Geometric Effects of Liquid Rocket Engine Pintle Injectors in Supercritical Combustion

The effects of the total momentum ratio (TMR) and blockage factor (BF) of pintle injectors with nine combinations in the supercritical combustion condition were studied experimentally. Oxidizer-centered pintle injectors with discrete two-row orifices were considered. The combustion test conditions using liquid oxygen and Jet A-1 as propellants were a combustion pressure of 70 bar and an OFR of 2.45. The decrease in the TMR with the fuel momentum growth enhanced characteristic velocity efficiency. The BF determined by the aspect ratio of the second row orifice contributed to the characteristic velocity efficiency change. However, the BF effect on the efficiency was not as significant as the TMR in the supercritical conditions. Furthermore, TMR affected the BF effect on the characteristic velocity efficiency by limiting the effective collision area between the two propellants in the second row orifices. Chugging was the most dominant in combustion pressure fluctuation modes and weakly correlated with the TMR and BF. In the supercritical combustion of pintle injector discrete orifice configuration, an increase in TMR reduced the combustion perturbation ratio slightly.