JP7724168B2 - Diesel engine and control method thereof - Google Patents

Description

This disclosure relates to a diesel engine and a control method thereof.

In diesel engines, the amount of NOx in the exhaust gas increases as the combustion temperature increases, so it is known that injecting water into the combustion chamber lowers the combustion temperature within the combustion chamber and suppresses the generation of NOx.

For example, Japanese Utility Model Laid-Open Publication No. 5-10761 (Patent Document 1) discloses setting the amount of water injection to achieve the combustion temperature required to reduce NOx levels, depending on the engine speed and load (see Patent Document 1).

Japanese Utility Model Application Laid-Open Publication No. 5-10761

Engine speed and load may not adequately reflect changes in engine conditions during transient operation. In this case, the amount of water injected may not be appropriate for the combustion conditions, which may result in insufficient suppression of NOx emissions or a drop in power output due to an excessive drop in combustion temperature.

This disclosure has been made to solve these problems, and its purpose is to provide a diesel engine and a control method for the same that can inject an appropriate amount of water even during transient operation when the engine's condition changes.

The diesel engine disclosed herein comprises an engine body having a combustion chamber, a fuel injection device configured to inject fuel into the combustion chamber, a water injection device configured to inject water into the combustion chamber, a control device that controls the water injection device, and an acquisition unit that acquires a state quantity indicating the amount of oxygen contained in the intake gas supplied to the combustion chamber. The control device estimates the spray temperature from the state quantity acquired by the acquisition unit according to a predetermined relationship between the state quantity and the spray temperature of the fuel injected into the combustion chamber, and determines the amount of water injected by the water injection device from the temperature difference between the estimated spray temperature and a target spray temperature.

The control method disclosed herein is a control method for a diesel engine equipped with a fuel injection device that injects fuel into a combustion chamber and a water injection device that injects water into the combustion chamber, and includes the steps of: acquiring a state quantity indicating the amount of oxygen contained in the intake gas supplied to the combustion chamber; estimating the spray temperature from the acquired state quantity in accordance with a predetermined relationship between the state quantity and the spray temperature of the fuel injected into the combustion chamber; and determining the amount of water injected by the water injection device from the temperature difference between the estimated spray temperature and a target spray temperature.

In the above-described diesel engine and control method, the water injection amount is determined from the above-described state variables that directly affect the combustion state in the combustion chamber, making it possible to determine an appropriate water injection amount based on the combustion state even during transient operation. Therefore, with this diesel engine and control method, it is possible to inject an appropriate amount of water even during transient operation. As a result, the amount of NOx can be sufficiently suppressed, and a decrease in output due to an excessive drop in combustion temperature can be suppressed.

The diesel engine may further include an EGR device. The EGR device connects the exhaust passage to the intake passage without passing through the engine body, and is configured to recirculate a portion of the exhaust gas to the intake passage. The control device may then determine the amount of water injection based on the temperature difference when changing the amount of exhaust gas recirculated by the EGR device.

By using an EGR device to recirculate a portion of the exhaust gas back into the combustion chamber, it is possible to suppress the combustion temperature and reduce the amount of NOx generated. However, for example, during transient operation when the required amount of EGR gas increases, there is a delay in the increase in the actual amount of EGR gas. In this case, if the water injection amount is set according to the engine speed and load, there may not be enough water until the actual amount of EGR gas reaches the required amount, and as a result, the amount of NOx may not be sufficiently suppressed. In the above-mentioned diesel engine, the temperature difference and water injection amount are determined from the above-mentioned state quantities that directly affect the combustion state in the combustion chamber, so it is possible to suppress the above-mentioned water shortage during transient operation. Therefore, the amount of NOx can be sufficiently suppressed.

The control device may determine the amount of water injection based on the temperature difference during a cold start of the engine body, when operation of the EGR device is restricted.

