Kinetic modeling of a rich, atmospheric pressure, premixed n-heptane/O-2/N-2 flame

A detailed reaction mechanism has been evaluated by comparison of computed species mole fraction profiles with experimental profiles measured in a ric h n-heptane/O-2/N-2 flame stabilized at atmospheric pressure. A similar stu dy was carried out previously in our laboratory, at low pressure (6 kPa) wi th molecular beam-mass spectrometer as the analytical tool. In the present work, species mole fractions are measured by gas chromatography so that iso mers that could not be distinguished by the mass spectrometer were identifi ed and analyzed separately. Hence, although the main objective of this work was to extend the n-heptane combustion mechanism to atmospheric pressure, it was also to take advantage of the new data on the isomers to refine the mechanism. Modifications to the low-pressure mechanism have been strictly l imited to (i) calculation of high pressure values for reactions in the fall -off regime and (ii) distinction of the isomeric forms of heptenes. The rel iability of the mechanism was evaluated by comparison of computed mole frac tion profiles with those measured in a rich premixed n-heptane flame (equiv alence ratio 1.9). Good agreement was obtained for most molecular species, especially intermediate olefins, dienes, alkynes. Computed benzene concentr ations are also in reasonable agreement with experimental observation. Anal yses of the main reaction pathways show that the main effect of the change of pressure from 6 to 101 kPa is to increase the relative importance of the thermal decomposition reactions, especially for the intermediate olefins. (C) 1999 by The Combustion Institute.