Hydrogen enrichment for improved lean flame stability

The stability characteristics of a premixed, swirl-stabilized flame were studied to determine the effects of hydrogen addition on flame stability under fuel-lean conditions. The burner configuration consisted of a centerbody with an annular, premixed methane/air jet introduced through five, 45° swirl vanes. Flame stability was studied over a range of operating conditions. Under fuel-rich conditions the flame was lifted from the burner surface due to the mixing with entrained ambient air that was needed to form a flammable mixture. As the fuel/air mixture ratio was decreased toward stoichiometric, the resulting increase in flame speed allowed the flame to propagate upstream through the low-velocity wake region and attach to the centerbody face. The maximum blowout velocity occurred at stoichiometric conditions, and decreased as the mixture became leaner. OH PLIF measurements were used to study the behavior of OH mole fraction as the lean stability limit was approached. Near the lean stability limit the overall OH mole fraction decreased, the flame decreased in size and the high OH region took on a more shredded appearance. The addition of up to 20% hydrogen to the methane/air mixture resulted in a significant increase in the OH concentration and extended the lean stability limits of the burner.