Theoretical analysis and experimental confirmation of exhaust temperature control for diesel vehicle NOx emissions reduction

Abstract

Selective catalyst reduction (SCR) has been demonstrated as an efficient technology for the abatement of NOx emissions from diesel vehicles. However, it has become more and more challenging to meet stringent vehicle emissions standards due to fluctuating exhaust temperatures and high temperature exhaust gas caused by the regeneration of diesel particulate filters (DPFs). Therefore, a novel design for exhaust temperature control, based on controllable heat pipes and latent thermal energy storage, is proposed to realize more durable and efficient NOx emissions reduction. By adopting the concept of peak load shifting, the excess thermal energy of exhaust gas can be stored in phase change materials (PCMs), and released to maintain a relatively stable temperature if a temperature difference exists between the working fluid inside the heat pipes and the PCMs. In order to investigate the feasibility of our novel design, theoretical analysis and numerical simulations are combined to fully describe the dynamic behavior of temperature control. The exhaust temperature effects on NOx emissions reduction is evaluated by an accurate SCR model which is validated by the relevant experiments. The results indicate that the fluctuation of exhaust temperature is limited to 30K after finishing the preheating process during the European transient cycle (ETC) test with an objective temperature of 563K. However, stable exhaust temperatures require an additional 400s for the PCMs to be prepared for an adequate supply of thermal energy. Compared with bare emissions, the improved elimination efficiency of NOx emissions can reach more than 90% in ETC testing, which satisfies the severe emission regulations with more sustainable and environmentally friendly practical application.