Influence of the resonant frequency on the control of knock in diesel engines

Abstract

This paper presents an alternative approach to investigating the origin and the development process of knock vibrations that occur in an indirect injection (IDI) diesel engine. In contrast to the conventional analysis of the pressure rise rate, this study focuses on the analysis of instantaneous resonant frequencies at different moments during combustion. The smoothed pseudo-Wigner-Ville distribution (SPWVD) and Hilbert transform methods are applied to estimate the resonant frequency under different conditions representing various knock intensities. Two important factors are found significantly to influence knock development. Finally, design strategies and preferable fuel injection patterns are suggested for reducing knock intensity.

Bayesian models for the determination of resonant frequencies in a DI diesel engine

“…The isolation of resonant frequencies also has important implications in the detection of knock [5,8]. Moreover, instantaneous resonant frequency information is of more practical use in the elimination of knock than more easily measured factors, such as the rate of pressure rise [5].…”

“…Conventional spectral analyses, such as those carried out a by Fourier transform, fail to accurately interpret the resonant frequencies precisely if the resonance is non-stationary [5]. A common approach to get around non-stationary frequencies is the use of the Wigner-Ville Spectrum [4,5,8,9,10,11,12].…”

“…A common approach to get around non-stationary frequencies is the use of the Wigner-Ville Spectrum [4,5,8,9,10,11,12]. We propose, however, the use of Bayesian statistical inference which allows us to configure precisely a model for the observable information of interest.…”

“…This model fails to capture significant observed behaviour. However, given that it is known that resonant frequencies decay over time [5,8,22] it seems intuitive to include a parameter that models the frequency decay. Hence, we extend the model by defining:…”

“…Calculating the resonant frequency accurately in an engine combustion chamber enables the characterisation of resonant frequencies that are associated with the speed of sound, and hence temperature [3,4,5,6,7]. Therefore, accurate isolation of resonant frequencies and their decay, as a function of time, or crank-angle, will allow the bulk temperature of the gas in the combustion chamber to be determined at any point within the region of interest.…”