Bidirectional vortex stabilization of a supersonic ICP torch

RF inductively coupled plasma (ICP) torches with a supersonic nozzle are used for materials processing and have also been proposed as electrothermal plasma thrusters for space propulsion applications. At the relatively high operating pressures used, the gas injection method plays an important role in stabilizing the ICP discharge. Bidirectional vortex gas injection is a novel configuration that has been proposed for both subsonic ICP torches and liquid propellant combustion chambers for chemical rocket engines. In this configuration, gas is injected tangentially at the downstream end near the nozzle and first spirals up along the outer edge of the chamber before reversing direction at the upstream chamber end and spiralling back down through the central region towards the nozzle exit. Here we investigate such a bidirectional vortex with a supersonic ICP torch and show that both the effective torch stagnation temperature and thermal efficiency can be increased by almost 50% compared with conventional gas injection configurations. This enhancement occurs because of the unique vortex flow field which leads to reduced gas-wall heat losses and consequently an increased flow enthalpy leaving the torch.