JP4010822B2 - Premixed compression self-ignition engine and start-up operation method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a premixed compression self-ignition engine that supplies oxygen-containing gas and fuel to a combustion chamber and compresses and automatically ignites an air-fuel mixture formed in the combustion chamber. The present invention relates to a startup operation technique for stably starting a self-ignition engine.
[0002]
[Prior art]
The above-mentioned premixed compression auto-ignition engine has been conceived for the purpose of preventing particulate injection of fuel-injected diesel, but injects fuel into high-pressure air compressed in a combustion chamber like a diesel engine. Rather than combusting, mainly, in the intake stroke, fresh air such as air-fuel mixture or air is sucked into the combustion chamber to form an air-fuel mixture in the combustion chamber, and the air-fuel mixture formed in the combustion chamber is compressed in the compression stroke. It is configured to self-ignite, burn in the expansion stroke, and exhaust the exhaust gas in the combustion chamber to the exhaust passage in the exhaust stroke, increasing the compression ratio and improving efficiency, and burning the fuel in a lean state Low NOx can be achieved.
In particular, when the fuel constitutes a gas fuel engine such as natural gas city gas, it is difficult to inject the gas fuel at a high pressure by configuring it as a diesel engine. It is easier to burn the air-fuel mixture by compression ignition.
[0003]
In such a premixed compression self-ignition engine, fuel is burned using self-ignition of the fuel due to a temperature rise due to compression, so that the wall temperature of the combustion chamber or the like does not reach a certain temperature during start-up operation, It becomes difficult to stably ignite the air-fuel mixture. For this reason, in order to stably operate the premixed compression self-ignition engine during start-up operation, it is necessary to warm up the wall temperature of the combustion chamber by performing a warm-up operation for a certain period of time.
Therefore, as a starting operation method of the premixed compression auto-ignition engine for solving such problems, fuel is supplied to the heated gas generated by the burner device provided in the intake passage to form a heated premixed gas, There is a warm-up operation method in which the wall surface of the combustion chamber is sufficiently heated by performing a forced self-ignition operation in which the heated premixed gas is compressed and ignited in the combustion chamber (see Japanese Patent Application Laid-Open No. 2001-221074).
[0004]
[Problems to be solved by the invention]
Generally, in a premixed compression auto-ignition engine, the lower the temperature of the air-fuel mixture sucked into the combustion chamber, the more efficient the charging into the combustion chamber and the higher the knock limit value of the air-fuel mixture equivalence ratio. Efficiency and output can be improved.
Therefore, in the forced ignition operation of the start-up operation method of the premixed compression self-ignition engine described above, the temperature of the air-fuel mixture sucked into the combustion chamber after the heated air-fuel mixture has been stably self-ignited and combusted in the combustion chamber. However, if the temperature of the air-fuel mixture is reduced excessively in the premixed compression auto-ignition engine, so-called misfire occurs in which no self-ignition of the air-fuel mixture occurs in the combustion chamber. This is a problem because the combustion state of the air-fuel mixture becomes unstable.
[0005]
Accordingly, an object of the present invention is to solve the above-mentioned problems, and in a premixed compression auto-ignition engine, a start-up operation that can smoothly shift from forced ignition operation to high-efficiency and high-power steady operation with a simple configuration. The point is to provide technology.
[0006]
[Means for Solving the Problems]
In order to achieve this object, the first characteristic configuration of the premixed compression auto-ignition engine according to the present invention supplies oxygen-containing gas and fuel to the combustion chamber as described in claim 1 of the claims. A premixed compression self-ignition engine that compresses and self-ignites the air-fuel mixture formed in the combustion chamber,
Heating means capable of heating the oxygen-containing gas or gas mixture sucked into the combustion chamber with a heating amount adjustment;
Fuel flow rate adjusting means capable of adjusting the flow rate of the fuel to the combustion chamber;
A knocking detecting means for detecting knocking,
At the time of start-up, after the forced ignition operation in which the air-fuel mixture heated by the heating means is compressed and self-ignited in the combustion chamber, the temperature of the air-fuel mixture formed in the combustion chamber is adjusted by adjusting the heating amount of the heating means. There is a transition operation means for performing a transition operation for increasing the flow rate of the fuel by the fuel flow rate adjusting means until knocking is detected by the knocking detection means each time the reduction is performed by a predetermined amount.
