Propagation of Premixed Flame Kernels in High Speed Channel Flows with Moderate Turbulence

Nathan Grady, Robert Pitz Vanderbilt University Brad Ochs, Tom Slais, David Scarborough, Suresh Menon Georgia Institute of Technology A premixed CH4/air wind tunnel with active turbulence generated with a vane grid design has been implemented to study turbulent combustion in high speed flows. The current experiment focused on stoichiometric kernels in M = 0.1-0.3 mean flows with turbulence from 0.4 m/s to 2.0 m/s (u’/SL = 1 and 5 respectively). Flame kernels were laser ignited using ~10 mJ/pulse from a 532 nm Nd:YAG laser, and allowed to freely propagate downstream. Combined OH/CH2O PLIF diagnostics were used to study the flame growth as a function of downstream distance/propagation time. CH2O images did not indicate any significant local extinction, so the preliminary results shown here only examine the OH PLIF images. Flame surface density was found to decrease with respect to time due to the decaying turbulence in the tunnel. However, flame brush thickness increased resulting in an increase in the consumption rate until the kernel’s expansion waves interacted with the wall. Additionally, instantaneous flame lengths determined from single-shot images were found to increase with turbulence as well.