JP4229795B2 - Premixed compression ignition engine and operation control method thereof - Google Patents

Description

  The present invention relates to a premixed compression ignition engine that compresses an air-fuel mixture taken into a combustion chamber and performs self-ignition combustion and an operation control method thereof.

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 supplies a mixture of air and fuel to a combustion chamber as in a spark ignition engine to increase the mixture. The compressor is configured to compress and raise the temperature to the self-ignition temperature of the air-fuel mixture to cause self-ignition combustion. 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.

One of the major issues for realizing the premixed compression ignition engine is the control of the self-ignition timing.
In the SI engine, the self-ignition timing can be controlled to an appropriate timing by adjusting the spark ignition timing, and in the fuel-injection diesel by adjusting the fuel injection timing. However, in the case of the premixed compression ignition engine, the air-fuel ratio is increased. Because it compresses and raises the temperature to the self-ignition temperature of the air-fuel mixture and self-ignition combustion, the self-ignition timing is likely to change due to changes in elapsed time, engine load, air ratio, etc. from the start of start-up operation, and self-ignition occurs If the self-ignition timing is not properly controlled, knocking or misfire may occur, and furthermore, the operation may not be continued.
In particular, in a multi-cylinder type premixed compression ignition engine, conditions such as in-cylinder temperature and pressure history in each cylinder are slightly different, so the self-ignition timing differs for each cylinder. It needs to be in an appropriate state.

  As a technique for making the combustion state such as the self-ignition timing into an appropriate state in this way, main fuel such as natural gas mainly used and control fuel such as n-butane having higher ignitability than that fuel are used. Prepare and mix the main fuel and control fuel into the combustion chamber and adjust the amount of control fuel supplied to the combustion chamber to control the self-ignition timing of the air-fuel mixture in the combustion chamber There are known (see, for example, Patent Document 1).

JP 2000-274285 A

  However, the premixed compression ignition engine of Patent Document 1 needs to include a mechanism for storing and supplying the control fuel separately from the main fuel, or a mechanism for reforming the main fuel to generate and supply the control fuel. is there. The premixed compression ignition engine having such a mechanism is complicated and large in size, and becomes a problem particularly when it is used for driving a generator of a home cogeneration system.

  Furthermore, in a premixed compression ignition engine, the air-fuel mixture is ignited at multiple points in the combustion chamber. Therefore, if the equivalent ratio of the air-fuel mixture is increased to increase the output, knocking is likely to occur, so that knocking can be avoided. Otherwise, the output adjustment range is limited to a narrow range.

  Further, in the premixed compression ignition engine, it is necessary to compress the air-fuel mixture in the combustion chamber and raise the temperature to the self-ignition temperature to self-ignite, for example, when natural gas having a low cetane number is used as the fuel, During start-up operation where the cylinder temperature is relatively low, it is difficult to raise the temperature to the self-ignition temperature even if the air-fuel mixture is compressed as it is, and stable operation may not be maintained due to the occurrence of misfire, etc. .

  Accordingly, the present invention has been made in view of the above-described problems, and an object of the present invention is to make it possible to make the combustion state an appropriate state with a simple and miniaturizable configuration, and to maintain an appropriate combustion state. It is another object of the present invention to realize an operation control technique for a premixed compression ignition engine that can be operated in a wide output adjustment range and can be stably started while maintaining an appropriate combustion state.

In order to achieve the above object, a premixed compression ignition engine according to the present invention is a premixed compression ignition engine that compresses an air-fuel mixture sucked into a combustion chamber and performs self-ignition combustion. A new air flow adjusting means capable of adjusting the self-ignition timing in the combustion chamber by adjusting the size of the new air flow generated in the combustion chamber;
Combustion state detection means for detecting self-ignition timing in the combustion chamber as a combustion state;
When the self-ignition timing is advanced, the size of the new airflow is decreased, and when the self-ignition timing is delayed, the size of the new airflow is increased. The operation control means for controlling the size of the new airflow is provided.

Further, the characteristic configuration of the operation control method of the premixed compression ignition engine according to the present invention for achieving the above object is that self-ignition in the combustion chamber is achieved by adjusting the size of a new air flow generated in the combustion chamber. When the timing can be adjusted, the self-ignition timing in the combustion chamber is detected as a combustion state, and when the self-ignition timing is advanced, the size of the new airflow is reduced and the self-ignition timing is delayed Is a mode of increasing the size of the new airflow, and in the combustion chamber so that the combustion state for controlling the size of the new airflow is appropriate so that the self-ignition timing is appropriate. The point is to control the size of the new airflow generated.

