Several models involving spray atomization, wall impingement, evaporation and urea pyrolysis were built through a commercial code to study the influence of parameters of Urea Selective Catalytic Reduction (Urea –SCR) injection system on critical performances at low exhaust temperatures. The spray development,NH3 concentration distribution and wall film thickness have been studied. Results suggest that the wall impingement of the Urea Water Solution (UWS) is more at the temperature of 180°C than at 430°C. Lower temperatures tend to hinder evaporation and pyrolysis. NH3 concentration is uneven at low temperatures and the fuel film generated on the wall is also incomplete. Low temperatures could help injection system with a tilting nozzle raise its injection pressure and accelerate the evaporation and pyrolysis of the droplets. The distributionof spray impingement, however, is narrower and the fuel film thickness on the wall is increased. Smaller injection angle made it easier to expel gas stream and the droplets would then follow the direction of the gas stream. The droplets distribution is therefore more uniform and the spray wall-impingement reduced.

The non-circular diesel nozzles have influence on the inner cavitation and near-field spray patterns. For this investigation, two different non-circular diesel injectors with the same equivalent diameter were adopted. A detailed comparison of near-field spray and inner cavitation behaviors were investigated by using near-field spray experimental visualization method and numerical model. The elliptical nozzle has larger discharge coefficient, indicating that using the elliptical nozzle could increase the circulation ability. Also, the elliptical nozzle outlet has higher vorticity magnitude at all injection conditions than those of the circular nozzle. Besides, the cavitation is evenly distributed in the circular orifice inner wall. While for elliptical nozzle, the cavitation is mainly distributed along the major axis. Moreover, the near-field spray cone angle and projection area at the major axis of the elliptical nozzle are all wider than the circular nozzle. Because the nozzle exit turbulence vorticity and the cavitation along the major axis direction are both more intense than the circular nozzle, and these factors could increase the diffusion of the initial spray. Finally, it is possible to predict that theatomization quality of the elliptical spray is better than that of the circular spray from the larger spray cone angle and projected area of the near-field elliptical spray.