Infrared radiation suppression mechanism of exhaust plumes in helium-injected solid-gas hybrid rocket motors

The significant infrared radiation of rocket motors severely degrades their stealth performance. Solid-Gas Hybrid Rocket Motors (SGHRMs) offer a promising solution through helium injection, which simultaneously enhances specific impulse and suppresses plume infrared signatures. To investigate the plume infrared radiation characteristics of SGHRMs, a numerical model incorporating 14-step afterburning reactions and a spectral radiation model based narrow band theory are developed. The influence of helium mass flow rate, flight altitude, and flight velocity on plume structure and infrared radiation are systematically analyzed. The results show that helium suppresses infrared radiation through three synergistic pathways, including cooling of high temperature plume, dilution of strongly radiating species, and inhibition of afterburning phenomenon. Under the 0 km condition, a helium mass flow rate of 2.5 kg/s reduces the total infrared radiation by up to 95%. Meanwhile, the suppression effect is spatially non-uniform, with the strongest reduction in the helium-rich plume core zone, while weakening in the mixing zone where ambient air dilutes the helium. Therefore, the infrared suppression performance varies with plume expansion states. Helium injection is most effective under low altitude and low Mach number conditions where radiation is concentrated, while reduced but still significant suppression is maintained at higher flight altitudes and velocities.