Comparative study on the laminar flame speed enhancement of methane with ethane and ethylene addition

Abstract A systematic analysis of the flame speed enhancement effects of ethane and ethylene addition to methane was performed. Flame speeds of outwardly propagating spherical flames were measured in a high-pressure, cylindrical flame speed vessel using schlieren photography. It was ensured that the measured data were outside the ignition- and chamber-confinement-affected radii. The unstretched, unburnt flame speeds were obtained using nonlinear extrapolation methods from the experimentally determined stretched flame speeds. The AramcoMech 1.3 kinetics mechanism was validated against flame speeds of ethane, ethylene, and acetylene over a wide range of pressures and equivalence ratios. Good agreement between the measured data and those reported in the literature was seen. The model agreed closely with the measurements at fuel-lean conditions, but a slight over prediction was observed for the fuel-rich cases. Flame speeds of 80/20 and 60/40 (by volume) CH 4 /C 2 H x mixtures in air and in air with excess nitrogen were measured over a wide range of fuel concentrations. In all cases, the addition of ethylene increased the flame speed more than did an equivalent addition of ethane. The Arrhenius effect (predominantly kinetic effect) was the principal driver for flame speed enhancement of methane with ethane/ethylene addition. Sensitivity analysis revealed that thermal and diffusive pathways were equally contributing to the flame speed enhancement of CH 4 /C 2 H 6 mixtures, but the latter played a comparatively minor role in the C 2 H 4 -based blends.