Plasmadynamics model for nonequilibrium processes in N2/H2 arcjets

Abstract

A two-temperature chemical nonequilibrium model is developed for nitrogen/hydrogen (N 2/H2) arcjet thrusters. All viscous flow properties are considered assuming steady, laminar, continuum, and axisymmetric flow. A seven-species N2/H2 plasma composition of molecules, atoms, ions, and electrons is assumed, and a finite rate chemistry model is employed to model collisional processes among the species. Separate energy equations are formulated for the electrons and heavy species. The anode temperature distribution is included, and propellant electrical conductivity is coupled to the plasma properties, allowing for a selfconsistent current distribution. The numerical solution employs the compressible form of the pressureimplicit with splitting of operators algorithm to solve the continuity and momentum equations. Numerical results are presented for a low-power simulated hydrazine thruster. The centerline constrictor region of the arcjet flowfield is predicted to be near thermal equilibrium, whereas a high degree of thermal nonequilibrium is predicted in the near-anode region of the arcjet nozzle. Strong electric fields near the anode produce elevated electron temperatures that enhance ionization levels and electrical conduction through the arcjet boundary layer. Radial diffusion of electrons from the arc core also enhances the near-anode ionization levels. Thus, the nonequilibrium approach is required to accurately model the plasma current distribution.