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An experimental study has been made of a single cylinder, direct-injection diesel engine having a re-entrant combustion chamber designed to enhance combustion so as to reduce exhaust emissions. Special emphasis has been placed on controlling the inert gas concentration in the localized fuel-air mixture to lower combustion gas temperatures, thereby reduce exhaust NOx emission. For this specific purpose, an exhaust gas recirculation (EGR) system, which has been widely used in gasoline engines, was applied to the DI diesel engine to control the intake inert gas concentration. In addition, supercharging and increasing fuel injection pressure prevent the deterioration of smoke and unburned hydrocarbons and improve fuel economy, as well.

From the viewpoint of utilizing methanol fuel in an automotive turbocharged direct-injection diesel engine, an intercooling system supplying liquid methanol has been devised and its effects on engine performance and exhaust gas emissions have been investigated. With an electronically controlled injector in this system, methanol as a supplementary fuel to diesel fuel can be injected into the intake pipe in order to intercool a hot air charge compressed by the turbocharger. It has been confirmed that especially at heavy load conditions, methanol-intercooling can yield a higher thermal efficiency, and lower NOx and smoke emissions simultaneously, compared with three other cases without using methanol: natural aspiration and the cases with and without an ordinary intercooler. However, methanol fueling must be avoided at lower loads since sacrifices in efficiency and hydrocarbon emissions are inevitably involved.