JP4225672B2 - Premixed compression auto-ignition engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a premixed compression self-ignition engine that maintains the rotation of a crankshaft by compressing a premixed mixture of fuel and oxygen-containing gas supplied from a fuel supply means in a combustion chamber to cause self-ignition combustion.
[0002]
[Prior art]
Recently, the concept of a premixed compression auto-ignition engine that actively uses spontaneous ignition has become a hot topic. This type of premixed compression auto-ignition engine was developed for the purpose of preventing the particulates of diesel engines, and has just begun. The ignition type is a natural ignition type using adiabatic compression, similar to a diesel engine, but it does not inject fuel into compressed air, but mainly air (oxygen-containing) like a spark ignition type engine. An example of gas) and a fuel premixed gas are formed in the combustion chamber, the premixed gas is adiabatically compressed and spontaneously ignited and combusted, and the crankshaft continues to rotate.
If this method is applied to a gas engine, the compression ratio is increased and the ultra-lean premixed gas is compressed and ignited, thereby enabling high thermal efficiency and low NOx.
[0003]
[Problems to be solved by the invention]
However, in a premixed compression self-ignition engine, the temperature of the premixed gas is increased by adiabatic compression and self-ignition is performed, so that the engine elapsed time, ambient environment (temperature, humidity, etc.), engine output, etc. When the operating state changes, the wall temperature of the intake passage and combustion chamber changes, so the self-ignition timing of the premixed gas changes, or self-ignition does not occur, causing a decrease in engine thermal efficiency or engine shutdown It becomes.
When the elapsed time from start-up as an engine operating state changes, in other words, when the engine warm-up state changes, especially during engine start-up, the wall temperature of the intake passage and the combustion chamber is low and the Adiabatic compression is not possible until the temperature necessary to auto-ignite the mixture is reached. Therefore, since it is difficult to start the premixed compression self-ignition engine by warming up the engine by some method and causing the premixed gas to start by compression autoignition, the conventional premixed compression self-ignition engine is After the engine is started as a spark ignition engine and warmed up sufficiently, or after the engine is sufficiently warmed up by some warming-up means, it is necessary to perform an operation of compressing and pre-igniting the premixed gas, which complicates the engine. Above, smooth start-up operation could not be realized.
In addition, when changing the engine output as the engine operating state, the equivalence ratio of the pre-mixed gas that is sucked into the combustion chamber is changed. There was no effective technique to maintain high thermal efficiency over to partial load.
Therefore, the present invention eliminates the above problems and obtains a technique capable of maintaining high indicated thermal efficiency even when the engine operating state changes in a high thermal efficiency and low NOx premixed compression auto-ignition engine. Objective.
[0004]
[Means for Solving the Problems]
[Configuration 1]
The premixed compression self-ignition engine according to the present invention includes an operation state detection means for detecting an operation state of the engine as described in claim 1,
Equivalence ratio setting means for setting an equivalence ratio of the premixed gas by setting a supply amount of fuel supplied from the fuel supply means; and adjusting a pressure of the combustion chamber before the self-ignition to adjust the combustion chamber and a actual compression ratio setting means for setting the actual compression ratio in,
The operating state detecting means is means for detecting a setting output of the engine as the operating state,
In order to control the equivalence ratio and the actual compression ratio based on the relationship between the equivalence ratio and the actual compression ratio stored in advance, the equivalence ratio is increased as the set output increases. Control means is provided for increasing and decreasing the actual compression ratio, and decreasing the equivalent ratio and increasing the actual compression ratio as the set output decreases .
[0005]
[Function and effect]
As in the present configuration, the premixed compression auto-ignition engine of the present invention uses the operation state detection means to detect the timing of compression auto-ignition in the combustion chamber, the elapsed time since the start of the engine, the ambient environment (temperature, humidity, etc.) of the engine. Alternatively, the engine operating state such as the engine setting output can be detected, and the equivalence ratio setting means sets the supply amount of fuel supplied from, for example, the fuel supply means to Adjustable by adjusting the closing timing of the intake valve in the compression stroke, for example, or adjusting the supercharging pressure of fresh air by the actual compression ratio setting means, and adjusting the pressure of the combustion chamber before self-ignition The actual compression ratio in the combustion chamber can be set.
