Numerical study on the combustion characteristics of ethylene-assisted Al particles in the scramjet combustor with wall/strut injection schemes

To address the poor combustion performance of aluminum (Al) particles in traditional powder-fueled scramjet engines, this study proposes a novel combustion-organizing approach to enhance the combustion of Al particles by utilizing combustible hydrocarbon cracking gas as the carrier gas. A new combustion model for Al particles has been developed to analyze combustion performance under reducing (ethylene) and oxidizing (air) carrier gases in a Mach 8 combustor. The combustion-assisted effect of ethylene is evaluated under different fuel injection configurations, revealing the underlying mechanisms. Results indicate that ethylene achieves a relative improvement of 140 % in particle combustion efficiency. Notably, the significant combustion-assisted effect of ethylene can only be leveraged by the strut injection scheme. In this scheme, ethylene combustion creates favorable low-velocity, high-temperature physicochemical environments that prolong particle residence time and facilitate heat accumulation, ultimately accelerating particle combustion. While, in the wall injection scheme, the spatial separation between gas-solid two-phases exposes most particles to the mainstream rather than the burned gas from ethylene, yielding only a 59.7 % relative improvement in combustion efficiency. Besides, particles in wall schemes are directly driven by the high-speed mainstream, resulting in insufficient residence time for heat accumulation. This limitation renders their combustion efficiency inferior to that of strut schemes. In contrast, the ample heat release from fuel combustion in strut schemes effectively compensates for the total pressure loss induced by struts, leading to a superior specific impulse compared to wall schemes.