Two-temperature plasma modeling of nitrogen/hydrogen arcjets

A two-temperature chemical equilibrium model is presented for nitrogen/hydrogen arcjet thrusters. The model is fully viscous and assumes steady, laminar, continuum, axisymmetric flow. A seven-species nitrogen/hydrogen plasma composition of molecules, atoms, ions, and electrons is assumed, and 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 self-consistent current distribution. The numerical solution employs the compressible form of the pressure-implicit with splitting of operators algorithm to solve the continuity and momentum equations. Numerical results are presented for a low-power thruster with simulated hydrazine propellant. The centerline constrictor region of the arcjet flowfield is predicted to be near thermal equilibrium, while a high degree of thermal nonequilibrium is predicted in the near-anode and downstream regions 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. Thus, the two-temperature approach is required to model the plasma current distribution accurately.