Sooting Structure in a Laminar Diffusion Flame

Laser light scattering and extinction measurements are used to determine the soot loading and particle number density field in an under‐ventilated flat laminar ethylene‐air diffusion flame, in which particle oxidation is avoided. Soot occurs in a region a few millimetres wide 1 to 2 mm to the fuel side of the stoichiometric fuel‐air interface. The particle number density N is highest (N > 1012 cm−3) closest to the flame zone, where temperature and radical concentration are high, here the particles are generated and therefore very small (d < 40 Å), the soot volume fraction is low. Further into the fuel region, N falls sharply while the particles grow by surface growth and coagulation. The soot volume fraction first increases and then decreases again deep into the unburned fuel.