Session: 04-07 Ammonia Combustion I

Paper Number: 153023

Towards the Development of a RRQL System Part 1: Swirl Pattern Effect on Exhaust Emissions and Chemiluminescence Distribution for NH3-Air Premixed Swirl Flames 

Ammonia (NH₃) is a carbon-free energy source and hydrogen carrier, but its fuel-bound nitrogen can lead to significant nitrogen oxides (NO_x) emissions. Staged combustion strategies, such as Rich-Quench-Lean (RQL), have achieved low NO_x emissions with other fuel types. However, if used with ammonia, improper design may result in high NO_x levels due to the fuel-bound nitrogen.  A Rich-Relaxation-Quench-Lean (RRQL) configuration can minimize NO_x emissions in Ammonia combustors. This study focuses on how different swirl geometries affect exhaust emissions and flame morphology in rich, premixed NH₃-air flames, to be used in the design of a rich relaxation head end of an RRQL combustor. Experiments were conducted using a modular swirl burner, and five swirlers were tested, featuring geometric swirl numbers of S_g = 0.7 and 1.1, with varying numbers of vanes (8, 12, and 16) and vane shapes (curved or straight). The paper presents measured NO_x, N₂O, and NH₃ emissions, and recorded natural flame luminosity and NH₂^* and OH^* chemiluminescence images. The equivalence ratio (ϕ) varied from 1.05 to 1.18 to identify an optimal low NO_x and NH₃ balance for each swirler. S_g1.1-C8 swirler with a swirl number of S_g = 1.1 and eight curved vanes achieved its optimal NO_x-NH₃ performance at a leaner ϕ, exhibiting high N₂O concentrations, possibly due to heat losses from flame interaction with the wall. Increasing the number of vanes to 16 with S_g1.1-S16 shifted the low NO_x-NH₃ sweet spot toward a richer ϕ. Chemiluminescence images revealed that the Sg1.1-C8 swirler displayed strong flame-to-wall interactions, with significantly higher NH₂^* intensity near the wall compared to Sg1.1-S16, which had the highest OH^* intensity regardless of swirl pattern. In addition, Abel-inverted images showed that maximum isocontour of NH₂^* was located on the outer edge of the flame, while OH^* was more concentrated on the inner side, regardless the swirler design. Axial and radial emissions measurements in the post-flame Relaxation stage of the combustor for both Sg1.1-C8 and Sg1.1-S16 at ϕ = 1.13 and 1.15 indicated that NO_x concentrations decreased with increased sampling location, i.e. residence time. Although Sg1.1-C8 produced slightly lower NO_x values at 3” downstream from the flame brush compared to Sg1.1-S16, the latter resulted in lower N₂O and much lower NH₃ emissions. Consequently, among the tested swirler designs, Sg1.1-S16 is preferred for a RRQL configuration, as it generates a compact flame with a richer sweet spot, potentially enhancing H₂ production during the Relaxation phase without increasing overall primary stage NO_x emissions, thereby improving system efficiency.

Presenting Author: Renee Cole Georgia Institute of Technology

Presenting Author Biography: Renee Cole is a PhD student from Georgia Institute of Technology advised by Dr. Tim Lieuwen in the Ben T. Zinn Combustion Lab.

Authors:

Renee Cole Georgia Institute of Technology
Cristian D. Avila Jimenez Georgia Institute of Technology
David R. Noble EPRI
Robert Steele EPRI
David Wu Georgia Institute of Technology
Benjamin L. Emerson Georgia Institute of Technology
Timothy C. Lieuwen Georgia Institute of Technology