Design of pintle injector using Kerosene-LOx as propellant and solving the problem of pintle tip thermal damage in hot firing test

The pintle injector is considered to have high reliability because it can control engine thrust by adjusting pro-pellant flow rate via adjusting the orifice area and is strong against combustion instability. Although many studies have been conducted on pintle injectors, their accessibility is limited and studies on performance opti-mizations for propellant type and propellant mixing efficiency according to pintle shape and atomization are incomplete. In this study, a 1.5-tonf class liquid-liquid pintle injector with rectangular two-row orifices that uses kerosene/liquid oxygen as the propellant was designed and manufactured. Combustion tests were performed on the pintle injector to verify performance and stability under supercritical conditions, which are the actual operational conditions of liquid rocket engines. From the combustion tests on the initial prototype, the pintle tip was observed to be damaged by heat, so the pintle injector design was changed, and thermal fluid analysis was performed to analyze the pintle tip cooling and combustion performances. To increase the cooling performance of the pintle tip, we devised a method of changing the shape of the pintle orifice and inserted a cooling device called an insert nozzle into the pintle without material changes or applied coatings, as in previous studies. The thermal fluid analysis results showed that there was a difference of up to 147-400 K in the pintle tip cooling performance depending on the insert nozzle and blockage factor, which was verified through combustion tests. The characteristic velocity efficiency and heat flux showed increasing tendencies with increase in total mo-mentum ratio, and a difference of up to 2.0% was confirmed for the characteristic velocity efficiency.