Compression ignition gasoline engine
A compression ignition gasoline engine includes a fuel injection valve for injecting fuel containing gasoline as a main component into a cylinder; an EGR device operative to perform high-temperature EGR of introducing burnt gas generated in the cylinder into the cylinder at a high temperature; an octane number determination unit for determining whether fuel injected from the fuel injection valve has a prescribed octane number; and a combustion control unit for controlling the fuel injection valve and the EGR device in such a way that HCCI combustion occurs within the cylinder. The combustion control unit controls the EGR device, in at least a partial load operating range in which HCCI combustion is performed, in such a way that the EGR rate increases, as compared with a case where fuel is determined to have a prescribed octane number, when fuel is determined not to have a prescribed octane number.
1. A compression ignition gasoline engine comprising:
a cylinder for accommodating a piston to be reciprocally movable;
a fuel injection valve for injecting fuel containing gasoline as a main component into the cylinder;
an EGR (exhaust gas recirculation) device operative to perform high-temperature EGR of introducing burnt gas generated in the cylinder into the cylinder at a high temperature;
an octane number determination unit for determining whether fuel injected from the fuel injection valve has a prescribed octane number; and
a combustion control unit for controlling the fuel injection valve and the EGR device in such a way that HCCI (homogeneous charge compression ignition) combustion in which fuel injected from the fuel injection valve self-ignites within the cylinder occurs, wherein
the combustion control unit controls the EGR device in such a way that, in at least a partial load operating range in which HCCI combustion is performed, an EGR rate increases, as compared with a case where fuel is determined to have the prescribed octane number, when the octane number determination unit determines that fuel does not have the prescribed octane number; and
the combustion control unit controls the EGR device in such a way that the EGR rate at which a coefficient K of an octane index (OI) expressed by the following Equation (1) becomes equal to or larger than zero is achieved:
OI= (1- K )× RON+K×MON (1)
where RON denotes a research octane number, and MON denotes a motor octane number.
2. The compression ignition gasoline engine according to claim 1 , wherein
the octane number determination unit determines whether fuel has the prescribed octane number, based on an ignition timing of the fuel when the engine is operated in a predetermined condition.
3. The compression ignition gasoline engine according to claim 1 , wherein
the combustion control unit controls the EGR device in such a way that the EGR rate at which a torque change amount for each combustion cycle is suppressed to a predetermined value or smaller is achieved.
4. The compression ignition gasoline engine according to claim 1 , wherein
a geometric compression ratio of the cylinder is set to be not smaller than 18 but not larger than 22.
5. The compression ignition gasoline engine according to claim 1 , wherein
the EGR device is a valve variable mechanism operative to perform internal EGR of letting burnt gas generated in the cylinder remain in the cylinder, as the high-temperature EGR.
6. The compression ignition gasoline engine according to claim 1 , wherein
the coefficient K is configured to be larger than 1 when the EGR rate is 80%.
7. The compression ignition gasoline engine according to claim 1 , wherein
the coefficient K is configured to decrease proportionally as the EGR rate decreases.
8. The compression ignition gasoline engine according to claim 6 , wherein
the coefficient K is configured to decrease proportionally as the EGR rate decreases.
9. The compression ignition gasoline engine according to claim 1 , wherein
the coefficient K is configured to be substantially equal to zero when the EGR rate is 40%.
10. The compression ignition gasoline engine according to claim 6 , wherein
the coefficient K is configured to be substantially equal to zero when the EGR rate is 40%.
11. The compression ignition gasoline engine according to claim 7 , wherein
the coefficient K is configured to be substantially equal to zero when the EGR rate is 40%.