摘要
为了研究燃料物性差异对喷孔内流动特性的影响,通过GAMBIT软件建立三维喷嘴模型,利用FLUENT软件采用混合多相流模型,对柴油、生物柴油、生物柴油/乙醇混合燃料的喷孔内压强分布、速度分布和空化程度进行仿真分析。结果表明:燃油在压力室与喷孔入口衔接处压强迅速下降,进入喷孔后压强趋于稳定,在喷孔出口处压强略有上升;生物柴油的压强降幅最大,在喷孔不同截面处,与柴油相比生物柴油的压强平均下降了23.91%;生物柴油/乙醇混合燃料与柴油的压强降幅差别不大。燃油流速在喷孔入口处迅速增加,进入喷孔后增速放缓,在喷孔出口处燃油流速略有下降;在喷孔径向方向,由于壁面黏滞力作用导致速度从中心轴线向外围呈递减趋势;在喷孔不同截面处柴油的流速最快,其在喷嘴出口处的流速为229.8 m/s;生物柴油/乙醇混合燃料在喷嘴出口处的流速为223.1 m/s;生物柴油的流速最小,其在喷嘴出口处的流速为214.9 m/s。空穴现象首先发生在喷孔入口拐角处,随后向喷孔出口发展,并逐渐减弱。喷孔不同截面处,柴油的气相体积分数最大,生物柴油的气相体积分数最小,其气相体积分数比柴油平均下降了11.1%,与柴油相比生物柴油的空化程度较弱;生物柴油/乙醇混合燃料的气相体积分数与柴油差别不大,仅降低了1.8%,在生物柴油中添加乙醇能够降低燃料的密度、粘度和表面张力,改善燃料在喷孔内的流动特性,促进空化产生,喷孔内的空化现象能够为圆射流喷雾提供初始扰动,促进燃油雾化。该研究可为生物柴油/乙醇混合燃料流通特性研究提供理论支持。
The internal turbulent flow and cavitation flow of the nozzle have effect on the fuel spray and atomization of diesel engine, and especially they have a great impact on the process of primary atomization. Biodiesel is a kind of renewable alternative fuel of diesel. Previous studies have shown that biodiesel has higher density, viscosity and surface tension. Compared with diesel, biodiesel is less likely to generate cavitation flow inside nozzle. Therefore, this paper intends to add ethanol to biodiesel so as to improve cavitation flow of biodiesel in nozzle and advance biodiesel atomization. The geometry of the actual nozzle is very small and visual experimental research on full-size jet nozzle is relatively difficult. Therefore, in this paper, the effects of the fuel properties on the internal flow characteristics of nozzle were studied by computational simulation approaches. A three-dimensional nozzle model was created by GAMBIT, in which, pressure distribution, velocity distribution and cavitation distribution of diesel, biodiesel and biodiesel/ethanol blended fuel in nozzle were simulated with the mixture multiphase model of FLUENT. During the simulation, for validating the mixture multiphase model, turbulence model and cavity model, the comparison between visual experiment and computational simulation results of diesel cavitation area was carried out under different injection pressures. These models were confirmed to be effective. The simulation results show that the pressure drops rapidly at the joint connecting the pressure chamber and nozzle entrance, and the pressure tends to be stable after entering the nozzle, while the pressure increases slightly near nozzle exit. The pressure decline range of biodiesel is the greatest. Compared with diesel, the pressure of biodiesel reduces by 23.91% at the different cross section of nozzle. The pressure decline range is comparable between diesel fuel and biodiesel/ethanol blended fuel. The fuel flow velocity increases rapidly at the entrance of the nozzle, and the f
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2017年第21期70-77,共8页
Transactions of the Chinese Society of Agricultural Engineering
基金
陕西省交通新能源开发
应用与汽车节能重点实验室开放课题资助项目基金项目(310822161121)
中央高校基本科研业务费资助项目(310822172203)
关键词
生物燃料
乙醇
模拟
混合燃料
喷嘴内空穴流动
biofuels
ethanol
simulation
blended fuel
internal cavitation flow of nozzle
