Electrical control of the combustion of solid and liquid particulate suspensions

Abstract

The individual steps in using electric fields for dispersing solid and liquid fuels, for controlling the trajectories of the resulting charged particles and for manipulating their burning, are studied in turn—both experimentally and theoretically. After establishing the feasibility of the basic principles using powdered solids and distilled water, the remaining work is carried out using paraffin, with an antistatic additive, as fuel. The experimental conditions under which sprays are monodisperse are established, using a magnifying schlieren system and MgO-coated microscope slides, and accounted for theoretically. This makes possible the prediction of droplet size and charge in terms of the applied electrical, geometrical and flow parameters and permits the deduction of mobility. The measurement of droplet velocities in control fields, using both photographic particle tracking and the interference of Dopplershifted laser light scattered by the droplets, confirms these theoretical calculations. Similar methods are then applied to burning droplets but difficulties are encountered due to leakage of charge occasioned by chem i-ionization in the flames. These difficulties are overcome by separating the flames electrically from the preceding stages of electrical air induction, fuel atomization, mixing and vaporization. This leads to the development of burners operated entirely by fields which draw in and accelerate air from the surroundings using corona discharges in multi-stage ion pumps, the last stage of which atomizes and disperses the fuel. The theory of such devices indicates how optimum conditions of operation can be achieved in practice.