Uncooled choked plasma torch for ignition and flameholding in supersonic combustion

An experimental investigation on an uncooled choked plasma torch using hydrogen/argon mixtures as a propellant was conducted. This low-power plasma torch was designed to be used as an ignitor and flameholder in supersonic combustion. The anode and cathode were made of two-percent thoriated tungsten, and no cooling system was required. Sonic flow through the nozzle was obtained by using a small throat diameter (0.813 mm).

The plasma torch can operate stably over a wide range hydrogen/argon mixtures at power levels of 500 to 2000 W. Voltage-current characteristics of the arc are presented for discharge currents ranging from 5 to 40 A and for various flow rates and mixture fractions. The electrical input power is found to be a linear function of the hydrogen flow for a constant argon flow and for a current of 20 A. Measurements with a calorimeter reveal that the thermal efficiency, defined as the rate of increase of total enthalpy of the gas flowing through the torch divided by the electrical input power, is about 88 percent.