[0007]
That is, according to the first characteristic configuration of the premixed compression auto-ignition engine according to the present invention, for example, the air (oxygen-containing gas) flowing through the intake passage or the fresh air that is a mixture is heated by the heating means. , Maintaining the rotation of the crankshaft by a drive source such as a motor or other engine, forming a heated air-fuel mixture heated in the combustion chamber, and performing a forced self-ignition operation to compress the heated air-fuel mixture in the combustion chamber Then, after the heated air-fuel mixture can be stably ignited in the combustion chamber, the transition operation means performs the transition operation, and the transition operation means includes the temperature of the mixture and the flow rate of the fuel. Is set to an appropriate value, the temperature of the air-fuel mixture is made as low as possible, high efficiency and high output are realized, and a transition to steady operation can be made.
[0008]
Specifically, after the heated air-fuel mixture heated by the heating means in the forced self-ignition operation can be stably self-ignited in the combustion chamber, the transition operation means is configured to change the heating amount of the heating means in the transition operation. However, the temperature of the air-fuel mixture is not lowered significantly, but is lowered by a predetermined amount that can avoid misfire. The transition operation means knocks the flow rate of combustion by the fuel flow rate adjusting means until the knocking detection means detects knocking every time the temperature of the air-fuel mixture is decreased by a predetermined amount as described above. It can be increased to near the limit.
[0009]
Therefore, by performing such a transition operation, the temperature of the air-fuel mixture can be lowered as much as possible while maintaining the equivalent ratio of the air-fuel mixture in the vicinity of the highly efficient knocking limit, so that the combustion state is kept stable. Thus, it is possible to smoothly shift to a steady operation with high efficiency and high output.
[0010]
In the second feature configuration, in addition to the first feature configuration, the transition operation means performs the transition operation as described in claim 2 of the column of claims. A step of decreasing the fuel flow rate by a predetermined amount, a step of increasing the flow rate of the fuel until knocking is detected by the knocking detection means, and a step of decreasing the fuel supply amount by a predetermined amount to avoid knocking. The configuration is such that the mixture is repeated until the temperature of the air-fuel mixture reaches a predetermined lower limit temperature.
[0011]
That is, according to the second feature configuration, the transition operation means sequentially executes the above steps in the transition operation, and further repeats these steps until the temperature of the mixture reaches a predetermined lower limit temperature. By executing, the temperature of the air-fuel mixture sucked into the combustion chamber can be reduced as much as possible and the equivalence ratio can be increased as much as possible to shift to steady operation with high efficiency and high output.
[0012]
In addition to the first or second feature configuration, the third feature configuration is self-ignition determination means for determining the occurrence of the self-ignition in the combustion chamber, as described in claim 3 of the claims. With
In the forced ignition operation, there is a forced self-ignition operation means for increasing the flow rate of the fuel at a predetermined increase rate until the self-ignition determination means determines that the self-ignition has occurred.
[0013]
That is, according to the third characteristic configuration described above, the heating means that can heat the air-fuel mixture supplied to the combustion chamber by heating the fresh air flowing through the intake passage, etc. By maintaining the rotation of the crankshaft by the drive source, the fuel flow rate adjusting means based on the determination result of the self-ignition determining means by the forced self-ignition operating means during the forced auto-ignition operation in which the heated air-fuel mixture is compressed in the combustion chamber The fuel flow rate can be set so that stable self-ignition occurs in the combustion chamber.
[0014]
Specifically, in the forced self-ignition operation, in the forced self-ignition operation, when setting the flow rate of the fuel supplied to the combustion chamber, a comparison that can prevent pre-ignition set at the start of the forced self-ignition operation In the combustion chamber, the fuel flow rate adjusting means increases the fuel flow rate continuously or stepwise until the self-ignition determining means determines that self-ignition has occurred with respect to the initial small flow rate of the fuel. As time elapses from the start of forced self-ignition operation in which self-ignition hardly occurs, self-ignition occurs smoothly in the combustion chamber.
When self-ignition occurs in the combustion chamber, the flow rate of the fuel set at that time is maintained, and when a misfire occurs again in the combustion chamber once self-ignition occurs, the fuel flow rate is further increased. Thus, the self-ignition can be stably generated in the combustion chamber.
Therefore, by performing such forced self-ignition operation, the heated air-fuel mixture can be self-ignited stably and smoothly in the combustion chamber. For example, the state of the wall temperature of the combustion chamber can be quickly and smoothly transferred. Operation can be started.
[0015]
In the fourth feature configuration, in addition to any one of the first to third feature configurations, as described in claim 4 of the column of claims, the heating means may include a part of oxygen in the intake passage. It is a burner device that heats the air-fuel mixture by using the burner fuel to burn and heating fresh air.
