What is the use of automotive urea solution?

[MacKayden]

Automotive urea solution serves the following purposes: treating exhaust gases to reduce pollutants, optimizing engine performance, and improving fuel consumption. Vehicle urea is a colorless, transparent liquid stored in the urea tank. When sensors detect nitrogen oxides in the exhaust pipe, they automatically spray atomized urea solution, which mixes with nitrogen oxides. In the SCR (Selective Catalytic Reduction) reaction tank, a redox reaction occurs, producing and emitting non-polluting nitrogen and water. The consequences of not using urea in vehicles include: 1. Exceeding emission standards, causing environmental pollution; 2. Oxidation of chemical substances in the vehicle system, leading to clogged urea nozzles and rendering the entire system inoperable; 3. Reduced vehicle power performance.

[SanConnor]

Last time at the truck repair shop, the mechanic mentioned this thing is mainly for environmental protection. Spraying urea solution into the truck's exhaust pipe is like pouring descaling agent into a kettle—it turns the toxic nitrogen oxides in diesel exhaust into harmless nitrogen and water. I know Old Liu who does long-haul drives, and he said trucks now have a dedicated urea level gauge on the dashboard. If it runs out and isn’t refilled, the truck immediately gets limited to 20 km/h. When refilling, you have to use the dedicated filler port—never pour it into the fuel tank. Last time someone messed up and the entire fuel system got ruined, costing 20,000 to fix. This liquid is also finicky; it freezes at -11°C, so in cold weather you need a heated urea tank.

[LydiaLynn]

Now, urea systems are standard on China VI diesel vehicles. Simply put, it uses a catalyst in the exhaust pipe to trigger a chemical reaction between urea and exhaust gases, breaking down pollutants. According to my research, using high-quality urea solution can reduce nitrogen oxide emissions by 80%. Some drivers try to save money by diluting it with tap water, but this leads to nozzle crystallization and clogging—repairing the nozzle once costs as much as buying three years' worth of genuine urea solution. Always buy qualified products labeled with a 32.5% concentration; otherwise, the sensor will keep throwing fault codes. Wear gloves when refilling, as it’s highly alkaline and can cause burns on contact with skin.

[TheoFitz]

See that square box on the diesel vehicle's exhaust pipe? That's where the urea spray takes effect. The working principle is quite ingenious: the urea solution is sprayed into the high-temperature exhaust pipe and turns into ammonia gas, which then reacts with pollutant gases in the exhaust on the catalyst surface. However, it's said that northern car owners find the winter freezing issue most troublesome, with some inventing makeshift solutions like wrapping electric blankets around the urea tank. If the urea warning light suddenly comes on during a long trip, don't panic—just head to a service area and buy a 10L bucket to refill it. Remember, the urea tank cap is blue, distinguishing it from the black fuel tank cap.