JP4730264B2 - Premixed compression ignition internal combustion engine - Google Patents

Description

  The present invention relates to a premixed compression ignition internal combustion engine, and more particularly to a technique for preventing the occurrence of knocking by slow combustion.

In Patent Document 1, an exhaust gas is recirculated only to one of two intake ports to form an EGR layer and an air layer in a combustion chamber, and fuel is injected into a boundary region between the EGR layer and the air layer. Thus, it is described that the pre-reaction is started from the boundary region where the temperature gradient is large, and thereafter, the self-ignition proceeds sequentially to the region where the temperature is low according to the temperature gradient, thereby avoiding rapid combustion.
JP 2001-214741 A

By the way, while EGR gas is high temperature, it has a reaction promoting effect, while EGR gas is an inert gas and has a reaction suppressing effect at the same time.
For this reason, even if fuel is injected into the boundary region between the EGR layer and the air layer, the reaction promotion effect due to the temperature is offset by the reaction suppression effect due to the inert gas, and the effect of slow combustion due to the temperature stratification is sufficiently obtained. There was a problem that it was difficult to obtain.

  The present invention has been made in view of the above problems, and an object of the present invention is to more reliably prevent knocking due to rapid combustion in a premixed compression ignition internal combustion engine.

Therefore, the present invention provides a premixed compression ignition internal combustion engine in which an air-fuel mixture formed by a plurality of types of fuels having different ignition temperatures is in a combustion chamber, and an air-fuel mixture with a relatively low ignition temperature is ignited. A layer is formed so as to be surrounded by an air-fuel mixture having a relatively high temperature .

  According to the above invention, a pre-reaction is started from an air-fuel mixture formed by a fuel having a low ignition temperature and ignition is performed, and thereafter combustion in the air-fuel mixture formed by a fuel having a high ignition temperature is performed, so that the combustion period is extended. Thus, the occurrence of knocking can be prevented, and the operating range in which premixed compression ignition can be performed can be expanded to the high load side.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 show a premixed compression ignition internal combustion engine in the first embodiment.
The internal combustion engine 101 shown in the figure is provided with two intake valves 102a and 102b and two exhaust valves 103a and 103b in each cylinder.
The two intake valves 102 a and 102 b are valves that open and close the open ends of the two intake ports 104 a and 104 b on the combustion chamber 105 side, and are driven to open and close by a cam 107 provided on the intake camshaft 106.

On the other hand, the exhaust valves 103a and 103b are valves that open and close the open ends of the two exhaust ports 108a and 108b on the combustion chamber 105 side, respectively, and are opened and closed by a cam 110 provided on the exhaust camshaft 109.
In the center of the cylinder head 111 forming the combustion chamber 105, a first fuel injection valve 112 and a spark plug 113 are arranged.

The first fuel injection valve 112 is supplied with high-pressure fuel boosted by a high-pressure pump 114 driven by the intake camshaft 106.
The high-pressure pump 114 is supplied with fuel (gasoline) in a fuel tank (not shown) by an electric low-pressure pump.
On the other hand, a second fuel injection valve 115 is provided upstream of one of the two intake ports 104a and 104b, and fuel is supplied to the second fuel injection valve 115 by the low-pressure pump. Supplied.

Further, a bypass passage 116 is provided on the downstream side of the portion where the second fuel injection valve 115 of the intake port 104a is installed, and a catalyst 117 as a fuel reformer is interposed in the bypass passage 116. Has been.
The catalyst 117 is an oxidation catalyst in which a noble metal such as rhodium, ceria, or platinum is supported on a carrier.

On the inlet side of the bypass passage 116, the intake air is switched between a state in which the inlet of the bypass passage 116 is closed and air is allowed to flow only to the intake port 104a, and a state in which the intake port 104a is closed and air is allowed to flow only to the bypass passage 116 side. A control valve 118 (switching means) is provided.
The intake control valve 118 is driven by an actuator such as a motor (not shown).

