Nonequilibrium Vibrational and Chemical Kinetics in Air Flows in Nozzles

Quasi-one-dimensional nonequilibrium nozzle flows of reacting air mixture N2/O2/NO/N/O are studied based on the state-to-state description for vibrational and chemical kinetics. Zeldovich exchange reactions of NO formation, dissociation, recombination, and various vibrational energy transitions are considered. The equations for the vibrational-level populations of N2 and O2 molecules are combined with the conservation equations of momentum and total energy and solved numerically for different conditions in the nozzle throat. The vibrational spectra of molecules are simulated based on the anharmonic Morse oscillator. Three nozzle profiles are considered. The variation in the vibrational distributions of nitrogen and oxygen molecules, number densities of species, and the gas temperature along the nozzle axis are studied. The formation of nonequilibrium non-Boltzmann distributions of N2 and O2 molecules with a plateau region at intermediate vibrational levels is shown for different conditions in the throat. The level populations of N2 and O2 molecules obtained in the most accurate state-to-state approximation are compared with those found by using the one-temperature thermal equilibrium approach. The underestimated vibrational-level populations are obtained in terms of the one-temperature simplified kinetic model for the considered conditions. Three kinetic models are used for the Zeldovich exchange reactions of NO formation. The influence of the exchange-reaction models, throat conditions, and the nozzle profile on the gas temperature and vibrational distributions are also studied in the paper.