What is Automotive Urea?
2 Answers
Automotive urea is a colorless, transparent liquid stored in the urea tank. When sensors detect nitrogen oxides in the exhaust pipe, it automatically sprays atomized automotive urea, which mixes with the nitrogen oxides and undergoes a redox reaction in the SCR catalytic reaction tank, ultimately producing non-polluting nitrogen and water that are expelled. Automotive urea is an essential additive for the SCR (Selective Catalytic Reduction) solution. The SCR system includes a urea tank (containing diesel exhaust fluid) and an SCR catalytic reaction tank. The primary harmful substances in diesel vehicle exhaust are nitrogen oxides and particulate matter. While particulate emissions can be reduced through technical means within the engine, nitrogen oxides remain the main component of the exhaust. By injecting urea into the exhaust after-treatment device, the urea decomposes into ammonia at high temperatures. Under the action of a catalyst, the ammonia reacts with nitrogen oxides to produce harmless nitrogen and water. This device is called the SCR after-treatment system.
Just helped my buddy add this stuff to his truck a few days ago. Diesel exhaust fluid (DEF) is a liquid used for diesel vehicle exhaust treatment, specifically targeting those black smoke emissions. The principle is quite interesting - diesel vehicles have a device called SCR system in the exhaust pipe that sprays urea solution, which turns into ammonia gas when meeting high-temperature exhaust. This ammonia gas can neutralize the irritating nitrogen oxides in the exhaust, eventually converting them into harmless nitrogen and water. What many people don't know is that this isn't just any diluted water solution - it requires 32.5% high-purity automotive-grade urea. Those attempts using agricultural urea mixed with water are completely wrong and can damage the SCR system. Truck drivers especially need to pay attention to carrying two barrels onboard - during long hauls, running out of DEF can lead to immediate torque limitation and fines.
