Numerical Analysis Of Mixture Formation For A Spray And Wall Complex Guided LPG DI Engine Adopting Stratified Lean Combustion

The cavitating flow phenomenon in a LPG high pressure swirl injector with needle movement was analyzed using multiphase module of AVL’s FIRE CFD code. The validated spray model was used in simulation, the simulation results showed that the cavitation zone existed during the entire injector needle opening process for LPG, but for gasoline, the cavitation zone was formed on the wall of the nozzle entrance during the early stage of the needle opening. As the needle moving further, the cavitation zone became small and eventually disappeared. Then modified the spray formulation, the free spray process of LPG and gasoline was simulated using initial conditions of calculated results of the internal flow of the swirl injector. The calculated results have a good agreement with the experimental results. It was also found that the spray cone angle of LPG increases but the spray penetration decreases compared with gasoline, which is caused by flash boiling occurred in the spray process.In order to obtain ultra lean air-fuel ratio and reduce engine-out NOx and HC emissions induced by the richer mixture near the spark plug. A spray and wall complex guided combustion system is presented by utilizing the fuel characteristics of LPG. The new combustion system configuration is optimized by using a commercial CFD code, FIRE V2011, on the basis of the reliability verification of the simulation method. Then the mixture formation for the new combustion system under part load (2000rpm) is numerical simulated. The simulation results show that with an ignition timing of20degrees BTDC there is ignitable mixture near the spark plug. By applying this new combustion system, the mixture can be stable ignited with an ultra lean air-fuel ratio of65.