Numerical simulation of pulsed plasma thrusters

MACH2 was used to simulate the plasma flow in cablegun (developed at UTSI) and pulsed plasma thruster (PPT-4, developed at the University of Illinois at Urbana-Champaign) geometries, and the corresponding results were compared to the experimental operation of the devices. The capabilities of MACH2 were extended by incorporating a new radiation model as well as new thermodynamic equation of state tables for plasmas containing either Teflon or a mixture of 39% Teflon and 61% copper (by mass). In developing the tables, the thermodynamic variables at low temperatures were calculated using the NASA Equilibrium Code (CEA). The high temperature calculations were performed by iterating the multi-component Saha equation. Cubic polynomials were then used to blend the high and low temperature calculations together over the intermediate temperature regions. The Saha-calculated specific heats contained large numerical fluctuations and were filtered using a (1,1)-fold trimmed mean filter. The data was also smoothed over suitable temperature intervals using cubic polynomials. Using spectroscopic data gathered in the cablegun experiments at UTSI, a preliminary analysis was performed to obtain a rough estimate of plasma temperature.; In the MACH2 simulations, the plasma absorption coefficient (“fox”) and the propellant absorptivity were adjusted to give the correct values for plasma velocity and ablated mass. The resulting impulse bits for the cableguns were 6.89e-04 N·s for a plasma consisting of only Teflon and 1.84e-03 N·s for a plasma containing 39% Teflon and 61% copper (by mass) The corresponding specific impulses are 1254 s and 695 s, respectively. The PPT-4 thruster produced a total impulse of 2.03e-04 N·s and an; average specific impulse of 521 s. Although providing less impulse per shot, the PPT-4 thruster output more impulse per energy stored in the capacitor.