Then, the control means always relates to the relation between the equivalence ratio stored in advance and the actual compression ratio regarding the operation state, that is, the detected operation state obtained and stored in advance through experiments or the like. Since the equivalent ratio and the actual compression ratio are controlled based on the relationship between the equivalent ratio and the compression ratio that can achieve high indicated thermal efficiency, the indicated indicated thermal efficiency is always maintained even when the operating state changes. Can do. Specifically, when the engine operating state is a state in which it is difficult to self-ignite the premixed gas in the combustion chamber, in other words, even if the premixed gas is adiabatically compressed in the combustion chamber, autoignition occurs later than the preferred time point. Alternatively, when autoignition does not occur, adjust the actual compression ratio to the higher side and reduce the equivalent ratio of the premixed gas to the lower side in order to avoid knocking that occurs with an increase in the actual compression ratio. By adjusting, the engine can be operated in a preferable state and high thermal efficiency can be maintained.
Furthermore, the engine setting output, in other words, the required engine output is set manually or by detecting the load applied to the crankshaft of the engine. And configured as means for detecting the set output, and the control means controls the equivalence ratio and the actual compression ratio based on the detected set output, thereby changing the engine output and increasing the thermal efficiency of the engine. It can be maintained at a preferable level.
That is, the control means sets the engine setting based on the relationship between the pre-stored equivalence ratio and the actual compression ratio regarding the set output, that is, the relation between the equivalence ratio and the actual compression ratio for maintaining high thermal efficiency. In order to increase the output, the actual compression ratio is decreased while increasing the equivalent ratio, and conversely, to decrease the set output of the engine, the actual compression ratio is increased while decreasing the equivalent ratio.
Therefore, it is possible to realize a premixed compression self-ignition engine capable of avoiding knocking or the like and maintaining the engine's thermal efficiency always high even if the output is greatly changed.
[0010]
[Configuration 2 ]
HCCI engine according to the present invention, as set forth in claim 2, in addition to the above configuration 1 of the premixed compression ignition engines, to set the temperature of the fresh air to be sucked into the combustion chamber Equipped with fresh air temperature setting means,
The control means is based on a relationship relating to the operating state among the equivalent ratio, the actual compression ratio, and the fresh air temperature stored in advance, and the equivalent ratio setting means, the actual compression ratio setting means, and the new compression ratio. The air temperature setting means is operated to control the equivalent ratio, the actual compression ratio, and the temperature of the fresh air.
[0011]
[Function and effect]
As in this configuration, the control means controls the equivalence ratio and the actual compression ratio, and at the same time, stores the equivalence ratio, the actual compression ratio, and the fresh air temperature in relation to the operation state. Based on this, the fresh air temperature setting means can be operated to control the temperature of fresh air taken into the combustion chamber. Specifically, when changing the output of the engine, the equivalence ratio of the premixed gas is set to a higher side, but at that time, the engine operation state is likely to cause knocking or the like. Therefore, the actual compression ratio and the fresh air temperature are controlled together with the increase in the equivalent ratio. Specifically, the actual compression ratio is decreased and the fresh air temperature is decreased as the output increases. And knocking can be avoided. Therefore, it is possible to realize a premixed compression auto-ignition engine that can always maintain high thermal efficiency even if the output or the like is significantly changed.
[0012]
[Configuration 3 ]
HCCI engine according to the present invention, as set forth in claim 3, in addition to the above configuration 1 or 2 of the premixed compression ignition engine, said actual compression ratio setting means, the intake intake valve The amount of fresh air taken into the combustion chamber is set by closing earlier or later than the bottom dead center timing after the stroke, and adjusting the difference between the bottom dead center timing and the closing timing of the intake valve. It is a means for setting the actual compression ratio.
