by a processor in a gas engine (10) including a piston (13) that reciprocates in a cylinder and a fuel injection valve (31) that directly injects gas fuel, the pressure of which is adjusted to a predetermined fuel pressure, into a combustion chamber (14), the gas fuel injected from the fuel injection valve being combusted in the combustion chamber,
a calculation process for calculating a homogeneity indicating a degree of homogeneity of a mixture of the gas fuel injected from the fuel injection valve and air in the combustion chamber as a homogeneity estimation value by using a fuel injection timing of the fuel injection valve, a fuel pressure, an engine rotation speed, and an engine load as parameters;
a homogeneity determination process for determining whether or not the interior of the combustion chamber is in a predetermined low homogeneity state, in which the homogeneity is reduced, based on the homogeneity estimated value calculated by the calculation process;
a control process for controlling at least one of a fuel injection timing and a fuel pressure of the fuel injection valve in order to increase the degree of homogeneity when it is determined that the low homogeneity state has occurred;
Including, the program.

Images