Effects of GH/LOX Velocity and Momentum Ratios on Shear Coaxial Injector Atomization

Abstract

Introduction S HEAR coaxial injectors are currently found in liquid propellant rocket engines that use liquid oxygen and hydrogen as the propellants, such as the Space Shuttle Main engine (SSME) and the Ž rst stage Ariane 5 Vulcain engine. Liquid oxygen is injected into the combustion chamber through a central tube while hydrogen in a gaseous form is fed through an outside annular passage at a high velocity relative to the liquid jet. Impelled by liquid turbulence and gas-to-liquid interfacial interactions, liquid is stripped from the jet and entrained into the surrounding shear  ow where the liquid ligaments and droplets experience further breakup and atomization. The resulting spray then vaporizes and mixes with the gaseous fuel to produce a volatile mixture for combustion. There have been several previous experimental investigations to measure droplet sizes and velocities produced by shear coaxial injectorsbymeans of phaseDoppler interferometrywhere the fuel and oxidizer simulants were evaporating or combusting. Sankar et al. analyzed a GN2/LN2 spray for both a shear coaxial and quadruplet injector. The gas pressure and liquid injection post recess were varied for the shear coaxial injector.Data were presented for the mean axialvelocityandSautermean diameter for different locationsin the spray. They found no deŽ nite relationship between the recess and atomization.However larger gas pressures, or higher gas velocities, improved atomization. Glogowski et al. examined shear coaxial sprays with both an air/water system and a GN2/LN2 system. The injector design was based on the SSME injector. They measured droplet velocity and diameter with the phase Doppler particle analyzer (PDPA) for both air/water and GN2/LN2 . The GN2/LN2 tests looked at the effect of mixture ratio and chamber pressure past the critical pressure of nitrogen and showed improved atomizationwith lowermixture ratios. Pal et al.3 alsomodeled their injectorafter the SSME rocket injector. The paper included a comparison of PDPA data from air/water and liquid-oxygen/gaseous-hydrogenexperiments. Both tests were run with similar  ow conditionsexcept for the Reynolds andWeber numbers and the ambient pressure. The authors found that Sauter mean diameters from the hot-Ž re experimentswere larger than those from the cold- ow experiments. The mean droplet velocity was smaller for the GH2/LOX tests than for the air/water tests. The purpose of this study was to measure LOX droplet sizes as a function of the relative velocity between the LOX and the hydrogen under combusting conditions.