The theme of this research is to develop new diagnostic system of marine diesel engine by acoustic sound in order to substitute for the crew's diagnosis.
This paper discusses the experiment of diagnosing the gas leakage from the exhaust valve of the fourstroke engine in a training ship, Yuge-maru, in motion. The original acoustic sound from the engine is analysed through (1) power spectrum analysis, (2) filtering analysis, (3) enveloping analysis, (4) ‘partial extraction' analysis, and then displayed in a colored pattern. In the colored pattern, one may easily read that, in the frequency range higher than 6.3 kHz, the power levels at both times of opening and closing the exhaust valve become lower as the size of the slit on the exhaust valve is incressed. Therefore the crew can easily find a fault of the engine at a glance.
