(682c) Effects of Ammonia Substitution On Stability Limits and Emissions of Premixed Hydrogen/Air Flames

The potential of partial ammonia (NH₃) substitution to improve the safety of hydrogen (H₂) use was evaluated, using premixed NH₃/H₂/air flames at normal temperature and pressure generated on a tube type burner. The effects of NH₃ substitution on the stability limits and nitrogen oxide (NO_x) emissions of premixed H₂/air flames and the effects of inert (nitrogen, N₂) coflows on the NH₃-substituted H₂/air flames were investigated. The lower stability limits due to heat losses are observed for all the present test conditions, while the upper stability limits due to insufficient residence times of injected mixture jet are observed for limited test conditions. Results also show reduction of the stability limits with NH₃ substitution in H₂/air flames, supporting the potential of NH₃ as a carbon-free, clean additive for improving the safety of H₂ use in premixed H₂/air flames. Opposite tendencies of the upper stability limits with and without the coflow are observed since nonpremixed flames near the burner exit cannot be generated with the coflow. Ammonia substitution enhances the NO_x formation in general; however, the NO_x emission index that is defined as the fraction of the mass of the produced NO_x per the mass of the provided NH₃ and H₂ is almost constant with the enhanced ammonia substitution. At fuel-rich conditions, the NO_x emission index is reduced with increasing burner exit velocities of the injected mixtures.