Large eddy simulation of the dynamics of lean premixed flames using global reaction mechanisms calibrated for CH4–H2 fuel blends

Abstract

The effects of hydrogen addition on the flame dynamics of a bluff-body stabilized methane–hydrogen turbulent flame are studied with large eddy simulation (LES). The LES is carried out with the thickened flame model and global kinetic mechanisms calibrated for the methane–hydrogen mixtures. Conjugate heat transfer is included in the LES to consider a proper wall temperature while the flame shape changes with hydrogen addition. A data-based calibration of the global mechanisms is done with a methodology based on reproducing the net species production rates computed with a detailed kinetic mechanism. An improvement in this methodology is proposed to increase its accuracy and reliability. The calibrated mechanisms accurately describe the variation of the laminar flame speed and the thermal flame thickness with hydrogen addition and equivalence ratio in a freely propagating premixed flame. The variations of the consumption speed and the thermal flame thickness with the strain rate in a symmetric counterflow premixed flame are also well predicted. The numerical simulations reproduce the transition from V- to M-shape flame induced by hydrogen addition, and the axial distribution of the heat release agrees with the experimental measurements of OH chemiluminescence. The unit impulse response and the flame transfer function are computed from the LES data using system identification (SysID). The flame transfer functions show a remarkable agreement with the experimental data, demonstrating that the LES-SysID approach using properly calibrated global mechanisms can predict the response of turbulent methane–hydrogen flames to velocity fluctuations. A comparison of the unit impulse response for the various hydrogen additions is presented, and the effect of hydrogen in the flow–flame interaction of the burner evaluated is discussed.