Modeling the decomposition and byproduct formation of a urea-water-solution droplet

A mathematical model for evaporation of water from a urea-water-solution (UWS) droplet and subsequent decomposition of urea, including a semi-detailed kinetic scheme for byproduct formation, was developed. The model provided a good description of experimental water evaporation rates from UWS droplets, but generally underestimated the urea decomposition rates. The depletion of 7-70 µm UWS droplets was investigated at ambient temperatures of 200-400 oC corresponding to urea-SCR conditions. The results indicate that the risk of deposition may be reduced by minimizing the droplet size and maximizing the exhaust temperature and reaction time. The present work can provide guidance for designing an efficient evaporation system, to facilitate a stable SCR operation with high NO reduction.