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Leakage characteristics of the screw gas seal having a rectangular screw groove on a shaft were investigated by varying the peripheral velocity up to 250 m/s and by using room temperature air. The various effects of helix angle, groove width ratio, aspect ratio, number of threads, etc, were examined both in stationary and rotating states. As a result, it was found that the seal performance was optimized by using a dimensionless parameter, the ratio of the cross-sectional areas of screw groove to screw rotor. Thus, the seal performance was optimized when this parameter was nearly equal to 1 × 10-3 or when the cross-sectional area of screw groove became nearly 0.1% of the cross-sectional area of screw rotor. The effects of aspect ratio, helix angle, groove width ratio and number of threads on the seal performance appear to be relatively unimportant.

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.

Leak and seal performances in stationary state and rotating state for each brush mounted labyrinth and ordinary labyrinth were studied and presented hereunder in this paper. It was found in this research work that seal performance of brushmounted labyrinth is much better than that of ordinary labyrinth. Brush mounted labyrinth has two remarkable characteristics: In the case that the brush is positioned behind fin against flow, i.e. positioned downstream of fin, amount of leakage is suppressed as increasing of rotation speed. In the case that brush is positioned upstream of fin, leakage increases as increasing of rotation speed.

Labyrinth seals as a type of non-contact seal have been used very often in gas turbine and in many kind of fluid machines. They have various type of shapes. Most of them had been designed from the view point of very practical use and it is difficult to explain their characteristics. However, one of the fundamental design policies of labyrinth seal is to design the configuration which can produce larger differential leakage in the direction of fluid flow. Especially, if there is a periodical variation of pressure difference between both sides of labyrinth seal or there is reciprocal pressure difference, it is very significant in the seal performance to have large difference of leakage in the direction of flow. In this research work, variation of leakage and fluid resistance depending on the flow direction were investigated for the narrow flow path.

In order to clarify theoretically the advantages of crankcase-supercharging, the proportion of the drive load of crankcase-supercharger to the output of engine and the increase ratio of mean effective pressure were studied through thermodynamic theory, and then suitable inlet systems were also examined. The validity of estimated values were checked with the experimental data. As a result, it became theoretically clear that a mean effective pressure rise of about 9% to 17% could be obtained by crankcase-supercharging. And it was estimated theoretically that comparing the crankcase pumping load with the output of engine, the former became only about 2.5% of the latter and the suitable inlet plenum volume is about 150 times the displacement volume. Additionally, estimated values are proved to be adequate for practical use by comparing with experimental results.

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.