Estimation of Flammability Limits of Selected Fluorocarbons with F(sub 2) and CIF(sub3) Page: 72 of 78
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parameter values are:
Best Fit Lean A= 110 ; B=1100
Rich A=140; B= 800
Conservative Fit Lean A = 70; B = 1050
Rich A= 95; B=800
D.4 NOTES ON EXPERIMENTAL FLAMMABILITY LIMIT DATA
Flammability limits obtained from literature data were from several sources. Fletcher and Ambs
 examined combustion of binary mixtures of CIF3 with C2F6, C3F8, and c-C4F8. They
suggested that the ignition temperature. for such mixtures might be fairly low and similar for all
fluorocarbons but did not propose a value for that temperature. This work was mainly a study of
flame speeds and quench distances, rather than composition boundaries, but as compositions
were varied, some information was obtained relevant to the current study. For ClF3 + C2F6, at
the lower flammability limit, 54.4% fuel didn't burn, while 57.8% did; at the upper limit, 69.7%
was the highest mixture that burned. For the C3F8 mixtures, the lower limit lies between 26.2%
(not ignitable) and 34.4% (ignitable) and the upper limit lies at 64.9% 0.1% fuel. Data on
c-C4F8 was of poorer quality, as the mixtures had a tendency to detonate. From the limited data,
a rough estimate of the flammable composition range is 11% to 45% c-C4Fs. Unfortunately,
there was no mention in the article of the initial pressure and temperature of the gas mixtures. In
using the boundary limit information, we assume standard conditions (1 atm, 25*C).
Fletcher and Kittelson  studied detonation limits of F2 + c-C4Fs mixtures, observing detonation
velocities between 1000 and 1600 m/s over compositions ranging from 62% down to 7.62% fuel.
(Incidentally, these detonation velocities are in approximate agreement with those predicted in
the spreadsheet models discussed in this report). Flame boundaries were not explicitly studied
and are likely to lie a bit outside the composition envelope which can generate a detonation. One
run was reported in which a 6.08% fuel mixture burned. Again, the initial pressure and
temperatures were not reported in this study.
Fletcher and Hinderman examined the combustion of rich mixtures of F2 and one or more of
C2F6, C3F, and c-C4F8 . These studies concentrated primarily on product composition and did
not explicitly seek the upper flammability limit. Gas mixtures at room temperature and 600 Torr
were ignited by spark and products analyzed by gas chromatography. An approximate upper
-flammability boundary can be obtained by examination of graphs showing the compositions at
which formation of reaction products ceases. For C2F6:, this level was 75 % fuel; for C3Fs , it
was 75.3 % fuel; for c-C4F8, a 76% fuel mixture burned, but no higher fuel concentration results
were displayed, so the boundary presumably lies somewhat higher than this.
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Trowbridge, L.D. Estimation of Flammability Limits of Selected Fluorocarbons with F(sub 2) and CIF(sub3), report, September 1, 1999; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc623234/m1/72/: accessed May 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.