[0013]
[Function and effect]
As in this configuration, for example, by operating the intake valve that is open in the intake stroke in a so-called Miller cycle method that closes earlier or later than the bottom dead center timing, combustion at the closing timing of the intake valve is performed. Since only the volume of the chamber can be inhaled, the actual compression ratio is smaller than when it is closed at the bottom dead center. That is, by adjusting the difference between the bottom dead center timing and the closing timing of the intake valve, the amount of fresh air taken into the combustion chamber can be adjusted, and thereby the actual compression ratio can be arbitrarily adjusted. . Therefore, by operating this actual compression ratio setting means, the actual compression ratio can be arbitrarily set, and with such a simple configuration, it is possible to always maintain high illustrated thermal efficiency even if the operating state changes. The premixed compression auto-ignition engine of the present invention can be realized.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the premixed compression self-ignition engine 100 of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the premixed compression auto-ignition engine 100 supplies a natural gas city gas as fuel by a fuel nozzle 8 to the air pressurized by the supercharger 17 and circulated through the intake passage 11. An air-fuel mixture is formed, and the formed pre-air mixture is supplied to the combustion chamber 7 formed in the cylinder 3 via the intake valve 1, and the pre-air mixture is compressed and self-ignited in the combustion chamber 7. The reciprocating motion of the piston 4 is output as the rotation of the crankshaft 6 through the connecting rod 5. Further, the exhaust gas after combustion is discharged from the combustion chamber 7 through the exhaust valve 2 to the exhaust passage 12.
[0015]
Further, the premixed compression self-ignition engine 100 of the present invention includes a control valve 9 that adjusts the amount of fuel supplied from the fuel nozzle 8 and a crank angle sensor 10 that detects the rotational speed of the crankshaft 6. Each of them is connected to the control device 20. The control device 20 can calculate the intake air amount from the rotational speed of the crankshaft 6 detected by the output signal of the crank angle sensor 10. Therefore, the control device 20 determines the fuel supply amount based on the calculated air amount, and operates the control valve 9 to supply the determined supply amount of fuel to the air in the intake passage 11 to be formed. The equivalence ratio of the gas mixture can be set. The means for setting the equivalence ratio of the premixed gas by operating the control valve 9 in this way is referred to as equivalence ratio setting means A.
[0016]
The intake valve 1 and the exhaust valve 2 are connected to an opening / closing timing setting mechanism 19 and can be opened / closed at an arbitrary timing.
Therefore, the open / close state of the intake valve 1 of the premixed compression self-ignition engine 100 according to the present invention has a timing of closing after the bottom dead center, as shown in FIG. It is possible to set a time T that is closed from the point time. As a result, the premixed gas once taken into the combustion chamber 7 in the intake stroke and the premixed gas for the locus of the piston 4 that moved during the time T in the compression stroke can be blown back to the intake passage 13 side. Is possible. As a result, the premixed air sucked into the combustion chamber 7 corresponds to the volume of the combustion chamber 7 at the timing when the intake valve 1 is closed, and by adjusting this time T, the premixed air is preliminarily sucked into the combustion chamber 7. The amount of air-fuel mixture can be adjusted, and therefore the actual compression ratio can be adjusted. The means for adjusting the actual compression ratio by adjusting the closing timing later than the bottom dead center of the intake valve 1 is referred to as the actual compression ratio setting means B.
[0017]
Further, the engine 100 is provided with an internal pressure sensor 21 for detecting the internal pressure of the combustion chamber 7. The output information from the internal pressure sensor 21 is compared with a preset set value, and the comparison result and the detected crank angle are sent to the control device 20 provided in the engine. Therefore, the control device 20 obtains information on the state of the internal pressure of the combustion chamber 7 with respect to the crank angle and the set value at each time point, and the combustion chamber is the timing of the actual compression auto-ignition. The timing at which the internal pressure of 7 exceeds the set value can be detected. Further, a means for detecting the self-ignition timing as the engine operating state, such as the internal pressure sensor 21, is referred to as an operating state detecting means C.
