Combustion analysis of a CI engine with biodiesel blends based on vibro-acoustic measurement

In this paper, a combustion analysis of a compression ignition (CI) engine operating with biodiesel blends has been experimentally investigated to examine the effects of biodiesel on the combustion process and the characteristics of the engine noise produced by the combustion process. The experiment with different loads and speeds was conducted on a four-cylinder, four-stroke, direct injection and turbocharged diesel engine fuelled with biodiesel (B50 and B100) and normal pure diesel. The signals of vibration, acoustic and the in-cylinder pressure were measured for analysing the engine combustion. In order to examine these signals, a coherent power spectrum analysis method is used to investigate the engine noise signals for locating the frequency band which is closely related to the combustion process. Subsequently, the Wigner-Ville distribution is employed to analyse the energy distribution of engine noise in the time-frequency domain. A band-pass filter based on fractional Fourier transform is developed to extract the main combustion induced noise from the engine noise for comparison. The interim results show that the sound energy level of combustion noise of engine fuelled by biodiesel and its blends is higher than that of engine fuelled by diesel. This is also identical to the variation of in-cylinder pressure. Hence, acoustic signals of the CI engine provide useful features for remote engine condition monitoring and supply fuel monitoring.