The Influence of Ferrocene on PAH Synthesis in Acetylene and Methane Diffusion Flames

Abstract

Laminar argon diluted acetylene and methane diffusion flames are seeded with ferrocene vapor by means of a small crucible in the heated fuel line. Using microprobe sampling, combustion products are extracted from the flame and immediately cooled and diluted. A steel tube with a pinhole is shown to provide an equivalent alternative sampling system. PAH concentrations are measured as function of time spent in the combustion zone using time of flight mass spectrometry. In the acetylene flame PAH concentrations are almost unaffected by ferrocene addition, whereas in the methane flame PAH are found to be formed earlier and in considerably lower concentrations in the presence of ferrocene. The additive primarily suppresses the synthesis of acetylene in the methane flame, which results in diminished PAH growth through successive acetylene addition. Other growth mechanisms, like reactive dimerization of PAH, are found to be not affected or even promoted by the additive. As ferrocene addition is known to result in accelerated particle formation and soot inception, heterogeneous catalysis on the surface of carbonaceous soot particles is suggested as a major PAH formation pathway.