Combustion characteristics of solid fuel ramjets with multi-ring diaphragms

Solid fuel ramjets (SFRJs) are air-breathing propulsion systems that utilize solid fuel for combustion, offering simplicity and efficiency. Since last century, SFRJs have drawn much interest due to their extended flight vehicle range, but the difficulty of combustion realization limits their application for propulsion systems. This paper proposes a novel multi-ring diaphragm configuration in the afterburning chamber to improve the combustion performance of SFRJs. Various afterburning chamber configurations including none, single, double, and triple diaphragms are compared. The exhaust plume shape and combustion efficiency, along with the particle size distribution and scanning electron microscopy (SEM) analysis of the condensed-phase combustion products, are measured experimentally. The internal flow field and thrust performance are analyzed numerically. The experimental results show that the C* based average combustion efficiency increases with 5.30%, 23.71%, and 26.50% (compared to the original configuration without a ring diaphragm) respectively as the number of diaphragms increases from 1 to 3. Simulation results reveal that enhancing mixing in this configuration is achieved by inducing complex vortex structures and enhancing turbulence through the diaphragms. Ultimately, the ring diaphragm structure has proven to be an efficient design feature for enhancing mixing and combustion, making it suitable for optimizing afterburner chambers in SFRJs.