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The uniform lean gasoline-air mixture was provided to diesel engine and was ignited by direct diesel fuel injection. The mixing region that is formed by diesel fuel penetration and entrainment of ambient mixture is regarded as combustible turbulent jet. The ignition occurs in this region and the ambient lean mixture is burned by flame propagation. The lean mixture of air-fuel ratio between 150 and 35 could be ignited and burned by this ignition method. An increase of diesel fuel injection is effective to ensure combustion and ignition. As diesel fuel injection increases, HC concentration decreases, and NOx and CO concentration increases.

We have investigated combustion characteristics of lean gasoline-air pre-mixture ignited by gas-oil injection using a high compression D.I. diesel engine. Gasoline was supplied as an uniform lean mixture by using carburetors, and gas-oil was directly injected into the cylinder. Two different types of combustion chamber were attempted. It was confirmed that the lean mixture of air-fuel ratio between 150 and 35 could be ignited and burned by this ignition method. An engine with the re-entrant type combustion chamber had an advantage for combustion and ignition. The brake mean effective pressure increased when relatively rich mixture was provided with a small amount of the gas-oil injection. As the gas-oil injection increased, HC concentration decreased, and NO and CO concentration increased. The exhaust gas emission of pollutants could be reduced when lean mixture was ignited by an optimum gas-oil injection.