The fuel injection system is the main process in supersonic vehicles. In this article, injection of fuel jet through a trapezoidal strut in the coaxial supersonic air stream is investigated. The numerical method is applied for the simulation of three-dimensional trapezoidal lobe strut in supersonic flow. Hydrogen gas is injected from the end of the trapezoidal strut injector to augment fuel mixing and diffusion downstream by intensifying vortices inside the domain. The power of the vortices varies by the injector velocity and free stream condition. To simulate our model, RANS equations with the SST turbulence model are solved. Effects of free-stream velocity and fuel jet total pressure on fuel distribution and mixing are also investigated. Our results indicate that fuel mixing enhances about 18% when a rectangular strut is replaced by a trapezoidal one. An achieved finding disclosed that the strength of vortices is amplified by the presence of a trapezoidal strut injector. (C) 2021 Elsevier Masson SAS. All rights reserved.