High-temperature flames impinging normally onto adiabatic surfaces are considered. These are important in the CVD (chemical vapor deposition) diamond synthesis method for diamond growth on surfaces. Problems of complex chemistry and the mechanism of diamond growth are discussed. The present paper has illustrated the effects of several key parameters on the substrate surface temperature and flowfield for CVD diamond synthesis by impinging oxy-acetylene jet flames. The studies were concerned with combustion flowfield predictions, oxy-acetylene flames, axisymmetric-vertical impingement on an adiabatic surface, and the effects of varying the nozzle-substrate separation distance, nozzle size, overall equivalence ratio and flow rate on the substrate surface temperature and flowfield. This investigation provides a key to linking the flame with diamond growth rate on the substrate surface, complements the other facets of the project, and shows that the parametric influences can be predicted with relative ease, thereby extending the range of previously found experimental data.