Numerical studies on the impact of equivalence ratio oscillations on lean premixed flame characteristics and emissions

In this work, the numerical investigation of laminar and turbulent one-dimensional lean premixed methane-air flames subject to equivalence ratio oscillations is presented. Harmonic perturbations at various frequencies and with various amplitudes are regarded and their influence on CO and NO emissions, heat release fluctuations, and burning velocity is evaluated. The results indicate a strong non-linear behavior of the flame response for high forcing amplitudes attributed partly to the extension into the stoichiometric and rich combustion regime and partly to non-linear effects imposed due to the interaction of burning velocity and equivalence ratio oscillations leading to non-sinusoidal oscillations at the flame front. Furthermore, the turbulent considerations expose decreasing mean burning velocities and heat release rates with increasing amplitudes due to damping of turbulent fluctuations induced by the oscillations