Influence of Operating Conditions on Urea Deposit Formation in the Urea-SCR System on a Diesel Engine Exhaust-like Test Bench

Abstract

A rapid urea and byproduct deposit experimental platform was built and an integrated after-treatment device model of the nonroad agricultural diesel engine was established based on CONVERGE software. The effects of exhaust temperature, exhaust flow rate, and urea injection mass on urea and byproduct deposits were studied by both experiments and simulation. The model was validated using the back pressures of catalysts, mixer wall temperature, and distribution of urea and byproduct deposits. The performance of the mixer was evaluated using the concentration, mass, and uniformity of NH 3 at the front-end cross-section of its selective catalytic reduction catalyst. Wall temperature is the key influence factor on the composition of the liquid film and is affected by the urea injection mass and exhaust flow rate. When the wall temperature is low, the liquid film is mainly composed of urea solids, but when it is above 423 K, urea solids begin to decompose into biuret, cyanuric acid, ammelide, and other byproducts. As for mixer performance, the uniformities of NH 3 , temperature, and velocity are above 0.9, 0.975, and 0.965, respectively, under all working conditions.

Study on Diesel Engine Selective Catalytic Reduction Performance at Different Atmospheric Pressures Using the Response Surface Method

“…Much research has been carried out on the factors affecting SCR performance. Liu et al 5 conducted experiments on the urea rapid deposition test bench and combined with the CFD software simulation results studied the effects of exhaust temperature, exhaust mass flow rate, and urea injection quality on SCR urea deposits. The results showed that exhaust temperature, exhaust mass flow rate, and urea injection amount would affect the wall temperature of SCR, thus affecting the formation of urea deposits.…”

Commentary on Earth Day and the Relationship to Historical Developments in Air Pollution Control and Scientific Next Steps

“…32 Zeolites have also been added to trap hydrocarbons to help with cold start emissions performance. 33 Today, pollution control is still a very vibrant area, with researchers at the interface of engineering chemistry and industry focusing on remaining challenges including diesel emissions solutions 34 such as diesel oxidation catalysts, 35,36 selective catalytic reduction (SCR) catalysts, 37,38 urea-SCR devices, 39 lean NOx traps, 40,41 ammonia slip catalysts, 42 and diesel particulate filters, 43 but also in long-standing debates such as deactivation mechanisms of three-way catalysts. 44 Investigations into new supports for these catalysts such as FeCrAl alloys forming Al 2 O 3 surface layers also show considerable promise.…”