Combustion performance of RP-1/GO₂/GH₂ Tripropellants

An experimental investigation was conducted to evaluate the combustion performance and stability of injecting gaseous hydrogen during the combustion of RP-1 and gaseous oxygen in a rocket combustion chamber. A single, tripropellant, swirl coaxial injection element fed a 1 inch hexagonal crosssection chamber of heat-sink design. Modular injector allowed control of the momentum ratios and subsequent atomization and mixing of the propellants. 84 tests were completed at various mixture ratios, injection velocities, and chamber pressures, with and without the addition of 10% hydrogen per total fuel mass. The combustion performance (c*), combustion efficiency (η_c*), and high frequency dynamic chamber pressure were recorded. The injection of 10% hydrogen to the RP-1/O2 combustion was shown to increase the efficiency, improve stability and decrease soot. Results from the rocket combustor hotfire testing showed an average increase in combustion efficiency from 92% to 97% under similar operating conditions. High frequency pressure measurements in the combustion chamber indicated a pronounced drop in the acoustic intensity. The total acoustic power was reduced by a factor of 9. The average power spectral density (PSD) at the first longitudinal chamber frequency was reduced from 1.10 to 0.15 [psi-rms²/Hz]. In addition to these results, soot accumulation on the chamber walls and in the exhaust plume was greatly reduced with the addition of the hydrogen. Correlation of the results on the basis of injector type, hydrogen injection location, and injection momentum indicate a change in the RP-1/O₂ chemical kinetics occurred with the addition of hydrogen.