Control apparatus for engine

A control apparatus for an engine, the control apparatus comprising:

• an engine having a combustion chamber;
• a state quantity setting device mounted to the engine, including an exhaust gas recirculation (EGR) passage connected between an intake passage of the engine and an exhaust passage of the engine, and an EGR valve disposed in the EGR passage, the state quantity setting device configured to adjust introduction of fresh air and burned gas into the combustion chamber;
• an injector mounted to the engine, the injector configured to inject fuel;
• a spark plug disposed so as to face an inside of the combustion chamber;
• and
• a controller connected to the state quantity setting device, the injector, and the spark plug, the controller configured to output control signals to the state quantity setting device, the injector, and the spark plug, wherein
• the controller sets a G/F that represents an index associated with a weight ratio between total gas, containing burned gas, in the combustion chamber, and fuel such that the G/F is in in a range from 18 to 50, by the controller outputting control signals to the EGR valve of the state quantity setting device and the injector, and
• the controller causes the spark plug to perform ignition at predetermined timing, and thus controls a flame propagation combustion time of ignited air-fuel mixture, to further control an autoignition time, of unburned air-fuel mixture, after start of flame propagation combustion in a highest engine load region.