Non-equilibrium vibrational and chemical kinetics in air flows in nozzles

Abstract

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