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Frictional force as a function of crank angle of a piston assembly and piston rings alone were measured after the following devices were developed. (1) A gas sealing device that did not affect the measuring values. (2) A device to minimize the effect of gas pressure on the cylinder head and block deformations. (3) A device to minimize the effect of piston slap force. From the measurement of the frictional force diagrams the following characteristics have been found. (1) Lubricating oil temperature has the greatest effect upon the frictional loss of the piston. (2) Piston friction does not increase to the point of becoming proportional to the engine speed. (3) Friction in the expansion stroke increases at high load by the piston slap phenomenon. But the increase of total losses are small because the duration is short. (4) Piston rings account for the majority of the entire frictional force of the piston.

To reduce the friction loss, the size of compression height and the weight of piston in the automobile gasoline engines, two-ring-pistons instead of usually used three-ring-pistons have been developed at many manufacturers. In many designs of piston ring arrengement, up to now, the second ring has been used for oil control not for gas sealing. And the second ring loses the sealing effect at a high speed by the ring movement in the groove. Therefore, it is expected that the trouble caused by an increase of blow-by is not large. However, an increase in thermal load caused by a decrease of the piston cooling passage and also an increase of the lubricating oil consumption are considered to be crucial problems, especially in case of high output engines. With respect to these problems, some improvement are indicated on the basis of the experiments.

A hydrogen powered vehicle system consisted of LH2 tank high pressure LH2 -pump, a device to inject hydrogen onto the hot surface, and ignitor in turbo-engine of CR 12:1 had been developed by Musashi Institute of Technology- Recently the authors applied this system to a medium duty truck produced by Hino Motors Ltd. Then following improvement were required. (1) Gas tightness and endurance of hydrogen injector were improved by the selection of material, size, finishing and by suppling a small amount of lubricating oil. (2) Mixture formation of the injected hydrogen with the compressed air was improved by tuning up the size and number of the nozzle holes and injection timing with the hydraulic pump and valve. (3) A small amount of hydrogen was supplied into the intake manifold. It reduced the combustion noise and also it recovered the evaporation loss in the LH2 -tank.

This paper describes a measurement method using laser induced fluorescence we have developed for simple simultaneous measurements of piston ring oil film thickness at plural points for internal combustion engines. The findings obtained by the measurements of oil film thickness on both thrust and anti-thrust sides of the piston for a mono-cylinder compact diesel engine using this new measurement method are also discussed in this paper. One of main findings is that the oil film thickness of each ring on both sides differs markedly in terms of the absolute value and the stroke- to-stroke variation. It is found that this difference in oil film thickness is caused by the difference in the amount of lubricating oil supplied to the oil ring, and the effect is greater than that of engine speed or load.