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In order to improve the volumetric efficiency of a crankcase-supercharged 4-stroke cycle engine in the high speed range, rotary disc valves were used at both the inlet and the outlet sides of the crankcase. The effects of the size of the opening and the phasing of the disc valves on volumetric efficiency were investigated and compared with a system using reed valves. It was found that a volumetric efficiency higher than 120 % could be obtained over a speed of 3000-6000 rpm, which was not possible by using the reed valve system. SUPERCHARGING SYSTEMS utilizing Roots type blowers and/or exhaust turbochargers have been used effectively for increasing the brake mean effective pressure of 4-stroke cycle engines. The authors built a prototype cranckcase-supercharged 4-stroke cycle engine, which used the underside of the piston as a supercharging pump, and confirmed the effectiveness of the concept by motoring and firing tests.

In order to reduce the knock of spark-ignition engines in the heavy load region, the effects of EGR on engine performance were investigated on two engines, one with a turbocharger and the other naturally aspirated with a high compression ratio. It was found that EGR was effective not only for reducing the knock, but also for improving the brake specific fuel consumption compared with the ignition timing retarding system.