LAMINAR FLAME SPEEDS OF ETHANOL, n-HEPTANE, ISO- OCTANE AIR MIXTURES

ABSTRACT – One of the most important properties of premixed flames is burning velocity. Laminar burning velocities play essential roles in determining several important aspects of the combustion process in spark ignition engines; among these are the ignition delay, the thickness of the wall quench layers, and the minimum ignition energy. It is found that a detailed knowledge of laminar premixed flames will provide insights into such properties as heat release rate, flammability limits, propagation rates, quenching and emissions characteristics. It is also common to use measured burning velocities to validate chemical kinetic schemes. The production of accurate measurements on laminar premixed flames therefore plays a key role in the process of understanding a large range of flames. Although the majority of fuel is probably burnt in turbulent combustion, data on laminar burning velocities are still needed as input to many turbulent combustion models. Also, in internal combustion engines the initial combustion is laminar, so again there is a need for the laminar burning velocity. In this study, laminar burning velocities of ethanol, iso-octane and n-heptane-air mixtures were determined experimentally over a wide range of equivalence ratio at atmospheric pressure, employing spherically expanding flames. Using linear extrapolations, the effects of stretch was minimized by extrapolating the reference flame speed to vanishing stretch. The laminar burning velocities of iso-octane were found to be lower than those of ethanol and n-heptane throughout the range of experimental equivalence ratios. The measured burning velocities were also compared with those of other researchers, suggesting there were good agreement between present data and those of other researchers. In addition, the effects of ethanol addition to n-heptane and iso-octane-air flames were investigated, suggesting that ethanol addition was found to make n-heptane and iso-octane-air flames stable for fuel rich region