Further, an exhaust pipe 119 is extended in the vicinity of the bypass passage 116 where the catalyst 117 is provided, and heat exchange is performed between the bypass passage 116 where the catalyst 117 is provided and the adjacent exhaust pipe 119. A vessel 120 is provided.
The heat exchanger 120 is a heating unit that heats the catalyst 117 with exhaust heat.
An exhaust bypass passage 121 is branched and extended from the exhaust pipe 119 upstream of the portion where the heat exchanger 120 is provided, and the exhaust bypass passage 121 is downstream of the portion where the heat exchanger 120 is provided. To the exhaust pipe 119.

At the entrance of the exhaust bypass passage 121, there is an exhaust control valve 122 that controls the ratio between the flow rate of exhaust flowing through the exhaust bypass passage 121 and the flow rate of exhaust flowing directly through the exhaust pipe 119 without flowing into the exhaust bypass passage 121. Is provided.
By controlling the flow rate of the exhaust gas flowing into the heat exchanger 120 by the exhaust control valve 122, the heating amount of the catalyst 117 by the heat exchanger 120 is controlled.

By the way, generally, between the octane number and the ignition temperature of gasoline, as shown in FIG. 3, there is a characteristic that the ignition temperature decreases as the octane number decreases.
On the other hand, when gasoline is oxidized (reformed) by the catalyst 117, the octane number is lowered, and the gasoline after passing through the catalyst 117 (the gasoline after reforming) is not passed through the catalyst 117 (before reforming). The ignition temperature is lower than that of gasoline (see FIG. 3).

  The first and second fuel injection valves 112 and 115 are supplied with the same type of fuel (gasoline) supplied from a common fuel tank, but the first fuel injection valve 112 receives fuel. Although the fuel is directly injected into the combustion chamber, if the air is made to flow toward the bypass passage 116 by the intake control valve 118, the fuel injected from the second fuel injection valve 115 is reformed by the catalyst 117 and then the combustion chamber. Will be aspirated.

  Here, the fuel that is injected from the second fuel injection valve 115 and has undergone reforming that lowers the ignition temperature (octane number) in the middle is sucked into the combustion chamber 105 in the intake stroke. By causing the fuel injection by the first fuel injection valve 112 to be performed in the intake stroke, as shown in FIG. 4, the fuel-air mixture whose ignition temperature has been lowered by reforming has an ignition temperature that has not been reformed. A mixture layer can be formed in the combustion chamber 105 so as to be surrounded by a mixture of relatively high fuel.

That is, the air-fuel mixture formed by two fuels having different ignition temperatures forms a layer in the combustion chamber 105 during the compression stroke.
The pre-reaction is started from the gas mixture layer (middle gas mixture layer) with the fuel having a low ignition temperature among the two gas mixture layers, and the calorific value in the initial stage of the compression combustion is not so large as to cause knocking, When the reformed fuel is ignited, combustion in the air-fuel mixture layer is started by the surrounding non-reformed fuel. Therefore, when a uniform air-fuel mixture is formed with uniform fuel in the combustion chamber 105 In comparison, the combustion period can be extended and knocking can be avoided (see FIG. 5).

Here, the operations of the first and second fuel injection valves 112 and 115, the intake control valve 118, the exhaust control valve 122, and the spark plug 113 are controlled by a control unit 130 incorporating a microcomputer.
The control unit 130 receives detection signals from an accelerator opening sensor 131 that detects an accelerator opening (required load), a rotation sensor 132 that detects an engine rotation speed, a water temperature sensor 133 that detects an engine coolant temperature, and the like. Entered.

The control unit 130 controls the combustion of the engine 101 as shown in the flowchart of FIG. It is assumed that the load on the engine 101 is controlled by the amount of fuel input.
In the flowchart of FIG. 6, in step S101, the engine operating state such as the engine load and the engine speed is read.

