Effect of Buoyancy on the Radiative Extinction Limit of Low-Strain-Rate Nonpremixed Methane-Air Flames.
Effect of Buoyancy on the Radiative Extinction Limit of
Low-Strain-Rate Nonpremixed Methane-Air Flames.
Hamins, A.; Bundy, M.; Oh, C. B.; Kin, S. C.
Combustion and Flame, Vol. 151, No. 1/2, 225-234,
nonpremixed flames; buoyancy; extinction; flame
structure; microgravity; experiments; fire suppression;
temperature measurements; nitrogen; flame
extincuishment; gravity; equations; heat release
The structure and extinction of nonpremixed flames were
investigated through comparison of experiments and
calculations using a counterflow configuration.
Experiments were conducted at the NASA Glenn Research
Center's 2.2-s drop tower to attain suppression and
temperature measurements in low-strain nonpremixed
methane-air microgravity flames. Suppression
measurements using nitrogen added to the fuel stream
were performed for global strain rates from 7 to 50 s-1.
Judicious hardware selection and an optimized
experimental procedure facilitated rapid, controllable,
and repeatable flame extinction measurements. The
minimum nitrogen volume fraction in the fuel stream
needed to ensure suppression for all strain rates in
microgravity was measured to be 0.855 - 0.016,
associated with the turning point, which occurred at a
global strain rate of 15 s?1. This value was higher than
the analogous value in normal gravity. Flame temperature
measurements were attained in the high-temperature
region of the flame (T >1200 K) using visible emission
from a SiC filament positioned axially along the burner
centerline. The suppression and temperature measurements
were used to validate a two-dimensional flame simulation
developed here, which included buoyancy effects and
finite-rate kinetics. The simulations yielded insight
into the differences between microgravity and normal
gravity suppression results and also explained the
inadequacy of the one-dimensional model results to
explain the microgravity suppression results.