Research Progress on Deposits in Diesel Vehicle Urea-SCR
Systems: Composition, Mechanism, Impact and Mitigation

Vehicle Engine ›› 2026, Vol. 0 ›› Issue (4) : 1-11.

Research Progress on Deposits in Diesel Vehicle Urea-SCR Systems: Composition, Mechanism, Impact and Mitigation

CHEN Xue^1,2,ZHAO Yang^1,2,HAN Boyuan³,YAN Feng³

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Abstract

Selective catalytic reduction(SCR) technology is the mainstream approach for controlling nitrogen oxide(NO_x) emissions from diesel engines, and urea-water solution(UWS) serves as the key precursor for the reductant. However, the formation of solid deposits due to incomplete decomposition of UWS under low-temperature and transient operating conditions severely impacts the efficiency, reliability, and durability of SCR systems. Recent research progress on the issue was reviewed, the complex composition of urea deposits was systematically summarized and the detailed reaction mechanism was analyzed with isocyanic acid serving as the key intermediate and the liquid film acting as a "micro-reactor". The coupled influence of multiple factors(such as exhaust temperature, injection parameters, and structural design) on deposit formation was emphatically analyzed. Multi-level synergistic mitigation strategies were further comprehensively outlined, including physical process control through optimized spray mixing and thermal management, chemical modification by adding surfactants to alter droplet interfacial properties, and the development of intelligent predictive control. The results indicate that a fundamental solution to the deposit problem requires precise mechanistic understanding, synergistic system-level design and process integration to achieve efficient, stable, and low-maintenance operation of SCR systems across all operating conditions and throughout the lifecycle.

Key words

diesel vehicle / selective catalytic reduction(SCR) / urea / deposit

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CHEN Xue, ZHAO Yang, HAN Boyuan, YAN Feng. Research Progress on Deposits in Diesel Vehicle Urea-SCR Systems: Composition, Mechanism, Impact and Mitigation[J]. Vehicle Engine. 2026, 0(4): 1-11