Oc. Kwon et Gm. Faeth, Flame/stretch interactions of premixed hydrogen-fueled flames: Measurements and predictions, COMB FLAME, 124(4), 2001, pp. 590-610
Fundamental unstretched laminar burning velocities, and flame response to s
tretch (represented by the Markstein number) were considered both experimen
tally and computationally for laminar premixed flames. Mixtures of hydrogen
and oxygen with nitrogen, argon and helium as diluents were considered to
modify flame transport properties for computationally tractable reactant mi
xtures. Freely (outwardly)-propagating spherical laminar premixed flames we
re considered for fuel-equivalence ratios of 0.6 to 4.5, pressures of 0.3 t
o 3.0 atm, volumetric oxygen concentrations in the nonfuel gases of 0.21 to
0.36, and Karlovitz numbers of 0 to 0.5, at normal temperatures. For these
conditions, both measured and predicted ratios of unstretched-to-stretched
laminar burning velocities varied linearly with flame stretch (represented
by the Karlovitz number), yielding constant Markstein numbers for particul
ar reactant conditions. The present flames were very sensitive to flame str
etch, exhibiting ratios of unstretched-to-stretched laminar burning velocit
ies in the range 0.6 to 3.0 for levels of flame stretch well below quenchin
g conditions. At fuel-lean conditions, increasing flame temperatures (by di
lution with argon rather than nitrogen) tended to reduce flame sensitivity
to stretch whereas increasing pressures tended to increase tendencies towar
d preferential-diffusion instability behavior. At low pressures, helium-dil
uted flames had reduced tendencies toward preferential-diffusion instabilit
y behavior compared to nitrogen- and argon-diluted flames due to stabilizat
ion of flame properties by strong effects of preferential diffusion of heat
. Predicted and measured flame properties exhibited encouraging agreement u
sing contemporary reaction mechanisms. Finally, flame structure predictions
suggest that H and OH radical production and transport are important aspec
ts of preferential-diffusion/stretch interactions, reflecting the strong co
rrelation between laminar burning velocities and H+OH radical concentration
s for present test conditions. (C) 2001 by The Combustion Institute.