High-temperature laminar flame speed measurements in a shock tube

High-temperature methane and propane laminar flame speed measurements were conducted behind reflected shock waves in a shock tube. A high-power Nd:YAG laser was used to spark-ignite the shock-heated gas mixtures and initiate laminar flame propagation. High-speed, OH* endwall imaging was used to record the propagation of the spherically expanding flames in time, and a non-linear stretch correlation was applied and used to determine the unburned, unstretched laminar flame speed. “Low-temperature” (<600 K) flame speed results are presented for stoichiometric methane/air and propane/air mixtures at initial unburned gas conditions of 489–573 K and 391–556 K, respectively, and 1 atm. The low-temperature measurements show close agreement with available literature data and kinetic modeling results, thereby validating the shock-tube laminar flame speed measurement approach. “High-temperature” (>750 K) flame speed results are presented for a propane/21% O₂-47% N₂-32% He mixture (ϕ = 0.8) at initial unburned gas conditions of 764–832 K, 1 atm. The high-temperature measurements fall between kinetic model predictions, but the kinetic model results show significant disagreement, highlighting the need for high-temperature flame speed validation data of this kind. We believe that these results represent the first laminar flame speed measurements conducted in a shock tube, and that the high-temperature results are the highest-temperature, 1-atm flame speed measurements available in the literature.