When the engine is cold started, operation of the EGR device may be restricted because condensed water is generated when the EGR device is activated. Restricting operation of the EGR device may increase the combustion temperature and the amount of NOx. In this diesel engine, the amount of water injection is determined from the above state quantities as described above, so the combustion temperature can be appropriately suppressed. Therefore, the amount of NOx can be sufficiently suppressed.

The target spray temperature may be determined based on the engine speed and load.
This allows the spray temperature to approach the target spray temperature determined based on the engine speed and load, thereby making it possible to appropriately suppress the amount of NOx.

The predetermined relationship may be the relationship between the state quantity and the maximum value of the spray temperature in one stroke of the engine body. The control device may then estimate the maximum value of the spray temperature from the state quantity acquired by the acquisition unit in accordance with this relationship, and determine the water injection amount from the temperature difference between the estimated maximum value of the spray temperature and the target maximum value of the spray temperature.

By using the maximum spray temperature in this way, the spray temperature can be sufficiently and appropriately controlled.

The control device may calculate the amount of water injection by multiplying the mass of spray gas in the combustion chamber, which is determined depending on the operating state of the engine body, the constant pressure specific heat of the spray gas, and the temperature difference, and dividing the result by the latent heat of vaporization of water.

This allows the amount of water sprayed to be calculated appropriately.

The diesel engine and control method disclosed herein enable an appropriate amount of water to be injected even during transient operation when the engine's condition changes. As a result, the amount of NOx can be sufficiently suppressed, and a decrease in output due to an excessive drop in combustion temperature can be suppressed.

1 is an overall configuration diagram of a diesel engine according to an embodiment of the present disclosure. FIG. 2 is a diagram illustrating an example of the arrangement of fuel injection valves and water injection valves in a cylinder. FIG. 10 is a diagram showing an example of the transition of the NOx amount during transient operation of the engine, as a reference example. FIG. 10 is a diagram showing an example of transition of the maximum value of the average spray temperature in the combustion chamber. FIG. 10 is a diagram showing an example of the relationship between the temperature difference of the spray temperature from the base condition and the amount of water injection. 4 is a flowchart illustrating a process for calculating the amount of water injection from the water injection valve, which is executed by the control device.

Embodiments of the present disclosure will now be described in detail with reference to the drawings. Note that identical or equivalent parts in the drawings will be designated by the same reference numerals and their description will not be repeated.

Figure 1 is an overall configuration diagram of a diesel engine according to an embodiment of the present disclosure. Referring to Figure 1, the diesel engine 1 includes an engine body 10, intake pipes 11A and 11B, an intake manifold 11C, an exhaust manifold 12A, exhaust pipes 12B and 12C, a turbocharger 30, an EGR device 13, and a control device 50.

The diesel engine 1 also includes an intake flow sensor 21, an intercooler 16, a throttle device 47, and a pressure sensor 24.

The intake pipe 11A is connected to the inlet side of the compressor 35 of the turbocharger 30, and the intake pipe 11B is connected to the outlet side of the compressor 35. An intake manifold 11C is provided on the intake side of the engine body 10, and the intake pipe 11B is connected to the intake manifold 11C.

The intake air flow sensor 21 is provided in the intake pipe 11A and detects the flow rate of air introduced into the intake pipe 11A. The turbocharger 30 includes a compressor 35 having a compressor impeller 35A and a turbine 36 having a turbine impeller 36A. The compressor impeller 35A is driven to rotate by the turbine impeller 36A, which is driven to rotate by exhaust gas, and supercharges the air drawn in through the intake pipe 11A and supplies it to the intake pipe 11B.

The intercooler 16 is an air-cooled or water-cooled heat exchanger provided in the intake pipe 11B that cools the air supercharged by the compressor 35. The throttle device 47 is provided downstream of the intercooler 16 in the intake pipe 11B and adjusts the intake air flow rate by driving a throttle valve 47A based on a control signal from the control device 50. The pressure sensor 24 is provided downstream of the throttle device 47 in the intake pipe 11B and detects the pressure of the intake gas supplied to the intake manifold 11C and outputs the detected pressure to the control device 50.

