Optimization of the Urea Injection Angle and Direction: Maximizing the Uniformity Index of a Selective Catalytic Reduction System

The uniformity of ammonia is very crucial for reducing the NO X emissions in a selective catalytic reduction system since the uniformity highly affects the chemical reaction between the ammonia and NO X emission. However, increasing ammonia uniformity in a short time period while injecting a urea solution is not a trivial task. Therefore, in this study, the uniformity of various urea injector designs is compared and an optimal design for the urea injector angle and direction is selected. The uniformity index (UI) was calculated using numerical analysis and compared with experimental result to achieve high reliability. The boundary condition of the analysis is extracted from the dominant operating region of the non-road transient cycle (NRTC) to guarantee a realistic analysis result. The design candidates were generated from the combination of three urea injection angles and eight urea injection directions and thoroughly compared to provide an insightful analysis. The conclusion is that injecting urea in the opposite direction to the main stream of exhaust gas increases the kinetic energy and thus the uniformity is highly increased. For example, urea injection in the opposite direction and angle to the mainstream flow could increase the UI to 0.966, which is a 16.7% improvement compared to the same direction and angle injection.