Revisit flame chemistry of propene at elevated pressures: Insight into pressure effects on chemical structure and laminar flame propagation

Abstract

This work reports an experimental and kinetic modeling investigation on flame chemistry of propene at elevated pressures. The chemical structures of premixed propene/O₂/Ar flames at 2–5 atm and the equivalence ratio of 1.5 including reactants, major products and a series of intermediates were measured using the flame sampling molecular beam mass spectrometry. The maximum mole fractions of H, CH₃ and C₂H₆ decrease with increasing pressure, while that of CH₄ follows the opposite trend. Laminar burning velocities (LBVs) of propene/air mixtures at equivalence ratios of 0.7–1.5 and initial pressures up to 10 atm were measured using the spherically propagating flame method. Remarkable pressure effects can be observed, especially under the lean and rich conditions. A kinetic model for propene combustion was developed based on our recent model for ethylene combustion and recently reported chemically termolecular reactions and HCO prompt dissociation reactions. Key reactions in the propene flames were revealed using the modeling analysis, especially for those playing significant roles in the pressure effects. Two chain termination reactions including the self-combination of CH₃ and the recombination between CH₃ and H are found to be crucial for the observed pressure effects in maximum mole fractions of H, CH₃, CH₄ and C₂H₆. The HCO prompt dissociation can significantly promote the laminar flame propagation of propene/air mixtures due to the substantial formation of CH₂O through CH₂+O₂ and CH₃+O pathways, while the chemically termolecular reactions exhibit weak inhibition effects at equivalence ratios smaller than 1.2. The reason for the stronger pressure effects of LBVs under the lean and rich conditions is that the excess O₂ and abundantly produced CH₃ enhances the roles of H+O₂(+M)=HO₂(+M) and CH₄(+M)=CH₃+H(+M) in chain termination, respectively.