FLAMELET STRUCTURE OF RADIATING CH4-AIR FLAMES

The structure of radiating laminar flamelets of CH4-air diffusion flam es is presented. Radiative heat transfer effects are examined by using the optically thin and full radiation models. The predictions are bas ed on the solution of a one-dimensional set of conservation equations with the mixture fraction, f, as the independent variable for differen t fixed values of the scalar dissipation rate, chi. A reduced three-st ep chemical kinetic mechanism is used for the whole range of f (0 less than or equal to f less than or equal to 1.0). The results of the num erical computations yield values of the temperature and main species f or different values of chi until extinction of the flamelet eventually occurs. Both the adiabatic flamelet and nonadiabatic flamelet with ra diative heat loss are studied and their respective flamelet structures are presented. Good agreement is obtained with limited experimental d ata available. Also, the effect of thermal radiation on NO formation i n the flamelet has been investigated. Due to the sensitivity of therma l NO kinetics to temperature, thermal radiation is found to have a pro found effect on thermal NO formation, practically at all ranges of chi except near the extinction point where flamelets are excessively stre tched.