Flame Characteristics and NO Emission Behaviors in (CH4+NH3)/air Counterflow Premixed Flames Having Downstream Interaction with Opposed NH3/air Premixed Flames

Abstract

Flame characteristics and NO emission behaviors are studied for (80% CH 4 +20% NH 3 )/air premixed counterflow flames having downstream interactions with NH 3 /air premixed flames, by varying strain rate and equivalence ratio. Extinction strain rates against equivalence ratio (ϕ sec ) in the secondary zone are numerically presented for the equivalence ratios (ϕ pri ) in the primary combustion zone ϕ pri = 0.8 and 1.2 as representative cases. The flame structures are analyzed, and the concept of local equilibrium temperature and loss ratio are introduced to clarify the mechanisms of flame extinction. NO emission indices are presented for a specified ϕ pri = 1.2 (a favorable mixture condition in ammonia-blended fuel) by varying ϕ sec . NO related reaction paths are examined to explain the important paths in NO reduction. The results show that NO reduction is obtained via enhancing the paths of NH → NNH and NH → N 2 , though it should be confirmed by further future works because these cover only such case studies. The present study can mimic a two-stage swirl combustion with having a small separation distance between the primary and secondary combustion zones. Therefore, the present results can be utilized in a two-stage swirl combustion with having a small separation, where the primary and secondary premixed flames experience strong interactions.