Numerical analysis of homogeneous mixture formation in a LPG engine with liquid phase low pressure direct injection

A combustion system consisting of a pent-roof type of combustion chamber, a flat-top piston and a center-located injector to form homogeneous mixture for LPG direct injection engine is presented. Taking advantage of the easy evaporation property of liquid phase LPG, the injection pressure of this system can be much less than that used in gasoline direct injection engine. The mixture formation processes for this system were simulated and validated at different engine loads. The correctness of the simulation method was confirmed by comparing the results with those obtained from schlieren experiment. The simulated results showed that, at high load conditions with two intake valves opened, the intake tumble would break into small-scale vortex (turbulence) near the end of compression stroke; while at part load conditions with one of the two intake valves closed, an inclined intake swirl was formed, which enhanced the turbulence in combustion chamber near the end of compression stroke. The results also showed that if the liquid phase LPG was injected at 60~80°CA ATDC in intake stroke, the homogeneous mixture would form in spite of the engine load.