Evolution of a Small Two-Stroke Engine with Direct Liquid Injection and Stratified Charge

Two-stroke S.I. engine survival is submitted to direct fuel injection and charge stratification. An exhaustive activity concerning a 50 cm³ two-stroke S.I. engine with liquid direct injection and charge stratification has given really satisfactory results as regards engine aptitude to operate unthrottled at every speed and load. However, unthrottled operation does not necessarily lead to the best overall result. By CFD investigation and experimental tests, this paper proves that some throttling reduces HC and NO_x emissions as well as pumping loss and increases exhaust gas temperature at light loads, with evident advantage for catalytic converter efficiency.