NO and Soot trade off is an important challenge for engineers in DI Diesel engines. This paper, introduces multiple injection as a strategy for simultaneous reduction of NO and Soot emissions on a DI diesel engine and also proposes a new concept of variable injection pressure and studies its effect on the engine emissions. To evaluate the benefits of multiple injection strategies and to reveal combustion mechanism, modified three dimensional CFD code KIVA-3V was developed. Results showed that using post injection with appropriate dwell between injection pulses has a great effect on simultaneous reduction of the emissions. Based on computational results, NO reduction formation mechanism in multiple injection strategy is as a single injection with retarded injection timing. It is shown that reduction in soot formation is because of the fact that in split fuel injection the soot, which is producing rich regions at the head of fuel spray, are not replenished by newly injected fuel in post injection pulse. Also increasing injection pressure in post injection will reduce the Soot emission dramatically while NO emission is in control for increase of fuel burning rate in post injection pulse.

In this study, the combustion process of gaseous Oxygen on the surface of HTPB (Hydroxyl-Terminated Polybutadiene) solid fuel has been investigated. To simulate the chemically reactive flow, Navier-Stokes equations and species transport equations were solved using LU-SW implicit scheme. Modeling this kind of combustion process demands a deep understanding of the pyrolysis phenomenon on the solid fuel surface. Experimental studies conducted in this field show that the main gaseous product of the pyrolysis process is C 4 H 6 . An experimental equation which is dependent to the temperature of the fuel surface is used to determine the gas production rate during pyrolysis process. The temperature of the fuel surface can be obtained by applying energy equation in gas-solid interface. The combustion process of gaseous Oxygen and C 4 H 6 has been described by two quasi-global chemical kinetics models. According to the obtained results, the main characteristic parameters of combustive flow such as the flame temperature and mass fraction of chemical species are strongly affiliated to the applied chemical kinetics model. Finally, the results of modeling based on two different models of chemical kinetics are presented and solid fuel surface regression rate is compared with other numerical results.