Chamber Wall Heat Flux Measurements for a LOX/CH4 Propellant Uni-Element Rocket

Abstract

Wall heat flux measurements in a 1.0 in. diameter circular cross-section rocket chamber for three uni-element injector elements operating on liquid oxygen (LOX) / gaseous methane (GCH4) propellants are presented. The wall heat flux measurements were made using a rocket chamber instrumented with coaxial thermocouples. Wall heat flux measurements were made for three uni-element injectors, viz., two versions of a shear coaxial element and a swirl coaxial element. The three injectors were designed for a chamber pressure of 1200 psia, LOX flowrate of 0.7 lbm/s and mixture ratio of 3.0. Experiments were conducted at the design pressure of 1200 psia and also at reduced pressures of 1000, 800, 600 and 300 psia for each injector at the design mixture ratio of 3.0 and also at 2.5 and 3.25. For experiments at the lower pressures, the propellant mass flowrates were scaled down linearly. The local wall heat flux measurements show higher heat flux levels for the swirl coaxial injector than the two versions of the shear coaxial injector at near injector face locations. This is attributed to enhanced LOX atomization, mixing and combustion provided by the conical swirling spray in the near injector face region for the swirl coaxial injector. The two tested shear coaxial injectors differ in the design fuel-to-oxidizer momentum flux ratios. The shear coaxial injector with the higher fuel-to-oxidizer momentum flux ratio showed higher heat flux levels in the near injector face region. One of the two shear coaxial injectors was designed such that the LOX post could be configured flush or recessed with respect to the injector face. The configuration with the LOX post recessed showed higher heat flux levels in the near injector face region than its LOX post flush counterpart, indicating that the mixing cup provided by recessing the LOX post has a positive effect on the mixing and combustion characteristics of the injector. Finally, the axial wall heat flux profiles for different chamber pressures were scaled with respect to chamber pressure to the power 0.8. The scaling brought the profiles closer together but not to the extent of collapsing the data, indicating that for liquid/gas injectors where the fuel-to-oxidizer momentum flux ratio decreases with chamber pressure, the resulting coupled atomization/mixing/combustion phenomena does not scale simply with pressure.