Chemical flame inhibition using molecular beam mass spectrometry. Reaction rates and mechanisms in a 0. 3 percent CF/sub 3/Br inhibited methane flame

Technical Report · Wed Jan 01 04:00:00 EST 1975

OSTI ID:7309164

Biordi, J C; Lazzara, C P; Papp, J F

Composition profiles for atomic, radical, and stable species, as well as temperature and area expansion ratio profiles, have been determined for a nearly stoichiometric CH/sub 4/-O/sub 2/-Ar flame and one to which 0.3 percent CF/sub 3/Br inhibitor had been added. Net reaction rate profiles were calculated for all the observed species. For the normal flame, these and the mole fraction profiles gave rate coefficient information about the elementary reactions in the methane flame, for example, CH/sub 3/ + O/sup 4/ ..-->.. H/sub 2/CO + H, k/sub 4/ = 1.05 x 10/sup 14/ cm/sup 3/ mole/sup -1/ s/sup -1/ for 1,550 less than or equal to T less than or equal to 1,725/sup 0/K; CO + OH ..-->.. CO/sub 2/ + H, k/sub 6/ = 4.7 x 10/sup 11/ for 1,350 less than or equal to T less than or equal to 1,750/sup 0/K. Comparison between the inhibited and normal flame showed that (H) and (CH/sub 3/) were significantly reduced at the lower temperatures in the inhibited flame even though in the hot gas region the (H), (OH), and (O) were essentially the same in both flames. The CF/sub 3/Br disappears very early in the flame, relative to the fuel, and the reaction primarily responsible for its disappearance is H + CF/sub 3/Br/sup 7/ ..-->.. HBr + CF/sub 3/, where k/sub 7/ is found to be 2.2 x 10/sup 14/ exp(-9460/RT) for 700 to 1,550/sup 0/K. Reaction of the inhibitor with methyl radicals provides for the relatively small amounts of CH/sub 3/Br observed, but CH/sub 3/ + Br/sub 2/ ..-->.. CH/sub 3/Br + Br must also occur. The HBr formed reacts rapidly with H atoms to form H/sub 2/ and Br, but the reaction is soon ''balanced'' in the flame as may be demonstrated by calculation of the equilibrium constant at various temperatures. The fluorocarbon fragment produced in reaction also reacts rapidly, in part with methyl radicals to give the observed elimination product CH/sub 2/CF/sub 2/. Later in the flame, above approx.1,400/sup 0/K, F/sub 2/CO is formed from the reaction CH/sub 2/CF/sub 2/ + O/sup 18/ ..-->.. F/sub 2/CO + CH/sub 2/ and k/sub 18/ approx.1.5 x 10/sup 13/ at 1,600/sup 0/K.

• Research Organization: Bureau of Mines, Pittsburgh, PA (USA). Pittsburgh Mining and Safety Research Center
• OSTI ID: 7309164
• Report Number(s): BM-RI-8029
• Country of Publication: United States
• Language: English

Related Subjects

090110* -- Hydrocarbon Fuels-- Properties-- (1979-1989)
10 SYNTHETIC FUELS
ADDITIVES
ALKANES
ARGON
BROMINATED ALIPHATIC HYDROCARBONS
CARBON COMPOUNDS
CARBON FLUORIDES
CHEMICAL PROPERTIES
CHEMICAL REACTION KINETICS
COMBUSTION KINETICS
CRYOGENIC FLUIDS
ELEMENTS
FLAMES
FLUIDS
FLUORIDES
FLUORINATED ALIPHATIC HYDROCARBONS
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
HALOGENATED ALIPHATIC HYDROCARBONS
HYDROCARBONS
INHIBITION
KINETICS
MASS SPECTROSCOPY
METHANE
NONMETALS
ORGANIC BROMINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC FLUORINE COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
RARE GASES
REACTION KINETICS
SPECTROSCOPY
STOICHIOMETRY
TEMPERATURE DEPENDENCE
THERMODYNAMICS