Flame stabilization by plasma jets

Abstract

The possibility of increasing flame reaction rates, stability and hence the throughput of chemical energy achievable by the addition of a small proportion of electrical power is stuided. The power is added to a subsidiary stream of different gases by a magnetically rotated plasma jet. Rates of rotation of the order 10 5 rev/min contribute to uniform heating and mixing with the very much larger main stream flow (up to blow-out) of methane + air mixtures. The products are sampled by a traversing micro-probe and analysed. Quite small additions of electrical power (e. g. 10% of the chemical energy flux—equivalent to an increase of approx. 116 °C in final temperature) produce large increases in throughput— almost 700 % with N 2 plus argon as the carrier gas. This compares with about 50 % predicted for a perfectly stirred system on the basis of measured global kinetics. Even the effect of argon alone, as the carrier gas, cannot be accounted for by such predictions. Radicals known to be important in flame propagation, such as OH, H and O were deliberately produced by including H 2 O, O 2 and CH 4 in the carrier stream . These were an improvement over argon alone but none appreciably exceeded N 2 in effectiveness. The conclusion is that a limited amount of electrical power used to stabilize a large throughput of flame reactants is most effective if employed to generate energetic and long-lived molecular fragments by imparting it in high concentration to a species of large dissociation energy which is capable of producing, subsequently, radicals important in flame propagation. The practical implications may be important, e. g. for stabilizing large throughputs in jet propulsion.