The diesel engine 1 further includes a common rail 41, fuel pipes 42A-42D, fuel injection valves 43A-43D, a water supply common rail 61, water pipes 62A-62D, water injection valves 63A-63D, a supply pipe 65, a pump 66, and a water tank 67.

The engine body 10 is provided with multiple cylinders 45A-45D. Note that in this example, four cylinders 45A-45D are shown, but the number of cylinders is not limited to this.

Fuel injection valves 43A to 43D are provided in cylinders 45A to 45D, respectively. Fuel is supplied to the fuel injection valves 43A to 43D from the common rail 41 via fuel pipes 42A to 42D, respectively. The fuel injection valves 43A to 43D are driven by control signals from the control device 50, and inject fuel into the cylinders 45A to 45D, respectively.

Water injection valves 63A-63D are also provided in cylinders 45A-45D, respectively. Water (non-flammable liquid) is supplied to the water injection valves 63A-63D from the water supply common rail 61 via water pipes 62A-62D, respectively. The water injection valves 63A-63D are driven by control signals from the control device 50, and inject water into the cylinders 45A-45D, respectively.

The water supply common rail 61 is connected to a water tank 67 via a supply pipe 65. A pump 66 is provided on the supply pipe 65, and the pump 66 supplies water from the water tank 67 through the supply pipe 65 to the water supply common rail 61.

An exhaust manifold 12A is provided on the exhaust side of the engine body 10, and an exhaust pipe 12B is connected to the exhaust manifold 12A. The outlet side of the exhaust pipe 12B is connected to the inlet side of the turbine 36 of the turbocharger 30, and an exhaust pipe 12C is connected to the outlet side of the turbine 36.

The diesel engine 1 further includes a temperature sensor 29 and a pressure sensor 26. The temperature sensor 29 is provided in the exhaust pipe 12B and detects the temperature of the exhaust gas discharged from the engine body 10. The pressure sensor 26 is provided in the exhaust pipe 12B and detects the pressure of the exhaust gas in the exhaust pipe 12B and outputs the detected pressure to the control device 50.

Although not shown in FIG. 1, an exhaust gas purification device is provided in the exhaust pipe 12C. The exhaust gas purification device may include, for example, an oxidation catalyst, a particulate filter, a selective reduction catalyst, etc.

The EGR device 13 includes EGR pipes 13A and 13B, a path switching device 14A, an EGR valve 14B, an EGR cooler 15, and a bypass pipe 13C. The EGR pipe 13A is connected to the exhaust pipe 12B, and the EGR pipe 13B is connected to the intake pipe 11B. The EGR pipes 13A and 13B connect the exhaust pipe 12B and the intake pipe 11B, allowing a portion of the exhaust gas (EGR gas) in the exhaust pipe 12B to be recirculated to the intake side of the engine body 10.

The path switching device 14A is a path switching valve that switches between an EGR cooler path that returns the EGR gas recirculated through the EGR pipe 13A to the intake pipe 11B via the EGR cooler 15, and a bypass path that bypasses the EGR cooler 15 via the bypass pipe 13C and returns the EGR gas to the intake pipe 11B.

The EGR valve 14B is provided in the EGR pipe 13B, downstream of the junction with the bypass pipe 13C. The EGR valve 14B adjusts the flow rate of EGR gas flowing through the EGR pipe 13B (i.e., the flow rate of EGR gas recirculated to the intake pipe 11B) based on a control signal from the control device 50.

The EGR cooler 15 is a heat exchanger that is provided between the EGR pipes 13A and 13B and cools the EGR gas. The EGR cooler 15 cools the EGR gas flowing in from the EGR pipe 13A and discharges it into the EGR pipe 13B.

