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.

Automated summary

Compared to hydrocarbons, ammonia's low reactivity and higher NOx emissions limit its practical application. This study investigates the flame stability, NO emissions, and flame structure of NH3/CH4/air premixed flames in a novel combustor comprising a double swirl burner. The results provide insights into the development of combustion systems using ammonia as a fuel.