EXPLORING OLD AND NEW BENZENE FORMATION PATHWAYS IN LOW-PRESSURE PREMIXED FLAMES OF ALIPHATIC FUELS

摘要

A modeling study of benzene and phenyl radical formation was performed for three low-pressure pre-mixed laminar flat flames having an unsaturated C_2 or C_3 hydrocarbon fuel (acetylene, ethylene, and propene). Predictions using three published detailed elementary-step chemical kinetics mechanisms were tested against molecular beam mass spectrometry (MBMS) species profile data for all three flames. The differences between the predictive capabilities of the three mechanisms were explored, with an emphasis on benzene formation pathways. A new chemical kinetics mechanism was created combining features of all three published mechanisms. Included in the mechanism were several novel benzene formation reactions involving combinations of radicals such as C_2H + C_4H_5, C_2H_3 + C_4H_3, and C_5H_3 + CH_3. Reactions forming fulvene (a benzene isomer) were included, such as C_3H_3(propargyl) + C_3H_5(allyl), as well as fulvene to benzene reactions. Predictions using the new mechanism showed virtually all of the benzene and phenyl radical to be formed by reactions of either C_3H_3 + C_3H_3 or C_3H_3 + C_3H_5, with the relative importance being strongly dependent on the fuel. C_5H_3 + CH_3 played a minor role in fulvene formation in the acetylene flame. The C_2H_x + C_4H_x reactions did not contribute noticeably to benzene or phenyl radical formation in these flames, sometimes being a major decomposition channel for either fulvene or phenyl radical. The formation pathways for C_3H_3 and C_3H_5 were delineated for the three flames; although the key reactions differed from flame to flame, ~1CH_2 + C_2H_2 <=> C_3H_3 + H was important for all three flames.