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Spray simulations based on a Eulerian−Lagrangian framework were conducted to predict ammonia uniformity in a urea-based compact selective catalytic reduction (SCR) system and validated against laser absorption tomography measurements at various operating points. Since ammonia distribution profile at the SCR inlet can change over time due to the transient nature of spray-induced wall cooling, changes in spray-wall interaction regime and wallfilm transport, simulations were conducted for a sufficiently long time to achieve quasi-steady temperature and wallfilm distribution profiles on the mixer walls. Simulation runtime was reduced using a database approach and frozen field approximation. Subsequently, one final spray injection cycle was simulated to obtain quasi-steady ammonia distribution at the SCR inlet. Prediction of ammonia rich and lean zones and uniformity index using this approach showed excellent correlation against measured data at various operating points and mixer designs.

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