In step S102, the combustion pattern is determined.
In the engine 101 of this embodiment, as shown in FIG. 7, an operation region in which premixed compression ignition combustion is performed and an operation region in which spark ignition combustion is performed are set in advance according to the engine load and the engine speed. It is designed to perform premixed compression ignition combustion at medium load and medium rotation range.
In step S102, it is determined whether the engine load and engine speed at that time correspond to the premixed compression ignition combustion region or the spark ignition combustion region shown in FIG.

Here, if it is determined that the current engine load and engine speed fall within the spark ignition combustion region, the process proceeds to step S103, and the intake control valve 118 is driven and controlled to a position where the inlet of the bypass passage 116 is closed. In step S104, spark ignition control is performed.
In the spark ignition control in step S104, the fuel injection from the second fuel injection valve 115 is stopped, while the fuel injection by the first fuel injection valve 112 is performed in the intake stroke or the compression stroke, The premixed fuel is ignited and burned by spark ignition by the spark plug 113.

On the other hand, if it is determined in step S102 that the current engine load and engine speed correspond to the premixed compression ignition combustion region, the process proceeds to step S105.
In step S105, it is determined whether or not the temperature of the catalyst 117 is the activation temperature.
For example, when the cooling water temperature exceeds a threshold, it can be estimated that the temperature of the catalyst 117 has reached the activation temperature, and a sensor for detecting the temperature of the catalyst 117 is provided, and the temperature of the catalyst 117 is detected by the sensor. You may make it detect directly.

From the start of the engine 101 until the warm-up is completed, the catalyst 117 is heated via the heat exchanger 120 by controlling the exhaust control valve 122 so that the exhaust does not flow into the exhaust bypass passage 121. Allow the activation temperature to be reached early.
In the spark ignition combustion state after activation, the exhaust control valve 122 may be continuously controlled so that the exhaust does not flow into the exhaust bypass passage 121, or the engine load at that time according to the characteristics shown in FIG. The opening degree of the exhaust control valve 122 (exhaust flow rate released to the exhaust bypass passage 121) may be controlled so as to reach a target temperature according to the engine speed.

If the catalyst 117 has not reached the activation temperature, the fuel (gasoline) reforming using the catalyst 117 cannot be performed. Therefore, the process proceeds to step S106, while the fuel injection from the second fuel injection valve 115 is stopped. The fuel injection by the first fuel injection valve 112 is performed in the intake stroke or the compression stroke, and the compression self-ignition combustion is performed.
When it is determined that the catalyst 117 has reached the activation temperature, the process proceeds to step S107.

In step S107, the intake control valve 118 opens the inlet of the bypass passage 116 so that the fuel injected from the second fuel injection valve 115 is introduced into the catalyst 117. Control the catalyst temperature.
The reformed fuel injection ratio control is the ratio of the fuel to be injected from the second fuel injection valve 115 in the required fuel amount. In other words, the reformed fuel is injected from the second fuel injection valve 115 and modified by the catalyst 117. It is the ratio of the fuel that lowered the ignition temperature by improving the quality.

As shown in FIG. 8, the injection ratio of the reformed fuel is determined in advance according to the engine load (accelerator opening) and the engine speed, and increases as the engine speed increases and the engine load decreases. Is set.
When the engine 101 is at a low load, the amount of fuel input to the engine 101 is small and the air-fuel ratio is lean, and compared to a high load at which the fuel input amount is large and the air-fuel ratio is rich, combustion is likely to be unstable.

Therefore, at low loads, the proportion of reformed fuel having a low ignition temperature is increased in order to improve combustion stability.
Further, when the engine speed is high, the time required for the reaction in the catalyst 117 cannot be secured, so that the combustion stability is improved by increasing the proportion of reformed fuel having a low ignition temperature.

