Abstract: A stream of hydrocarbon fuel is catalytically decomposed to produce hydrogen and lower molecular weight fuel fragments, which may separated by molecular size. The hydrogen and low molecular weight fuel fragments are introduced along with a stream of nondecomposed hydrocarbon fuel into the combustor of a high speed propulsion unit. The method results in a wider combustor operating range, with higher combustion rates and increased flame stability, achieved through more rapid diffusional mixing. The process effectively extends the operating limits of gas turbines, and especially ramjet and scramjet combustors.