机动车加油过程中气液两相流动特性的CFD数值模拟

CFD Numerical Simulation onto the Gas-Liquid Two-Phase Flow Behavior During Vehicle Refueling Process

随着环保法规的不断完善,机动车加油过程中所产生的油气排放污染问题越来越受到重视.国外自20世纪90年代中后期开始采用数值模拟手段对机动车的加油过程进行研究,而国内迄今尚处于空白阶段.对机动车加油过程所涉及的"加油枪喷嘴+加油管+油箱+回气管"物理体系进行适当简化,采用商业计算流体动力学(CFD)软件Fluent中提供的VOF气液两相流模型和RNG k-ε湍流模型,在基于Gambit软件确定网格划分方案和进行适当的边界条件设置后,建立了合理可行的加油过程气液两相流动CFD数值模拟模型,讨论了加油速度对油箱内气相空间静压力的影响,揭示了汽油在加油管内的回流现象.结果表明,加油枪的流量越大,油箱内气相空间的静压总体上也逐渐增大;同时油箱内气相空间的静压总体上可以划分为3个较为明显的阶段.而当加油流量较大时,往往会引起汽油在加油管油帽段内回流,从而使得加油枪过早跳枪.本研究为国内自主开展机动车加油以及油气排放污染控制技术和设备方面的研究开发奠定了一定基础.

With the gradual improvement of environmental regulations,more and more attentions are attracted to the vapor emissions during the process of vehicle refueling.Research onto the vehicle refueling process by means of numerical simulation has been executed abroad since 1990s,while as it has never been involved so far domestically.Through reasonable simplification about the physical system of ＂Nozzle ＋ filler pipe＋ gasoline storage tank ＋ vent pipe＂ for vehicle refueling,and by means of volume of fluid（VOF） model for gas-liquid two-phase flow and Re-Normalization Group k-ε turbulence flow model provided in commercial computational fluid dynamics（CFD） software Fluent,this paper determined the proper mesh discretization scheme and applied the proper boundary conditions based on the Gambit software,then established the reasonable numerical simulation model for the gas-liquid two-phase flow during the refueling process.Through discussing the influence of refueling velocity on the static pressure of vent space in gasoline tank,the back-flowing phenomenon has been revealed in this paper.It has been demonstrated that,the more the flow rate and the refueling velocity of refueling nozzle is,the higher the gross static pressure in the vent space of gasoline tank.In the meanwhile,the variation of static pressure in the vent space of gasoline tank can be categorized into three obvious stages.When the refueling flow rate becomes higher,the back-flowing phenomenon of liquid gasoline can sometimes be induced in the head section of filler pipe,thus making the gasoline nozzle pre-shut-off.Totally speaking,the theoretical work accomplished in this paper laid some solid foundation for self-researching and self-developing the technology and apparatus for the vehicle refueling and refueling emissions control domestically.