As one of the most important parts of the four emission of diesel vehicles, vehicle urea is used to reduce the emission of nitrogen oxides. So in the process of heavy vehicle emissions in four countries, the role of urea in the car, how to reduce emissions? You do not understand the use of urea will continue to work with you to interpret the role of urea in the SCR system. At present, the main route of upgrading China's heavy-duty diesel engine is four SCR, which is the use of selective catalytic reduction technology. The operation process is shown in figure, is roughly from the turbine exhaust after it enters into the exhaust pipe, the exhaust pipe is provided with a urea measuring jetting device, injected into the aqueous solution of urea, nitrogen oxides and urea solution in tail gas occurs in SCR reaction tank redox reaction, the formation of nitrogen and water discharge.