Specific impulse gain mechanism of swirling helium-injected solid–gas hybrid rocket motor

Compared to liquid rocket motors, solid rocket motors have lower specific impulse and weaker thrust regulation capabilities. Therefore, the concept of helium-injected solid–gas hybrid rocket motor (SGHRM), which can effectively improve specific impulse and achieve thrust regulation function, was introduced by our research group. The injected helium is used as working medium with strong expansion capacity, and the high-temperature combustion gas is used as a heat source to heat the helium. A mixture of gases, including combustion gas and helium, then flows through the nozzle producing high thrust. In the present paper, swirling helium is injected into the combustion chamber to further improve the specific impulse of SGHRM. The effects of helium mass flow and swirl intensity are numerically investigated, and the mechanism of specific impulse gain is revealed by one-dimensional gas dynamics analysis. Results indicate a maximum specific impulse gain of 11.28% and a thrust adjustment range of 100%–225% by varying the helium injection ratio. Compared with the axial helium injection scheme, the swirling helium injection scheme effectively improves the mixing degree of helium and combustion gas, and the behavior of rotating helium passing through combustion gas enhances the thermal convection. These two actions together strengthen the heat transfer from combustion gas to helium, effectively improve the total temperature and working capacity of helium, and further increase the exit velocity of mixed gas. In addition, the centrifugal force caused by the swirl elevates the mass flux in the velocity increase zone near the wall and further enhances the specific impulse.