A Study on the Factors Affecting Heated Wall Impinging Characteristics of SCR Spray

摘要

Many studies show that under diesel engine operating conditions, SCR reductant sprays will impinge on the wall of exhaust pipes. In order to understand this impinging process of SCR reductant spray, and to analyze what factors affect it, a test bench was set up by means of high speed video camera. At atmospheric pressure, SCR spray was injected on a heated metal wall, the impacts of wall temperature, injection pressure, injection height and angle on developing characteristics of SCR reductant spray after impinging on the heated wall have been researched and analyzed. The results show that the heated wall temperature has a great impact on the spray developing process, when wall temperature is lower than 405K, after water evaporated the crystallized urea will remain on the wall to block exhaust pipes. When wall temperature is higher, the atomization and evaporation of SCR reductant spray will be better, and the hydrolysis process of urea will be faster. Under different wall temperatures and injection heights, there may exist an optimal injection angle, at which the atomization and evaporation of SCR reductant spray will be the best. When injection pressure goes higher, the spray angel will be greater, and the spray droplets will be much smaller, it is good for the contact of SCR spray and exhaust gas. The evaporation of SCR reductant spray, the generation of NH_3 are all improved, meanwhile the mixing process of NH_3 and exhaust gas as well as the reduction of NO_x are enhanced.