Effects of Orifice Internal Flow on Breakup Characteristics of like-Doublet Injectors

Under cold-flow and atmospheric ambient pressure conditions, the breakup characteristics of liquid sheets formed by a like-doublet injector were investigated. The sheet breakup wavelength, which induces the sheet to be broken into ligaments, and the sheet breakup length, which is important for finding the flame location, were measured using stroboscopic light. After sheet breakup, liquid ligaments are formed intermittently, and their wavelengths are believed to be related to the combustion instability of liquid-rocket engine. Therefore, the wavelength and the breakup length of ligaments broken into fine drops were also measured. Because these spray characteristics are affected by the flow characteristics of the two liquid jets before they impinge on each other, the focus was on the effects of orifice internal flow, such as the cavitation phenomenon that occurs inside a sharp-edged orifice. From the experimental results, it was found that liquid jet turbulence delays sheet breakup and shortens the wavelengths of both sheets and ligaments. Because the turbulence strength of a sharp-edged orifice is stronger than that of a round-edged orifice, the shape of orifice entrance gives large differences in the spray characteristics. With these results, empirical models of the spray characteristics of a like-doublet injector were proposed, and these models can provide useful and practical data for use in designing liquid-rocket combustors.