The effect of various diluents on soot production in laminar ethylene diffusion flames

Soot production in laminar ethylene diffusion flames has been studied by measurement of smoke points and of the rates at which soot leaves a smoking flame. An apparatus for measuring sooting rates has been described. The effect on smoke point of diluting the flame with nitrogen, argon, helium, carbon dioxide and water vapour has been investigated over a wide range of diluent concentrations. Results were obtained both for the addition of diluent to the oxidant stream and for its addition to the fuel stream. Sooting rate data are reported for flames diluted with nitrogen. The effect of diluent flow on soot production depended on the diluent, the conditions of dilution and the dimensions of the burner. Several factors suggest that the relatively high efficiency of carbon dioxide and water vapour as soot suppressors depends on their ability to influence soot combustion in the flame. For the ‘inert’ diluents a qualitative model is proposed to account for the complex variation in soot production with degree of dilution and with diluent.