A Study on Shockless Combustion Change Control of Direct Injection Gasoline Engine

A direct injection gasoline engine featuring a center-injection method that incorporates a high-pressure injector at the top center of the combustion chamber, has been developed. The engine is characterized by a significantly improved fuel economy and emissions performance as the result of the application of direct-injection stratified charge, DISC, which is one of the main features of the direct-injection engine. This paper describes a study on a change control method for switching between DISC and homogeneous charge combustion. The two forms of combustion employed in the new direct-injection engine differ in terms of combustion limits in relation to recirculated exhaust gas and air-fuel ratio. This causes the torque difference which is a specific issue in direct injection gasoline engines. The authors attempted to cope with the issue from the viewpoints of misfire prevention and fuel amount restriction in accordance with the torque required. Misfire was avoided by injecting fuel during the intake as well as compression strokes, which widened the combustion limit. Restricted fuel supply according to the required torque generation was ensured through performing a calculation of the current restriction limit of the fuel supply. This calculation is based upon the torque requirement immediately before the change in combustion, the fuel flow amount and the current requirement value.

By incorporating these two measures, it was possible to develop a combustion change control specifically designed for the Direct injection gasoline engine that would result in no abrupt change in torque and superb emissions control.