[0016]
That is, according to the fourth characteristic configuration, the burner device as the heating means combusts the burner fuel injected into the intake passage by using a part of oxygen contained in the fresh air, and this combustion exhaust gas is renewed. It is possible to heat fresh air by mixing it in the air and to heat the air-fuel mixture formed by this fresh air.
Further, the burner device burns the burner fuel by using part of the oxygen contained in the fresh air in the intake passage. Therefore, in the combustion chamber, the remaining oxygen is used to burn the fuel by compression ignition. It will be.
Therefore, a heating means can be easily comprised with a burner apparatus.
[0017]
When the heating means is configured as a burner device, the burner device may be configured as a pulse burner that intermittently burns burner fuel or an impact burner that jets and burns burner fuel so as to collide with each other. it can.
Such a pulse burner and impact burner have a wider range (TDR) for changing the combustion amount than that of a normal Bunsen burner, for example, so that it is easy to obtain an optimum combustion amount, which is advantageous. Since the pulse burner burns burner fuel intermittently, a wide TDR can be obtained by changing the intermittent combustion time. The impact burner ejects burner fuel from a plurality of nozzles and collides with each other, thereby generating vortices at the collision portion and facilitating flame holding, so that a wide TDR can be obtained.
[0018]
In order to achieve this object, the start-up operation method of the premixed compression auto-ignition engine according to the present invention is characterized in that an oxygen-containing gas, fuel, and Is a start-up operation method of a premixed compression self-ignition engine that compresses and self-ignites the air-fuel mixture formed in the combustion chamber,
At the time of start-up, after the forced ignition operation in which the heated air-fuel mixture is compressed and self-ignited in the combustion chamber, knocking is performed each time the temperature of the air-fuel mixture formed in the combustion chamber is decreased by a predetermined amount. The point is that a transition operation is performed in which the flow rate of the fuel supplied to the combustion chamber is increased until detection is made.
[0019]
That is, the start-up operation method of the premixed compression auto-ignition engine according to the present invention can be executed by the premixed compression auto-ignition engine having any one of the first to fourth characteristic configurations, and the second characteristic configuration described above. The same operational effects can be exhibited.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments relating to the premixed compression self-ignition engine 1 of the present invention will be described below with reference to the drawings.
A premixed compression self-ignition engine 1 shown in FIG. 1 includes a cylinder 7 having an intake valve 5 and an exhaust valve 6 and a piston 8 accommodated in the cylinder 7.
A space formed between the cylinder 7 and the piston 8 is a combustion chamber 9. The piston 8 is connected to the crankshaft 11 by a connecting rod 10, and the reciprocating motion of the piston 8 is obtained as a rotational movement of the crankshaft 11 by the connecting rod 10. With this configuration, the air-fuel mixture in the intake passage 12 is taken into the combustion chamber 9 through the intake valve 5, and after undergoing compression and expansion strokes, the exhaust gas E is exhausted to the exhaust passage 13 side through the exhaust valve 6.
[0021]
The premixed compression self-ignition engine 1 includes a mixer 15. The mixer 15 supplies the fuel A for engine G, which is natural gas, to the air A supplied from the upstream side, and a shutoff valve 21 and an MFC (mass flow controller). By supplying through 20, the air-fuel mixture is formed in the intake passage 12.
[0022]
The MFC 20 is controlled by an ECU (Engine Control Unit) 22 and functions as a fuel flow rate adjusting means capable of adjusting the flow rate of the engine fuel G to the air A, that is, the flow rate of the engine fuel G to the combustion chamber 9.
Further, the ECU 20 estimates the flow rate of the air A to the combustion chamber 9 from the output signal of the crank angle sensor S1 that can detect the rotation angle of the crankshaft 11, that is, the crank angle, and determines the MFC 20 based on the flow rate of the air A. It is configured so that the equivalence ratio of the air-fuel mixture formed in the intake passage 12 can be set.
Note that the air-fuel mixture formed by the mixer 15 is taken into the combustion chamber 9 from the intake passage 12.
[0023]
The operation cycle of the premixed compression self-ignition engine 1 is configured as a four-cycle engine that completes one cycle through an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke.
