A computer code has been developed to simulate the combustion flowfield of an axisymmetric jet flame impinging normally on to a flat plate. Premixed oxygen and acetylene emerges from the jet nozzle, and complexities include turbulence and high temperature chemical kinetics. In CVD diamond synthesis, parameters of interest include the fuel-oxygen ratio and the distance from the heat nozzle to the surface. Combustion flow field predictions are given for acetylene and oxygen flames (all fuel rich), axisymmetric-vertical impingement on an adiabatic surface to show the effects of varying the nozzle-substrate separation distance, nozzle size, overall equivalence ratio and flow rate on the flowfield and substrate temperature. These have been shown to have dramatic effects on the rate of diamond growth on the surface.