Electrical control of flame carbon

Abstract

The electrical characteristics of carbon formation and deposition are studied for a flat counterflow diffusion flame to which electric fields are applied so as to draw flame ions of either sign through the pyrolysis zone and on to the nearer burner-electrode. The dependences of flame emission, rates of carbon formation and deposition, and of particle size, on field intensity and ion flux are investigated. It is concluded that particles are charged both by electron emission and by attachment, and either a net positive or a negative charge can be induced by the appropriate field configuration. The effect of fields on the net charges induces many diverse effects. Changes in radiation from the pyrolysis zone and in the site and form of carbon deposition are only the most apparent ones. By varying the residence time in the pyrolysis zone, particle size an d hence the total amount of carbon formed can be varied very greatly. Positive flame ions appear to act as nuclei and their neutralization by secondary negative charge decreases carbon formation. Practical applications are discussed in terms of the theory under each of the headings of nucleation, growth and deposition in the presence of fields.