Low-power ammonia arcjet - Numerical simulations and laser-induced fluorescence measurements

Abstract

Numerical simulations were performed for a 1-kW ammonia arcjet using the University of Tennessee Space Institute equilibrium arcjet computational code. Thrust predicted by the code was compared with experimental data obtained from a thrust stand, and calculations of exit plane flow conditions were compared with data obtained from multiplexed laser induced fluorescence (LIF) experiments. The code predictions for thrust follow the same trends as the experimentally measured values, but they significantly overpredict the absolute values. Multiplexed LIF experiments were performed using both atomic nitrogen and atomic hydrogen in the plume. When nitrogen is used the effects of scattering can be significantly reduced by spectral discrimination of the fluorescence. The experiments reveal that the two species have different velocities at a position 1 mm downstream from the nozzle exit plane. The code predictions of the velocity at the exit plane have been compared with the LIF experiments. These comparisons were not conclusive because the propellant velocity can change significantly between the exit plane, where the code predictions are made, and 1 mm downstream, where the LIF measurements are made. The discrepancy between these code predictions and the experimental results highlight the inadequacy of equilibrium computational codes to accurately simulate arcjet flows.