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

Experimental data were obtained from a Rover K4 optical access engine and a nalysed with a combustion analysis package. Cyclic NO values were calculate d by mass averaging the measurements obtained by a fast NO analyser. The mo delled NO results were compared with the experimental values on plots of NO versus peak cylinder pressure, P-max. The model achieves its cyclic variab ility through the input of experimentally derived burn rates and a complete ness of combustion parameter. This is based on the Rassweiler and Withrow m ethod for calculating the mass fraction burned and is derived from the pres sure-crank angle record of the engine. The cycle-by-cycle NO modelling resu lts are found to compare well with the experiments in terms of the mean val ue for all cycles, the general slope of the NO versus P-max line and the ma ximum and minimum values (or spread). The modelled results do not, however, exhibit the same degree of scatter as the experimental data. This is attri buted to the model utilizing a fixed blow-by rate, a constant temperature a t inlet valve closure and a constant residual mass fraction for all cycles at a given operating point.