Inhibition of Premixed Methane-Air Flames by Fluoromethanes.
Inhibition of Premixed Methane-Air Flames by
Fluoromethanes.
(889 K)
Linteris, G. T.; Truett, L.
Combustion and Flame, Vol. 105, No. 1/2, 15-27, April
1996.
Keywords:
chemical inhibition; flame chemistry; flame models;
flame retardants; flame speed
Abstract:
This paper presents the first calculations and
measurements of the burning velocity of premixed
hydrocarbon flames inhibited by the three one-carbon
fluorinated species CH2F2, CF3H, and CF4. The chemistry
of these agents is expected to be similar to that of
some agents that may be used as replacements for CF3Br,
so that studying their behavior in methane flames
provides an important first step towards understanding
the suppression mechanism of hydrocarbon fires by
fluorinated compounds. The burning velocity of premixed
methane-air flames stabilized on a Mache-Hebra nozzle
burner is determined using the total area method from a
schlieren image of the flame. The inhibitors are tested
over a range of concentration and fuel-air equivalence
ratio. The measured burning rate reduction caused by
addition of the inhibitor is compared with that
predicted by numerical solution of the species and
energy conservation equations employing a detailed
chemical kinetic mechanism recently developed at the
National Institute of Standards and Technology (NIST).
Even in this first test of the kinetic mechanism on
inhibited hydrocarbon flames, the numerically predicted
burning velocity reductions for methane-air flames with
values of equivalence ratio of 0.9, 1.0, and 1.1 and
inhibitor mole fractions in the unburned gases up to
0.08, are in excellent agreement for CH2F2 and CF4 and
within 35% for CF3H. The numerical results indicate
that the agents CF3H and CH2F2 are totally consumed in
the flame and the burning velocity is reduced primarily
by a reduction in the H-atom concentration through
reactions leading to HF formation. In contrast, only
about 10% of the CF4 is consumed in the main reaction
zone and it reduces the burning velocity primarily by
lowering the final temperature of the burned gases.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899