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4 crankcase-supercharged 4-stroke spark-ignition engine was made and tested in both the motoring and firing modes. It was found that a 20 to 30 % torque rise compared with the naturally-aspirated baseline engine was obtained in the low and middle engine speed ranges without any sacrifice in brake specific fuel consumption. Additionally, the throttle response of the modified engine was better than that of the naturally-aspirated baseline engine, and there was no deterioration in part-load brake specific fuel consumption.

In order to boost the torque of a 4-stroke cycle diesel engine, a crankcase-supercharged 4-stroke cycle diesel engine was made and tested in the firing mode. As a result, a remarkable reduction of smoke density and brake specific fuel consumption compared with the naturally aspirated baseline diesel engine was obtained. Additionally, a Jet Air Port (JAP), which was opened and closed by piston movement near bottom dead center, was installed. The JAP utilized air furnished by the crankcase-supercharging system. A reduction of smoke density and brake specific fuel consumption compared with the naturally-aspirated baseline diesel engine was found.

A hybrid combustion engine in which a premixed gasoline homogeneous charge was ignited by a small amount of injected diesel fuel under a high compression ratio was made by modifying a 4-stroke cycle diesel engine and was tested on a bus. It was found that the premixed of gasoline was effective not only for decreasing the fuel consumption but also for reducing the smoke density during an acceleration road test. The effect of introducing a small amount of N2 gas for supressing the diesel knock under heavy load operation was examined. These days diesel engines are widely used because of their excellent fuel economy. Particulates emitted from a diesel engines, consist of dry soot observed as smoke and the Soluble Organic Fraction (SOF) containing Polynuclear Aromatic Compounds (PAC).

As a mechanical supercharging system for 4-stroke cycle engines, crankcase-supercharging seems attractive because of its low production cost and simple construction. Therefore, a crankcase-supercharged 4-stroke cycle spark-ignition engine was developed and tested in both motoring and firing modes. It was found that the motoring volumetric efficiency could be increased over the entire engine speed range, but the increase was more noticeable at lower engine speeds. In the firing mode it was proved that a favorable throttle response and a 20 to 30% torque rise could be obtained by crankcase-supercharging without sacrificing the brake specific fuel consumption of the naturally aspirated baseline condition.