혼합챔버 형상에 따른 urea의 열분해 특성에 관한 실험적 연구

Abstract

In the exhaust gas of diesel engines, the urea-water solution (UWS) is injected into the exhaust gas and decomposed into ammonia, isocyanic acid, and water by the thermal decomposition of the urea. The thermolysis rate of the urea has a great influence on the NOx conversion efficiency and the ammonia slip of the SCR catalyst. Therefore, it is essentially required to increase the residence time of the exhaust gas within the exhaust pipe to promote the conversion of the urea to ammonia. In the present work, the two Shapes of the mixing chambers are designed and fabricated to increase the residence time of the exhaust gas. Then, the characteristics of the urea thermolysis for the shapes of the mixing chambers are experimentally examined two range of the velocity (6, 12 ㎧) and temperature (350-500℃) and compared to those without mixing chamber. The ammonia and isocyanic acid are measured at the 5 points along the exhaust pipe from urea injection nozzle using a Fourier transform infrared spectroscopy (FT-IR). The thermal decomposition of the urea is greatly enhanced at low velocities and high temperatures of the exhaust gas. Furthermore, the conversion of the urea to ammonia with the mixing chambers is significantly improved due to the attendant increase in the residence time of the exhaust gas, compared to that without the mixing chambers.