Automotive urea is a necessary addition for the treatment of diesel vehicle exhaust, the main role is to make diesel vehicle exhaust nitrogen oxides in SCR technology, used to reduce the diesel vehicle exhaust nitrogen oxide pollution of the liquid, the generation of pollution-free nitrogen and water vapor. The main components of automotive urea are 32.5% high-purity urea and 67.5% deionized water.

The concentration of urea solution is calculated by measuring the refractive index of the standard urea solution and the sample solution. The refractive index itself is also an indicator of automotive urea solution, domestic and foreign standards generally specify the refractive index of 1.3814-1.3843, similar to density, at a certain temperature of urea solution refractive index and concentration has a corresponding relationship, measurement of refractive index is helpful to judge and verify the concentration and quality of automotive urea solution.