Control system for compression-ignition engine

A control system for a compression-ignition engine, comprising:

• an engine including a cylinder, a piston for reciprocating inside the cylinder along a center axis thereof, and a cylinder head, and formed with a combustion chamber defined by the cylinder, the piston, and the cylinder head;
• a spark plug disposed in the combustion chamber;
• an intake port configured to introduce intake air into the combustion chamber;
• a swirl control valve provided in an intake passage connected to the intake port, wherein the swirl control valve is configured to generate an inclined swirl flow inside the combustion chamber flowing obliquely with respect to a center axis of the combustion chamber;
• a fuel injection valve disposed at a radial center of a ceiling portion of the combustion chamber, such that the fuel injection valve is configured to inject fuel so that a spray thereof radially spreads obliquely downward from the radial center of the ceiling portion of the combustion chamber;
• an air-fuel ratio control valve configured to adjust an air-fuel ratio of mixture gas inside the combustion chamber;
• and
• a control unit connected to the spark plug, the fuel injection valve, the swirl control valve, and the air-fuel ratio control valve and configured to output a control signal to the spark plug, the fuel injection valve, the swirl control valve, and the air-fuel ratio control valve,
• wherein a geometric compression ratio of the engine is 14:1 or above, wherein the control unit includes a processor configured to execute:
• an air-fuel ratio controlling module to, when the engine being in a given operating state is detected, control the air-fuel ratio control valve to bring the air-fuel ratio of the entire mixture gas inside the combustion chamber to a given lean air-fuel ratio that is larger than a stoichiometric air-fuel ratio;
• and
• a spark plug controlling module to, after the control by the air-fuel ratio controlling module, output the control signal to the spark plug to perform the ignition at a given ignition timing so that the mixture gas starts combustion by flame propagation and then unburned mixture gas self-ignites, the given ignition timing being stored in a memory,
• wherein the control unit controls the swirl control valve and the fuel injection valve so as to achieve a state where an air-fuel ratio of the mixture gas near the spark plug is smaller than an air-fuel ratio of the mixture gas therearound, and
• wherein the control unit controls the fuel injection valve to inject the fuel at a given injection timing at which the state where the air-fuel ratio of the mixture gas near the spark plug is smaller than the air-fuel ratio of the mixture gas therearound is achieved.