A SCR system with an integrated nozzle was designed for a certain type of diesel engine to meet the national Ⅴ emissions standard with crystallized urea less than3 g. First the structure of a perforated pipe combined with a mixer was studied. The results show that both the uniformity coefficient of steam at the carrier front face and the urea evaporation cannot meet the requirements

and there is large block of crystal on the mixer. Then a new type of mixing chamber structure was proposed. With the new structure

the velocity and steam uniformity coefficient at the carrier front face are 0.95 and 0.98 respectively

and the catalyst carrier can be utilized fully. The injection system composed of three-hole nozzle with air-aid spray makes injected droplets hit against the cylinder surface directly. Due to high temperature

liquid film evaporates entirely. In addition

urea injection trajectory forms two large vortexes at the bottom

which promotes the atomization and mixing of the droplets. Finally

an experiment was made

and it verified that this new SCR system meets the national Ⅴ emissions standards. The conversion efficiency of NOxis higher than other structures at low temperature and the urea deposition meets the design requirements.