Interaction behavior and droplet characteristics of multi-injector sprays

Abstract

The injector faceplate of a liquid propellant rocket engine is comprised of numerous single-element atomizers to inject propellants into the engine thrust chamber. The sprays from these single-element atomizers interact and mix, and then develop a combined spray. The present study investigates the characteristics of combined spray from a multi-injector assembly discharging three identical hollow cone swirl sprays arranged in an equilateral triangular configuration. The experiments are carried out in a spray test facility using water as the experimental liquid for different values of pressure drop (ΔPl) across the atomizers. The images of combined spray, captured using the technique of backlighted shadowgraphy, are used to deduce quantitative details of spray interaction behavior, and laser-based optical diagnostic systems (Phase Doppler Interferometry, and Spraytec) are used to record droplet characteristics of the combined spray. A mechanical patternator is used to describe the evolution of liquid mass distribution of the combined spray at different values of axial distance (Z) from the atomizer exit. The interaction process between the individual sprays influences spray width and liquid sheet breakup characteristics of the combined spray, particularly for sprays with low ΔPl. The interaction zones of the combined spray are marked by three lobes of high liquid mass flux, which develop asymmetry in the spray cross section perpendicular to the spray axis. It is showed quantitatively that the level of asymmetry in the combined spray decreases with increase in Z. The analysis of droplets characteristics of the combined spray reveals the presence of droplet coalescence for sprays with low ΔPl and droplet shattering for sprays with high ΔPl, which highlights droplets collision effects caused by the interaction and mixing of individual sprays in multi-injector thrust chamber.