An excellent flame suppression effect can be achieved using a novel porous brake. To understand the flame-suppression mechanism of a porous brake, combustion using a muzzle brake is investigated. A set of internal ballistic equations is employed to provide accurate velocity and pressure for a projectile moving to the muzzle. The multispecies transport Navier–Stokes equations, which incorporate complex chemical reactions, are solved by coupling a real gas equation of state, the Soave–Redlich–Kwong model, and a detailed chemical reaction kinetic model. The development of muzzle flow with a chemical reaction is simulated, and the interaction between chemical reactions with the muzzle flow field is numerically calculated to explain the muzzle combustion mechanism with a porous brake. The underlying mechanism is analyzed in detail. The results demonstrate that, first, the gas is fully expanded in the brake, leading to a reduction in pressure and temperature at the muzzle, thereby reducing the initial flame. In addition, the shock wave weakens due to the expansion and separation process, leading to a reduction in the mixture of gas and air, ultimately resulting in a reduction in the intermediate and secondary flames. [ABSTRACT FROM AUTHOR]