Combustion analysis and cycle-by-cycle variations in spark ignition engine combustion Part 1: An evaluation of combustion analysis routines by reference to model data

Abstract

This paper investigates a number of new approaches to mass fraction burned analysis for application to spark ignition engine combustion processes. The rationale for these new approaches is to retain the simplicity and computational efficiency of the technique of Rassweiler and Withrow, but to overcome some of the limitations inherent in the standard methods. The approaches investigated include the use of a two-zone model to determine information about the burned and unburned gas temperatures and the modification of the standard Rassweiler and Withrow expression to incorporate polytropic indices for compression and expansion. The investigation makes use of an engine simulation model, which was used to generate the pressure data. This technique provided a ‘known’ burn rate against which to evaluate the methods investigated. Some experimental data taken from a Rover K4 optical access engine is also presented. The successful aspects of this investigation are the use of the Rassweiler and Withrow equation with different compression and expansion indices, and the application of this analysis to investigate crevice gas burn-up. What was found to be not successful was the use of a two-zone model for calculating gas temperatures. The results indicate that the model is, in general, not reliable for computing temperatures and this is due to the temperature gradient in the burnt zone and the disproportionately high rate of heat transfer from the mixture that burns first during combustion. The mass fraction burned calculations using this model were also found to be not as accurate as those based on simpler models.