Abstract
A two-cylinder diesel engine was modified for a dimethyl ether (DME) homogeneous charge compression ignition (HCCI)-direct injection (DI) engine. Knock characteristics are investigated based on in-cylinder pressure signals. The in-cylinder pressure is decomposed into four levels using discrete wavelet transform (DWT). The maximum pressure amplitudes and wavelet energy at four levels are approximately equal in normal combustion. With knock, both the maximum pressure amplitude and wavelet energy at the third level are the greatest. The correlation analysis shows that the correlation coefficients for maximum pressure amplitude and wavelet energy are quite valid for the second and third levels. It indicates that the correlation is stronger at frequencies which belong to resonant frequencies. The wavelet energy has slightly better performance than maximum pressure amplitude for identification of knock.
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