Comparisons of numerical model calculations to experimental data from a one kilowatt arcjet

An arcjet is an electrical space propulsion device that creates thrust by adding energy to a propellant gas by passing it through an arc discharge. A computational arcjet model has been developed previously at the University of Tennessee Space Institute. For this thesis, the performance of a one kilowatt arcjet using simulated ammonia propellant was modeled. Global performance parameters calculated by the model are compared to experimental data obtained with a thrust stand. The model's calculations of exit plane flow conditions are compared to data obtained from laser induced fluorescence (LIF) experiments.

The UTSI arcjet model accurately predicts the experimental trends in performance parameters, but it significantly over-predicts the numerical values. It is believed that the over-predictions are due to energy loss mechanisms not included in the model and inaccurate calculation of electrical power absorption due to the incorrect assumption of local thermodynamic and chemical equilibrium. The LIF experiments reveal that hydrogen and nitrogen in the plume have different velocities. The comparisons between the model velocity calculations and the LIF experiments are concluded to be unreliable because the propellant velocity can change significantly between the exit plane, where the calculations occur, and one millimeter downstream, where the LIF measurements are made.

It is recommended that the arcjet model be expanded to include non-equilibrium chemistry and separate calculation of electron and heavy particle temperatures. In addition, the model needs to be modified so it can calculate the flow field in the free expansion downstream of the nozzle exit for direct comparison to the LIF experiments. It is suggested additional LIF experiments be performed to learn more about the differences in the velocities of the individual plume species.