Calculated chemical and vibrational nonequilibrium effects in hypersonic nozzles

Effects of hydrogen–air non–equilibrium chemistry on the performance of a model scramjet thrust nozzle

“…5, the ratio was 0⋅956. This is in accord with previous investigations (3)(4)(5)(6)(7) , where nozzle freezing caused only a small loss in thrust.…”

“…An early study (3) of freezing of hydrogen-air chemical recombination in a ramjet thrust nozzle, where the expansion takes place from a low subsonic Mach number, showed that if equilibrium flow is maintained past the low supersonic area ratios the loss in thrust caused by chemical freezing is not exceedingly high. In later numerical studies of scramjet thrust nozzles at high flight Mach numbers, where the nozzle expansion takes place from supersonic Mach numbers, it was shown that although molecular vibration was in equilibrium throughout the nozzle, the chemical composition was not (4) , that at precombustion pressures of the order of an atmosphere there was little recombination in the nozzle (5) and that, in spite of this, the lack of complete recombination yielded an overall thrust which was only 1% less than the value for an equilibrium expansion (6) . Also, a study of thrust loss mechanisms in scramjets (7) showed that nozzle freezing represented only a small fraction of the overall losses.…”