Stability and characteristics of NH3/CH4/air flames in a combustor fired by a double swirl stabilized burner

Compared to hydrocarbons, ammonia's low reactivity and higher NO x emissions limit its practical application. Consequently, its implementation in combustion systems requires a different combustor geometry, by adapting existing systems or developing new ones. This study investigates the flame stability, NO emissions, and flame structure of NH 3 /CH 4 /air premixed flames in a novel combustor comprising a double swirl burner. A lean premixed CH 4 /air mixture of equivalence ratio, (I:lout , was supplied to the outer swirl, while a NH 3 /CH 4 /Air mixture fed the inner swirl. The molar fraction of NH 3 in the inner fuel blend, x NH3 , was varied from 0 (pure CH 4 ) to 1 (pure NH 3 ) over far-lean to far-rich inner stream equivalence ratio, (I:lin . This new burner's stability map was established in terms of (I:lin versus x NH3 for different (I:lout . Then, NO emissions were measured versus (I:lin for various x NH3 and (I:lout . Finally, based on the NO emissions, eight flames were downselected for in-flame measurements, which included temperature and OH-PLIF. The stability measurements revealed that increasing x NH3 modifies the stability map by increasing the lean blowout limits and narrowing the flashback region. At (I:lout & GE; 0.6, a stable flame was achieved for a pure inner NH 3 /air mixture. Low NO emissions were achieved in this burner configuration at x NH3 = 1 by either enriching or far-leaning (I:lin . Enriching (I:lin led to a steep decrease in NO concentrations. However, to achieve low NO concentrations, precise control of (I:lout was needed. At (I:lin = 1.4, 220 ppm NO at (I:lout = 0.7 versus 690 at (I:lout = 0.6 was measured. Moreover, substantially enriching (I:lin > 1.2 led to a slight decrease in measured NO. Generally, the OH-PLIF images revealed a conical OH-layer at the burner exit. Certain flame conditions created OH-pockets inside the conical structure or formed a V-shaped OH-layer far downstream. This change in flame structure was found to impact NO emissions strongly. & COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.