FORMATION OF POLYCYCLIC AROMATIC-HYDROCARBONS (PAH) IN METHANE COMBUSTION - COMPARATIVE NEW RESULTS FROM PREMIXED FLAMES

Direct sampling and GC/MS analysis of fuel-rich, laminar, premixed fla mes of methane indicates the production of higher in-flame peak concen trations of benzene and polycyclic aromatic hydrocarbons (PAH) than in the flames of ethane under similar combustion conditions. These findi ngs are surprising and significant because the methane flame not only had a higher H/C ratio and lower carbon density, but also produced les s acetylene and soot than the ethane flame. These results suggest the significance of species containing an odd number of carbon atoms in PA H formation processes in the methane flame, as well as the importance of soot surface reactions. Although aromatic and polyaromatic intermed iates constitute trace by-products of combustion, their formation is o f practical concern due to their potential adverse health effects.