Aromatic and polycyclic aromatic hydrocarbon formation in a premixed propane flame

Experimental and detailed chemical kinetic modeling has been performed to investigate aromatic and polycyclic aromatic hydrocarbon (PAH) formation pathways in a premixed, rich,sooting, propane-oxygen-argon burner stabilized flame. An atmospheric pressure, laminar Rat flame operated at an equivalence ratio of 2.6 was used to acquire experimental data for model validation. Gas composition analysis was conducted by an on-line gas chromatograph/mass spectrometer (GC/MS) technique. Measurements were made in the main reaction and post-reaction zones for a number of low molecular weight species, aliphatics, aromatics, and polycyclic aromatic hydrocarbons (PAHs) ranging from two to five-fused aromatic rings. Reaction flux and sensitivity analysis were used to help identify the important reaction sequences leading to aromatic and PAH growth and destruction in the propane flame. Benzene formation was shown to be dominated by the propargyl recombination reaction. A secondary benzene formation pathway occurred from the reaction sequence of allyl plus propargyl leading to fulvene and H-atoms whereupon the fulvene is converted to benzene by H-atom catalysis. Large negative sensitivity coefficients were calculated for the H2CCCH + H <----> C3H2 + H-2 reaction in the propargyl, benzene, and naphthalene sensitivity analysis study. This result implicates propargyl consumption by H-atoms as an important reaction step that limits aromatic and PAH growth. Naphthalene formation through the reaction step of cyclopentadienyl self-combination and phenanthrene formation from indenyl and cyclopentadienyl combination were shown to be plausible global reaction steps for PAH production.