Prediction of NO x considering NO and NO 2 for a CI engine

Abstract

Nitrogen oxides (NO _x ) are one of the main harmful emissions from diesel engines. Regulations on emissions are becoming more stringent; consequently, research should aim at reducing both engine-out NO _x and tail-pipe NO _x emissions. Exhaust gas recirculation is mainly used to reduce engine-out NO _x emissions. After-treatment methods such as lean NO _x trap systems and selective catalyst reduction are used to minimize tail-pipe NO _x emissions. Real-time feedback control during transient conditions can further reduce these emissions and be utilized when information about real-time engine-out NO _x emissions is available. It would be helpful to evaluate the proportion of NO₂ in NO _x emissions because the conversion efficiency of an after-treatment system is affected by temperature and the NO-to-NO₂ ratio. Therefore, a semi-empirical NO _x model considering NO and NO₂ separately was developed for a diesel engine in this study. The NO estimation model was established based on the extended Zeldovich mechanism. The NO₂ estimation model focused on chemical reactions between NO and other species and was based on formation and decomposition mechanisms. This NO _x model can contribute to the cost reduction of engine systems by replacing existing NO _x sensors and can also be applied to real-time feedback control strategies to minimize NO _x emissions.