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