Numerical Investigation of the Effects of Chemical Species and Chemical Kinetic Mechanisms on Laminar Premixed Flame-Acoustic Wave Interactions

Numerical simulation of interactions between acoustic waves and flames is of utmost importance in thermo-acoustic instability research. In this study, interactions between a one-dimensional Methane-Air laminar premixed flame and acoustic waves with a frequency of 50 to 50000 Hz are simulated by simultaneously solving the equations for energy conservation, chemical species transport, state and continuity in one-dimensional space. By assuming that the flame thickness is smaller than the acoustic wavelength, the spatial pressure fluctuations can be neglected and the flame experiences only a time-varying acoustic pressure. The GRI mechanisms, as well as their reduced mechanisms, are considered to obtain results for steady flames without acoustic waves, and the interaction of unsteady flames with acoustic waves. Results show that the total heat-release-rate fluctuations for the flame is affected by increasing the frequency of the acoustic wave. An increase in frequency first increases the total heat released, and then decreases it. The obtained results are in good agreement with those of other researchers. Furthermore, at the presence of acoustic waves, various chemical species can affect the total heat-release-rate fluctuations. With Rayleigh's instability criterion, it can be shown that H2O, CO2 and O2 are the main species to the fluctuations of the total heat release rate and lead to flame instability. Results show that heat-release-rate of H2O specie is the most important on the total heat-release-rate. Therefore, for the flame-acoustic waves interaction problem, the best mechanism is the one that could predict the concentration of H2O more precisely.