ON THE ADEQUACY OF CERTAIN EXPERIMENTAL OBSERVABLES AS MEASUREMENTS OF FLAME BURNING RATE

This work presents detailed chemical kinetic computations and experime ntal measurements of a premixed stoichiometric N-2-diluted methane-air flame in two-dimensional unsteady vortical Bow, which are used to inv estigate the utility of several experimental observables as measuremen ts of local burning and heat release rates. The computed mole fraction of HCO is found to have excellent correlation with flame heat release rate over the whale range of unsteady curvature and strain-rate inves tigated, for the flame under consideration. HCO planar laser induced f luorescence (PLIF) imaging is discussed and demonstrated in a V-flame experiment. On the other hand, we find the utility of peak dilatation rate as an indicator of heat release rate to he dependent on the unste ady strain-rate and flame curvature environment, and the associated mo dification in diffusional thermal fluxes within the flame. The integra ted dilatation rate is found to be more robust under unsteady strain-r ate, but still questionable in regions of high flame curvature. We als o study the utility of a particular formulation for CO2 chemiluminesc ence, OH, and CH PLIF imaging, as well as OH, C-2*, and CH* chemilumi nescence, as measurements of flame burning and heat release rates. We generally find these measures to be inferior to HCO. Experimental resu lts suggest that CH, OH, C-2*, and CH* are not adequate indicators of local extinction; rather they provide signals of subtle shifts of hyd rocarbon consumption among different chemical pathways. Moreover, nume rical results suggest that both OH mole fraction and an existing CO2 chemiluminescence model do not correlate with burning or heat release rate variations in regions of high unsteady flame curvature. The prese nt numerical investigation uses a single flame/vortex condition and a specific 46-step C-(1) chemical mechanism. The conclusions reached her ein may be generalized with further studies using more detailed mechan isms over ranges of stoichiometry, dilution, and flow time and spatial scales. (C) 1998 by The Combustion Institute.