Predicting Chemical Flame Lengths and Lift-off Heights in Enclosed, Oxy-Methane Diffusion Flames at Varying O2/CO2 Oxidizer Dilution Ratios

Gautham Krishnamoorthy, Mario Ditaranto

Abstract


Experiments have shown reactor confinement, wall temperatures and radiative transfer to influence the flame length and lift-off
characteristics of oxy-methane flames. In this study, the performances of the Shear Stress Transport (SST) k-! turbulence
model, a skeletal methane combustion mechanism (16 species and 41 reactions) and two weighted sum of gray gas models
(WSGGM) towards capturing these flame characteristics are evaluated against measurements obtained from oxy-methane
flames across a wide range of oxidizer O2/CO2 ratios and fuel Reynolds numbers. Gas composition, gas and wall temperatures,
flame length measurements and inferences of lift-off heights from OH* chemiluminescence imaging are employed in
the assessment. The corresponding numerical estimate of flame length and lift-off heights were made by determining the
flame shape by the locus of points at which the CO concentrations reduce to 1% of their peak values within the flame.
The predicted gas temperatures and compositions compared reasonably well against measurements. The criterion for
defining the flame shape based on CO concentrations appears promising since the trends in chemical flame length and
lift-off height predictions agreed reasonably well with the measurements across the range of oxidizer concentrations and
fuel Reynolds numbers. Flame length prediction sensitivities to the wall temperatures and the WSGGM model were also
assessed.


Keywords


Oxy-methane; combustion model; flame length; lift-off height; WSGGM.

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