Spray development and flash boiling characteristics of alternative fuels with a multi-hole direct-injection injector

Abstract

In this study, the spray development and atomization characteristics of a multi-hole direct-injection injector were investigated using the following test fuels: n-heptane, gasoline, LPG summer, LPG winter, methanol and ammonia. In addition, the effect of the physical properties of the fuels on spray development behavior and atomization characteristics was analyzed. Various the optical- and laser-based flow field measurement techniques were applied in this study, including injection quantity and injection rate measurement equipment, liquid spray and vapor phase visualization systems, spray visualization using a long-distance microscope (LDM), and a phase Doppler particle analysis (PDPA) system. To analyze the spray development behavior influenced by the effect of flash boiling in various test fuels, a constant volume chamber and a heating system for fuel temperature were used. Furthermore, to analyze the spray development behavior and atomization characteristics for spray-wall impingement, the experiments were conducted on the free spray of fuel in the atmosphere and flat spray using an acrylic wall. A constant volume combustion chamber was used to analyze the spray development behavior of various test fuels as a function of ambient temperature and ambient pressure. In addition, quantitative data (such as spray tip penetration, spray angle and spray area) were obtained using the MATLAB program for quantitative analysis. The results of this study were formulated in four parts. First, the spray development behavior and atomization characteristics were investigated with the application of a step hole inside the injector. The presence of a step hole produced excellent spray atomization characteristics due to the interaction between the fuel and air in the step hole, although the results of the wet area were higher than without a step hole. Second, the liquid and vapor spray characteristics of various test fuels were studied, and it was confirmed that the vapor pressure and surface tension of the fuels influenced the spray development. Furthermore, the wet area characteristics were found to be influenced by the surface tension and vapor pressure of the fuel, producing different results depending on the time after injection. The spray development behavior within a constant volume chamber was analyzed using gasoline, LPG summer, methanol and ammonia fuels. In particular, some of the test fuels, LPG fuel, methanol and ammonia, had a low boiling point, resulting in a longer spray tip penetration and a narrower spray angle. Third, the effects of fuel temperature on the spray development behavior and nozzle tip wetting characteristics of n-heptane and LPG summer fuels were analyzed. The fuel temperature affected the flash boiling phenomenon and provided a quantitative comparison of spray development behavior and nozzle tip wetting as a function of different fuel temperatures. The spray tip penetration of LPG summer fuel was longer than that of n- heptane due to vaporization effects caused by the lower boiling points, and the spray angle was narrower. Furthermore, the vapor pressure of fuel increased with increasing fuel temperature, resulting in enhanced evaporation characteristics and a reduction in nozzle tip wetting. Finally, a spray-wall impingement experiment was conducted to determine the spray development behavior and atomization characteristics of n-heptane and LPG summer fuels. As the injection pressure and fuel temperature increased, the spray width and spray area also tended to increase. However, when the distance between the injector and the wall was reduced, the spray width increased while the spray area decreased. A comparison of the spray width and spray area of the test fuels in the free spray revealed that, n-heptane fuel had a larger spray width and spray area than that of LPG summer fuel. As a result of comparing the spray-wall impingement, it was determined that LPG summer fuel had a larger spray width and spray area than that of n-heptane fuel.