The control device 50 is configured to include at least a processor 51 and a storage device 53. The processor 51 is configured with a CPU (Central Processing Unit), an MPU (Micro Processing Unit), etc. The storage device 53 is configured to include a ROM (Read Only Memory), a RAM (Random Access Memory), a hard disk, etc. The ROM stores processing programs executed by the processor 51, and the processor 51 loads the processing programs stored in the ROM into the RAM and executes them.

The control device 50 detects the operating state of the diesel engine 1 based on detection signals from various sensors and controls various actuators, including the fuel injection valves 43A-43D, water injection valves 63A-63D, and EGR valve 14B.

The diesel engine 1 further includes a rotation angle sensor 22, an atmospheric pressure sensor 23, an accelerator pedal sensor 25, and a vehicle speed sensor 27. The rotation angle sensor 22 detects the rotation angle (crank angle) of the crankshaft of the engine main body 10. The atmospheric pressure sensor 23 detects the surrounding atmospheric pressure. The accelerator pedal sensor 25 detects the amount of accelerator pedal depression by the driver. The vehicle speed sensor 27 detects the rotation speed of the wheels of the vehicle in which the diesel engine 1 is installed.

In the diesel engine 1 described above, the amount of NOx in the exhaust gas increases as the combustion temperature in the combustion chambers formed in cylinders 45A-45D increases. Therefore, water injection valves 63A-63D are provided to inject water into cylinders 45A-45D (inside the combustion chambers) to lower the combustion temperature.

Figure 2 shows an example of the arrangement of the fuel injection valve 43A and water injection valve 63A in cylinder 45A. Note that the arrangement of the fuel injection valves 43B-43D and water injection valves 63B-63D in the other cylinders 45B-45D is similar to the arrangement of the fuel injection valve 43A and water injection valve 63A in cylinder 45A.

Referring to Figure 2, the engine body 10 includes a cylinder block 71 in which a cylinder 45A is formed, and a cylinder head 72. A piston 73 that reciprocates within the cylinder 45A is provided within the cylinder 45A. A combustion chamber 75 in which the air-fuel mixture is burned is formed within the cylinder 45A between the piston 73 and the cylinder head 72. A concave cavity 76 is formed in the top surface of the piston 73.

The fuel injection valve 43A is located at the center of the upper wall of the combustion chamber 75 and is configured to inject fuel F directly toward the periphery of a cavity 76 formed in the piston 73 (see the bottom diagram in Figure 2). The water injection valve 63A is located at an angle relative to the fuel injection valve 43A on the periphery of the upper wall of the combustion chamber 75. The water injection valve 63A is configured to inject (supply) water 68 into a predetermined region FL around multiple (e.g., eight) fuel injection ports (not shown) of the fuel injection valve 43A (see the top diagram in Figure 2). As a result, the predetermined region FL is cooled to a temperature lower than the ignition temperature of the fuel F by the heat of vaporization of the water 68.

While water injection into the combustion chamber using water injection valves 63A-63D can suppress the combustion temperature and reduce the amount of NOx in the exhaust gas, excessive water injection can result in a decrease in output due to an excessive drop in combustion temperature, so an appropriate amount of water must be injected using water injection valves 63A-63D. Therefore, for example, it is possible to set a water injection amount that can reduce the amount of NOx without excessively lowering the combustion temperature, depending on the engine speed and load.

However, setting the water injection amount according to the engine speed and load may not be able to sufficiently suppress NOx emissions during transient operation when the engine state changes. Specifically, during transient operation when the required EGR gas amount increases, there is a delay in the increase in the actual EGR gas amount. Therefore, setting the water injection amount according to the engine speed and load may result in an insufficient amount of water until the actual EGR gas amount reaches the required amount, and as a result, NOx emissions may not be sufficiently suppressed.

Figure 3 is a diagram showing, as a reference example, an example of the change in NOx amount during transient engine operation. In Figure 3, the EGR rate indicates the proportion of EGR gas in the intake gas supplied to the engine body. Line L1 (dotted line) is the target value of the EGR rate (target EGR rate), which in this example is determined from the engine speed and load (fuel injection amount, etc.). Line L2 (solid line) is the actual value of the EGR rate (actual EGR rate). Line L3 shows the change in NOx amount.

