Chemical reaction modeling for hypervelocity collisions between O and HCl

Abstract

The sensitivity of a rarefied-to-transitional flow to the fidelity of the chemical reaction model is investigated for a new molecular dynamics/quasiclassical trajectory (MD/QCT)-derived model and compared with the widely used total collision energy (TCE) model of Bird. For hypervelocity collisions that occur in the space environment, it is not clear, a priori, that the TCE model will provide reasonable results for the required high energy range and, particularly, if strong favoring of the reaction among different forms of reactant energy occurs. In fact, in previous work, the TCE model, using available Arrhenius parameters, has been found, for these flow conditions, to give unphysical probabilities. A chemical reaction model, suitable for use in the direct simulation Monte Carlo (DSMC) method, is developed to simulate the hypervelocity collisions of O(P3)+HCl(Σ+1)→OH(Π2)+Cl(P2), an example of an important reaction in high-altitude atmospheric-jet interactions. The model utilizes the MD/QCT method with a new benchmark triplet A″ surface. Since the modeling of chemical reactions in DSMC simulations requires the use of a reaction probability, the adequacy of the overall collision cross section, usually modeled by the variable hard sphere (VHS) model, is also considered. To obtain an accurate collision cross section, the approach of Tokumasu and Matsumoto was used in the MD/QCT method with the aforementioned potential energy surface. Energy transfer between the target HCl translational and internal energy modes was investigated and it was found that the variation of the inelastic cross section has a negligible effect on the transport cross section. Therefore, a MD/QCT VHS equivalent collision cross section was obtained and along with the MD/QCT reaction cross sections were utilized in the full DSMC calculation of the flow field. It was found that for a low enthalpy reaction, in hypervelocity collisions, the TCE model with accurate Arrhenius rates appears to agree well with the rigorous MD/QCT calculations which shows that the reaction does not exhibit strong favoring.

Rovibrational Energy Transitions and Coupled Chemical Reaction Modeling of H+H2and He+H2in DSMC

“…In Eqs. (7) and (8), 6 dependent on the vibrational states of the molecule. In the previous thermo studies of N 2 , the same result was also observed in that the state-specific tota mostly depend on the vibrational states [19].…”

“…In this energy e dissociation of H 2 are occurred by coupling with the rovibrational states of H 2 [7, specific total cross sections can accurately describe the nonequilibrium chemical (6) where Ω (2,2) is collision integral and T is equilibrium temperature. The collision integral Ω (2,2) are taken from the works of Stallcop et al [24] and Park et al [25].…”

“…In most of the previous DSMC studies [2][3][4][5][6], the phenomenological model of Larsen-Borgnakke [1] was adopted to describe the rotational-translational (RT) and vibrational-translational (VT) transitions. However, in the H 2 molecule, the rovibrational states are fully coupled [7,8] and the RVT energy transitions have an important role in describing the thermochemical nonequilibrium of H 2 , and the LB model has a limitation in describing the RVT energy transitions [19].…”

“…In the previous DSMC works [2][3][4][5][6], chemical reactions were described at the microscopic level for atom-molecule collisions by using the results of quasi-classical trajectory (QCT) calculations of the bound-free transitions. However, these models are insufficient: the chemical reactions are dominantly affected by the thermal nonequilibrium of rotational and vibrational modes induced by the state-to-state kinetics.…”

Simulation of Plasma Interaction with Io’s Atmosphere

“…Therefore, the O+SO 2 reaction cross section has been modeled by MD/QCT simulations at eight relative velocities and five internal energies of the target SO 2 [1]. Similar MD/QCT collision data for high velocity O+HCl collisions were used in DSMC simulations of a lateral side jet on a rocket [22]. In the current work, the DSMC simulation includes the O+SO 2 →2O+SO reaction cross section versus internal energy at a specific relative velocity through polynomial curve-fits to the MD/QCT dissociation cross section data at 4, 8, 16, 30, 45, 60, and 80 km/s.…”