Validation of a Cyclic NO Formation Model with Fast NO Measurements

Experimental data was obtained from a Rover K4 optical access engine and analyzed with a combustion analysis package. Cyclic NO values were calculated by mass averaging the measurements obtained by a fast NO analyzer. While the mass averaged results were used as the basis of comparison for the model, results indicate that mass averaging a fast NO signal is not nearly as critical as mass averaging a fast FID signal. A computer simulation (ISIS - Integrated Spark Ignition engine Simulation) was used to model the NO formation on a cyclic basis by means of the extended Zeldovich equations. The model achieves its cyclic variability through the input of experimentally derived burn rates and a completeness of combustion parameter, which is based on the Rassweiler and Withrow method of calculating mass fraction burned and is derived from the pressure-crank angle record of the engine. The cycle-by-cycle NO modeling results are found to compare well with the experiments in terms of the mean value for all cycles, the general slope of the NO vs. P_max line, and the maximum and minimum values (or spread). The modeled results do not, however, exhibit the same degree of scatter as the experimental data. This is attributed to the model utilizing a constant temperature at inlet valve closure and constant residual mass fraction for all cycles.