Referring to Figure 3, the change in the actual EGR rate (line L2) lags behind the change in the target EGR rate (line L1). Specifically, the target EGR rate peaks at time t1, while the actual EGR rate peaks at time t2, which is later than time t1. This is because there is a time lag between when the opening of the EGR valve increases in response to an increase in the target EGR rate and when this change in opening is reflected in a change in the EGR rate of the intake gas supplied to the combustion chamber. Due to this delay, the actual EGR rate is lower than the target EGR rate between time t1 and time t2.

In this reference example, the target EGR rate is determined from the engine speed and load, and the water injection amount is also determined based on the engine speed and load. Therefore, between time t1 and time t2, the water injection amount is small for an actual EGR rate that is lower than the target EGR rate, and as a result, the combustion temperature cannot be sufficiently suppressed, causing an increase in the amount of NOx (line L3). The same is true for times t3 and t4, where the amount of NOx increases due to the EGR delay between time t3 and time t4.

In the diesel engine 1 according to this embodiment, the amount of water injection is determined based on the engine speed and load of the engine body 10, and also using the amount of intake oxygen, a state quantity that directly affects the combustion state. Intake oxygen is oxygen contained in the intake gas supplied to the combustion chamber, and in this embodiment, the mass fraction of intake oxygen in the intake gas is used as the state quantity. By determining the amount of water injection from such a state quantity that directly affects the combustion state in the combustion chamber, an appropriate amount of water injection can be determined based on the combustion state even during transient operation.

Figure 4 shows an example of the progression of the maximum value of the average spray temperature in the combustion chamber. In Figure 4, line L4 indicates the maximum value of the average spray temperature (hereinafter sometimes simply referred to as the "spray temperature") Tmax, and line L5 indicates the target value of the spray temperature Tmax (hereinafter simply referred to as the "target spray temperature") Tmax0. In Figure 4, as a reference example, line L4 shows the temperature progression when the water injection amount setting in this embodiment as described above is not performed.

Note that the average spray temperature refers to the spatial average value of the combustion temperature within the combustion chamber, and the maximum average spray temperature refers to the maximum average spray temperature during one stroke of the engine. The target spray temperature Tmax0 is the spray temperature Tmax required to achieve the target amount of NOx, and in this embodiment, is determined based on the engine speed and load of the engine body 10. The target spray temperature Tmax0 is determined in advance through experiments, simulations, etc., and is stored in the storage device 53 as a map with the engine speed and load of the engine body 10 as parameters.

Referring to Figure 4, due to a change in the state of the engine body 10 (for example, the transient change described in Figure 3), the spray temperature Tmax (line L4) rises relative to the target spray temperature Tmax0 (line L5) at times t11 and t12. In this example, at time t11, a temperature difference ΔT(1) occurs between the spray temperature Tmax and the target spray temperature Tmax0, and at time t12, a temperature difference ΔT(2) occurs between the spray temperature Tmax and the target spray temperature Tmax0. This rise in spray temperature Tmax leads to an increase in the amount of NOx.

In this embodiment, this temperature difference ΔT is estimated from the intake oxygen amount (mass fraction of intake oxygen). Then, based on the estimated temperature difference ΔT, the water injection amount of the water injection valves 63A to 63D is determined so as to suppress the temperature difference ΔT. This makes it possible to inject an appropriate amount of water even during transient operation. As a result, the amount of NOx can be sufficiently suppressed, and a decrease in engine output due to an excessive drop in spray temperature can be suppressed. Below, we will explain the above temperature difference ΔT and the method for calculating the water injection amount based on it.

In the diesel engine 1 according to this embodiment, the fuel spray temperature Tmax (K) is calculated using the following empirical formula (1), which was derived from prior experiments or simulations.

