A study of propagation of spherically expanding and counterflow laminar flames using direct measurements and numerical simulations

Abstract

Spherically expanding and counterflow flame configurations are used extensively to determine laminar flame speeds. Significant advances have been made over the years with both the theoretical and experimental aspects of these standard experiments. However, discrepancies still persist in reported laminar flame speed data raising the question of accuracy and consistency. Laminar flame speed being a derived and not a directly measured physical quantity, leaves room for the way in which experimental measurements are interpreted, thus introducing additional uncertainties. In the present investigation, a combined experimental and modeling study was carried out for first time in both configurations. Ethylene and n-heptane flames were considered and the flow velocities were measured using particle image velocimetry in both spherically expanding and counterflow flames. The accuracy and consistency of the results were assessed by comparing directly measured and directly computed physical properties. It was shown that the directly measured data in both configurations are consistent based on comparisons against the results of direct numerical simulations. It was shown also, that notable uncertainties are introduced when extrapolations and density corrections are implemented in spherically expanding flames.