Analysis of the Influence of Mixture Composition on Cycle by Cycle variability of an High Performance Engine

The Cycle by Cycle Variation (CCV) of an high performance engine is evaluated by means the analysis of the Coefficient of Variance (COV) of IMEP. Both numerical and experimental investigations are computed in order to study the influence of Air-to-Fuel Ratio on cyclic variability. The experimental analysis of the pressure traces in the chamber shows an increase in CCV towards leaner mixture conditions. The extrapolation of Heat Release Rate reveals the strong influence of the early stages of combustion on the variability of the flame evolution. In order to evaluate the influence on CCV of local air equivalence ratio cycle-to-cycle variability and mixture homogeneity in the chamber, a numerical CFD methodology for the simulation of the combustion process has been proposed. The results reproduce with reasonable accuracy the increase in CCV with leaner combustions and put the basis for a deeper insight into the complex phenomena involved in the combustion process by the use of parametric analysis.