Chemical Kinetics Modelling of Exhaust After-Treatment System: A One Dimensional Simulation Approach

The Indian automotive industry has taken a big leap towards stringent Bharat Stage VI (BS VI) emission standards by year 2020. A digital driven design and development focusing on innovative and commercially viable technologies for combustion and exhaust after-treatment system is the need of the time. One-dimensional (1D) simulation serves as a best alternative to its counterparts in terms of obtaining faster and accurate results, which makes it an ideal tool for carrying out optimization studies at system level. In this work, 1D chemical kinetics modelling and analysis of exhaust after-treatment system (EAT) for a heavy-duty diesel has been performed using GT-Power.

Initially, a single site 1D model for a diesel oxidation catalyst (DOC) has been developed and then, a two-site, 1D model for a selective catalytic reduction (SCR) catalyst was also developed based on reactor data. Genetic algorithm was used to calibrate the rate constants of the Arrhenius equations for the reactions with the experimental data. The calibrated 1D SCR model along with 1D models of other sub-components of the EAT system has been used to carry out system performance and optimization studies. It is seen that the effect of increasing PGM loading had almost no effect on THC conversion in the DOC while increasing the size showed a significant improvement in THC conversion. The use of a Catalyst coated DPF (CSF) has improved the THC conversion efficiency of the system at higher RPMs. It was found that exhaust gas temperature is a key factor in deciding the NO_x conversion efficiency of the system.