A numerical and experimental investigation of premixed methane-air flame transient response

We report the results of a numerical and experimental investigation of the response of premixed methane-air flames to transient strain-rate disturbanc es induced by a two-dimensional counter-rotating vortex-pair. The numerical and experimental time histories of flow and flame evolution are matched ov er a IO ms interaction time. Measurements and computations of CH and OH pea k data evolution are reported and compared. Despite the matching of experim ental operating conditions, the full resolution of flame length and time sc ales, and the use of a detailed C1C2 chemical mechanism and temperature-dep endent transport properties, we find disagreements with experimental measur ements of the transient response of both CH and OH. Besides quantitative di sagreements in response time scales, the qualitative transient features of OH at rich conditions are not predicted in the computations. These disagree ments suggest deficiencies in the chemical and/or transport models. On the other hand, evolution of computed and measured peak HCO mole fractions are in reasonable agreement, suggesting that certain components of flame chemis try may indeed be accurately predicted by the present model. We also report computed CH3O response, which exhibits a strong transient driven by change s to internal flame structure, namely temperature profile steepening, induc ed by the flow field. Steady state experimental PLIF CH3O data is reported and compared to numerical results, but experimental transient CH3O data is not available. In general, the present study highlights the importance of v alidation of chemical-transport models of flames in unsteady how environmen ts. (C) 2001 by The Combustion Institute.