MODELING OF AROMATIC AND POLYCYCLIC AROMATIC HYDROCARBON FORMATION INPREMIXED METHANE AND ETHANE FLAMES

Detailed chemical kinetic modeling has been performed to investigate a romatic and polyaromatic hydrocarbon formation pathways in rich, sooti ng, methane and ethane premixed flames. An atmospheric pressure, lamin ar flat flame operated at an equivalence ratio of 2.5 was used to acqu ire experimental data for model validation. Gas composition analysis w as conducted by an on-line gas chromatograph / mass spectrometer techn ique. Measurements were made in the flame and post-flame zone for a nu mber of low molecular weight species, aliphatics, aromatics, and polyc yclic aromatic hydrocarbons (PAHs) ranging from two to five-aromatic f used rings. The modeling results show the key reaction sequences leadi ng to aromatic and polycyclic aromatic hydrocarbon formation primarily involve the combination of resonantly stabilized radicals. In particu lar, propargyl and 1-methylallenyl combination reactions lead to benze ne and methyl substituted benzene formation, while polycyclic aromatic s are formed from cyclopentadienyl and fused rings that have a shared C-5 side structure. Naphthalene production through the reaction step o f cyclopentadienyl self-combination, and phenanthrene formation from i ndenyl and cyclopentadienyl combination were shown to be important in the flame modeling study. The removal of phenyl O-2 leading to cyclope ntadienyl formation is expected to play a pivotal role in the PAH or s oot precursor growth process under fuel-rich oxidation conditions.