Combustion stability characteristics of coax-swirl-injectors for oxygen/kerosene

A number of Coaxial Swirl injectors were hot fire tested in a single-element rocket thruster. The experiments were conducted at combustion pressures in the range of 4.0 MPa to 8.5 MPa and mixture ratios between 2.4 and 3.5. The injector performance was assessed by static wall pressure measurement and the analysis of heat transfer to the water cooled combustion chamber wall. Other criteria to describe the behavior of the injectors are the discharge coefficients of fuel and oxidizer orifices as well as the combustion efficiency η_c*. The investigations were completed by dynamic pressure measurements located in the oxidizer feed line as well as in the combustion chamber itself. In some configurations, combustion instability was encountered. The analysis of dynamic pressure measurements confirmed the assumption that the instability matched the first longitudinal mode and its harmonics. Within this paper, four design variations are discussed with respect to their influence on combustion stability.