Flamelet structure of radiating CH4-air flames

The structure of radiating laminar flamelets of CH4-air diffusion flames is presented. Radiative heat transfer effects are examined by using the optically thin and full radiation models. The predictions are based on the solution of a one-dimensional set of conservation equations with the mixture fraction, f, as the independent variable for different fixed values of the scalar dissipation rate, χ. A reduced three-step chemical kinetic mechanism is used for the whole range of f (0 ≤ f ≤ 1.0). The results of the numerical computations yield values of the temperature and main species for different values of χ until extinction of the flamelet eventually occurs. Both the adiabatic flamelet and nonadiabatic flamelet with radiative heat loss are studied and their respective flamelet structures are presented. Good agreement is obtained with limited experimental data available. Also, the effect of thermal radiation on NO formation in the flamelet has been investigated. Due to the sensitivity of thermal NO kinetics to temperature, thermal radiation is found to have a profound effect on thermal NO formation, practically at all ranges of χ except near the extinction point where flamelets are excessively stretched.