Comparison of experimental and numerical results for radiation cooled and water cooled hydrogen arcjets

Electric arcjet thrusters provide moderate thrust (1 N, typical) and relatively high specific impulse (900 sec, typical) for space propulsion. The University of Tennessee Space Institute has developed and app&ed a computational model of an arcjet fimister to gain a better understanding of arcjet experimental results. In this work, a water cooled arcjet and a radiation cooled arcjet are modeled using the UTSl arcjet computation code based on thermodynamic and chemical equilibrium flow. The results are compared with experimental results obtained by researchers at the Institut fur Raumfahrtsysteme, Universtat Stuttgart. Solution convergence problems and physical model inadequacies are addressed. A well-converged solution was obtained for the radiation cooled arcjet. Although not unacceptable, the solution of the water cooled arcjet only attained fair convergence. Solutions for the arcjets predict results that exceed the experimental performance by up to nine percent for the radiation cooled arcjet and up to seventy-three percent for the water cooled arcjet. Discrepancies are attributed to energy loss mechanisms that are neglected in the computation code. These include recombination losses and convection losses that are under predicted. It is concluded that a finite rate chemistry model and a two temperature model that allows the electron temperature to be different from heavy particle temperature should be incorporated into the arcjet code. In addition, the modeling of electrical conductivity near the anode walls needs to be modified to account for significantly greater energy losses than are currently predicted by the code. Turbulent diffusion processes for both viscous and thermal processes should also be considered to help stabilize code solutions and increase conduction losses at fire walls.