That is, the present inventors changed the size of a new air flow such as a swirl flow generated in the combustion chamber in a premixed compression ignition engine that compresses the air-fuel mixture sucked into the combustion chamber and performs self-ignition combustion. The present inventors have found a new finding that the combustion state in the combustion chamber changes in a state where the self-ignition timing is delayed as the new air flow is larger, and the present invention has been completed.
In addition, in premixed compression ignition engines, the reason why the size of the new airflow affects the combustion state is that the gas mixture in the combustion chamber (mixed state of fuel and air) changes as the size of the new airflow changes. Or the mixed state of the air-fuel mixture and the recirculated exhaust gas) and the thickness of the temperature boundary layer of the combustion chamber wall surface in addition to the change of the average gas temperature of the combustion chamber. It is done. The reason why the self-ignition timing is delayed as the new airflow increases is that the larger the new airflow, the more the cooling loss of the air-fuel mixture due to the wall of the combustion chamber increases and the average gas temperature in the combustion chamber decreases. It is conceivable that the concentration and temperature of the air-fuel mixture are homogenized due to the accelerated mixing of the air-fuel mixture and the maximum concentration and temperature of the combustion chamber are lowered.

That is, according to the first characteristic configuration of the premixed compression ignition engine and the control method thereof, the operation control means operates the new airflow adjusting means based on the detection result of the combustion state detecting means, so that the size of the new airflow is increased. By controlling the above, the combustion state in the combustion chamber can be maintained in an appropriate state even if the elapsed time from startup, the engine load, the air ratio, and the like change.
In addition, by controlling the size of the new airflow based on the combustion state, it is possible to maintain an appropriate combustion state, so that knocking that tends to occur during high-power operation and misfire that tends to occur during low-power operation are good. And can be operated in a wide output adjustment range.

Moreover, by adjusting the size of the new airflow by the new airflow adjusting means, the self-ignition timing, which is difficult to adjust directly in the premixed compression ignition engine, It can be adjusted with a simple configuration according to the combustion state in the combustion chamber.

Furthermore, the combustion state detection means detects the self-ignition timing as a combustion state directly or indirectly by knocking or misfire state, and the self-ignition timing tends to be delayed as the new airflow increases. When the self-ignition timing is advanced by the operation control means, the new airflow is reduced, and conversely, when the self-ignition timing is delayed, the new airflow is increased to control self-ignition. The timing can be reliably maintained at an appropriate timing.

In addition to the first characteristic configuration, the second characteristic configuration of the premixed compression ignition engine according to the present invention is configured to minimize the size of the new air flow by the new air flow adjusting means during start-up operation. There is in point.

According to the second characteristic configuration, at the start of the start-up operation or at the start-up operation until a predetermined time has elapsed, the cylinder temperature is in a relatively low state, and the air-fuel mixture is not easily ignited. By the above operation control means, during the start-up operation, the new airflow is set to the minimum and the air-fuel mixture is surely self-ignited, and then the size of the new airflow is controlled based on the combustion state changing from the start-up operation. Therefore, it is possible to smoothly shift to a stable operation.
Note that minimizing the new airflow includes a state in which the new airflow is not generated.

The third characteristic configuration of the premixed compression ignition engine according to the present invention is a means for adjusting the magnitude of the swirl flow as the new airflow, in addition to the first or second characteristic configuration. In the point.

According to the third characteristic configuration, the size of the swirl flow is controlled easily and quickly by configuring the new air flow adjusting means as a swirl adjusting valve or the like for adjusting the size of the swirl flow as the new air flow. Thus, the combustion state in the combustion chamber can be surely set to an appropriate state.
The 4th characteristic structure of the premixed compression ignition engine which concerns on this invention is the new airflow which generate | occur | produces in the said combustion chamber by adjusting the inflow direction of the fresh air from an intake passage to the said combustion chamber as said new airflow adjustment means. The adjustment valve which adjusts the magnitude | size of is in the point provided.

