Maximum ion currents from flames and the maximum practical effects of applied electric fields

Abstract

The maxima limiting all practical effects of the movement of flame ions in electric fields are shown to depend on the current densities available. The theory of the electric field and space charge distributions inside and outside the flame is developed, checked experimentally, and used to deduce such maxima. Two factors are identified as limiting current densities; the rate of ion generation per unit flame area and the space charge-induced breakdown at the electrodes. The latter is shown to be ultimately limiting and the theory is used to calculate numerical values for all practical maxima. The former is limiting only in some flat laminar flames parallel to electrodes, but it leads to a method of measuring rates of ion generation in flames. The method is developed experimentally on the basis of the theory and applied to a series of hydrocarbon/air and hydrogen/hydrocarbon/air flames. As an example of its use, the results are applied to calculations of activation energies and orders of the ion-forming process.