This equation (1) assumes that the Arrhenius equation holds between NOx generation rate and spray temperature, and employs an Arrhenius-type model with a temperature parameter in the exponential term of e (Napier's number). In equation (1), Y represents the mass fraction of intake oxygen, and Y0 represents the mass fraction of intake oxygen under base conditions.

The mass fraction Y of intake oxygen can be calculated using known methods from the intake air volume detected by the intake flow sensor 21 and the EGR volume (rate). The EGR volume (rate) can be estimated using known methods from the intake air volume detected by the intake flow sensor 21 and the value detected by the pressure sensor 24.

The base conditions are conditions based on the engine speed and engine load at the time of calculation under steady-state operation of the diesel engine 1. Specifically, Y0 is the mass fraction of intake oxygen at the engine speed and load of the engine body 10 at the time of calculation, and Tmax0 is the spray temperature (maximum value of the average injection temperature) at the engine speed and load of the engine body 10 at the time of calculation. The intake oxygen mass fraction Y0 and spray temperature Tmax0 under these base conditions correspond to the target values of the intake oxygen mass fraction Y and spray temperature Tmax, respectively. The intake oxygen mass fraction Y0 and spray temperature Tmax0 are determined in advance by experiments, simulations, etc. using the engine speed and load of the engine body 10 as parameters, and are stored in the storage device 53 as a map.

The intake oxygen mass fraction Y0 and spray temperature Tmax0 under base conditions are obtained from the map based on the engine speed and load of the engine body 10 at the time of calculation, and the spray temperature Tmax can be calculated from the intake oxygen mass fraction Y using equation (1). The engine speed of the engine body 10 can be calculated from the detection value of the rotation angle sensor 22. The load on the engine body 10 is calculated, for example, from the fuel injection amount from the fuel injection valves 43A-43D and/or the accelerator pedal depression amount detected by the accelerator pedal sensor 25.

Then, the temperature difference ΔT between the calculated spray temperature Tmax and the spray temperature Tmax0 under base conditions is calculated using the following equation (2):

ΔT=Tmax-Tmax0...(2)
In this embodiment, the water injection amount Qw (g) of each water injection valve 63A to 63D is calculated from this temperature difference ΔT. The water injection amount Qw is the amount required to lower the spray temperature Tmax by the temperature difference ΔT, and is calculated using the following formula:

Qw=Ms×Cp×ΔT/Hw…(3)
Ms denotes the mass (g) of the spray gas (a mixture of intake gas and fuel) generated by spraying fuel into the combustion chamber, Cp denotes the constant pressure specific heat of the spray gas (kJ/(kg·K)), and Hw denotes the latent heat of vaporization of water (kJ/kg).

The spray gas mass Ms is a parameter that depends on the amount or injection pressure of fuel injected from each fuel injection valve 43B-43D and varies depending on the operating conditions of the engine body 10. The spray gas mass Ms is determined in advance, for example, through experiments or simulations using the engine speed and load (fuel injection amount, etc.) of the engine body 10 as parameters, and is stored in the storage device 53 as a map.

Figure 5 shows an example of the relationship between the temperature difference ΔT in the spray temperature from the base conditions and the water injection amount Qw. In Figure 5, the horizontal axis represents the temperature difference ΔT between the spray temperature Tmax and the spray temperature Tmax0 under the base conditions, and the vertical axis represents the water injection amount Qw.

5, line L11 shows the relationship when the engine speed is 1200 rpm and the fuel injection amount is 20 qv ( ^mm3 /st) ("st" indicates stroke), line L12 shows the relationship when the engine speed is 1600 rpm and the fuel injection amount is 30 qv, and line L13 shows the relationship when the engine speed is 2000 rpm and the fuel injection amount is 50 qv.

In this way, in the diesel engine 1 according to this embodiment, the fuel spray temperature Tmax is calculated from the intake oxygen amount (intake oxygen mass fraction Y) using equation (1), and the water injection amount Qw of each water injection valve 63A-63D is determined based on the temperature difference ΔT in the spray temperature from the base conditions.