On the other hand, the control of the catalyst temperature is to control the temperature of the catalyst 117 to the target temperature by controlling the opening degree of the exhaust control valve 122 (exhaust flow rate released to the exhaust bypass passage 121).
Here, as shown in FIG. 9, the target temperature of the catalyst 117 is determined in advance according to the engine load (accelerator opening) and the engine speed, and the higher the engine speed and the lower the engine load, the higher the temperature. Set to

Since the amount of fuel that can be reformed (oxidized) increases as the temperature of the catalyst 117 increases, the target temperature is increased (the heating amount is increased) in the high rotation / low load region where the injection ratio of the reformed fuel is increased. And increase the amount of fuel that can be reformed (oxidized) to ensure combustion stability.
In step S108, the amount of fuel injected from the first fuel injection valve 112 and the amount of fuel injected from the second fuel injection valve 115 are determined based on the accelerator opening at that time and the reformed fuel ratio, By injecting fuel from the fuel injection valves 112 and 115, the air-fuel mixture formed by two fuels having different ignition temperatures forms a layer in the combustion chamber 105, and in two stages depending on the difference in the ignition temperature. Compressive self-ignition combustion is performed.

That is, the fuel that has not been reformed because the pre-reaction starts from the fuel mixture layer with the low ignition temperature of the two gas mixture layers and burns, and after the reformed fuel is ignited, the temperature further rises To compression self-ignition combustion (see FIG. 5).
Therefore, since the rapid combustion is not performed and the slow combustion with a long combustion period can be realized, and the occurrence of knocking can be prevented, the compression self-ignition combustion region can be expanded to the high load side.

Although the catalyst 117 is heated by using the exhaust heat from the heat exchanger 120, a heater is provided as a heating means for the catalyst 117, and the power supply to the heater is controlled to control the heating amount. be able to.
By the way, instead of reforming the fuel injected from the second fuel injection valve 115, the fuel reformed by the fuel reformer (catalyst) can be injected from the second fuel injection valve 115. FIG. 10 and FIG. 11 show the second embodiment.

10 and 11, the same elements as those in FIGS. 1 and 2 are denoted by the same reference numerals.
As shown in FIGS. 10 and 11, in the second embodiment, the bypass passage 116, the intake control valve 118, the exhaust control valve 122, and the exhaust bypass passage 121 provided in the first embodiment are omitted.

In place of the catalyst 117, a fuel reformer (catalyst) 141 is provided upstream of the second fuel injection valve 115, and the second fuel injection valve 115 is reformed (oxidized) by the fuel reformer (catalyst) 141. ) Is injected into the intake port 104a.
The fuel reformer (catalyst) 141 can be heated using a heat exchanger that exchanges heat with the exhaust as in the first embodiment, and a heater may be used. The heating amount can be controlled in accordance with the engine load and the engine rotation speed in the same manner as the embodiment.

  In addition, the injection ratios by the first and second fuel injection valves 112 and 115 are controlled according to the engine load and the engine rotation speed in the same manner as in the first embodiment, and the modified fuel injected from the second fuel injection valve 115 is controlled. An air-fuel mixture layer formed of a quality fuel (a fuel with a low ignition temperature) is disposed in the center of the combustion chamber 105, and is formed with an unreformed fuel (a fuel with a high ignition temperature) so as to surround the periphery. An air-fuel mixture layer is provided, and the combustion chamber 105 is stratified by the air-fuel mixture layer with fuels having different ignition temperatures.

According to the above configuration, since the fuel reformed in advance is injected from the fuel injection valve, the air-fuel mixture can be stably formed by the reformed fuel.
As described above, when fuel that has been reformed in advance is injected from the fuel injection valve, the first fuel injection valve 112 that directly injects fuel into the combustion chamber 105 is reformed by the fuel reformer (catalyst) 141. The second fuel injection valve 115 that injects the injected fuel and injects it into the intake port 104a can inject the fuel before reforming.

