Estimation of excitation energy of diatomic molecules in expanding nonequilibrium flows

The energy contained in the highly excited vibrational and rotational states in a diatomic gas in a thermochemical nonequilibrium state during expansion is estimated. The population distribution of the vibrational and rotational states is assumed to be describable by a polynomial. The parameters in the polynomial are determined by invoking known physical constraints. The energy contained in the internal states in excess of that accounted for in the conventional method is calculated for N2, O2, NO, CO, and H2. The calculation is carried over a wide range of conditions, and the results are fitted with polynomials. The population distributions so determined agree with the theoretical and experimental results of others. A sample calculation made for a typical nozzle flow shows that the excess energy may reach 6% of the total enthalpy of the flow, and that the flow velocity may decrease by 3% due to this phenomenon. Nomenclature A = cross-sectional area of nozzle a{ =