JP2007024001A - Engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain a stable operating state even if EGR is performed by an EGR means X in an engine 100 comprising a fuel feed means 21 forming an air-fuel mixture by feeding a fuel G into an air A flowing in a suction passage 13 and the EGR means X recirculating exhaust gases E in a combustion chamber 10. <P>SOLUTION: The EGR means X is a means to discharge the exhaust gases E to the suction passage 13 by temporarily bringing a suction valve 1 into an open state in an exhaust stroke. The fuel feed means 21 is so formed that it can feed the fuel G into an exhaust gas area EA in which the exhaust gases E are discharged in the suction passage 13. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an engine including fuel supply means for supplying fuel to air flowing through an intake passage to form an air-fuel mixture, and EGR means for recirculating exhaust gas in a combustion chamber.

There is a premixed compression ignition engine that actively uses self-ignition of fuel as an engine that can achieve high efficiency and low NOx by high-compression and self-ignition combustion of fuel in a lean state.
Such a premixed compression ignition engine does not inject fuel into compressed air as in a diesel engine, but uses a fuel supply valve (fuel supply means) provided in the intake path as in a spark ignition engine. Fuel is supplied to the flowing air to form an air-fuel mixture, and the air-fuel mixture sucked into the combustion chamber is highly compressed and is heated to the self-ignition temperature of the air-fuel mixture to be self-ignited and combusted. Also, such a premixed compression ignition engine does not need to be highly compressed and injected into the combustion chamber like a diesel engine, so it can be easily applied to a gas engine using a gaseous fuel such as natural gas. Can do.
In such an engine, there is a problem that the load range is narrowly limited due to combustion fluctuation or misfire and knock, etc. Especially in a premixed compression ignition engine, the occurrence of knock which is considered to be caused by rapid heat generation during self-ignition Therefore, the equivalence ratio of the air-fuel mixture sucked into the combustion chamber needs to be relatively low and is limited to operation in a low load region.

In such an engine, so-called EGR is performed to recirculate the exhaust gas discharged from the combustion chamber to the combustion chamber, so that the combustion of the air-fuel mixture can be slowed to suppress the generation of knock and the generation of NOx.
In addition, as a premixed compression ignition engine that performs such EGR, a relatively high temperature exhaust gas is recirculated to the combustion chamber, and an EGR amount that is the amount of the exhaust gas is adjusted, whereby an air-fuel mixture that is sucked into the combustion chamber. A premixed compression ignition engine that can adjust the self-ignition timing of the air-fuel mixture to an appropriate timing is known (for example, see Patent Document 1).

JP 2000-274246 A

However, even if EGR is performed on the engine as described above to suppress the generation of knock or the generation of NOx, there are cases where a stable operating state cannot be maintained.
For example, in a stratified combustion engine, when EGR is performed in a case where an air-fuel mixture is stratified in a combustion chamber in a state in which a rich portion rich in fuel is unevenly distributed, and the air-fuel mixture is ignited and burned in the rich portion, The occurrence of knocking and NOx formation at the time of ignition of the air-fuel mixture in the zone can be suppressed. However, in the light zone where the fuel other than the rich zone is thin, the recirculated exhaust gas causes an excessive decrease in the combustion rate. The fuel component may increase and the efficiency may decrease.

  In particular, in a premixed compression ignition engine, by performing EGR, sudden heat generation during self-ignition is suppressed and knocking is suppressed, but the subsequent combustion of a relatively lean mixture becomes excessively slow. May end up.

  Further, in the premixed compression ignition engine, even when the EGR amount is adjusted to adjust the self-ignition timing of the air-fuel mixture to an appropriate timing, the EGR amount is increased in order to change the self-ignition timing to the retard side. Then, the combustion of the relatively lean air-fuel mixture becomes excessively slow.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to supply a fuel to air flowing through an intake passage to form an air-fuel mixture, and to recirculate exhaust gas into a combustion chamber. An engine provided with EGR means is to provide a technique capable of maintaining a stable operation state even when EGR is performed by the EGR means.

