The urea solution is a high-purity aqueous solution used in diesel engines with a selective catalytic reduction (SCR) system to reduce nitrogen oxide (NOx) emissions. It is injected into the exhaust gases before the SCR catalyst, where it decomposes into ammonia with the heat, which reacts with the NOx and converts them into nitrogen and water vapor, substances that are environmentally friendly.
It consists of urea and deionized water in a predetermined ratio and is neither a fuel nor a diesel additive, but a separate liquid necessary for the proper functioning and compliance of diesel engines with current environmental emission standards.