Specific impulse gain mechanism of micro-holes helium injected solid-gas hybrid rocket motor

Limited by the energy level of solid propellant, the specific impulse of solid rocket motor is relatively low. The helium-injected solid-gas hybrid rocket motor can effectively improve the specific impulse of solid rocket motor by injecting helium with low molecular weight and strong expansion capacity into the rocket motor. To improve the performance of the helium-injected solid-gas hybrid rocket motor, the effect of micro-hole arrays on the performance of the helium-injected solid-gas hybrid rocket motor is investigated. Results show that the specific impulse of the motor presents a parabolic trend with the variation of helium injection ratio (mass flow ratio of helium to combustion gas), and the peak value is reached when the helium injection ratio is 1∶4. The motor can obtain a maximum specific impulse gain of 5.77% with the micro-hole diameter of 2 mm. The mixed gas with low helium mass fraction provides positive gain to the specific impulse of the motor, while the mixed gas with high helium mass fraction causes negative gain due to the low total temperature and weak expansion capacity. Therefore, the specific impulse of the motor depends on the combination of the mixed gas with high and low helium mass fraction. Furthermore, motor thrust increases with the increase of helium injection ratio. By changing the helium injection ratio from 0 to 2∶1, a motor can achieve a maximum thrust regulation range of 100%–313%. The injection of helium greatly reduces the nozzle outlet temperature by up to 1 600 K. Therefore, the helium-injected solid-gas hybrid motor can effectively reduce the plume temperature of the rocket motor, suppress the infrared radiation characteristics, and achieve a better infrared stealth effect.