Effect of Ethanol/n-Hexane Blending Ratio on Behaviors of Shock Waves in Flash-Boiling Jets

The rapid phase change of flash boiling jets would induce shock waves, but there is a lack of investigations on how the component blending ratios influence the characteristics of such shock waves. In this study, ethanol/n-hexane blends with different blending ratios were used to investigate this sort of shock waves using high-speed microscopic Schlieren photography. The tests were carried out in a constant volume vessel under varying ambient pressures (Pamb) and liquid temperatures (Tliquid). The shock size was carefully examined in terms of length and width. For all the test blends, both increasing Tliquid and decreasing Pamb could enlarge the shock length and width, but with different increments. Furthermore, with the increase in ethanol blending ratio, monotonic decrease in shock length and non-monotonic change in shock width were found, which can be attributed to the change in hydrogen bond concentration, which alters the axial distribution of evaporation intensity. The evaporation for the liquids with high ethanol blending ratios (>20 %) was weakened in contrast to that of pure n-hexane due to the existence of hydrogen bonds, causing the smaller shock size. At the low ethanol blending ratios (10 % & 20 %), the hydrogen bonds within ethanol were diluted and destroyed by n-hexane, enhancing the escape of ethanol from the blends. Thus, in contrast to the evaporation of pure n-hexane, the evaporation for the liquids with low ethanol was stronger, and the excessive energy due to the sudden pressure drop was released more rapidly at the nozzle exit. The former caused the increase in shock width, and the latter led to the shorter shock length. Finally, a good correlation was proposed between shock size and ΔG·Pamb-0.5(ΔG denoting the Gibbs energy difference during phase change).