Identification and temporal behavior of radical intermediates formed during the combustion and pyrolysis of gaseous fuels: kinetic pathways to soot formation. Progress report, September 1, 1979-August 31, 1982

The primary focus of our work has dealt with the detection, identification, and concentration of intermediates and products formed during the pyrolyses of fuels that are known to produce soot. These efforts have concentrated on the decompositions of toluene, benzene, butadiene, and acetylene. Product and reactant profiles were constructed during typical observation periods of one millisecond and spanned a temperature range of 1400 to 2300/sup 0/K. The total carbon atom concentration was maintained at about 2 x 10/sup 17/ atoms/cm/sup 3/. The apparatus employed consisted of a shock tube coupled to a time-of-flight mass spectrometer. Reacting gases were analyzed dynamically from the reflected shock zone. Spectra in the mass range m/e 12 to 300 were recorded at 30 ..mu..sec intervals during the observation period. Numerous calibration experiments under no reaction shock conditions were performed with known concentrations of fuel compounds in order that the various peak heights recorded during pyrolysis could be placed on concentration vs. reaction time plots. These data were used to construct tables of mass balance as a function of temperature. Mixture compositions were prepared in order to maximize the overlap of experimental conditions with other studies which utilized a variety of techniques to measure soot yields,more » final product distributions, and rate constants for some of the decompositions of key compounds and radicals. Dynamic product analysis and carbon atom mass balance of toluene, benzene, butadiene, and acetylene decompositions investigated under total carbon atom concentrations of 2 x 10/sup 17/ atoms cm/sup -3/ reveal the dominance of fragmentation as opposed to condensation reaction routes. These facts are used to set an upper limit of 10% for the soot yield from toluene pyrolysis.« less