Performance comparison of full-scale ramjet and scramjet using boron-based propellant

This study investigates the performance boundaries of ramjet and scramjet engines fueled by boron-based propellant through full-scale engine modeling and three-dimensional computational fluid dynamics simulations. Results show that the performance boundary between ramjets and scramjets occurs near Mach 7. Specifically, at Mach 6, the ramjet exhibits a 1290 m/s higher specific impulse than the scramjet; however, at Mach 7, their performance becomes comparable. The ramjet's higher static temperature promotes boron particle vaporization and B 2 O 2 dissociation, limiting the total temperature increase, unlike in scramjets. The boron vapor mass fraction significantly impacts this temperature difference, with ramjets exhibiting values 8.5 and 3.9 times higher than scramjets at Mach 6 and Mach 7, respectively. Despite lower total temperatures, ramjets achieve more efficient boron combustion due to the combined effects of higher pressures and longer particle residence times. These findings offer valuable insights for engine designers in selecting ramjet or scramjet configurations for boron-fueled propulsion systems.