Effects of injection distance and droplet size on an LH2/LOX torch igniter

Compared with the conventional igniters, a liquid hydrogen/liquid oxygen (LH2/LOX) torch igniter has significant advantages of ignition energy, reliability, and reusability for LH2/LOX rocket motors. However, the mechanisms that underpin the LH2/LOX torch igniter are not fully understood yet. In this study, the effects of the injection distance and droplet size on the igniter, typically on the torch power (i.e., ignition energy) and thermal protection, were numerically investigated. Meanwhile, two fire tests with different conditions were conducted to validate the numerical model prior to the simulation. The simulation results show that increasing the injection distance is beneficial to improve the torch power but not conducive to thermal protection under our conditions. Moreover, LOX droplet size marginally affects the torch power and thermal protection because of the fuel-rich combustion in our study. Nevertheless, the increase of LH2 droplet size results in a higher inner wall temperature, which contradicts the purpose of thermal protection.