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The potential of high efficiency zero-emission engines fueled by hydrogen, which is regarded as a promising form of energy for the future, is being researched. The argon circulated hydrogen engine [ 1 ] is one system theoretically capable of achieving both high efficiency and zero emissions, and its feasibility for use in vehicles has been studied. Specifically, tests were performed to verify the following issues. It was examined whether stable hydrogen combustion could be achieved under an atmosphere of argon and oxygen, which has a high specific heat ratio, and whether the substantial thermal efficiency improvement effect of the argon working gas could be achieved. An argon circulation system was also studied whereby steam, which is the combustion product of the hydrogen and oxygen emitted from the engine, is separated by condensation to enable the remaining argon to be re-used.

The noise generation mechanism of a direct-acting valve train such as used in sporty and luxury cars was determined for both mechanical and hydraulic tappets through measurements of sound pressure levels and vibrations and the use of computer graphics to observe actual valve and tappet movement. Two phenomena were clarified: chatter at low engine speeds and a mechanical noise at high engine speeds. Further experiments established that the noise of a mechanical tappet can be greatly reduced and its tonal quality improved by optimizing the cam profile and by increasing the acoustic damping ratio of the tappet.