Experimental Study and Visualization of the Combustion Dynamics and Behavior of a Single Swirl Coaxial Injector Element in a High Pressure LOX/CH4 Rocket Combustor

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To study the characteristics of liquid-centered swirl coaxial injectors representative for combustion chambers of large, regeneratively cooled liquid oxygen/methane main stage engines, a single element was designed, manufactured and subsequently hot-fired. The tests were performed in a single-element research combustion chamber with large optical access windows. Achieved chamber pressures ranged between 41.4 and 80.2 bar with corresponding propellant mass flow rates of 0.189 - 0.364 kg/s for liquid oxygen and 0.053 - 0.109 kg/s for methane. The injector element showed stable operation for all load points. When compared with previous tests of a shear coaxial element, it was found that wall heat loads close to the injection plane were significantly higher for the swirl injector. Simultaneous high-speed CH* and OH* chemiluminescence visualization was performed. From the high speed images, flame expansion angles were extracted and compared for different steady-state load points. It was shown that flame expansion angle and resulting wall heat loads are more dependent on injector mixture ratio, rather than chamber pressure. Further optical data evaluation was done by computing the inverse abel transformation of the time-averaged CH*/OH* images. The location of the reactive shear layer was obtained form the deconvoluted images and compared between load points and test cases from literature. Stable flame anchoring at the injector element’s oxygen post tip for all operating conditions was verified. The tests were also accompanied by spectroscopic measurements inside of the combustion volume. The spectra of three load points are qualitatively compared to each other.

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