A detailed chemical mechanism to predict NO cycle-to-cycle variation in homogeneous engine combustion

Abstract

Cycle Combustion Variation (CCV) is an undesirable characteristic of Spark Ignition (SI) engines as a result of random perturbation of the combustion parameters, the equivalence ratio and the turbulence of the flow. Previous studies investigated the impact of some engine parameters on nitric oxide (NO) variability as well as the impact of these parameters on engine performance. The impact of these parameters on the mean value of NO distribution due to CCV and the amplitude of the NO variation are very important for engine tuning in order to meet the emission limits. In this study a detailed chemical mechanism for the prediction of NO formation in a homogeneous engine combustion chamber is presented. The mechanism receives as an input the thermodynamic analysis from a commercial Engine Simulation Tool (EST) and calculates the NO chemical kinetics for each crank angle step. Data found in literature were used for the validation of model approach. The second step of this study is the investigation of the nitric oxide variation due to CCV. Assuming that the combustion parameters values form a normal distribution, random perturbations for these parameters were introduced in the thermodynamic model. The varied thermodynamic data are then imported in the detailed chemical mechanism and NO distributions are estimated. The main target of this study is the investigation of the CCV impact on NO emissions as well as the correlation of imep variation and nitric oxide variation due to CCV.