Characterization of Mixture Formation Process of Fuel Jet Injected into Superctirical Environment

在定容容器中对超临界环境(环境气体的温度和压力均高于燃料的临界点)喷射燃料射流的混合气形成特性进行了实验研究。采用双波长激光吸收散射(LAS)技术对超临界燃烧室环境下的柴油机和直喷式汽油机的喷雾特性和混合气特性进行了研究。考察了喷嘴孔径、孔L/D和注射压力的影响。对单脉冲进样和双脉冲分流进样进行了比较。主要研究结果如下：随着喷嘴孔径的减小，由于Sauter平均直径的减小，燃料的蒸发增加，进入燃料射流的空气量减少，从而使汽相当量比略高。随着喷油压力的增加，由于索特尔平均直径的减小，燃油蒸发增加，携带的空气量增加，作为这些变化的平衡，汽相的当量比变得略低。与单脉冲喷油相比，二次脉冲喷油前的分流喷油具有较小的索特尔平均直径、较高的燃油汽化比和较低的带气量。因此，分流喷射的当量比更高。二次脉冲喷油后，分体式喷油比单脉冲喷油具有更小的索特尔平均直径、更低的燃油汽化比和相近的进气量。因此，分流喷射的当量比变得更低。

An experimental study was conducted on the mixture formation characteristics of the fuel jet injected into the supercritical environment (temperature and pressure of the ambient gas were both higher than the critical point of the fuel) in a constant volume vessel. The 2-wavelength laser absorption scattering (LAS) technique was adopted to quantitatively measure the spray and mixture properties.In this study, the fuel jet in a Diesel engine or a D.I. gasoline engine, whose combustion chamber environment is supercritical for the fuel, was investigated. Effects of nozzle hole diameter, hole L/D and injection pressure were examined. A comparison was made between a single-pulse injection and a two-pulse split injection. The main results are summarized as follows.As the nozzle hole diameter is decreased, the fuel evaporation is enhanced due to the decrease in the Sauter mean diameter, the amount of air entrained into the fuel jet is decreased, and consequently the equivalence ratio of the vapor phase becomes a little higher. As the injection pressure is increased, the fuel evaporation is enhanced due to the decrease in the Sauter mean diameter, the amount of air entrained is increased, and as a balance of these changes, the equivalence ratio of the vapor phase becomes a little lower. Comparing with the single-pulse injection, the split injection before the start of the second pulse shows smaller Sauter mean diameter, a higher ratio of the vaporized fuel to the total fuel and lower amount of air entrained. As a result, the equivalence ratio of the split injection is higher. After the second pulse injection, the split injection shows smaller Sauter mean diameter, a lower ratio of the vaporized fuel and the similar amount of air entrained comparing with the single-pulse injection. Consequently, the equivalence ratio of the split injection becomes lower.