Simulation of a CH4/H2 Diffusion Flame using Unsteady and Steady Flamelet Combustion Models

Reduction of environmental pollutants caused by combustion in power plant systems is one of the main challenges for the researchers. To pinpoint the mechanisms of formation and transport of combustion pollutants, it is necessary to have an accurate prediction of temperature field and combustion products. For this reason, simulation of turbulent combustion flows has attracted much attention in recent years. An appropriate combustion model is required for simulation of these flows. Flamelet model is the most favorite combustion model, due to inherent separation of the turbulent flow field and the chemical reactions. Moreover, the consideration of unsteady flamelet in modeling complex physical phenomena such as radiation heat transfer and slow chemical processes (of pollutants) leads to better results than the steady flamelet assumption. The purpose of this study is to investigate the application of steady and unsteady flamelet models in the simulation of turbulent diffusion bluff body flame. Predictions of temprature and mean mixture fraction using steady flamelet model have shown very good agreement with experiment data. NO mass fraction in steady-state simulations using two different chemical mechanisms GRI3.0 and GRI2.11 is over predicted. While NO mass fraction in the unsteady flamelet modeling using mechanism GRI2.11 have shown good agreement with the experimental data. Thus, unsteady effects are important in slow processes such as the formation of NO.