[0018]
The control device 20 has actual compression auto-ignition timing information within one operation cycle of the engine 100 (actually, crank angle information in which the internal pressure of the combustion chamber 7 exceeds the set value at each crank angle). Is entered. On the other hand, the control device 20 includes a storage unit 200 therein, and preferable compression auto-ignition with respect to early / late information (an example of an operation state) with respect to the preferred compression auto-ignition timing of the actual compression auto-ignition timing. The relationship between the equivalence ratio and the actual compression ratio for maintaining the timing is stored in the storage means 200, and the equivalent ratio setting means is based on the relationship stored while detecting the actual compression ignition timing. A and the actual compression ratio setting means B are operated to control the equivalence ratio and the actual compression ratio of the premixed gas, so that the engine 100 can be operated while maintaining a high thermal efficiency. Based on the relationship between the equivalent compression ratio and the actual compression ratio to the early / late information for the preferred compression ignition timing of the actual compression ignition timing stored, and the equivalent compression ratio and actual compression ratio It means for controlling is called control unit D.
[0019]
The premixed compression self-ignition engine can secure a substantially preferable operation state with the above-described configuration, but is detected by, for example, a timer 201 provided in the control device 20 instead of the internal pressure sensor 21 as the operation state detection means C. The time elapsed since the start of the engine (an example of the operating state), the temperature in the intake passage 11 detected by the temperature sensor 15 provided in the intake passage 11, and the temperature sensor 16 provided in the exhaust passage 12 are detected. In some cases, it is preferable to appropriately control the equivalence ratio and the compression ratio to obtain a preferable operating state with respect to changes in the temperature in the exhaust passage 12, the ambient temperature or humidity of the engine (an example of the operating state) 22, etc. is there.
The elapsed time from the start of operation detected by the timer 201 is short, the engine is not sufficiently warmed up, the temperature of the intake passage 11 or the temperature of the exhaust passage 12 is low, or the ambient temperature of the engine is low. When the engine ambient humidity is high, the self-ignition timing in the combustion chamber 7 is later than the preferred self-ignition timing or no self-ignition occurs.
Therefore, when such an operating state is detected by the control means D, the actual compression ratio setting means B is operated to adjust the actual compression ratio to the higher side, and knocking that occurs as the actual compression ratio increases, etc. In order to avoid this, the equivalence ratio setting means A is operated to adjust the equivalence ratio of the premixed gas to a low side, so that the engine can be operated in a preferable state and high thermal efficiency can be maintained. , Set the equivalence ratio low at the start of operation and set the actual compression ratio high to start the engine operation, and decrease the actual compression ratio while increasing the equivalence ratio as the engine warms up Therefore, the operation can be shifted to the rated operation, and high thermal efficiency can always be maintained even during the start-up operation.
[0020]
Next, the configuration of the control means D when changing the output in the premixed compression self-ignition engine 100 of the present invention will be described below.
The storage unit 200 of the control device 20 stores the relationship between the equivalent ratio and the actual compression ratio regarding the output so-called illustrated effective pressure (an example of an operating state).
As shown in FIG. 3, this relationship can maintain the highest indicated thermal efficiency for each output value by the relationship of the output so-called indicated effective pressure with respect to the actual compression ratio and equivalent ratio obtained in advance by experiments or the like. It is the value of the equivalent ratio and the actual compression ratio that can be made.
[0021]
The premixed compression self-ignition engine 100 detects the setting output of the output setting command input to the control device 20 as the operation state detection means C, and sets the output of the premixed compression self-ignition engine 100.
That is, based on the preferred values of the above-described equivalent ratio and actual compression ratio stored in the storage means 200, the equivalent ratio and actual compression ratio are continuously set by operating the equivalent ratio setting means A and the actual compression ratio setting means B. For example, when the equivalence ratio is about 0.20 to 0.27, the actual compression ratio is 19, and when the equivalence ratio is about 0.27 to 0.32, the actual compression ratio is adjusted. When the ratio is 18 and the equivalence ratio is about 0.32 to 0.40, the actual compression ratio is adjusted to 17, and the effective pressure shown in the figure is changed from 0.27 MPa to 0.68 MPa. As shown in FIG. 4, the output thermal efficiency can be maintained at about 45% for most of the equivalent ratios. This is because, by setting the compression ratio to a preferable value with respect to the equivalent ratio, the rate of increase in the illustrated effective pressure is less than the knock generation limit, and the premixed gas is completely self-ignited in the combustion chamber 7. This is because the temperature can be set to be higher than the temperature at which heat treatment can be performed and the illustrated thermal efficiency can be maintained high. As described above, the control unit D is configured to adjust the equivalence ratio and the actual compression ratio based on the correlation with the set output as each operation state stored in the storage unit 200 and set the output. .
