Rate-Controlled Constrained-Equilibrium Modeling of H/O Reacting Nozzle Flow

A methodology based on the degree of disequilibrium of chemical reactions is proposed to select kinetic constraints in the method of rate-controlled constrained equilibrium (RCCE). Predictions of chemical relaxation of the combustion products within a supersonic nozzle are also made under the constraints identified using the proposed methodology. The quasi-one-dimensional steady Euler equations are employed. The RCCE method provides a general framework, which enables studying shifting equilibrium, frozen equilibrium, as well as nonequilibrium chemical kinetics under different sets of constraints, either a single or a linear combination of species. It is shown that the previously identified generalized constraints of the total number of moles, free valence, and free oxygen are implied as a consequence of this methodology for the kinetics considered and for the relaxation studied. The kinetic scheme involves an H/O reacting mixture with 24 reactions and eight species. The constraints identified are H + H(2), HO(2) + H(2)O2, and O + OH + H(2)O, which result in less than 0.06% local errors in temperature compared with the detailed kinetic model calculations throughout the nozzle.