Combustion analysis and cycle-by-cycle variations in spark ignition engine combustion Part 2: A new parameter for completeness of combustion and its use in modelling cycle-by-cycle variations in combustion

Abstract

This paper investigates a technique of calculating the completeness of combustion on a cycle- by-cycle basis. The technique introduces the normalized pressure rise due to the combustion parameter, ψ to describe the completeness of combustion. This parameter is based on the Rassweiler-Withrow method of calculating the mass fraction burned and is derived from the pressure-crank angle record of the engine. Experimental data were obtained from a Rover K4 optical access engine and analysed with a combustion analysis package. A computer simulation was then used to model the data on a cycle-by-cycle basis, both with and without the completeness of combustion parameter. The paper discusses the conditions under which it is suitable to model mean engine cycles, compared with the need to model cycle-by-cycle variability, and comments on the situations in which each type of modelling would be most appropriate. The engine simulation model is also used to investigate cycle-by-cycle variability of NO emissions that have recently been obtained experimentally. The successful aspects of this investigation are that the cycle-by-cycle variability in the completeness of combustion can be determined by use of the parameter ψ, that the inclusion of the completeness of combustion parameter improves the simulation's ability to model the experimental data both in a statistical sense (the coefficient of variation of the indicated mean effective pressure) and on a cycle-by-cycle basis and that cycle-by-cycle NO modelling results are found to compare well with experiment.