Measurements of propane–O2–Ar laminar flame speeds at temperatures exceeding 1000 K in a shock tube

Abstract

Laminar flame speed (SL) measurements of stoichiometric propane in an oxygen-argon oxidizer were performed in a shock tube at unburned-gas temperatures of 296–1234 K and near-atmospheric pressures. Non-intrusive laser-induced breakdown is used to ignite expanding flames following the reflected-shock passage. Flame propagation is recorded using schlieren imaging in a recently implemented side-wall imaging flame test section (SWIFT). In a refined approach to account for flame distortion and the slight residual motion of the post-reflected-shock gas, an area-averaged formulation of the linear-curvature model (the AA-LC model) is derived for use extrapolating flame data to zero stretch. Measured SL values extracted using the AA-LC model closely agree with previous experimental measurements performed in a conventional kinetics shock tube (CKST) using much smaller flame kernels, providing evidence of the earlier data having been ignition affected. Below the chemistry-affected limit of 1050 K, experimental SL values fall in the range of values simulated with the detailed AramcoMech 3.0 kinetic mechanism and propane-specific mechanisms from NUIG and San Diego but exhibit a stronger temperature dependence than predicted by the mechanisms. Over the wide temperature range of the present data, the ubiquitous power-law form of empirical fit is shown to be inadequate for capturing the SL temperature dependence; a non-Arrhenius form is shown to perform favorably. The uncertainties of flame speed measurements performed in the SWIFT average 3.0% and 4.4% for experiments performed under static and post-reflected-shock conditions, respectively, a reduction from the 5.8% average uncertainty of CKST experiments. This work represents a significant step forward in the development of experimental capabilities for high-temperature flame speed measurements. The present results illustrate the potential value of the shock-tube flame speed method to provide measurements useful for informing kinetic model tuning and validation at conditions for which experimental data were not previously obtainable.