A new modified pseudoequilibrium calculation to determine the composition of hydrogen and nitrogen plasmas at atmospheric pressure

This paper proposes a modified pseudoequilibrium calculation, which gives a lmost the same results as those of kinetic calculations to determine the co mposition of hydrogen and nitrogen plas,nas at atmospheric pressure. The co mputing time is tire to three orders of magnitude faster than that of the k inetic calculations. First, according to experimental results, a relationsh ip between the electron temperature T-e and the heavy species one T-h has b een proposed. The ratio T-e/T-h varies as a function of the logarithm of th e ratio n(e)/n(e)(max), n(e)(max) being the electron density in the plasma core for which equilibrium is achieved (n(e)(max) similar to 10(23)). The k inetic calculations have been performed assuming tire microreversibility wh ere the backward kinetic rate coefficient k(b) is calculated by k(d)/k(b) = K-x, where k(d) is the direct kinetic coefficient and K-x the molar fracti on equilibrium constant. When electrons are involved in both direct and bac kward reactions k(d) and K-X are expressed as functions of T-e. However, wh en the direct reaction involves electrons while the backward one is due to collisions between heavy species (ol the reverse), a temperature T* between T-e and T-h is introduced T* is determined as a function of the ratio of t he electron pur to that of neutral species in such a way that T* = T-e for n(e) > 10(23) and T* = T-h for low values of n(e) (n(e) < 10(15) m(-3)). Co mpared to hydrogen, the nitrogen composition exhibits a very abrupt variati on between 6000 and 6500 K, corresponding to a shift from the dissociation- dominated regime to that of ionization. It occurs because dissociation of n itrogen starts almost simultaneously with its ionization, which is not the case of H-2, for which dissociation is terminated long before ionization st arts. If the charge transfer reaction, whose activation energy is low for b oth gases, is neglected in both cases the electron density increases drasti cally below 9000 K. These results are quite similar to those obtained when calculating the composition with the multitemperature mass action law. The kinetic calculations are dominated by the reactions with a low activation e nergy: dissociation, dissociative recombination and charge transfer. Thus, a modified pseudoequilibrium calculation has been introduced, the plasma co mposition being calculated with the equilibrium constants corresponding to low activation energies [X-2 --> 2X, e + X-2(+) --> 2X, X-2(+) + X --> X+ X-2 both for hydrogen (X = H) and nitrogen (X = N)] at the temperature T* between T-e and T-h The results are in very good agreement with those of th e kinetic calculations.