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, ρ _cΣ(PAH), shows similarly to soot a p ²-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 f ^{v ∞} on those parameters: one finds bell shaped curves for the temperature dependence of the PAH concentrations and ${\rho _{c\Sigma (PAH)}} = {\left[ {{{({\textstyle{c \over o}})}_{actual}} - {{({\textstyle{c \over o}})}_{crit}}} \right]^n}\,with\,2.5 \le n \le 3.$