In order to achieve the above object, an engine according to the present invention includes fuel supply means for supplying fuel to air flowing through an intake passage to form an air-fuel mixture, and EGR means for recirculating exhaust gas to a combustion chamber. The engine is characterized in that the EGR means is means for exhausting exhaust gas into the intake passage by temporarily opening an intake valve in an exhaust stroke,
The fuel supply means is configured to be able to supply fuel to an exhaust gas region where exhaust gas is discharged in the intake passage.

According to the first characteristic configuration, when the exhaust gas in the combustion chamber is discharged to the exhaust passage during the exhaust stroke, the EGR means temporarily opens the intake valve during the exhaust stroke. The exhaust gas can be discharged to the intake passage via the intake valve instead of the exhaust passage, and the exhaust gas discharged to the intake passage can be recirculated to the combustion chamber together with the air-fuel mixture formed in the intake passage.
Further, after the exhaust gas is discharged into the intake passage in the exhaust stroke by the fuel supply means, the fuel is supplied to the exhaust gas region in which the relatively high temperature exhaust gas is discharged in the intake passage, so that the fuel becomes the exhaust gas. Therefore, when the mixture of the fuel and the air whose temperature has been raised is sucked into the combustion chamber and ignited, the ignitability of the fuel is improved and misfire is suppressed. it can. In addition, since the air-fuel mixture sucked into the combustion chamber is concentrated in a portion where the fuel is rich and exhaust gas exists, the combustion speed after ignition of the fuel is well suppressed to suppress the generation of knock and the generation of NOx. Can do. Further, since the exhaust gas is in a lean state in the portion where the fuel is lean in the air-fuel mixture, the lean air-fuel mixture can be sufficiently combusted to prevent generation of unburned components and improve the efficiency.
Therefore, according to the present invention, it is possible to realize an engine that can maintain a stable operation state even when EGR is performed by the EGR means.

  A second characteristic configuration of the engine according to the present invention is that the EGR means is configured to open the intake valve at an early stage of the exhaust stroke.

  According to the second characteristic configuration, the intake valve is temporarily opened at the initial stage of the exhaust stroke by the EGR means, so that the intake stroke is started again after the intake valve is closed in the exhaust stroke. The exhaust gas region formation period until the intake valve is opened can be secured long enough, and furthermore, the gas flow in the intake passage is almost stopped during the exhaust gas region formation time, so the exhaust gas region is combusted in the intake passage. It can be stopped at a certain location near the room. Therefore, the fuel supply means can supply the fuel to the exhaust gas region fixed in the vicinity of the combustion chamber with a margin in the exhaust gas region formation period secured for a sufficiently long time, and further the heat of the fuel and the exhaust gas. The fuel can be raised in temperature by sufficient replacement.

  According to a third characteristic configuration of the engine according to the present invention, the fuel supply means includes a first state in which fuel is supplied to the exhaust gas region, and a second state in which fuel is supplied to a non-exhaust gas region outside the exhaust gas region. , In that it is configured to be switchable.

  According to the third characteristic configuration, as described above, the first state in which fuel is supplied to the exhaust gas region when the fuel supply amount is decreased and the low load region operation is performed, for example, as described above. In addition to improving the ignitability of the fuel and the like, for example, when performing high load region operation by increasing the fuel supply amount, the second state in which fuel is supplied to the non-exhaust region outside the exhaust region in the intake passage Switch to ensure that the exhaust gas is present throughout the combustion chamber without concentrating on the dense part where the fuel is concentrated. Can be obtained.

  A fourth characteristic configuration of the engine according to the present invention is that it is configured as a premixed compression ignition engine that compresses the air-fuel mixture sucked into the combustion chamber and performs self-ignition combustion.