The data shown in FIGS. 3 and 4 indicate that the fresh air temperature, that is, the detected temperature by the temperature sensor 15 is 150 ° C., the supercharging pressure by the supercharger 7, that is, the detected pressure of the pressure gauge 18 provided in the intake passage 11. Is 75 kPa and the rotation speed of the crankshaft 6 is 1200 rpm.
[0022]
In addition, the premixed compression self-ignition engine 100 includes the cooling air cooled by a cooling tower (not shown) on the downstream side of the supercharger 17 in the intake passage 11 and fresh air flowing through the intake passage 11. The heat exchanger 13 that performs the heat exchange is provided, and the fresh air that has been pressurized by the supercharger 17 and raised in temperature can be cooled. Furthermore, the control valve 14 which adjusts the flow volume of the cooling water which distribute | circulates the heat exchanger 13 is provided, and the control apparatus 20 controls the opening degree of the control valve 14 based on the detection signal of the temperature sensor 15, The temperature of the air in the intake passage 11 can be set, and as a result, the temperature of the premixed gas (fresh air) supplied to the combustion chamber 7 can be set. The means for setting the temperature of fresh air by adjusting the amount of fresh air supplied to the combustion chamber 7 in this way is called fresh air temperature setting means E.
[0023]
And the memory | storage means 200 memorize | stores the relationship regarding the output of the equivalence ratio, the actual compression ratio, and the fresh air temperature corresponding to the fresh air pressure detected by the pressure gauge 18. That is, a preferable fresh air temperature capable of maintaining high thermal efficiency with respect to the intake air pressure detected by the pressure gauge 18 is set by the fresh air temperature setting means E, and the set fresh air temperature and the fresh air are set. The equivalent ratio and the actual compression ratio are set based on the relationship stored in advance regarding the output of the equivalent ratio to the pressure and the actual compression ratio, that is, the so-called illustrated effective pressure.
Therefore, for example, the rotational speed of the crankshaft 6 changes, the speed of the exhaust gas flowing through the exhaust passage 12 changes, and the rotational speed of the turbine (not shown) of the supercharger 17 changes to change the pressure of the intake air. Even if the pressure changes, the equivalence ratio and actual compression ratio can be set to the preferred values for the pressure and the new temperature, and each can be set by changing the output while maintaining the indicated thermal efficiency high. Can do.
[0024]
[Another embodiment]
<1> As the fuel that can be used in the premixed compression auto-ignition engine of the present invention, city gas is suitable, but any fuel such as gasoline, propane, methanol, hydrogen, and the like can be used.
[0025]
<2> In producing the premixed gas, it is sufficient to mix the fuel and a gas containing oxygen for combustion of the fuel. For example, it is common to use air as the oxygen-containing gas for combustion. It is. However, as such a gas, for example, an oxygen-enriched gas having an oxygen component content higher than that of air can be used.
[0026]
<3> Although the above embodiment has been described in relation to a so-called four-cycle engine, the present application can also be applied to a two-cycle engine.
[0027]
<4> In the above-described embodiment, the configuration in which the premixed gas that undergoes compression self-ignition combustion in the combustion chamber 7 is formed in the intake passage 11, but separately, a fuel injection valve that directly injects fuel into the combustion chamber 7 It is also possible to take in only air, inject fuel in the initial stage of the intake stroke or compression stroke to form a premixed gas in the combustion chamber, and compress the premixed gas to cause self-ignition.
