company news about What is the urea system in a car?

The urea system (SCR system) in diesel vehicles is a key technology for exhaust aftertreatment. Its core function is to reduce nitrogen oxide (NOx) emissions through selective catalytic reduction reactions. The following are the main features and operating mechanisms of the system:

I. System definition and function

The urea system converts harmful nitrogen oxides into harmless nitrogen (N₂) and water (H₂O) under the action of a catalyst by injecting urea solution (AdBlue) into the exhaust gas. This technology has become a core means to meet stringent emission standards such as National VI.

2. Working principle
Urea decomposition
Urea solution (concentration of 32.5%) is hydrolyzed into ammonia (NH₃) in the high temperature (180-400℃) environment of the exhaust pipe
Catalytic reduction
Ammonia and NOx in the exhaust gas undergo redox reaction in the SCR catalyst to generate nitrogen and water vapor
3. Core components
Component Functional description
Urea tank Stores urea solution, the capacity is usually 3-5% of the diesel tank (100 liters of diesel consumes about 4 liters of urea)
Metering pump Precisely controls the amount of urea injection and adjusts the injection frequency in response to ECU signals
SCR catalyst Contains vanadium-based/zeolite catalyst, provides a reaction interface, and the conversion efficiency can reach more than 90%
Sensor system NOx sensor, temperature sensor, and liquid level sensor work together to monitor the system status
IV. Key points for use and maintenance
Supply requirements: Urea level below 10% may cause engine torque limitation, and a solution that meets DIN70700/AUS32 standards must be used
Poor quality risk: Impurities may clog the nozzle (aperture of about 0.5mm), and crystal accumulation may damage the urea pump
Temperature management: The freezing point of urea solution is -11℃, and a heating device is required in cold areas to prevent freezing
This system can improve fuel economy by 3-5% while reducing NOx emissions by more than 85% through real-time closed-loop control. Hyundai models have integrated OBD monitoring modules, which will trigger instrument alarms and limit vehicle performance when the system fails.