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Recently environmental problems have been taken up more and more widely in the world. In the automobile industry as well, severe control of fuel consumption and exhaust gas have spread globally after first imposed in the United States. Meanwhile, users' demand for driveability is still strong and compatibility of high power with low fuel consumption and clean exhaust gas is required at a high level. As one of the suitable solutions, the mechanically supercharged engine has got a highlight in the market because unlike turbocharged one it has the advantages of emission at start and response(1). Under these circumstances, automobiles equipped with a Miller cycle gasoline engine were put on sale by Mazda Motor Corporation for the first time in the world in 1993 as mass-produced automobiles(2). Ishikawajima-Harima Heavy Industries Company, Ltd.

In Japan, the next stage exhaust gas emission registration will be introduced around 1994. In case of heavy duty diesel engines, the level of NOx will be limited to 6.0g/kWh and the limit of particulate will be added to it. Its limit will be 0.7g/kWh. In U.S.A, regulation of particulate was already effective in 1988 and it will be tightened in 1991 and 1994. To pass these regulations, turbocharging with an intercooler is recommended to increase air flow, because reduction of black smoke at high load condition will be achieved by the improvement of combustion process. Also it will reduce negative effects by retard of injection timing that reduce NOx level. Although this improvement will be effective over approximate 1000rpm of engine speed, it will not be effective under 1000rpm because an engine can not get sufficient air flow due to poor performance of a turbocharger at this range. This is still one of unsolved problems at present.