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

This paper investigates a number of new approaches to mass fraction bu rned analysis for application to spark ignition engine combustion proc esses. The rationale for these new approaches is to retain the simplic ity and computational efficiency of the technique of Rassweiler and Wi throw, but to overcome some of the limitations inherent in the standar d methods. The approaches investigated include the use of a two-zone m odel to determine information about the burned and unburned gas temper atures and the modification of the standard Rassweiler and Withrow exp ression to incorporate polytropic indices for compression and expansio n. The investigation makes use of an engine simulation model, which wa s used to generate the pressure data. This technique provided a 'known ' burn rate against which to evaluate the methods investigated. Some e xperimental data taken from a Rover K4 optical access engine is also p resented. The successful aspects of this investigation are the use of the Rassweiler and Withrow equation with different compression and exp ansion indices, and the application of this analysis to investigate cr evice gas burn-up. What was found to be not successful was the use of a two-zone model for calculating gas temperatures. The results indicat e that the model is, in general, not reliable for computing temperatur es and this is due to the temperature gradient in the burnt zone and t he 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.