Research On Visualization And Numerical Simulation Of Liquid Phase LPG Spray In The Flashing Boiling

Liquefied petroleum gas (LPG) has been considered one of the important alternative vehicle fuels for its lower fuel cost and lower emissions compared with traditional petroleum fuels. Comparing to the original gasoline engine, a main problem of the most common being used LPG engine, converted from the gasoline engine with a mixer or a gaseous phase injection fuel supply system, is the power loss. In contrast, direct injection (DI) liquid phase LPG injection seems to be a better choice of the fuel supply system since it will not bring such a problem. Spray process has significant effect on combustion and emissions of the engine, so it is very necessary and important to understand the LPG’s spray characteristics to control the fuel injection, optimize the combustion, improve the emissions and then exert the fuel’s potential. Therefore, the spray characteristics of LPG are investigated in this thesis using the visualization method and the multi-dimensional numerical simulation method.In order to understand the detail information of flash boiling spray phenomenon, so after reading a great number of literatures on relevant research field, this paper introduces the basic principles of flash boiling spray and different characteristics between the flash boiling spray and traditional spray. The physical and chemical properties of liquid phase LPG cause the flashing phenomena. However, the existing CFD software has not the multiphase model to describe the complex phenomena of flashing, so the evaporation and impingement function of spray model are modified and added in software.This paper designs a test installations of LPG spray visualization. A control device is designed to trigger the injector and the CCD camera according to a certain time sequence to obtain the spray image at a certain instant, swirl injecter and non-swirl injecter of the same diameter are used to capture the images of instant sprays at the different injection pressure. By analyzing the calculation results, With the injection pressure increasing, the spray tip penetration is increased while the spray angle is decreased. The flahing boiling of LPG make its spray tip penetration less than the gasoline’s,while the spray angle is greater than the gasoline’s swirl injector has promoted the atomization and evaporation of liquid phase LPG than the non-swirl injecter, therefore, it will produce a more homogeneous air-fuel mixture.Another part of the work in this dissertation is numerical simulation by FIRE software of CFD. the spray process of the liquid phase LPG is studied by numerical method the spray model is validated by being compared with the results of simulation and experiment. The results show that flash boiling phenomenon is accelerated the fuel atomization evaporation; the spray penetration is increased with the injection pressure; with the increase of ambient pressure the spray penetration is decreased and the sauter mean diameter (SMD) is diminished distinctly; Different spray angle have a larger impact on the space distribution of the fuel; the interaction of smaller sauter mean diameter (SMD) and the ambient gas is more obvious.