A computational study is performed to investigate the effects of hydrogen addition on the fundamental characteristics of stretched methane/air premixed flame in an opposed flow configuration. The problem is of interest as a potential application to gas turbines and spark-ignition engines, where it has been anticipated that addition of a small amount of hydrogen will extend the lean flammability limit, allowing combustion at leaner conditions to achieve lower NO_x emission. The flame response is first studied under steady conditions with different levels of hydrogen addition. The results show that the extinction strain rate and the lean flammability limit are significantly extended due to the presence of hydrogen in the mixture. On the other hand, the consumption speed and time scale of the flame close to extinction were found to be insensitive to the extent of blending. Further simulations were performed in an unsteady opposed-flow configuration to study the effects of mixture stratification at various time scales. The dependence of the dynamic flammability limits on the mean composition was determined at various frequencies and compared with a pure methane-air flame.
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