Chemical Nonequilibrium Modeling of Low-Power Nitrogen/Hydrogen Arcjet Thrusters

Abstract

Departures from thermal, chemical equilibrium of a plasma flow in a low-power arcjet thruster with a 1:2 nitrogen/ hydrogen mixture as the working gas have been studied by axisymmetric numerical simulations. Electrons, ions, atoms, and molecules are represented as separate chemical species in the plasma mixtures of nitrogen and hydrogen. The predicted temperatures and densities of the electrons, heavy particles, and plasma velocity are presented throughout the whole flowfield of the nozzle. Significant temperature discrepancies between electrons and heavy species have been found in the near-anode wall region, which indicates that thermal nonequilibrium largely controls the near-anode electron densities and furtherly governs current attachment on the anode. The distributions of nitrogen and hydrogen species inside the arcjet thruster are also examined. It is found that the enrichments of hydrogen species at the center of the thruster and anode surface are due to different reasons. Some important kinetic processes that determine the dissociation and ionization processes of nitrogen/hydrogen species are presented and the relative importance of these kinetic processes is analyzed. In the anode region, the ionization rate of the hydrogen species is much larger than that of the nitrogen species, which infers that the charge carriers for electric conduction to anode are most contributed from the ionization of hydrogen species.

Analyses on the nonequilibrium transport processes in a free-burning argon arc plasma under different operating conditions

“…In the past decades, various models have been developed for predicting the complex physical-chemical processes in the foregoing different subregions, especially concentrating on the flow-affected arc column region and/or the electrode boundary layers/sheaths. As shown in figure 2, for the flow-affected arc column region, the development of the numerical models started from the LTE model with good predictions of the bell-shaped temperature fields and the engulfment of the cold gas at the upstream of the cathode compared with the experimental measurements [1]; then, numerous studies on the transferred/nontransferred DC arc plasma torches and gas-tungsten welding arcs have been reported with an extension of the physical-mathematical models from the LTE model [3,4,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] to the two-temperature LCE (2T-LCE) model [2,[37][38][39][40][41][42][43], or even to the 2T non-LCE (2T-nLCE) model [44][45][46][47][48][49][50][51][52][53][54][55][56]…”

Numerical simulation of hydrogen arcjet thruster with coupled sheath model

“…However, calculating sheath voltage is cumbersome, and including it in the primary model considerably slows down the simulation. Therefore, some arcjet models [19,36,37] either ignore the sheath effect or assume some sheath potential. Megli et al [11] assumed a total sheath voltage fall of 13 V, and Miller et al [10] took cathode voltage drop equal to the ionization potential plus one-half of the dissociation potential of the gas.…”

Numerical simulation of constricted and diffusive arc–anode attachments in wall-stabilized transferred argon arcs

“…The governing equations consist of mass continuity, momentum, energy and species conversation equations. The electromagnetic field is closely coupled by the Lorentz force and Ohmic heating with the momentum equation and the energy equation while the chemical kinetic processes are coupled to energy equations and species continuity [49,[58][59][60][61][62][63][64].…”