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

在定容容器中对超临界环境（环境气体温度和压力均高于燃料临界点）下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技术对柴油机和直喷式柴油机的燃油射流和混合气的特性进行了定量测量。对燃烧室环境为超临界燃料的汽油机进行了试验研究。研究了喷孔直径、喷孔长径比和喷射压力对喷射效率的影响。对单脉冲喷射和双脉冲分次喷射进行了比较。主要结果如下：随着喷孔直径的减小，由于Sauter平均直径的减小，燃油的蒸发量增加，进入燃油射流的空气量减少，汽相的当量比略有增加。随着喷射压力的增加，由于Sauter平均直径的减小，燃料蒸发增强，夹带的空气量增加，并且作为这些变化的平衡，汽相的当量比变得稍低。与单脉冲喷射相比，第二脉冲开始前的分段喷射具有更小的Sauter平均直径、更高的汽化燃料占总燃料的比例和更低的空气夹带量。结果，分流喷射的当量比更高。第二次脉冲喷射后，与单次脉冲喷射相比，分段喷射具有较小的Sauter平均直径、较低的燃油汽化率和相近的空气夹带量。因此，分开喷射的当量比变得较低。

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.