According to the fourth characteristic configuration, when the premixed compression ignition engine is configured, the EGR unit and the fuel supply unit are configured as described above so that a relatively lean air-fuel mixture is self-generated. Even in the case of igniting and burning, it is possible to improve the ignitability of the fuel and suppress misfiring, while slowing the combustion after the self-ignition and avoiding knocking due to rapid heat generation. Further, when combustion progresses and a relatively lean air-fuel mixture burns, the exhaust gas is in a lean state like the fuel for the lean air-fuel mixture, so that the combustion of the lean air-fuel mixture becomes excessive. Slowing down can be suppressed, generation of unburned components can be prevented, and efficiency can be improved.
When configured as a premixed compression ignition engine, the fuel supply means includes a first state in which fuel is supplied to the exhaust gas region, and a second state in which fuel is supplied to a non-exhaust gas region outside the exhaust gas region. Is configured to be switchable, so that the temperature of the fuel is sufficiently raised in the first state to adjust the self-ignition timing of the air-fuel mixture to the advance side, and the second state is increased by the exhaust gas of the fuel. By suppressing the temperature, the self-ignition timing of the air-fuel mixture can be adjusted to the retard side, and this can be used to adjust the self-ignition timing to an appropriate timing.

  As an embodiment of the present invention, a premixed compression ignition engine 100 will be described with reference to the drawings.

  A premixed compression ignition engine 100 shown in FIG. 1 includes a combustion chamber 10 defined by an inner surface of a cylinder 3 and a top surface of a piston 4, and an intake passage 13 connected to the combustion chamber 10 via an intake valve 1. An exhaust passage 14 connected to the combustion chamber 10 via the exhaust valve 2 is provided.

  The piston 4 is swingably connected to the connecting rod 8, and the reciprocating motion of the piston 4 is obtained as a rotational movement of one crankshaft 9 by the connecting rod 8, and such a configuration is not different from a normal engine. .

  The intake passage 13 is provided with a fuel supply means 21 for supplying a fuel G, which is a natural gas city gas, to the air A flowing through the intake passage 13 to form an air-fuel mixture. As shown in FIG. 2, the air-fuel mixture formed in the intake passage 13 has an intake stroke in which the intake valve 1 is opened from a crank angle near TDC (top dead center) to near BDC (bottom dead center). In the combustion chamber 10.

  The premixed compression ignition engine 100 compresses the air-fuel mixture sucked into the combustion chamber 10 by the rise of the piston 4 in the compression stroke in which both the intake valve 1 and the exhaust valve 2 are closed, and the self-ignition temperature. The air-fuel mixture is self-ignited by raising the temperature to the same level, and in the combustion / expansion stroke, the piston 4 is pushed down by combustion of the air-fuel mixture to obtain a shaft output.

  Further, after the combustion / expansion stroke, the exhaust gas E in the combustion chamber 10 is discharged to the exhaust passage 14 in the exhaust stroke in which the exhaust valve 2 is opened from the vicinity of the BDC to the vicinity of TDC.

  An engine control unit (hereinafter referred to as ECU) 40 comprising a computer controls the amount of fuel supplied to the air A by the fuel supply means 21 so that the equivalent ratio of the air-fuel mixture sucked into the combustion chamber 10 is the target. It is configured to set the equivalence ratio suitable for the output.

  Such a premixed compression ignition engine 100 compresses the air-fuel mixture in the combustion chamber 10 and performs self-ignition combustion. Therefore, for example, the compression ratio can be set as high as about 21 and is highly efficient. Since the equivalent ratio can be burned in a lean state, for example, below the flame propagation lower limit, low NOx can be realized.

  In the premixed compression ignition engine 100, the pressure sensor 17 that can detect the actual self-ignition timing by measuring the pressure in the combustion chamber 10, the knock sensor 18 that can detect the occurrence of knock, and the rotation angle of the crankshaft 9 are set. A crank angle sensor 19 or the like that can detect the rotational speed of the crankshaft 9 by measurement is provided.

