Chemical Effects of CF3H in Extinguishing Counterflow CO/Air/H2 Diffusion Flames.
Chemical Effects of CF3H in Extinguishing Counterflow
CO/Air/H2 Diffusion Flames.
Fallon, G. S.; Chelliah, H. K.; Linteris, G. T.
Combustion Institute, Symposium (International) on
Combustion, 26th. Proceedings. Volume 1. July
28-August 2, 1996, Napoli, Italy, Combustion Institute,
Pittsburgh, PA, 1395-1403 pp, 1996.
combustion; chemical inhibition; flame chemistry;
diffusion flames; extinguishing
The relative importance of introducing CF3H as a fire
suppressant with the oxidizer or the fuel stream, and
its chemical and thermal effects on the extinction
condition of counterflow CO/air/H2 diffusion flames, are
investigated both experimentally and numerically. In
experiments, the extinction strain rate is evaluated by
measuring the jet velocities at extinction and the jet
separation distance. In numerical calculations, the
potential flow approximation is introduced to describe
the outer flow field and the strain rate at extinction
is determined from the axial velocity gradient on the
oxidizer side. By employing mixture fraction
concepts,the shift in flame location within the mixing
layer caused by increasing the CF3H mole fraction or
switching CF3H from air to fuel stream is shown to
affect the measured and predicted extinction strain
rates significantly. Flame structure and reaction
pathway analyses have been used to identify the
rate-controlling reactions and the influence of
introducing the suppressing agent from the oxidizer or
fuel side on the finite-rate chemistry. Subsequent
sensitivity analysis has shown that two alternate
CF3-consumption reaction pathways can either increase or
decrease the extinction strain rate, similar to the
sensitivities found in a recent premixed burning
velocity study. Finally, based on the numerical
calculations, the overall chemical and thermal effects
of CF3H are demonstrated by freezing the CF3H chemistry
and by replacing the heat capacity of CF3H with that of
N2 for the frozen case.