Normally, in the four-stroke engine, in the intake stroke, only the intake valve 5 is opened and intake of the air-fuel mixture in the intake passage 12 is performed. In the compression stroke, both the intake valve 5 and the exhaust valve 6 are closed, and the piston 8 moves in a direction to reduce the volume of the combustion chamber 9, and compression of the air-fuel mixture occurs in the combustion chamber 9. The position of the piston 8 in a state where the compression is completed is called a top dead center, and the compression auto-ignition of the air-fuel mixture in the premixed compression auto-ignition engine 1 occurs when the piston 8 is in the vicinity of this position. The expansion stroke is a stroke in which the piston 8 moves in a direction in which the volume of the combustion chamber 9 is increased by high-pressure gas generated by combustion. Even during this stroke, both the intake valve 5 and the exhaust valve 6 are closed. Further, in the exhaust stroke, only the exhaust valve 6 is opened, and the exhaust gas E in the combustion chamber 9 is discharged as the piston 8 moves in the direction of decreasing the space in the combustion chamber 9.
Basically, the premixed compression self-ignition engine 1 is also different from other engines except that the ignition type is the natural ignition of the premixed gas due to the heat generated by the adiabatic compression by compressing the premixed gas. There is no place.
[0024]
Furthermore, the premixed compression self-ignition engine 1 includes a burner device 14 as the heating means 3, and details of the burner device 14 will be described with reference to FIG.
The burner device 14 is configured to inject and burn the burner fuel G so as to collide with each other, thereby strengthening flame holding, and thereby, a large change rate (TDR) of the combustion amount can be obtained. It is a possible impact burner.
The burner device 14 defines a burner combustion chamber 49 that is narrowed at both ends, a cylinder 43 having an inlet 45 and an outlet 44 at both ends, a flange 42 at the outer periphery of the inlet 45, and an outlet 44. A flange 41 is provided on the outer periphery, the flange 42 is connected to the side where the air A flows in the internal combustion engine 1, and the flange 41 is connected to the mixer 15 and the premixed compression auto-ignition engine 1 side.
[0025]
Further, the burner device 14 includes a tube member 46 for guiding the burner fuel G to the burner combustion chamber 49 via the MFC 19 controlled by the ECU 22, a burner nozzle 46a at the end of the tube member 46 in the burner combustion chamber 49, And a spark lot 48 that generates sparks in the vicinity of the ejection direction of the burner nozzle 46a. Then, the ECU 22 causes the MFC 19 to work and causes the burner fuel G to be ejected from a plurality of nozzle holes (not shown) provided in the burner nozzle 46 into the burner combustion chamber 49 while colliding with each other. By igniting the jetted fuel G for the burner, the burner combustion chamber 49 can be burned with a compact flame. The burner device 14 burns the burner fuel G using part of the oxygen contained in the air A flowing through the intake passage 12, and discharges the air A that has been heated by mixing this high-temperature combustion exhaust gas. 44 can be discharged to the intake passage 12. Further, such an impact burner has better flame holding properties than a normal burner, for example, a Bunsen burner, and has a wide range (TDR) in which the amount of combustion can be changed, so that it is easy to take an optimum amount of combustion.
Further, the burner combustion chamber 49 is provided with a flame lot 47, and a flame in the burner combustion chamber 49 is detected and output to the ECU 22 to check whether the burner device 14 is operating normally.
[0026]
Further, in the premixed compression self-ignition engine 1 of the present embodiment, a temperature sensor T1 that detects a temperature (intake air temperature) in the vicinity of the intake valve 5 in the intake passage 12, and a temperature in the exhaust passage 17 near the exhaust valve 6 (exhaust temperature). ) For detecting the temperature near the outlet of the mixer 15 in the intake passage 12 (intake air temperature), the temperature sensor T4 for detecting the temperature of the wall of the combustion chamber 9 (combustion chamber temperature), and cooling. A temperature sensor such as a temperature sensor T5 for detecting the temperature of the cooling water discharged from the water jacket 18 (cooling water temperature) is appropriately provided, and a pressure sensor P1 for detecting the pressure of the intake passage 12 (an example of the intake pressure). A pressure sensor such as a pressure sensor P2 for detecting the pressure of the combustion chamber 9 (combustion chamber pressure) is appropriately provided.
The cylinder 7 is provided with a knocking sensor N1 that can detect the knocking intensity by detecting the vibration level.
The detection results of these sensors are input to the ECU 22.
[0027]
Next, the starting operation of the premixed compression self-ignition engine 1 configured as described above will be described.
The specifications of the premixed compression auto-ignition engine 1 of the present embodiment are such that the bore diameter of the cylinder 7 is 110 mm, the stroke of the piston 8 is 106 mm, and the compression ratio is 18, and the equivalent is about atmospheric pressure in steady operation. An air-fuel mixture having a ratio of about 0.3 is compressed and ignited and combusted, and the crankshaft 11 is rotated at a rotational speed of about 1200 ppm.
