Improvement of low-temperature NOx reduction performance of NH3-SCR with O3 injection under diesel engine transient conditions

Abstract

NH₃-based selective catalytic reduction (SCR) is an effective technology for reducing NO_x emissions, a major contributor to air pollution, but its efficiency significantly decreases at temperatures below 200°C. To enhance low-temperature NO_x reduction, O₃ was injected into the exhaust gas during the initial 600 s of the World Harmonized Transient Cycle (WHTC) cold phase in a diesel engine using a Cu/SSZ-13 catalyst. O₃ promotes the oxidation of NO to NO₂, which reacts with NH₃ below 150°C to form NH₄NO₃, thereby improving NO_x reduction efficiency. While NH₄NO₃ accumulates on the catalyst at low temperatures without participating in the SCR reaction, it acts as an intermediate for fast SCR as the temperature rises, further enhancing NO_x reduction. Furthermore, machine learning was applied to predict optimal NO_x reduction rates based on the O₃/NO molar ratio, revealing that the highest efficiency at catalyst inlet temperatures below 150°C is achieved when the O₃/NO ratio is set to 1. This approach demonstrates the potential of O₃ injection combined with data-driven optimization to improve SCR performance under cold-start conditions.