What does SCR mean on a car?

[Ophelia]

SCR on the car dashboard refers to the Selective Catalytic Reduction system. Its function is similar to the three-way catalyst in gasoline vehicles. It uses a catalyst in the traditional muffler while also employing a urea supply system and an injection regulation system. It is generally used to treat NOx in diesel engines. SCR system's fuel consumption is slightly lower compared to EGR and DPF systems, and the consumption of urea aqueous solution can also be compensated in fuel consumption. An illuminated SCR light can cause the engine to reduce power, and if not addressed promptly, it may even lead to pump burnout. Therefore, any issues must be dealt with immediately. The basic working principle of the SCR system is: exhaust gas exits the turbine and enters the exhaust mixing pipe, where a urea metering injection device is installed to spray urea aqueous solution. Urea undergoes hydrolysis and pyrolysis reactions at high temperatures to produce NH3. On the surface of the SCR system catalyst, NH3 is used to reduce NOx, releasing N2. Excess NH3 is also oxidized into N2 to prevent leakage. Generally, for every 100L of fuel consumed, 5L of liquid urea aqueous solution is consumed. The SCR system is also widely used in diesel engine exhaust after-treatment. By optimizing the fuel injection and combustion processes, it aims to control particulate matter (PM) generation within the engine and then treat nitrogen oxides formed under oxygen-rich conditions externally. Using automotive urea (which decomposes into ammonia at certain temperatures), it selectively catalytically reduces nitrogen oxides (NOx), achieving both energy-saving and emission-reduction goals. This technology is the mainstream technical route in Europe, where almost all long-haul trucks and large buses adopt this method.