Abstract
Kinetic models, incorporating elementary chemical reactions, are used to predict the concentrations of NO (nitric oxide) and CO (carbon monoxide) in spark-ignition engines during the expansion process. The kinetic equations are*** incorporated in a cycle synthesis computer programme, which can be used to calculate the thermodynamic state and the concentration of a number of species in the burnt gas. The stability and accuracy of the programme is discussed and the validity of the results is confirmed by comparing the theoretical predictions with experimental results.