Pressure dependence of formation of soot and PAH in premixed flames

Abstract

The influence of pressure on the stable products of a C2H4-air flame with special regard to PAH has been investigated by optical methods and chemical analysis for pressures up to 70·105 Pa. PAH could be analyzed up to the mass range of dicoronyl, C48H22, 598 u. The identified PAH in the mass range above coronene consist mainly of pure 6-ring-systems, systems containing 6- and 5-rings, and aza-aromates. They are relatively stable, that means that their concentrations are kinetically controlled. The carbon density of the PAH, ρcΣ(PAH), shows similarly to soot a p2-dependence in the pressure regime up to 10·105 Pa. Above 10·105 Pa this dependence changes into an approximately linear one. The dependence of the PAH concentrations on mixture composition and temperature is similar to the dependence of the final soot volume fraction fv∞ on those parameters: one finds bell shaped curves for the temperature dependence of the PAH concentrations and ρcΣ(PAH) = [(C÷O)actual - (C÷O)crit]n with 2.5 ≤n≤3.