A real time NOx model for conventional and partially premixed diesel combustion

In this paper a fast NOx model is presented which can be used for engine optimization, aftertreatment control or virtual mapping. A cylinder pressure trace is required as input data. High calculation speed is obtained by using table interpolation to calculate equilibrium temperatures and species concentrations. Test data from a single-cylinder engine and from a complete six-cylinder engine have been used for calibration and validation of the model. The model produces results of good agreement with emission measurements using approximately 50 combustion product zones and a calculation time of one second per engine cycle. Different compression ratios, EGR rates, injection timing, inlet pressures etc. were used in the validation tests. The model calculates thermal (high-temperature) NOx formation by the two reactions of the original Zeldovich mechanism but by using a simple empirical compensation algorithm, the model can also be used for low-temperature NOx formation associated with high EGR rates and long ignition delay.