3 shows the rotation speed of the crankshaft 11, the flow rate of the burner combustion G, the intake air temperature, the exhaust gas temperature, and the engine fuel measured when the premixed compression auto-ignition engine 1 of the present embodiment is started. It is a graph which shows the change state of the flow volume, net output, and net thermal efficiency.
[0028]
First, before starting the operation of the premixed compression auto-ignition engine 1, an operation start command is input to the ECU 22. However, the combustion chamber wall 9a of the premixed compression autoignition engine 1 is still at a low temperature at that time, and even if a premixed gas at normal temperature is supplied as in the steady operation, the compression autoignition cannot be completed completely.
[0029]
Therefore, in the premixed compression self-ignition engine 1 of the present invention, after the operation start command is input, the ECU 22 performs, for example, motoring for rotating the crankshaft 11 by the cell motor 23 at about 1200 rpm, and then the burner device 14. In a state where the engine fuel G is not supplied in the mixer 15, a high-temperature combustion exhaust gas is supplied to the combustion chamber 9 side, and a warm-up operation for warming up the premixed compression self-ignition engine 1 is performed.
Such warm-up operation is performed until the intake air temperature detected by the temperature sensor T3 rises to a predetermined target value.
[0030]
In this warm-up operation, the ECU 22 operates the MFC 19 until the intake air temperature detected by the temperature sensor T3 reaches the target value, and burns in the burner device 14, that is, for burner to the burner device 14. By increasing the flow rate of the fuel G at a predetermined increase rate, the warm-up of the premixed compression auto-ignition engine 1 can be completed quickly, and after the intake air temperature reaches the target value, the burner fuel G Is reduced at a predetermined reduction rate.
[0031]
Specifically, the ECU 22 operates the MFC 19 at the start of the warm-up operation, and sets the flow rate of the burner fuel G to, for example, 2.0 L / min as a relatively small initial flow rate. When the intake air temperature is less than 210 ° C. as a target value, the flow rate of the burner fuel G is increased by, for example, 0.01 L / min, and when the intake air temperature is equal to or higher than the target value, For example, the flow rate of the fuel G is decreased by 0.05 L / min.
[0032]
In the warm-up operation, in this embodiment, the burner device 14 uses the burner fuel G within a range of an equivalence ratio of about 0.1 to 0.2 using a part of oxygen in the intake passage 12. The target value of the intake air temperature is set to about 210 ° C., and the actual intake air temperature is about 50 ° C. to about 250 ° C.
[0033]
After the warm-up operation and the intake air temperature reach the target value, the ECU 22 keeps the rotation of the crankshaft 11 by the cell motor 23 and the heating of the air A by the heating means 3 while maintaining the fuel G for the engine G in the mixer 15 by the MFC 20. The forced self-ignition operation means 24 that performs the forced self-ignition operation for inhaling the heated air-fuel mixture heated in the combustion chamber 9 will be described below.
[0034]
That is, in the forced self-ignition operation, the ECU 22 operates the MFC 20 while operating the burner device 14 to supply the engine fuel G to the mixer 15, and the air A that has been heated by mixing the combustion exhaust gas in the intake passage 12. Then, the engine fuel G is supplied to the intake passage 12 to form a heated air-fuel mixture having an equivalence ratio of about 0.3. The flow rate of the engine fuel G when the equivalence ratio is about 0.3 is about 17.0 L / min.
[0035]
The heated air-fuel mixture is sucked into the combustion chamber 9 from the intake passage 12. At this time, the ECU 22 sets the combustion amount in the burner device 14 while detecting the temperature of the air-fuel mixture with the temperature sensor T3 or the like, and sets the temperature of the air-fuel mixture sucked into the combustion chamber 9 to 200 ° C. Set within the range of about 250 ° C.
[0036]
In this forced self-ignition operation, the ECU 22 is configured to function as self-ignition determination means 23 that determines the occurrence of self-ignition in the combustion chamber 9.
Specifically, the self-ignition determination means 23 is detected by the exhaust temperature detected by the temperature sensor T2 and the pressure sensor P2, for example, every predetermined determination time interval of 5 to 20 seconds, preferably 10 to 15 seconds. The combustion chamber pressure and the vibration level detected by the knocking sensor N1 are taken in, and when they become a predetermined set value or more, it is determined that the heated air-fuel mixture has self-ignited in the combustion chamber 9, and the exhaust temperature and When any one of the combustion chamber pressure and the vibration level is equal to or lower than the set value, it is determined that the heated air-fuel mixture does not self-ignite in the combustion chamber 9.
