Coraline is a special urea reducing agent for diesel engines. Vehicle urea refers to urea aqueous solution with urea concentration of 32.5% and ultrapure water as solvent. Raw materials are urea crystals and ultra-pure water, which are non-toxic, tasteless and harmless, and the operation is convenient and safe. It can effectively ensure the stable operation of SCR system. In order to meet the national standard of diesel vehicle exhaust treatment, vehicle urea is an essential additive for SCR system.