[0028]
<5> In the above embodiment, the actual compression ratio setting means B is closed at a time later than the bottom dead center of the intake valve 1, and the time T when the intake valve 1 is closed from the bottom dead center is set. Thus, the actual compression ratio is set, but the actual compression ratio setting means B is closed at a time earlier than the bottom dead center as shown in FIG. The actual compression ratio can also be set by setting the time T from when the valve 1 is closed until the bottom dead center timing is reached.
The actual compression ratio setting means B can also be configured by a throttle valve such as a rotary valve or a butterfly valve provided in the intake passage. That is, by changing the opening of the throttle valve, changing the pressure loss when fresh air or premixed air is drawn into the combustion chamber, adjusting the pressure of the combustion chamber before self-ignition, The actual compression ratio can be set. Specifically, by setting the opening of the throttle valve to the decreasing side, the pressure loss when fresh air in the intake passage is sucked into the combustion chamber increases, and the actual compression ratio can be set to the decreasing side.
[0029]
<6> In the premixed compression auto-ignition engine 100 described in the above embodiment, the pressure gauge 18 for detecting the pressure of the intake passage 11 is provided to detect the supercharging state of the supercharger 17, It is also possible to detect the supercharging state by detecting the rotational speed of the supercharger 17. In this case, it is preferable to store in the storage means 200 the set values of the equivalence ratio and the intake air temperature corresponding to the respective rotational speeds of the supercharger 17.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of a premixed compression auto-ignition engine according to the present invention. FIG. 2 is a diagram showing an open / close state of an intake valve and a piston position of the premixed compression auto-ignition engine. FIG. 4 is a graph showing the indicated mean effective pressure with respect to the equivalent ratio and the actual compression ratio of the premixed compression auto-ignition engine. FIG. 4 is a graph showing the indicated thermal efficiency with respect to the equivalent ratio and the actual compression ratio of the premixed compression auto-ignition engine. The figure which shows the opening and closing state of the intake valve and the position of the piston of the premixed compression auto-ignition engine
DESCRIPTION OF SYMBOLS 1 Intake valve 2 Exhaust valve 4 Piston 6 Crankshaft 7 Combustion chamber 8 Fuel nozzle (fuel supply means)
17 Supercharger 18 Pressure gauge 19 Open / close timing setting mechanism 21 Internal pressure sensor 100 Premixed compression auto-ignition engine A Equivalent ratio setting means B Actual compression ratio setting means C Operating state detection means D Control means E Fresh air temperature setting means

Claims (3)

A premixed compression self-ignition engine that maintains the rotation of a crankshaft by compressing a premixed mixture of fuel and oxygen-containing gas supplied from a fuel supply means in a combustion chamber and performing self-ignition combustion,
With an operating state detecting means for detecting the operating state of the engine,
Equivalence ratio setting means for setting an equivalence ratio of the premixed gas by setting a supply amount of fuel supplied from the fuel supply means; and adjusting the pressure of the combustion chamber before the self-ignition, and and a actual compression ratio setting means for setting the actual compression ratio in,
The operating state detecting means is means for detecting a setting output of the engine as the operating state;
In order to control the equivalent ratio and the actual compression ratio based on the relationship between the equivalent ratio and the actual compression ratio stored in advance, the equivalent ratio is increased as the set output increases. A premixed compression auto-ignition engine comprising control means for increasing and decreasing the actual compression ratio and decreasing the equivalent ratio and increasing the actual compression ratio as the set output decreases . A fresh air temperature setting means for setting a temperature of fresh air sucked into the combustion chamber;
The control means is based on the relation regarding the operating state among the equivalence ratio, the actual compression ratio, and the fresh air temperature stored in advance, and the equivalence ratio setting means, the actual compression ratio setting means, and the new compression ratio. and exercising air temperature setting means, wherein the equivalence ratio and the actual compression ratio and homogeneous charge compression ignition engine according to claim 1 for controlling the temperature of the fresh air. The actual compression ratio setting means closes the intake valve earlier or later than the bottom dead center timing after the intake stroke, and adjusts the difference between the bottom dead center timing and the closing timing of the intake valve. The premixed compression self-ignition engine according to claim 1 or 2, which is a means for setting the actual compression ratio by setting the amount of fresh air to be taken in.

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