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The leakage characteristics of the stepped type labyrinth gas seals were investigated both in stationary and rotating states by varying the thickness and position of the throttling fin. As a result, it was found that the leakage in the downward stepped type labyrinth seal was less than that in the upward stepped type. It was also found that, when compared with the conventional straight-through type labyrinth seal, the downward stepped type had a better sealing effect where the leakage rate decreased by about 70% in the stationary state and by 80% in the rotational state.

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 reduce diesel idle knock, the effects of EGR on the idling characteristics were investigated on three 4-stroke cycle engines having three different combustion chambers (precombustion, swirl and direct injection). It was found that EGR was effective not only for reducing idle knock, but also for decreasing fuel consumption, smoke density and exhaust emissions at idling operation regardless of the type of combustion camber. The same test results were obtained on a crankcase-scavenged 2-stroke cycle diesel engine (direct injection type) by means of inlet throttling.

In order to improve the part-load and idling characteristics of 2-stroke cycle diesel engines, the effect of throttling on engine performance was investigated on a separately scavenged engine with a Roots blower and on a crankcase-scavenged engine. For the first engine, it was found that decreasing the delivery ratio through bypassing a part of scavenging air into the inlet side, that is, by recirculation of scavenging air, made it possible not only to decrease the fuel consumption but also to raise the scavenging temperature which improved combustion. Also, a vehicle test using a bus powered by the same type of engine showed improved mileage through throttling. For the crankcase-scavenged engine, it was found that a slight increase in delivery ratio was very effective for improving the performance at low speed with heavy load, and throttling was also effective in improving not only the part-load but also the idling operation.

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.

In order to obtain the limiting delivery ratio curve, the relationships between the delivery ratio and the engine speed were investigated on crankcase-scavenged 2-stroke cycle engines by varying through wide limits the effective angle-areas Fia(e) of the inlet ports. It was found that the mean inlet Mach number Mim, already reported by the authors using 4-stroke cycle engines, showed well the characteristics of the limiting delivery ratio, and when Mim approached a limiting value the delivery ratio decreased hyper-bolically with an increase in engine speed.