Mixture fraction measurements via WMS/ITAC in a laminar diffusion flame

Abstract

A new approach to determine the mixture fraction at all position in a flame, using experimental measurements of as few as single species, is described. This approach combines measurements using diode laser wavelength modulation spectroscopy (WMS) and a method termed iterative temperature with assumed chemistry (ITAC). Combustion models used in ITAC include equilibrium and near-equilibrium chemistry and are based on the understanding of the important flow, fluid transport, and chemical properties of the system. The conserved scalar approach is used to model the flow-chemistry coupling and provides the state relationships to relate the reactants and products to mixture fraction in the case of equilibrium and near-equilibrium chemistry. In this work, the basic WMS/ITAC method is described and validated for a laminar diffusion flame in a Wolfhard-Parker burner. Methane concentration and temperature are measured and compared to published and ITAC results. There is good agreement between the direct measurements and ITAC results. These results agree well with published results, considering the differences in ambient pressure. Effects, including differential diffusion, radiative heat loss, and finite-rate chemistry, on the combustion models are addressed and found to be important for the simple laminar diffusion flame. Extension of WMS/ITAC to more complex combustion systems wich include turbulence and non-equilibrium chemistry are suggested.