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Urea-water solution (UWS) injection combined with Selective Catalytic Reduction (SCR) has developed as an effective method of meeting EPA and EURO NOx emissions regulations for diesel engines. Urea/SCR systems encompass a wide range of engine sizes, from light duty vehicles to large ship or power generation engines. One key challenge faced by modern urea/SCR systems is the formation of solid deposits of urea decomposition by-products that are difficult to remove. These deposits are proven to be detrimental to urea/SCR systems by decreasing ammonia uniformity, clogging injector nozzles and increasing pressure drop of the whole system. Urea deposits only form in a narrow range of wall temperatures and take many minutes to hours to form. The decomposition of urea into deposits begins with the formation of biuret and then progresses into the crystalline species cyanuric acid (CYA), ammelide, and ammeline.

The proposed Euro 7 regulation aims to substantially reduce the NOx emissions to 0.03 g/km, a trend also seen in upcoming China 6b and US EPA regulations. Meeting these stringent requirements necessitates advancements in Urea/Selective Catalytic Reduction (SCR) aftertreatment systems, with the urea deposit formation being a key challenge to its design. It’s proven that Computational Fluid Dynamics (CFD) can be an effective tool to predict Urea deposits. Transient wall temperature prediction is crucial in Urea deposit modeling. Additionally, fully understanding the kinetics of urea decomposition and by-products solidification are also critical in predicting the deposit amount and its location. In this study, we introduce (i) a novel film boiling model (IFPEN-BRT model) and (ii) a new urea by-product solidification model in the CONVERGE CFD commercial solver, and validate the results against the recent experiments.