Figure 6 is a flowchart illustrating the process executed by the control device 50 to calculate the water injection amount of the water injection valves 63A-63D. The series of processes shown in this flowchart are repeatedly executed at predetermined time intervals or whenever predetermined conditions are met while the diesel engine 1 is operating.

Referring to FIG. 6, the control device 50 first calculates the intake oxygen mass fraction Y, which indicates the amount of intake oxygen, a state quantity directly related to the combustion state in the combustion chamber (step S10). The intake oxygen mass fraction Y can be calculated using a known method from the intake air amount detected by the intake flow sensor 21 and the EGR amount (rate).

Next, the control device 50 detects the rotation speed and load of the engine main body 10 (step S20). The rotation speed is calculated from the detection value of the rotation angle sensor 22. The load of the engine main body 10 is calculated from the fuel injection amount from the fuel injection valves 43A-43D and/or the amount of depression of the accelerator pedal detected by the accelerator pedal sensor 25.

Furthermore, the control device 50 uses a map showing the relationship between the engine speed and engine load under steady-state operation and the intake oxygen mass fraction and spray temperature, respectively, to obtain the intake oxygen mass fraction Y0 and spray temperature Tmax0 under base conditions based on the engine speed and load detected in step S20 (step S30). This spray temperature Tmax0 under base conditions corresponds to the target value for the spray temperature Tmax (the target spray temperature required for NOx reduction).

Then, using the previously determined empirical formula (1) above, the control device 50 calculates the spray temperature Tmax at the time of calculation from the intake oxygen mass fraction Y calculated in step S10, and the intake oxygen mass fraction Y0 and spray temperature Tmax0 under the base conditions obtained in step S30 (step S40).

Next, the control device 50 calculates the temperature difference ΔT (= Tmax - Tmax0) between the spray temperature Tmax calculated in step S40 and the spray temperature Tmax0 under base conditions (the target spray temperature required for NOx reduction) (step S50).

Next, the control device 50 calculates the spray gas mass Ms under the operating conditions of the engine body 10 at the time of calculation (step S60). Specifically, the control device 50 calculates the spray gas mass Ms based on the rotation speed and load detected in step S20, using a map showing the relationship between the rotation speed and load (fuel injection amount, etc.) of the engine body 10 and the spray gas mass Ms.

Then, the control device 50 calculates the water injection amount Qw for each water injection valve 63A-63D from the temperature difference ΔT calculated in step S50 (step S70). Specifically, using the above-mentioned equation (3), the water injection amount Qw is calculated from the temperature difference ΔT calculated in step S50 and the spray gas mass Ms calculated in step S60.

As described above, in this embodiment, the spray temperature Tmax is estimated from the intake oxygen mass fraction Y according to the predetermined relationship (Equation (1)) between the intake oxygen mass fraction (fuel oxygen amount), which is a state quantity directly related to the combustion state in the combustion chamber, and the spray temperature of the fuel injected into the combustion chamber. The water injection amount Qw for each fuel injection valve 43A-43D is then determined from the temperature difference ΔT between the estimated spray temperature Tmax and the spray temperature Tmax0 (target spray temperature) under base conditions.

This allows the appropriate water injection amount Qw to be determined based on the combustion state even during transient operation. Therefore, according to this embodiment, an appropriate amount of water can be injected even during transient operation. As a result, the amount of NOx can be sufficiently suppressed, and a decrease in output due to an excessive drop in combustion temperature can be suppressed.

In addition, in the above embodiment, an EGR device 13 is provided, and when the amount of exhaust gas recirculated by the EGR device 13 is changed, the water injection amount Qw is determined from the intake oxygen mass fraction (intake oxygen amount). This prevents the problem of insufficient water injection due to delayed EGR gas response during transient operation. Therefore, according to this embodiment, the amount of NOx can be sufficiently suppressed.

