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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.

Annual surveys on Octane Number Requirement(ONR) of Japanese model passenger cars have been conducted, and the trend covering the period of 1982-1992 is described as a follow-up of the earlier report-SAE 830510. The ONRs showed a gradual decrease until 1990, but increased in later two years, reaching 91.2 and 95.3 ON at 50% and 90% car satisfaction levels, respectively, in 1992. The ONR at high speed range(80-120 km/hr) tended to increase and its differences from the low speed ONR(30-120 km/hr) have become gradually smaller for 1985-1992. Also, engine speed distribution at the maximum ONR values shifted to higher speed range above 2050rpm. Reflecting the recent increasing use of premium gasoline-spec cars, ONR distribution of these cars was separately measured, and resulted in 97.5 and 100.5 RON at 50% and 90% satisfaction levels respectively, in 1992 year model cars. This value is approximately 5 RON higher than regular gasoline spec cars at 90% satisfaction level.