  An embodiment of a premixed compression ignition engine 100 according to the present invention will be described with reference to FIG.

  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 fuel and air of the natural gas city gas are mixed in the mixer 21, and the mixture is circulated through the intake passage 13 while being pressurized by the supercharger 22, and is taken into the combustion chamber 10 as fresh air. The

  The premixed compression ignition engine 100 is configured to compress the air-fuel mixture sucked into the combustion chamber 10 by raising the piston 4 and raise the temperature to the self-ignition temperature, so that the air-fuel mixture is self-ignited and combusted. Has been.

  The control device 40 comprising a computer is configured to control the amount of fuel supplied to the air by the mixer 21 so that the equivalent ratio of the air-fuel mixture sucked into the combustion chamber 10 is set to an equivalent ratio that matches the target output. Yes.

  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.

  The premixed compression ignition engine 100 includes a pressure sensor 17 that can detect the actual self-ignition timing as a combustion state by measuring the pressure in the combustion chamber 10, and a knock sensor 18 that can detect the occurrence of knocking as a combustion state. A crank angle sensor 19 or the like capable of detecting the rotational speed of the crankshaft 9 as a combustion state by measuring the rotation angle of the crankshaft 9 is provided as the combustion state detection means A for detecting the combustion state.

  Further, in the premixed compression ignition engine 100, as a new air flow adjusting means B for adjusting the size of the new air flow generated in the combustion chamber 10, referring to FIG. A swirl adjustment valve 20 is provided for adjusting the magnitude of the swirl flow generated in the combustion chamber 10 by adjusting the inflow direction of. In addition, as this swirl adjustment valve 20, a well-known thing can be utilized, and also by adjusting the quantity of the fresh air which flows into the swirl port which generates a swirl flow among several intake ports. A configuration that adjusts the size of the swirl flow can also be used.

  In the premixed compression ignition engine 100, when the size of the swirl flow generated in the combustion chamber 10 is changed by the swirl adjustment valve 20 as described above, the self-ignition timing of the air-fuel mixture in the combustion chamber 10 increases as the swirl flow increases. It can be confirmed by experiment that the combustion state of the air-fuel mixture in the combustion chamber 10 changes in a slow state, and the effect of retarding the self-ignition timing due to the increase in swirl flow is It can also be confirmed that the lower the equivalent ratio is, that is, the smaller the mixture is, the larger the mixture becomes.

In other words, the self-ignition timing of the premixed compression ignition engine 100 can be adjusted by adjusting the magnitude of the swirl flow in the combustion chamber 10 by the swirl adjusting valve 20.
That is, by reducing the swirl flow, the self-ignition timing can be adjusted to the advance side, and conversely, by increasing the swirl flow, the self-ignition timing can be adjusted to the retard side.

  Further, the control device 40 of the premixed compression ignition engine 100 serves as operation control means C for controlling the swirl flow magnitude in the combustion chamber 10 by the swirl adjustment valve 20 based on the detection result of the combustion state detection means A. Configured to work.

  That is, when the actual self-ignition timing detected by the pressure sensor 17 is not an appropriate self-ignition timing, the control device 40 determines that the actual self-ignition timing detected by the pressure sensor 17 is an appropriate self-ignition timing. Thus, the swirl control valve 20 controls the magnitude of the swirl flow in the combustion chamber 10.

  Further, when the control device 40 recognizes the occurrence of knocking from the detection result of the knocking sensor 18, the control device 40 increases the swirl flow in the combustion chamber 10 by the swirl adjusting valve 20 to adjust the self-ignition timing to the retard side. By doing so, knocking can be avoided.

  Further, when the control device 40 recognizes the occurrence of misfire in the combustion chamber 10 based on the rotation speed of the crankshaft 9 detected by the crank angle sensor 19, the output torque fluctuation, or the detection result of the pressure sensor 17. The misfire can be avoided by reducing the swirl flow in the combustion chamber 10 by the swirl adjusting valve 20 and adjusting the self-ignition timing to the advance side.

