State-Resolved Dissociation and Exchange Reactions in CO₂ Flows

Abstract

State-resolved chemical reactions in CO 2 are studied by taking into account excitation of all vibrational modes and preferential reaction mechanisms. The effect of several parameters on the reaction rate coefficients is discussed; it is shown that the nonequilibrium factor in the expression for the rate coefficients of exchange reactions is much less sensitive to the number of accounted vibrational states and model parameters than that of dissociation. On the other hand, the choice of thermal equilibrium Arrhenius law parameters is crucial for the correct prediction of rate coefficients for both reactions. Developed models are implemented to the one-dimensional boundary layer code for coupled state-to-state simulations of nonequilibrium CO 2 flows under Mars entry conditions. Vibrational distributions, mixture composition, flow variables, and heat flux are studied for several kinetic schemes and different models of chemical reactions. Whereas including the exchange reactions weakly affects the flow, switching between the Park and McKenzie sets of parameters results in significant modification of the kinetic mechanisms; for the McKenzie model, recombination near the wall is a dominating reaction, whereas for the Park model, chemical reactions are frozen. Different contributions to the heat flux are evaluated and a satisfactory agreement with experiments is shown.

Advances in non-equilibrium $$\hbox {CO}_2$$ plasma kinetics: a theoretical and experimental review

“…A more complete vibrational energy ladder for CO 2 was developed by Armenise and Kustova for the investigation of CO 2 non-equilibrium vibrational kinetics in the hypersonic boundary layer of reentering bodies in Mars atmosphere [46,[273][274][275][276] (see also Sect. 7).…”

“…During the last decade, many studies of high temperature non-equilibrium CO 2 flows have been carried out using several approaches of various complexity: multi-temperature [47,[339][340][341][342][343], STS [46,[273][274][275][276] and reduced order coarse-graining techniques [344][345][346]. Different effects are discussed such as the influence of the flow conditions, thermo-chemical model, models for transport properties and radiation.…”

“…Since computational resources used in [46] were not capable to solve nine thousands differential equations describing the viscous flow in the STS approach, the model was limited by the threshold of 3 eV, thus taking into account only 1224 vibrational states. This approximation is justified by the strong interaction among the normal modes for the high vibrational states of CO 2 , i.e., at vibrational energies above 2 eV; this strong interaction causes the modes are no more well defined as at low vibrational energies but they turn into quasicontinuum of states [276]. Along with CO 2 molecules, the model includes species which appear due to carbon dioxide decomposition: CO, O 2 , O, C. Implementation of the full vibrational ladder allows to account for intramode VV 3 , VT 1 , VT 2 and VT 3 exchanges, intermode VV 1−2 , VV 2−3 and VV 1−2−3 transitions, vibrational energy transitions between different molecules VV 3−CO , VV 2−CO and VV 1−2−CO , as well as state-specific dissociation-recombination reactions and exchange reactions, i.e.…”

“…CO 2 (v 1 ,v 2 ,v 3 )+O CO(w)+O 2 (v), where v 1 , v 2 , v 3 are the quantum numbers of symmetric, bending and asymmetric modes, correspondingly. Such a kinetic scheme is described in details in [274][275][276].…”

“…State-resolved exchange reaction rate coefficients are calculated using the theoretical model proposed in [276]; the model takes into account vibrational excitation of both the reagents and products. The stateresolved dissociation rate coefficients are calculated by means of the generalized Marrone-Treanor model [247,275].…”