Abstract
The wavelet cross-correlation analysis was used for the in-cylinder pressure and the engine outer surface vibration acceleration to investigate the time delay from the combustion impact to the vibration acceleration for each frequency component. The main results are as follows: Acceleration peaks were observed at 2500 Hz and 8000 Hz on the outer surface near the combustion chamber. This is because the pistonconnection rod coupled vibration occurs at 2500 Hz and the combustion chamber resonance at 8000 Hz. At 2500 Hz and 8000 Hz, there is a time delay on which a large correlation of 0.8 or higher appears between the in-cylinder pressure and acceleration. At 800 Hz, 2000 Hz, 3150 Hz, 6300 Hz, 8000 Hz, 10000 Hz, there is no significant time delay, and therefore the vibration reaches the engine outer surface from the combustion chamber via the liner and cylinder head with the shortest path. At 1000 Hz, 1250 Hz, 1600 Hz, 2500 Hz, 4000 Hz and 5000 Hz, there is a time delay of 10 to 30 deg. This time delay is probably due to the excitation of some structural vibrations, such as the piston-connecting rod coupled vibration.