The control device 40 is configured to minimize the swirl flow by the swirl control valve 20 during the start-up operation of the premixed compression ignition engine 100. Thus, the swirl flow is minimized during the start-up operation. Then, even when the temperature of the cylinder 3 is relatively low, the air-fuel mixture can be surely self-ignited.
In addition, after performing the start-up operation of the premixed compression ignition engine 100 in this way, as described above, by controlling the magnitude of the swirl flow based on the combustion state in the combustion chamber 10, an appropriate The combustion state is maintained, and further, as the temperature of the cylinder 3 increases, the magnitude of the swirl flow is gradually increased, and the operation is shifted to a good operation in which the pumping loss is suppressed.

[Another embodiment]
Next, another embodiment of the present invention will be described.
<1> The new airflow adjusting means B of the premixed compression ignition engine 100 described in the above embodiment may be configured to adjust the size of the new airflow other than the swirl flow. For example, in order to adjust the tumble flow as a new air flow, the size of the tumble flow can be adjusted by adjusting the amount of fresh air flowing into the tumble port that generates the tumble flow among the plurality of intake ports. Can be configured.

<2> In the above embodiment, an example in which the premixed compression ignition engine according to the present invention is configured as a single cylinder type has been described. However, the present invention is also applied to a multicylinder type premixed compression ignition engine. can do.

<3> The combustion state detection means A of the premixed compression ignition engine 100 described in the above embodiment is based on the generation state of the ionic current between the pair of electrodes provided in the combustion chamber 10. it may be configured to detect a combustion state of the ignition timing. In addition, an electrode of an ignition plug provided in the combustion chamber 10 can be used as the pair of electrodes, and such an ignition plug is a spark ignition operation in which an air-fuel mixture having a theoretical equivalent ratio or the like is spark-ignited and burned. The spark ignition operation is performed for warm-up in the start-up operation of the premixed compression ignition engine 100 or the like.

< 4 > In the premixed compression ignition engine of the present invention, any hydrocarbon fuel such as natural gas, gasoline, methanol, hydrogen, light oil, etc. can be used.

< 5 > In a premixed compression ignition engine, air is generally used as the oxygen-containing gas for fuel combustion. However, instead of air, oxygen-rich content is high in oxygen content. A gas or the like can also be used.

Schematic side sectional view showing an embodiment of a premixed compression ignition engine 1 is a schematic cross-sectional view of the premixed compression ignition engine shown in FIG.

Explanation of symbols

10: Combustion chamber 17: Pressure sensor 18: Knocking sensor 19: Crank angle sensor 20: Swirl adjustment valve 21: Mixer 40: Controller 100: Premixed compression ignition engine A: Combustion state detection means B: New airflow adjustment means C: Operation control means

Claims (5)

A premixed compression ignition engine that compresses the air-fuel mixture sucked into the combustion chamber and performs self-ignition combustion,
A new air flow adjusting means capable of adjusting the self-ignition timing in the combustion chamber by adjusting the size of the new air flow generated in the combustion chamber;
Combustion state detection means for detecting self-ignition timing in the combustion chamber as a combustion state;
When the self-ignition timing is advanced, the size of the new airflow is decreased, and when the self-ignition timing is delayed, the size of the new airflow is increased. A premixed compression ignition engine comprising operation control means for controlling the size of the new airflow.   The premixed compression ignition engine according to claim 1, wherein the new airflow adjusting means minimizes the size of the new airflow during start-up operation.   The premixed compression ignition engine according to claim 1 or 2, wherein the new airflow adjusting means is a means for adjusting a magnitude of a swirl flow as the new airflow. The adjustment valve which adjusts the magnitude | size of the new airflow which generate | occur | produces in the said combustion chamber by adjusting the inflow direction of the fresh air from the intake passage to the said combustion chamber as said new airflow adjustment means is provided. The premixed compression ignition engine of any one of -3.   An operation control method for a premixed compression ignition engine that compresses a mixture gas taken into a combustion chamber and performs self-ignition combustion,
  By adjusting the size of the new airflow generated in the combustion chamber, the self-ignition timing in the combustion chamber can be adjusted,
  When the self-ignition timing in the combustion chamber is detected as a combustion state and the self-ignition timing is advanced, the size of the new airflow is decreased, and when the self-ignition timing is delayed, the size of the new airflow is increased. In the form of increasing the self-ignition timing, the size of the new airflow generated in the combustion chamber is adjusted so that the combustion state for controlling the size of the new airflow is in an appropriate state so that the self-ignition timing becomes an appropriate timing. Control method of a premixed compression ignition engine for controlling the height.

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