在较高燃油温度及较低环境背压下,直喷喷雾易发生闪沸.闪沸喷雾具有贯穿距小、易于雾化等优势,能够有效降低发动机排放、提高燃油经济性,在直喷发动机中具有较好应用前景.然而随着涡轮增压的使用,进气压力的提高导致喷雾较难达到闪沸状态.针对这种现象,在研究混合燃油蒸馏特性后提出了通过向高沸点燃油中添加低沸点燃油的方式来促进喷雾的闪沸.试验燃料为一系列不同比例低沸点燃油(异戊烷)与高沸点燃油(正十一烷)组成的混合燃油,通过蒸馏测试探究了不同组分燃料的蒸馏特性;通过在定容弹内拍摄不同燃油温度、环境背压下的燃油喷雾的米氏散射图,研究了混合燃油形态变化规律.结果表明,不同于单一油品仅在沸点时沸腾产生馏出物,混合燃油是在一定的温度范围内均会沸腾产生蒸馏物,表现为3段式蒸馏曲线;混合燃油蒸馏前期大部分馏出物为低沸点燃油,表明混合燃油受热时,低沸点燃油会优先蒸发;对喷雾宏观形态的测量结果表明,向高沸点燃料中添加低沸点燃油能够使喷雾在高背压下达到闪沸状态,且40%体积分数是最佳的添加量;另外,油温越高添加低沸点燃油对喷雾闪沸的促进效果越好.%Flash boiling was easy to happen at high fuel temperature and low ambient back pressure when direct injection was used.Flash boiling spray had an application prospect because it had short penetration and easy spray and could reduce exhaust emission and improve fuel economy.However, the application of turbocharger led to difficult flash boiling due to the increase of intake pressure.In view of this phenomenon, it was proposed to promote the flash boiling spray by adding the low boiling fuel to the high boiling fuel after studying the mixed fuel distillation characteristics.Test fuels were a series of blended fuel which was composed of the low boiling point fuel like isopentane and the high boiling fuel like n-undecane and their distillation characteristics were studied through the distillation test.Finally, the morphology changes of mixed fuel were studied by taking the Mie scattering diagram of fuel spray at different fuel temperatures and environmental back pressures inside constant volume bomb.The results show that the mixed fuel cannot be boiled to produce distillate at one boiling point like single fuel but in a certain temperature range.It is a three-stage distillation curve.The low boiling point fuel first produces during the distillation because of its evaporation.The macroscopic measurement results show that the method can realize the flash boiling state at high back pressure and 40% volume fraction is the best adding proportion.Besides, adding low boiling fuel to higher temperature fuel is beneficial to flash boiling.
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