Further Study on Effects of Hydrogen Addition on Laminar Flame Speeds of Fuel-Air Mixtures

Laminar flame speeds of mixtures of ethane, ethylene, acetylene, and carbon monoxide with small amounts of hydrogen addition at both atmospheric and elevated pressures were experimentally and computationally determined. It was found that the approximate linear correlation identified previously between the laminar flame speeds and an appropriate definition of the amount of hydrogen addition for methane, propane and n-butane at atmospheric pressure also largely applies to ethylene, ethane and acetylene, at both normal and elevated pressures, with the dependence for rich ethane-air mixtures and lean acetylene-air exhibiting minor deviations from linearity. The linear correlation, however, does not hold for carbon monoxide, at all pressures, due to the strong catalytic effect of hydrogen on carbon monoxide oxidation. A mechanistic analysis shows that both the Arrhenius and diffusive contribution to laminar flame speeds are near-linear functions of hydrogen addition, which explains this approximate linear correlation.