[0037]
In addition, this self-ignition determination means 23 can also be comprised as follows other than being comprised so that generation | occurrence | production of self-ignition may be determined using the said exhaust gas temperature.
That is, the self-ignition determination means 23 generates self-ignition in the combustion chamber 9 when the temperature of the heated air-fuel mixture detected by the temperature sensors T1 and T3 becomes equal to or higher than the temperature sufficient for self-ignition in the combustion chamber 9. It can be configured to estimate that the Further, the self-ignition determination means 23 estimates that self-ignition has occurred in the combustion chamber 9 based on the temperature of the wall 9a of the combustion chamber 9 detected by the temperature sensor T4 or the temperature of the cooling water detected by the temperature sensor T5. It can be configured to determine that self-ignition has occurred in the combustion chamber 9 when the set value exceeds the set value. In addition, the self-ignition determination means 23 generates self-ignition in the combustion chamber 9 when the vibration level detected by the knocking sensor N1 is equal to or higher than a set value estimated that self-ignition has occurred in the combustion chamber 9. It can be configured to determine.
[0038]
Further, in the case of including a turbocharger 25 that supercharges the air A in the intake passage 12 using the kinetic energy of the exhaust gas E discharged to the exhaust passage 13, the operating state of the turbocharger is as follows: Since the supercharging pressure gradually increases from the beginning of the start-up, in other words, with the progress of warm-up, in other words, the self-ignition determination means 23 detects the intake air detected by the pressure sensor P1. It can be configured to estimate that self-ignition has occurred in the combustion chamber 9 when the pressure is equal to or higher than the pressure sufficient for self-ignition in the combustion chamber 9.
The self-ignition determination means 23 can also comprehensively monitor the detection results of these sensors to determine whether self-ignition has occurred in the combustion chamber 9.
[0039]
Further, the ECU 22 performs the forced self-ignition operation as described above, and in this forced self-ignition operation, the forced self-ignition operation sets the flow rate of the engine fuel G by operating the MFC 20 based on the determination result of the self-ignition determination means 23. It is configured to function as the ignition operation means 24.
[0040]
That is, the forced self-ignition operation means 24 increases the flow rate of the engine fuel G at a predetermined increase rate until the self-ignition determination means 23 determines that the self-ignition has occurred in setting the fuel flow rate. Composed.
Specifically, the forced self-ignition operation means 24 compares the extent that the flow rate of the engine fuel G can be prevented from being prematurely ignited in the combustion chamber 9 by using the MFC 20 at the start of the forced self-ignition operation. For example, the initial flow rate is set to 2.0 L / min.
[0041]
The forced self-ignition operation means 24 generates self-ignition in the self-ignition determination means 23 that determines the occurrence of self-ignition at every predetermined determination time interval (5 to 20 seconds interval, preferably 10 to 15 seconds). When it is determined that there has not been, the flow rate of the engine fuel G is increased by, for example, 0.5 L / min. When the self-ignition determination means 23 determines that self-ignition has occurred, the flow rate of the engine fuel G is increased. By stopping, self-ignition can be stably generated in the combustion chamber 9.
Therefore, the forced self-ignition operation means 24 can stably and smoothly self-ignite the heated air-fuel mixture in the combustion chamber 9 while suppressing premature ignition and misfire during forced self-ignition operation.
[0042]
Further, in the forced self-ignition operation, the flow rate of the burner fuel G to the burner device 14 is adjusted based on the intake air temperature, so that it automatically decreases as the self-ignition occurs and the engine warms up. To do.
Further, when the flow rate of the burner fuel G to the burner device 14 becomes a predetermined value or less, the supply of the burner fuel G to the burner device 14 may be stopped.
[0043]
In addition, when the ECU 22 detects that knocking has occurred by the knocking sensor N1 after the occurrence of self-ignition in the forced self-ignition operation as described above, the MFC 20 reduces the engine fuel G by a predetermined decrease amount. Therefore, as shown in FIG. 3, the flow rate of the engine fuel G may slightly decrease after the self-ignition is started.
[0044]
The self-ignition determination means 23 is configured to determine that the self-ignition is stably generated in the combustion chamber 9 when the self-ignition has occurred in the combustion chamber 9 for a predetermined time such as 100 seconds continuously. Thus, the ECU 22 functions as the transition operation means 25 for performing the next transition operation after the self-ignition determination means 23 determines that the self-ignition is stably generated in the combustion chamber 9 as described above. Next, the transition operation will be described.
