CH-ATOM AND C-ATOM TIME HISTORIES IN DILUTE HYDROCARBON PYROLYSIS - MEASUREMENTS AND KINETICS CALCULATIONS

CH and C-atom concentration-time histories were measured during pyrolysis of highly dilute mixtures (6 to 100 ppm) of ethane or methane in argon behind reflected shock waves over the temperature range 2500 to 3800 K and pressure range 0.5 to 1.3 atm. CH was detected using narrow-linewidth laser absorption at 431 nm. C-atom concentrations were measured using atomic resonance absorption spectroscopy (ARAS) at 156.1 nm. These data allow improved understanding of dilute hydrocarbon pyrolysis. A pyrolysis reaction mechanism was developed which fits essential characteristics of the CH and C-atom profiles (time to peak, peak concentration, and 50% decay time) within +/- 25%. Critical reactions for which rate coefficient data were not previously available are: [GRAPHICS] Best-fit rate coefficients, valid over the range 2500 to 3800 K, are: k4 = 5.0 X 10(15) exp(-42800 K/T), k5 = 4.0 X 10(15) exp(-41800 K/T), k6 = 1.3 X 10(14) exp(-29700 K/T), and k7 = 1.9 X 10(14) exp(-33700 K/T) cm3 mol-1 s-1