Cycle-by-cycle modelling of NO formation and comparison with experimental data

Abstract

Experimental data were obtained from a Rover K4 optical access engine and analysed with a combustion analysis package. Cyclic NO values were calculated by mass averaging the measurements obtained by a fast NO analyser. The modelled NO results were compared with the experimental values on plots of NO versus peak cylinder pressure, Pmax. The model achieves its cyclic variability through the input of experimentally derived burn rates and a completeness of combustion parameter. This is based on the Rassweiler and Withrow method for calculating the mass fraction burned and is derived from the pressure—crank angle record of the engine. The cycle-by-cycle NO modelling results are found to compare well with the experiments in terms of the mean value for all cycles, the general slope of the NO versus Pmax line and the maximum and minimum values (or spread). The modelled results do not, however, exhibit the same degree of scatter as the experimental data. This is attributed to the model utilizing a fixed blow-by rate, a constant temperature at inlet valve closure and a constant residual mass fraction for all cycles at a given operating point.