[0045]
That is, in the transition operation, the transition operation means 25 of the ECU 22 operates the MFC 19 to decrease the flow rate of the burner fuel G, gradually lowers the intake air temperature, and detects the knocking by the knocking sensor N1, while the MFC 20 is detected. By gradually increasing the flow rate of the fuel G for the engine below the knocking limit, the temperature of the mixture is lowered as much as possible while maintaining the equivalent ratio of the air-fuel mixture sucked into the combustion chamber 9 near the highly efficient knocking limit. Thus, the combustion state is stabilized, and the operation is smoothly shifted to steady operation with high efficiency and high output.
[0046]
Specifically, the knocking generation region and the unstable combustion region with respect to the intake air temperature and the equivalence ratio in the premixed compression autoignition engine shown in FIG. 5 (a), and the premixed compression autoignition engine shown in FIG. 5 (b). As shown in the state of knocking occurrence region and unstable combustion region with respect to the intake air temperature and the indicated efficiency in FIG. Since a relatively high temperature air-fuel mixture of about 200 ° C. is sucked, the equivalence ratio and the efficiency of illustration are relatively low.
[0047]
The transition operation means 25 lowers the temperature of the intake air mixture (intake air temperature) as much as possible to improve the charging efficiency into the combustion chamber 9 and improve the upper limit of knocking of the equivalence ratio of the air mixture. To improve efficiency and output.
[0048]
Specifically, as shown in FIG. 4, the transition operation means 25 first decreases the burner fuel G to decrease the target value of the intake air temperature by a predetermined decrease amount of about 5 ° C., for example (# 101). ).
[0049]
Next, the transition operation means 25 determines whether or not the intake air temperature has reached the target value by the temperature sensor T3 (# 102), and when the intake air temperature has reached the target value, the MFC 20 is activated to flow the flow rate of the engine fuel G. Is increased by a predetermined increase amount of about 0.03 L / min, for example, in a cycle of 5 seconds (# 104).
[0050]
Then, every time the transition operation means 25 increases the engine fuel G by a predetermined increase amount, the transition sensor 25 determines whether knocking has occurred by the knocking sensor 1 (# 104), and determines that knocking has occurred. When this occurs (indicated by “♦” in FIG. 5), the engine fuel G is reduced by a predetermined reduction amount of, for example, about 0.3 l / min (# 106), and knocking is performed. After the avoidance, it is determined whether the target value of the intake air temperature is larger than a predetermined lower limit value of, for example, about 180 ° C. (# 106), and the steps # 101 to # 105 are performed until the intake air temperature reaches the lower limit value. Repeatedly, the next steady operation is performed later.
In the transition operation, the engine fuel G increase amount, the engine fuel G decrease amount for avoiding knocking, and the temperature decrease amount can be set as appropriate. In the period when the stable operation region with respect to the intake air temperature and the equivalence ratio is wide, the intake air temperature at the later stage of the transition operation in which the intake air temperature is close to the target value and the intake air temperature decrease amount and the engine fuel G decrease amount are set large. And, when the stable operation region with respect to the equivalence ratio is narrow, they may be set small.
[0051]
Thus, after the transition operation performed by the transition operation means 25 is completed (indicated with “O” in FIG. 5), by performing steady operation, in the vicinity of the limit where knocking can be avoided, The intake air temperature is as low as possible, and the flow rate of the engine fuel G, that is, the equivalence ratio of the air-fuel mixture that self-ignites and burns in the combustion chamber 9 can be increased to realize a highly efficient operation state. In (b), it can be confirmed that the output and efficiency increase from the transition operation to the steady operation.
[0052]
In addition, in the forced self-ignition operation, the transition operation, and the steady operation, mixing the combustion exhaust gas generated by the burner device 14 into the air-fuel mixture sucked into the combustion chamber 9 causes the exhaust gas to recirculate and burn in the combustion chamber 9 The effect of low NOx reduction similar to EGR that slows down the speed can be obtained, but the mixing amount of the combustion exhaust gas into the air-fuel mixture decreases due to the decrease in the flow rate of the burner fuel G during the transition operation and the steady operation. The exhaust gas corresponding to the reduction of the combustion exhaust gas is recirculated from the exhaust passage 13 to the combustion chamber 9 via the EGR flow path, or the closing timing of the exhaust valve 6 is advanced to remain in the combustion chamber 9. It is preferable to do.
[0053]
[Another embodiment]
<1> City gas is suitable as the engine fuel and burner fuel that can be used in the premixed compression auto-ignition engine of the present application, but any fuel such as gasoline, propane, methanol, hydrogen, etc. can be used. .
