MEASURED AND COMPUTER-SIMULATED HYDROCARBON AND OH RADICAL PROFILES IN FUEL-RICH ATMOSPHERIC-PRESSURE FLAT FLAMES - REACTIONS OF CH4 AND C2H2

Density-height profiles of CH4, C2H2, and OH, measured in the postflame gas of rich atmospheric-pressure flat flames fueled by methane, ethylene, acetylene, or propane, are compared to computer-simulated profiles generated by using a 69-reaction kinetic mechanism. In the mechanism chosen for the simulation, the acetylene decays in the postflame gas by reaction primarily with OH with a rate constant determined to be k24 = 9.2 (±1.5) × 1011 cm3/(mol·s) at 1700 K. The superequilibrium pool of partially equilibrated radicals formed in the flame zone decreases toward thermal equilibrium in the postflame gas. Simulation of the OH radical profile shows that recombination of methyl radicals with H atoms controls the shape of this profile and also those of the rest of the free-radical pool. As the acetylene density decreases, the methane density rises. The net methane yield per acetylene consumed varies with the fuel used, reaching 35% for the ethylene flame. This behavior is correctly simulated by using CH2CO + H as the product of the C2H2 + OH reaction, although other mechanistic paths could also be conceived which would yield CH4. For the acetylene-air flame, densities of allene, methylacetylene, and diacetylene were also measured. These species were near partial equilibrium with the acetylene density at the three heights observed. © 1990 American Chemical Society.