Ba. Williams et Jw. Fleming, COMPARISON OF SPECIES PROFILES BETWEEN O-2 AND NO2 OXIDIZERS IN PREMIXED METHANE FLAMES, Combustion and flame, 100(4), 1995, pp. 571-590
The profiles of the species H, OH, CH, NH, CN, NCO, NO2, and CH3O are
compared in a series of five premixed stoichiometric 15-torr CH4/O-2/N
O2/N-2 flames with NO2 comprising between 0% and 40% of the oxidizer.
Relative species concentrations were measured by laser-induced fluores
cence (LIF) and these results are compared with calculations using mea
sured temperature profiles. The reaction mechanism of Miller and Bowma
n incorrectly predicts the standoff from the burner in flames containi
ng more than 20% NO2; addition of several reactions involving NO, and
HONO produces excellent agreement with experiment for most species. Th
e reaction CH3 + NO2 --> CH3O + NO is found to be particularly importa
nt in the reaction mechanism. LIF profiles of CH3O show this species t
o be present in far larger quantities in the NO2 supported flames than
in the CH4/O-2 system. The nitrogen-containing intermediates CN, NCO,
and NH are all overpredicted by a factor of two in the 40% NO2 flame
relative to the 10% NO2 flame, This indicates an inaccuracy in either
the reburn reactions or the fuel nitrogen chemistry when large amounts
of NO are present. The kinetic modeling shows that in the 40% NO2 fla
me, the dominant pathway to N-2 formation is through N2O, which is pro
duced primarily by the reaction of NCO with NO. Comparison of emission
profiles of NO2 for the various flames indicates that the appearance
of an orange-yellow luminous zone at the base of NO2 supported flames
is caused by thermal excitation of NO2, not by a chemiluminescence me
chanism.