When the engine body 10 is cold started, operation of the EGR device 13 may be restricted because condensed water is generated when the EGR device 13 is operated. Restricting operation of the EGR device 13 may increase the combustion temperature and the amount of NOx. In this embodiment, the water injection amount Qw is determined from the intake oxygen amount (intake oxygen mass fraction Y), which is a state quantity directly related to the combustion state. Therefore, the amount of NOx can be sufficiently suppressed even when the engine body 10 is cold started.

The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The technical scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims.

1 Diesel engine, 10 Engine body, 11A, 11B Intake pipe, 11C Intake manifold, 12A Exhaust manifold, 12B, 12C Exhaust pipe, 13 EGR device, 13A, 13B EGR pipe, 13C Bypass pipe, 14A Path switching device, 14B EGR valve, 15 EGR cooler, 16 Intercooler, 21 Intake flow sensor, 22 Rotation angle sensor, 23 Atmospheric pressure sensor, 24, 26 Pressure sensor, 25 Accelerator pedal sensor, 27 Vehicle speed sensor, 29 Temperature sensor, 30 Turbocharger, 35 Compressor, 35A Compressor impeller, 36 Turbine, 36A Turbine impeller, 41 Common rail, 42A to 42D Fuel pipe, 43A to 43D Fuel injection valve, 45A to 45D Cylinder, 47 Throttle device, 47A throttle valve, 50 control device, 51 processor, 53 storage device, 61 water supply common rail, 62A to 62D water piping, 63A to 63D water injection valves, 65 supply pipe, 66 pump, 67 water tank, 71 cylinder block, 72 cylinder head, 73 piston, 75 combustion chamber, 76 cavity.

Claims (7)

an engine body having a combustion chamber;
a fuel injector configured to inject fuel into the combustion chamber;
a water injection device configured to inject water into the combustion chamber;
a control device for controlling the water injection device;
an acquisition unit that acquires a state quantity indicating an amount of oxygen contained in intake gas supplied into the combustion chamber,
The control device
estimating the spray temperature from the state quantity acquired by the acquisition unit in accordance with a predetermined relationship between the state quantity and the spray temperature of the fuel injected into the combustion chamber;
a water injection amount by the water injection device is determined based on a temperature difference between the estimated spray temperature and the target spray temperature. an EGR device configured to connect an exhaust passage to an intake passage without passing through the engine body and to recirculate a portion of the exhaust gas to the intake passage;
2. The diesel engine according to claim 1, wherein the control device determines the amount of water injection based on the temperature difference when the amount of exhaust gas recirculated by the EGR device is changed. The diesel engine described in claim 2, wherein the control device determines the water injection amount based on the temperature difference during a cold start of the engine body, when operation of the EGR device is restricted. A diesel engine according to any one of claims 1 to 3, wherein the target spray temperature is determined based on the engine speed and load of the engine body. the relationship is a relationship between the state quantity and a maximum value of the spray temperature in one stroke of the engine body,
The control device
estimating a maximum value of the spray temperature from the state quantity acquired by the acquisition unit in accordance with the relationship;
5. The diesel engine according to claim 1, wherein the water injection amount is determined from a temperature difference between the estimated maximum value of the spray temperature and a target maximum value of the spray temperature. A diesel engine according to any one of claims 1 to 5, wherein the control device calculates the water injection amount by multiplying the mass of spray gas in the combustion chamber, the spray gas constant pressure specific heat, and the temperature difference, which are determined according to the operating state of the engine body, and dividing the result by the latent heat of vaporization of water. 1. A control method for a diesel engine equipped with a fuel injection device that injects fuel into a combustion chamber and a water injection device that injects water into the combustion chamber, comprising:
acquiring a state quantity indicating the amount of oxygen contained in the intake gas supplied into the combustion chamber;
a step of estimating the spray temperature from the acquired state quantity in accordance with a predetermined relationship between the state quantity and the spray temperature of the fuel injected into the combustion chamber;
determining an amount of water injection by the water injection device from a temperature difference between the estimated spray temperature and a target spray temperature.