Diesel Exhaust Fluid (DEF): The urea solution for diesel engines

Diesel Exhaust Fluid (DEF)

Diesel exhaust fluid (also AdBlue) is a standardized urea solution consisting of a urea-water mixture. It is used to reduce nitrogen oxide emissions in diesel engines, which is achieved by a cathalytic reduction. Actually, you need ammonia, which is not easy to use in its pure form. Therefore, harmless urea is used, which is converted into ammonia only when needed.

While the name DEF is used in America, the German Association of the Automotive Industry (VDA) protected the name AdBlue for the standardized solution.


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Legal regulations

Since diesel vehicles have to comply with certain emission standards, they must not drive without the diesel exhaust fluid according to the legislature or only with lowered torque. The vehicles are therefore designed by the manufacturers so that they do not start the engine in such cases, or allow normal operation until the diesel exhaust fluid is refilled. For this reason it’s important to take the warnings in the dashboard seriously.

Storage of Diesel Exhaust Fluid

According to the current safety data, no special measures are required for the storage of DEF. It is chemically stable and does not cause any irritation on the skin or in the eyes. The freezing point of the urea solution is 12.2°F (- 11°C). Frozen DEF can be thawed and used as it does not affect its functional properties. Based on current knowledge, the product also has no harmful effect on the human body. Nevertheless, for safety’s sake, it is recommended to avoid contact with the skin.