SCR系统尿素水溶液喷雾分解影响因素数值模拟

Numerical Simulation of Influence Factors on Urea Solution Spray and Decomposition of SCR System

摘要:

为研究柴油机SCR系统的尿素水溶液喷雾分解规律，建立了SCR尿素水溶液喷射雾化模型，进行了尿素喷射及雾化过程的数值模拟，分析了排气温度、排气流量、喷射速率和喷嘴布置位置对尿素水溶液分解的影响。结果表明，随着排气温度的升高，排气管内壁尿素水溶液粒子密度逐渐降低，且排气管内壁出现尿素水溶液粒子堆砌的位置逐渐后移，NH3体积分数随排气温度的升高呈先升高后降低的变化趋势，400℃时的NH3体积分数较高；随着排气流量的增大，排气管内壁出现尿素水溶液粒子堆砌的位置明显后移，NH3体积分数降低；随着尿素水溶液喷射速率的增大，排气管内壁尿素水溶液粒子密度逐渐增大，NH3体积分数呈近似线性增加，排气管内壁出现尿素水溶液粒子堆砌的位置基本不变；随着距离喷嘴布置位置的增大，尿素水溶液粒子的热解和水解反应进行更为充分，NH3体积分数逐渐增大。

Abstract:

In order to investigate the spray dispersion regulation of urea solution of diesel engine SCR (selective catalytic reaction) system, a urea spray model was built up to simulate urea injection and atomization process. The correctness of the model was verified by comparing the simulation and experimental results, the influences of exhaust gas temperature, exhaust gas flow, injection rate and injector position on dispersion of urea spray were analyzed. The results indicated that with the increase of exhaust temperature, particle density of urea solution on the inner wall of exhaust pipe was gradually reduced and the volume fraction of NH3 was increased, which tended to be stable at 400℃. But with the temperature further increased, NH3 oxidation was enhanced in the exhaust pipe, so its volume fraction was decreased. With the increase of exhaust gas flow rate, the packing position of the urea solution particles on the inner wall was moved backward obviously and the volume fraction of NH3 was decreased. Because with the increase of exhaust gas flow rate, the residence time of urea solution in the exhaust pipe was decreased, which was not benefit for the decomposition of urea. With the increase of injection rate of urea solution, the density of urea solution particles and the volume fraction of NH3 were increased gradually, the packing position of the urea solution particles on the inner wall was almost unchanged. With the increase of distance between urea injector and catalyst, the thermal decomposition and hydrolysis reaction of urea became more complete and the volume fraction of NH3 was increased accordingly.