A STOCHASTIC-EXPERIMENTAL INVESTIGATION OF THE CYCLIC PRESSURE VARIATION IN A DI SINGLE-CYLINDER DIESEL-ENGINE

This paper presents an analysis of the cycle-by-cycle combustion varia tion as reflected in the pressure indicator diagram of a single-cylind er, naturally aspirated, four-stroke, direct-injection, Lister LV1 die sel engine. A measuring set-up consisting of piezoelectric transducers with charge amplifiers, in the cylinder and the fuel injection pipeli ne, and a fast data-acquisition board installed on an IBM-compatible m icrocomputer was used to gather the data of 650 successive combustion cycles of the cylinder, under various combinations of injection timing and load conditions. The measured data were corrected for drift, and the top dead centre of each cycle is determined thermodynamically. The data obtained by this technique were analysed for the peak pressure, the peak rate of pressure rise, the crank angles at which these maximu m values occur, and for the injection timing and ignition delay. The g roups of parameters have been further statistically analysed for avera ges, standard deviations, probability density functions, autocorrelati ons and power spectra. Crosscorrelation runs were also performed to ob serve any cause relationship between cyclic pressure variations and th e fuel-injection-system operation. The results of the stochastic analy sis technique have proved to be very useful for the investigation and interpretation of the existence of fluctuation phenomena in the diesel internal combustion engine and their cause relationships, thereby aid ing the correct interpretation of the relevant experimental results an d their associated errors.