Soot mass growth and coagulation of soot particles in C{sub 2}H{sub 4}/air-flames at 15 bar

The growth of soot particles has been studied in flat C{sub 2}H{sub 4}/air flames burning at 15 bar. Laser extinction and scattering were measured simultaneously as a function of distance from the burner, together with temperature and concentration profiles of aliphatic and polycyclic hydrocarbons. In 15 bar C{sub 2}H{sub 4}/air flames with surplus carbon densities {rho}{sub c} > 10{sup 18} C atoms/cm{sup 3}, final particle numbers N{sub {proportional_to}} are found that are higher than at lower pressures. The growth of f{sub {nu}{proportional_to}}, the final soot mass, proceeds via increasing particle number density and not as at normal pressure via larger particles. The particle coagulation rate decays quite rapidly with time leading to larger final particle number density. The apparent active lifetime of soot particles (k{sub f}{sup {minus}1}) at 15 bar depends on temperature and, in addition, on the surplus carbon density {rho}{sub c}. The quantity k{sub f}/{rho}{sub c} is a function of temperature. The polycyclic aromatic hydrocarbons (PAH) appear very early in the C{sub 2}H{sub 4}/air flame, but they are also consumed very rapidly to very low final mole fraction {chi}{sub PAH} {approx} 10{sup {minus}9}. The carbon density of C{sub 2}H{sub 2} decreases strongly in the phase of soot growth.more » The final value [C{sub 2}H{sub 2}]{sub {infinity}} of about 10{sup {minus}6} g/cm{sup 3} is high enough for further soot growth, so that the ceasing of coagulation and soot mass growth at 15 bar cannot be explained by a lack of C{sub 2}H{sub 2}. It rather seems to be the decreasing activity of soot particles.« less