In this study, numerical analysis is performed to adopt the equivalence ratio onthe high velocity oxygen fuel (HVOF) thermal spray coating systems equipped with a minimumlength nozzle. The analysis is applied to investigate the axisymmetric, steady-state, turbulent, andchemically combusting flow both within the torch and in a free jet region between the torch andthe substrate to be coated. The combustion is modeled using a single-step and eddy-dissipationmodel which assumes that the reaction rate is limited by the turbulent mixing rate of the fuel andoxidant. As the diameter of the nozzle throat is increased, the location of the Mach shock discmoves backward from the nozzle exit. As the throat diameter and the divergent portion are 6 mmand 8 mm, respectively, the pressure in the HVOF system is the lowest at the chamber and theexpanding gas is steadily maintained with both high velocity and high temperature for differentequivalence ratios. Thus, relatively minor amendments of the equivalence ratio and the geometryof HVOF can lead to improved control over coating characteristics. The analysis is applied to investigate the axisymmetric, steady-state, turbulent, andchemically combusting flow both within the torch and in a free jet region between the torch and the substrate to be coated. The combustion is modeled using a single-step and eddy-dissipation model which assumes that the reaction rate is limited by the turbulent mixing rate of the fuel andoxidant. As the diameter of the nozzle throat is increased, the location of the Mach shock discmoves backward from the nozzle exit. As the throat diameter and the divergent portion are 6 mmand 8 mm, respectively, the pressure in the HVOF system is the lowest at the chamber and theexpanding gas is steadily maintained with both high velocity and high temperature for differentequivalence ratios. Thus, relatively minor amendments of the equivalence lence ratio and the geometry of HVOF can lead to improved control over coating characteristics.