Investigation of Deposits in Urea-SCR System Based on Vehicle Road Test 2017-01-9275
In vehicles with urea-SCR system, normal operation of the urea-SCR system and engine will be influenced if there are deposits appearing on exhaust pipe wall. In this paper, a commercial vehicle is employed to study the influence factors of deposits through the vehicle road test. The results show that, urea injection rate, temperature and flow field have impacts on the formation of deposits. When decreasing the urea injection rate of calibration status by 20%, the deposit yield would reduce by 32%. If the ambient temperature decreased from 36 °C to 26 °C, the deposit yield would increase by 95%. After optimizing the exhaust pipe downstream of the urea injector by removing the step surface, only a few flow marks of urea droplets are observed on the pipe wall, and no lumps of deposits existing. In this case, we have improved exhaust flow field by removing step surface and placing the nozzle in the center of exhaust pipe and conducted a durability test of traveling for 5500km, but which couldn’t completely avoid the formation of deposits on the exhaust pipe wall. Then, the deposits-related problems have been solved after forwarding the injector close to the exit of turbo and wrapping the exhaust pipe with heat preservation material because the exhaust temperature increased by over 50 °C and the wall temperature increased by over 100°C. Finally, a calculation model of critical injection rate for avoiding deposit formation is proposed.