  Further, in the premixed compression ignition engine 100, the valve operating mechanism 30 for opening and closing the intake valve 1 and the exhaust valve 2 slows the combustion of the air-fuel mixture in the combustion chamber 10 to generate knock and generate NOx. In order to suppress this, the exhaust gas is recirculated to the combustion chamber 10 so as to function as EGR means X.

  That is, as shown in FIGS. 2 and 3, the EGR means X opens the intake valve 1 temporarily, preferably in the initial stage of the exhaust stroke, so that the exhaust gas E in the combustion chamber 10 is put into the intake passage 13. An exhaust gas area EA in which exhaust gas E is discharged is formed in the vicinity of the combustion chamber 10 of the intake passage 13 in the exhaust passage 13, and in the next intake stroke, the exhaust gas E of the exhaust gas area EA in the intake passage 13 is mixed with the mixture and the combustion chamber 10. It is configured to inhale.

  Further, the fuel supply means 21 of the premixed compression ignition engine 100 includes two first fuel supply valves 21a and second fuel supply valves 21b arranged in order from the side closer to the combustion chamber 10 in the intake passage 13. According to the command, the fuel G can be supplied to the intake passage 13 from each of the first fuel supply valve 21a and the second fuel supply valve 21b.

  Of the two first fuel supply valves 21a and 21b, the first fuel supply valve 21a on the side closer to the combustion chamber 10 temporarily closes the intake valve 1 by the EGR means X at the beginning of the exhaust stroke. By opening the exhaust gas region EA, the fuel G is formed in the intake passage 13 during the exhaust gas region formation period after the exhaust gas region EA is formed in the intake passage 13 and the intake valve 1 is closed in the exhaust stroke. It is arranged in the vicinity of the combustion chamber 10 so as to be supplied to the exhaust gas area EA. The state in which the fuel G is supplied to the exhaust gas region EA by the first fuel supply valve 21a in this way is referred to as a first state.

That is, as shown in FIG. 4, by supplying the fuel G to the exhaust gas area EA by the first fuel supply valve 21a, the temperature of the fuel G is increased by heat exchange with the relatively high temperature exhaust gas E, When the air-fuel mixture containing the warm fuel G is compressed in the combustion chamber 10, self-ignition can be performed with a relatively advanced self-ignition timing and good ignitability ensured, and misfire is suppressed. Furthermore, when the exhaust gas E acts on the fuel G satisfactorily, rapid heat generation due to the advance of the self-ignition timing is suppressed, and knock generation is suppressed.
Further, when combustion proceeds in the combustion chamber 10 and a relatively lean air-fuel mixture burns, the exhaust gas E is in a lean state like the fuel G with respect to the lean air-fuel mixture. The combustion of the gas is suppressed from becoming excessively slow, the generation of unburned components is suppressed, and the efficiency is improved.

  That is, the ECU 40 performs self-ignition as a first state in which the fuel G is supplied to the exhaust gas region EA by the first fuel supply valve 21a when the fuel supply amount by the fuel supply means 21 is decreased and the low load region operation is performed. While the timing is set to a relatively advanced side to ensure good ignition performance, the lean air-fuel mixture due to the decrease in the fuel supply amount can be burned well to improve efficiency.

  On the other hand, of the two first fuel supply valves 21a and the second fuel supply valves 21b, the second fuel supply valve 21b supplies the fuel G to the non-exhaust gas region NEA that is out of the exhaust gas region EA of the intake passage 13. In addition, the combustion chamber 10 is disposed farther than the exhaust gas area EA. The state in which the fuel G is supplied to the non-exhaust gas region NEA by the second fuel supply valve 21b is referred to as a second state, and the fuel supply means 21 is controlled by the ECU 40 in response to the first state and the second state. Are configured to be switchable.

