Investigation on the calculation method of ammonia storage correction and its effect on NOx reduction performance of Cu-based SCR system

Aiming at the problems of inaccurate ammonia storage estimation, fluctuating conversion efficiency, and high ammonia leakage risk of diesel engine copper-based selective catalytic reduction (SCR) system under transient operating conditions, this paper establishes a high-precision SCR catalyst simulation model based on GT-power and verifies the model combined with engine bench test. Through simulation analysis, the influence of ammonia storage characteristics on SCR conversion efficiency is systematically studied, the safe threshold of ammonia storage under variable operating conditions is determined, the error source of traditional ammonia storage calculations is revealed, and a dual-coefficient correction method coupling the NH 3 -O 2 reaction coefficient and the NH 3 -NO x reaction ratio coefficient is proposed. Finally, a segmented closed-loop control strategy based on the modified ammonia storage model is constructed and verified through the WHTC cycle. The results show that there is a critical temperature of 280 °C for the influence of ammonia storage on SCR conversion efficiency: an approximate linear correlation in the low-temperature range and a weak influence in the high-temperature range. Rapid temperature rise under variable operating conditions is easy to cause ammonia leakage, and 70% saturated ammonia storage can achieve the optimal balance between efficiency and leakage. Affected by the NH 3 -O 2 side reaction and the NO 2 proportion, the traditional 1:1 measurement method has a maximum calculation deviation of 8%. After introducing the dual-coefficient correction, the deviation in the ammonia storage calculation is reduced by 28.97%. The optimized control strategy can reduce NO x emissions in the World Harmonized Transient Cycle (WHTC) from 5.07 g/(kW·h) to 0.39 g/(kW·h), while keeping ammonia leakage consistently below 10 ppm. The research results can provide a theoretical basis and technical reference for the precise control of urea injection in diesel engine SCR systems.