Combustion Characteristics of Bi-Liquid Swirl Coaxial Injectors with Respect to a Recess

Uni-element combustion tests were conducted employing double swirl coaxial injectors fed by liquid oxygen and kerosene. In this study, two major experimental parameters have been considered: the recess length and fuel swirl chamber shape. It was revealed that combustion efficiency depends mainly on the mixing mechanism for the present swirl coaxial injectors, and acoustic intensities become reduced with a decrease of the recess length. Low-frequency pressure oscillations around 200 Hz have been observed for all injectors. Dynamic behavior examined by the measurements of pressure fluctuations considerably differs for external and internal mixing based on the recess length. Internal mixing induces a mixture ratio and a total mass flow rate that vary with strong bias at a single frequency, resulting in high-amplitude pressure fluctuations generated by combustion of pulsating coherent flow structures. However, the results for external mixing show that the fuel and oxidizer mixture flow carries more dispersed, multiple-wave characteristics due to the broad mixing region as well as disintegration and merging phenomena of propellant sheets before mixing.