Augmenting flames with electric discharges

Abstract

A few individual methods for augmenting flame enthalpies and ionization levels electrically have been considered previously. This communication summarizes a more general study of the problems involved and of the experimental approaches to their solution. It is shown that the maximum rates of electrical-energy input required are only a few times greater than those due to chemical energy and that the main obstacle lies in the requirement to spread the discharge energy throughout the flame, in spite of its tendency to be released along a thin arc channel. One of the chief attractions of distributing the discharge and associating it with the combustion zone is that the combination is very difficult to blow off and large throughputs thus become feasible for quite small burners. This attribute is lost once mixing becomes rate-controlling. The following approaches to this problem are considered theoretically and/or experimentally. o 1. The use of (a) “plasma jets”, (b) devices developed on allied principles. 2. Inducing turbulence. 3. Seeding with readily ionizable materials. 4. The use of high-frequency alternating discharges. 5. Inducing rapid oscillation or rotation of arcs by magnetic fields. The following are among the conclusions: Methods based on gas movement—either random or organized—convey the impression, to the eye or camera, that they succeed, without in fact doing so. The rapid movement of the gas-borne discharge occurs only with respect to the stationary observer, not with respect to the pockets of gas which carry it. Methods which can be applied only in hot product gas—such as No. 3, above—succeed in spreading the discharge but depend on the presence of the flame and blow off with it. They do not appreciably augment combustion intensity. Other quite feasible methods—notably No. 4—are very expensive in bulk, weight, and cost of equipment, as well as in incidental power losses. The most promising group of methods appears to be that based on feeding reactants through discharges, either held stationary or spinning at such high rates (order of 10 5 rpm) that every part of a fast gas stream experiences the passage of the discharge through it at least once. Power fluxes of 5.7 kW/cm 2 of burner area are attained, of which 40% can be chemical.