Analysis of Cycle-to-Cycle Engine Combustion Variations using Statistical and Wavelet Transform Methods

Cycle-to-cycle combustion variations not only degrade the performance and combustion characteristics of an engine, it also has a considerable influence on engine durability. Thus, a deeper understanding of cycle-to-cycle combustion variations, particularly at low loads, is required. In the present study, both statistical and wavelet transform methods have been used to investigate the cycle-to-cycle combustion variations at different operating loads. A single-cylinder spark-ignited engine was used, and cylinder pressure data was recorded for 1200 consecutive engine cycles at each operating point for the analysis of cycle-to-cycle variations. As expected, it was found from the statistical analysis that cycle-to-cycle variations in indicated mean effective pressure (IMEP) were decreased with the increase in load. Wavelet analysis revealed that cycle-to-cycle variations occur at multiple time scales for both loads. However, wavelet power spectrum at the lower load was characterized by intermittent high frequency oscillations, and with the increase in load, these high frequency oscillations were shifted to lower frequency range.