Review on selective catalytic reduction technology of diesel engines

Abstract

Diesel vehicles are an important source of nitrogen oxide (NO_x) emissions in the atmosphere. Selective Catalytic Reduction (SCR) systems are the primary post-treatment devices for reducing NO_x emissions from diesel engines. In China, diesel vehicles mostly adopt the high-efficiency SCR technology route to meet the China VI emission regulations, which requires a NO_x conversion efficiency of around 95% for SCR. To achieve low NO_x emissions in full working condition, it is necessary to develop wide-temperature-range, high activity, and high durability catalysts to ensure that SCR has a high NO_x conversion efficiency in a wide temperature window, and to improve catalyst hydrothermal aging and sulfur poisoning. The new regulations require stricter NO_x emission limits during cold-start phases, and close-coupled SCR and SCR capture technology can enable exhaust gas in SCR to quickly reach the urea injection temperature under low engine exhaust temperature conditions, which is beneficial for reducing NO_x emissions during the cold-start phases. The optimization of SCR system injection control strategy is a key factor in ensuring high NO_x conversion efficiency and avoiding NH_3 leakage. The development of SCR control strategy should consider the uncertainty of hardware measurements, and the increasing complexity of the post-treatment system configuration brings new challenges to the development of SCR system control strategies. New SCR reductants such as solid ammonium and reducing gases (hydrocarbons, hydrogen, and CO) can significantly improve the drawbacks of urea as a reductant carrier, but large-scale application of these new reductants has not been realized.

Keywords

• diesel vehicle
• scr system
• no_x conversion efficiency
• close coupled scr
• scr control strategy