  In this case, while the fuel injection by the first fuel injection valve 112 is performed in the compression stroke, the fuel injection by the second fuel injection valve 115 is performed in the intake stroke, so that the reformed fuel (fuel having a low ignition temperature) is used. An air-fuel mixture layer formed by unreformed fuel (fuel having a high ignition temperature) can be disposed so as to surround the air-fuel mixture layer formed at the center of the combustion chamber 105 and surround the periphery thereof. .

  A first fuel tank for storing a fuel reformed by a fuel reformer or a low-octane fuel replenished from the outside at a gas station, etc., instead of reforming in the middle of a fuel conveyance path; And a second fuel tank that stores high-octane fuel that is replenished externally at a fuel station or the like before reforming, and one of the first and second fuel injection valves 112 and 115 is the first fuel tank. The fuel in the second fuel tank is injected, and the other of the first and second fuel injection valves 112 and 115 injects the fuel in the second fuel tank.

Further, the fuel reforming process includes a known process capable of changing the ignition temperature, such as a fractional distillation based on a difference in boiling point and addition of an additive, in addition to an oxidation process using a catalyst.
Then, reformation produces a fuel with a higher octane number and higher ignition temperature than before reforming, and uses a fuel with a higher octane number obtained by this reforming and a fuel with lower octane number and lower ignition temperature before reforming. In addition, the reforming can simultaneously generate a fuel having a higher octane number and higher ignition temperature than before the reforming and a fuel having a lower octane number and lower ignition temperature than before the reforming. You can also.

Furthermore, a first fuel injection valve that directly injects fuel into the combustion chamber 105 and a second fuel injection valve that also directly injects fuel into the combustion chamber 105 are provided, and the ignition temperature of each of these fuel injection valves is mutually increased. By injecting different fuels, for example, in the intake stroke and the compression stroke, it is possible to form air-fuel mixture layers with different ignition temperatures.
It is also possible to prepare three or more kinds of fuels having different ignition temperatures and to form three or more gas mixture layers.

The figure which shows the premixing compression ignition internal combustion engine in 1st Embodiment. The figure which shows the premixing compression ignition internal combustion engine in the said 1st Embodiment. The diagram for demonstrating the characteristic of the modification | reformation in the said 1st Embodiment based on the correlation of an octane number and ignition temperature. The figure which shows the distribution of the air-fuel | gaseous mixture in the said 1st Embodiment. The figure for demonstrating the combustion characteristic in the said 1st Embodiment from the relationship between in-cylinder temperature and a heat release rate. The flowchart which shows the combustion control in the said 1st Embodiment. The figure which shows the pre-mixing compression ignition area | region and spark ignition area | region in the said 1st Embodiment. The diagram which shows the characteristic of the reformed fuel ratio in the said 1st Embodiment. The diagram which shows the characteristic of the target temperature of the catalyst in the said 1st Embodiment. The figure which shows the premixing compression ignition internal combustion engine in 2nd Embodiment. The figure which shows the premixing compression ignition internal combustion engine in the said 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Internal combustion engine, 102a, 102b ... Intake valve, 103a, 103b ... Exhaust valve, 104a, 104b ... Intake port, 105 ... Combustion chamber, 112 ... First fuel injection valve, 113 ... Spark plug, 114 ... High pressure pump, 115 DESCRIPTION OF SYMBOLS 2nd fuel injection valve, 116 ... Bypass passage, 117 ... Catalyst (fuel reforming device), 118 ... Intake control valve (switching means), 120 ... Heat exchanger, 121 ... Exhaust bypass passage, 122 ... Exhaust control valve, 130 ... Control unit, 141 ... Fuel reformer

Claims (1)

A fuel reformer;
Heating means for heating the fuel reformer so as to increase the amount of heating as the engine rotational speed is higher or the engine load is lower;
With
The mixture formed by the fuel reformed by the fuel reformer having different ignition temperatures and the fuel before reformed by the fuel reformer forms a layer in the combustion chamber. A premixed compression ignition internal combustion engine.

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