Measurements of Formaldehyde Concentrations and Formation Rates in a Methane-Air, Non-Premixed Flame and Their Implications for Heat-Release Rate.
Measurements of Formaldehyde Concentrations and
Formation Rates in a Methane-Air, Non-Premixed Flame and
Their Implications for Heat-Release Rate.
(840 K)
Tolocka, M. P.; Miller, J. H.
Combustion Institute, Symposium (International) on
Combustion, 27th. Proceedings. Volume 1. August 2-7,
1998, Boulder CO, Combustion Institute, Pittsburgh, PA,
633-640 pp, 1998.
Sponsor:
National Science Foundation, Washington, DC
Keywords:
combustion; formaldehyde; heat release rate; premixed
flames; lasers
Abstract:
Tunable diode laser absorption spectroscopy coupled with
microprobe sampling was used to quantitatiley determine
formaldehyde concentrations in a methane-air
non-premixed flame. Resulting concentration profiles are
similar in shape and peak locations to previous
qualitative measurements, and concentration levels are
in line with those predicted by direct numerical
simulation of methane-air flames. The resulting
concentrations were combined with other data from this
flame system in a mixture fraction-based code to predict
levels for species whose concentrations are not
available experimentally. An analysis was performed of
formaldehyde formation and destruction paths to
determine HCHO's dependence on specific reaction steps.
Formaldehyde formation is dominated by the reaction
between methyl radical and oxygen atom, and it is
destroyed by hydrogen abstraction. Both processes occur
near the stoichiometric surface. The analysis also
verified several points made by other researchers about
the heat-release rates in methane flames. Heat-release
rate correlates well with the destruction rate of
methane, the rate of the reaction between methyl
radicals and oxygen atoms, and HCO concentrations. A
condition of chemical steady state is found for HCO, and
the steady-state estimate of HCO concentration may also
be used to estimate local heat-release rate in methane
flames.
