Turbulent Premixed Methane-air Flames Research Articles

96/05321 Unsteady strain rate and curvature effects in turbulent premixed methane-air flames

96/05321 Unsteady strain rate and curvature effects in turbulent premixed methane-air flames

Unsteady strain rate and curvature effects in turbulent premixed methane-air flames

Turbulent premixed stoichiometric methane-air flames modeled with reduced kinetics have been studied using the direct numerical simulation (DNS) approach. The simulations include a four-step reduced mechanism for the oxidation of methane and the molecular transport is modeled with Lewis numbers for individual species. The effects of strain rate and curvature on the intermediate radical concentrations and heat release rate are evaluated. The topology of the flame surface is interpreted in terms of its propagation and statistics. The correlation of radical species with strain rate and curvature is found to be strongly dependent upon their individual mass diffusion rates; hence, a global Lewis number representation of all of the species may be inadequate in predicting the heat release rate and evolution of the flame surface. It is found that highly diffusive and fast reactive species, H and H 2, are well correlated with curvature, while less diffusive species, CO, with a slow oxidation rate is more susceptible to unsteady strain rate effects. The global response of the flame is presented in terms of volumetric heat release and fuel consumption rates. The contributions of flame surface wrinkling and flame structure are identified.

Velocity and Scalar Characteristics of Turbulent Premixed Flames Stabilized on Confined Axisymmetric Baffles

Abstract Measurements of velocity, temperature, species concentration and wall pressure arc reported for turbulent premixed methane-air flames stabilized on axisymmetric confined baffles and for the corresponding isothermal flows. A laser-Doppler velocimeter was used to measure the density-weighted longitudinal velocity characteristics, thin bare-wire thermocouples to determine unweighted temperature characteristics and quartz probes transported gas samples to various instruments which measured near density-weighted concentrations of O2, unburnt hydrocarbons, CO2, and CO. The purpose of the experiments was to extend information of local flow properties of axisymmetric bluff-body stabilized premixed flames and to provide a basis for evaluating the performance of current calculation procedures in recirculating combusting flows. The results quantify the influence of forebody shape, area blockage and of equivalence ratio. The velocity results show that combustion increases the length of the recirculation zone...

Stable species concentration of a turbulent premixed methane-air flame

Experimental and predicted values of species concentration in a premixed turbulent methane-air flame are reported. The flow-stabilized flame experiment explained in [1, 2] was investigated by means of gas samples taken by an isokinetic sampling probe. Five different gas analyzers were used to determine the gas composition at several locations within the flame. These measurements for oxygen, carbon dioxide, carbon monoxide, and nitric oxide are compared with calculated results. In the numerical calculation the κ-ϵ model of [3] was used to describe the turbulent flow. A system of 33 reactions [4] was used to calculate the 16 species concentrations. Experimental results and numerical prediction are in good agreement and the shape of the reaction cone of the premixed flame was predicted almost perfectly. The results for the pollutants NO and CO allow a validation of the reaction kinetic processes of small-scale turbulence in combusting systems.