That is, as shown in FIG. 5, by supplying the fuel G to the non-exhaust gas region NEA by the second fuel supply valve 21b, the fuel G is sucked into the combustion chamber 10 without being affected by the high-temperature exhaust gas E so much. Therefore, the temperature increase of the fuel G is suppressed, and when the air-fuel mixture containing the fuel G whose temperature increase is suppressed is compressed in the combustion chamber 10, it is self-ignited at a relatively retarded self-ignition timing. Knock generation due to rapid heat generation can be suppressed.
Then, when the ECU 40 increases the fuel supply amount by the fuel supply means 21 and performs the high load region operation, the ECU 40 sets the second state in which the fuel G is supplied to the non-exhaust gas region NEA by the second fuel supply valve 21b. By setting the ignition timing to a relatively retarded angle side, it is possible to suppress the occurrence of knock caused by the increase in the amount of fuel supply and maintain a stable operation state.

  Further, the ECU 40 may be configured to switch between the first state and the second state in order to set the actual self-ignition timing recognized from the detection result of the pressure sensor 17 to an appropriate timing. Further, when knocking is detected by the knock sensor 18 as the first state in which the fuel G is supplied to the exhaust gas area EA, the self-ignition timing is retarded by switching to the second state in which the fuel G is supplied to the non-exhaust gas area NEA. You may comprise so that a knock may be avoided by shifting to the side.

[Another embodiment]
Next, another embodiment of the present invention will be described with reference to the drawings.
(1) In the above embodiment, an example in which the engine according to the present invention is applied to a premixed compression ignition engine has been described. However, the engine according to the present invention is another engine such as a spark ignition type stratified combustion engine. It can also be applied to.
For example, in a stratified combustion engine in which a fuel-rich mixture is formed in a layered manner from an intake passage so that a thick portion where the fuel is dense is formed in the vicinity of an ignition plug of the combustion chamber and a thin portion where the fuel is thin is formed in the vicinity thereof. By supplying fuel to the exhaust gas region formed in the intake passage and sucking the mixture into the stratified intake, the exhaust gas is concentrated in the concentrated portion of the combustion chamber, so that knocking occurs when the mixture is ignited And NOx generation is suppressed well, and at the same time, in the light part in the combustion chamber, since the exhaust gas is in a lean state, the combustion rate is prevented from excessively decreasing to prevent the generation of unburned components. Efficiency can be improved.

(2) In the engine according to the present invention, any hydrocarbon fuel such as natural gas, gasoline, methanol, hydrogen, light oil or the like can be used. In general, air is used as the oxygen-containing gas for the combustion of the fuel. Instead of air, an oxygen-enriched gas having a higher oxygen component content ratio than air can be used. .

Schematic configuration diagram of premixed compression ignition engine Diagram showing lift amount of intake valve and exhaust valve The figure explaining the formation state of an exhaust gas area The figure explaining the fuel supply state in the 1st state The figure explaining the fuel supply state in the 2nd state

Explanation of symbols

1: intake valve 2: exhaust valve 10: combustion chamber 20: EGR valve 21: fuel supply means 21a: first fuel supply valve 21b: second fuel supply valve 40: engine control unit (ECU)
100: Premixed compression ignition engine X: EGR means

Claims (4)

An engine comprising fuel supply means for supplying fuel to air flowing through an intake passage to form an air-fuel mixture, and EGR means for recirculating exhaust gas to a combustion chamber,
The EGR means is means for exhausting exhaust gas into the intake passage by temporarily opening an intake valve in an exhaust stroke;
An engine in which the fuel supply means is configured to be able to supply fuel to an exhaust gas region from which exhaust gas has been discharged in the intake passage.   The engine according to claim 1, wherein the EGR means is configured to open the intake valve at an initial stage of the exhaust stroke.   The fuel supply means is configured to be switchable between a first state in which fuel is supplied to the exhaust gas region and a second state in which fuel is supplied to a non-exhaust gas region outside the exhaust gas region. 2. The engine according to 2.   The engine according to any one of claims 1 to 3, wherein the engine is configured as a premixed compression ignition engine that compresses the air-fuel mixture sucked into the combustion chamber and performs self-ignition combustion.

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