A series of detailed calculations have been carried out using a stagnation flow model to examine the dependence of diamond growth rate on hydrocarbon injector location in dc arcjet reactors. It is predicted that, for methane feed, growth rate can be increased by as much as 75% by relocating the injector from a position near the plasma torch exit to one near the diamond surface, but outside the boundary layer. As the injector is moved towards the surface from the plasma torch, the concentrations of C and CH3present at the surface increase. When the injector is located within the boundary layer, the lower atomic hydrogen concentration and short residence time leave most of the injected CH4unreacted, causing growth rates to drop. ©1995 American Institute of Physics.