This paper describes the improvement in combustion efficiency achieved using streamwise vorticity and fuel injections when using hypermixer struts at high Mach numbers. The effects of fuel injection conditions on combustion were investigated using numerical simulations of chemical reactive flows with a detailed reaction mechanism. Hydrogen fuel was injected from the trailing edges of a separation-resistant strut. Fuel injection at sonic speeds led to an enhancement in efficiency with an increased injection angle at Mach number 2.5, but this improvement was not observed at Mach number 3.5. It was found that hydrogen accumulated in the vortex core because of the strong circulation generated from the strut at high Mach numbers. With fuel injection at speeds exceeding the sonic speed, the efficiency increased, and it improved further with an increasing injection angle. From the results, an important indicator for combustion enhancement was derived from the streamwise vortex circulation, fuel injection velocity, and inflow Mach number. To increase the combustion efficiency using the strut, the indicator value should exceed a threshold. This is crucial for ensuring effective fuel consumption during combustion. These findings provide useful insights into a good design of hypermixer struts in supersonic combustion.