A Computational Study of Equivalence Ratio Effects in Turbulent, Premixed Methane-Air Flames John B. Bell, Marcus S. Day, Joseph F. Grcar, and Michael J. Lijewski Center for Computational Science and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Abstract In this paper we present numerical simulations of two-dimensional turbulent methane combustion using GRI- Mech 3.0 at equivalence ratios φ =0.55 and φ =1.00. The simulations are performed using a low Mach number adaptive mesh refinement algorithm coupled to an automatic feedback control algorithm that stabilizes the flame on the computational grid. We present probability density functions for curvature, strain and a local flame speed based on fuel-consumption. We also present joint probability density functions showing correlations of the local flame speed with curvature and showing that the local flame speed does not correlate with the tangential strain rate evaluated in the cool part of the flame. The simulation data is indicative of a change in Markstein number as we change equivalence ratio with the lean flame being thermo-diffusively unstable. We introduce a pathline diagnostic that allows us to computationally follow parcels of fluid through the flame and quantify the associated reaction and diffusive transport processes. Using this diagnostic, we examine the differences in the chemical and transport properties of the two flames that lead to the shift in Markstein number. Keywords: turbulent premixed combustion, low Mach number flow, adaptive mesh refinement