Simulation Research On Flash Boiling Process Of LNG Direct Injection

With rapid development of vehicle industry, the total amount of vehicles continues toincrease and pollution also becomes seriously. Therefore, many new resources are createdand developed, such as natural gas which has a large amount in the earth. There are twokinds of natural gas utilization: LPG and LNG. Although LNG has some advantages, itsvolumetric efficiency is low. So injecting LNG directly into the intake manifold has beencreated to solve this question. In this period, there is a phenomenon called flash boilingwhich can enhance fuels vaporization quality. In the paper, based on Fire, combustion modelis created and LNG characters are added into the model. Moreover, the vaporization model ismodified by a program based on FORTRAN language. The conclusion is shown as thefollowing:The results show that: under the conditions of2Mpa injection pressure,1barenvironment pressure, due to flash boiling phenomenon, the diameter of soot decreasequickly from80μm to10μm after5°CA injection. Finally, the average diameter of Sootwith flash boiling was less than the diameter without flash boiling. Moreover, becausedroplet evaporation in the process of LNG injection causes decreasing of the dropletmomentum and speed, the penetrate distance was10mm shorter than those without flashboiling. The flash boiling improve the fuel evaporation quality which is helpful for LNG andair mixing.Based on the modified vaporization models, the effect of80°CA、300°CA、320°CA injection on LNG and air mixing process were investigated. Through analyzing ofconcentration field, temperature field, speed field, the most proper injection timing is300°CA whose AFR is0.5.Additionally, based on the proper injection timing,90°and130°injection angles were researched. Comparing with0.85AFR of130°injection angle, AFRof90°injection angle is0.5which is more helpful for mixture mixing. Finally, based on theproper injection timing and angle, full load and sub-load conditions were calculated. Due tolonger vaporization timing and less vaporization quality, sub-load condition is more helpfulfor mixture uniformity.