[0054]
<2> The air-fuel mixture formed in the combustion chamber is a mixture of engine fuel and oxygen-containing gas containing oxygen for burning the engine fuel. For example, air is used as the oxygen-containing gas. It is common.
[0055]
<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.
[0056]
<4> In the above-described embodiment, the mixer 15 may be a fuel injection valve that injects the engine fuel G into the air A flowing through the intake passage 12 to form an air-fuel mixture. In order to form an air-fuel mixture in the combustion chamber 9, instead of forming an air-fuel mixture in the intake passage 12, a fuel injection valve that directly injects engine fuel G into the combustion chamber 9 is provided. It is also possible to intake only the gas, inject the engine fuel G in the initial stage of the intake stroke or the compression stroke to form an air-fuel mixture in the combustion chamber, and compress the pre-air-fuel mixture to self-ignite.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a premixed compression self-ignition engine showing an embodiment of the present invention.
2 is an enlarged cross-sectional view of a burner device provided in the premixed compression self-ignition engine shown in FIG.
FIG. 3 is a graph showing various changes when the premixed compression self-ignition engine 1 of the present embodiment is started.
FIG. 4 is a flowchart showing the flow of transition operation.
FIG. 5 is a graph showing the states of the knocking generation region and the unstable combustion region with respect to the intake air temperature, the equivalence ratio, and the indicated efficiency.
[Explanation of symbols]
1: Premixed compression auto-ignition engine
3: Heating means
4: Opening / closing timing variable mechanism
5: Intake valve
6: Exhaust valve
7: Cylinder
8: Piston
9: Combustion chamber
9a: combustion chamber wall
10: Connecting rod
11: Crankshaft
12: Air intake path
13: Exhaust path
14: Burner device
22: ECU
23: Self-ignition determination means
24: Control means
T1, T2, T3, T4, T5: Temperature sensor
P1, P2: Pressure sensor
N1: Knocking sensor
S1: Crank angle sensor
A: Air
G: Fuel
E: exhaust gas

Claims (5)

A premixed compression self-ignition engine that supplies oxygen-containing gas and fuel to a combustion chamber and compresses and self-ignites the air-fuel mixture formed in the combustion chamber,
Heating means capable of heating the oxygen-containing gas or gas mixture sucked into the combustion chamber with a heating amount adjustment;
Fuel flow rate adjusting means capable of adjusting the flow rate of the fuel to the combustion chamber;
A knocking detecting means for detecting knocking,
At the time of start-up, after the forced ignition operation in which the air-fuel mixture heated by the heating means is compressed and self-ignited in the combustion chamber, the temperature of the air-fuel mixture formed in the combustion chamber is adjusted by adjusting the heating amount of the heating means. Premixed compression auto-ignition provided with a transition operation means for performing a transition operation for increasing the flow rate of the fuel by the fuel flow rate adjustment means until knocking is detected by the knocking detection means each time it is lowered by a predetermined reduction amount engine. The transition operation means performs the transition operation by lowering the temperature of the air-fuel mixture by a predetermined amount, increasing the flow rate of the fuel until knocking is detected by the knocking detection means, 2. The premixed compression autoignition according to claim 1, wherein the step of reducing the supply amount by a predetermined amount to avoid knocking is sequentially repeated until the temperature of the air-fuel mixture reaches a predetermined lower limit temperature. engine. A self-ignition determining means for determining the occurrence of the self-ignition in the combustion chamber;
3. The forced ignition operation unit according to claim 1, further comprising: a forced auto-ignition operation unit configured to increase the flow rate of the fuel at a predetermined increase rate until the self-ignition determination unit determines that the self-ignition has occurred in the forced ignition operation. Premixed compression auto-ignition engine. 4. The burner device according to claim 1, wherein the heating unit is a burner device that heats the air-fuel mixture by burning a burner fuel by using a part of oxygen in an intake passage to heat fresh air. A premixed compression auto-ignition engine as described in the paragraph. A start-up operation method of a premixed compression self-ignition engine that supplies oxygen-containing gas and fuel to a combustion chamber and compresses and self-ignites the air-fuel mixture formed in the combustion chamber,
At the time of start-up, after the forced ignition operation in which the heated air-fuel mixture is compressed and self-ignited in the combustion chamber, knocking is performed each time the temperature of the air-fuel mixture formed in the combustion chamber is decreased by a predetermined amount. A start-up operation method for a premixed compression auto-ignition engine that performs a transition operation for increasing the flow rate of fuel supplied to the combustion chamber until detection is detected.

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