Cycle-to-cycle variation of the combustion process in a diesel engine powered by different fuels

We have studied the fluctuations in mean indicated pressure (MIP) in a diesel engine powered by different fuels. Three alternative fuels and the regular diesel oil (RD) were tested. The alternative fuels are: (1) mixture of fatty acid methyl esters (FAME) and anhydrous ethanol (ET), (2) mixture of FAME and ethyl tertiary-butyl ether (ETBE), and (3) mixture of RD and ETBE. Using statistical and wavelet analyses, we investigated the cycle-to-cycle MIP variations for each fuel, at three engine speeds of 1200, 1600 and 2000 rpm. The results for the alternative fuels were compared with those for RD. At all three speeds, the MIP variations for the alternative fuels were found to exhibit strong periodicities of 64-256 cycles, and these periodicities persist over many engine cycles, whereas shorter-term periodicities at 2-32 cycles appeared to be intermittent. In the case of RD, the MIP variations with longer periodicities appeared only at the highest engine speed but intermittent fluctuations of 2-32 cycles are present at all three speeds. Among the four fuels considered, the MIP variations for the RD were found to be closest to the Gaussian white noise.