Session: 04-30 Emissions I

Paper Number: 153904

Investigation of Impact of Steam Addition on Combustion Behavior and Pollutant Emissions in an RQL Combustor at High Pressure 

This paper reports on the demonstration of reliable operation of an aero-engine combustor with different air swirlers at high pressure under addition of water steam up to 20% related to the combustion air mass flow.

Reduction of pollutant emissions from aircraft operation remains a challenge for future aero-engine development. Steam or water injection has proven to reduce NOx formation due to reduction of combustion temperatures for stationary gas turbines which are typically operated at very lean conditions. In addition, water injection can serve to increase the gas turbine efficiency due to the induced higher mass flows [1]. However, the impact of water injection on soot formation and general combustor behavior at engine relevant conditions has rarely been studied in RQL combustors. Crayford et al. have demonstrated the potential to reduce soot emissions under such conditions [2]. A more detailed study involving laser-based diagnostics is yet missing.

In the presented work we used two air swirlers based on the design presented by Cohen and Rosfjord in reference [3] mounted into an optically accessible test carrier at the DLR Stuttgart high pressure combustor rig HBK-S. Steam at varying flow rates was fed into the heated combustion air, and the combustion was quenched by injection of additional air after the primary combustion zone.

The combustion behavior was characterized by application of OH* chemiluminescence for flame shape, particle image velocimetry (PIV) at non-reacting conditions for the flow field, Mie scattering for spray distribution and laser-induced incandescence (LII) for soot distribution. Exhaust gas emission measurements yielded information on gaseous species such as CO and NOx.

The combustor could successfully be operated with steam addition at pressures of 8, 10 and 14 bar for variations of the equivalence ratio of the primary combustion, not significantly different from dry operation; also, the global equivalence ratio could be modified by addition of various levels of secondary or quench air without detrimental impact of the steam added to the primary combustion air. Visual impression via video camera observation of the flame signature as well as detailed LII measurements revealed a prominent reduction of soot presence inside the combustor upon steam injection. At the same time, NOx emissions were reduced by a factor of up to 6. Stability and thermoacoustics of the burner were not significantly different with the addition of steam compared to without. In general, the results are promising for the studied configuration concerning stability of combustion and pollutant formation and emissions. Further studies are planned for significantly higher secondary air flow rates at realistic temperatures, which requires major modifications of the test setup.

References

[1] O. Schmitz, H. Klingels, P. Kufner, Aero engine concepts beyond 2030: Part 1—the steam injecting and re-covering aero engine, Journal of Engineering for Gas Turbines and Power 143 (2021) 021001.

[2] A. Crayford, P. Bowen, E. Durand, D. Pugh, Y. Sevcenco, M. Johnson, Influence of humidity and fuel hydrogen content on ultrafine non-volatile particulate matter formation in RQL gas turbine technology, Proc. ASME Turbo Expo 2020, GT2020-15168.

[3] J.M. Cohen, T.J. Rosfjord, Influences on the sprays formed by high-shear fuel nozzle/swirler assemblies, Journal of Propulsion and Power 9 (1993) 16-27.

Presenting Author: Joshua A.T. Gray German Aerospace Center (DLR)

Presenting Author Biography: Joshua Gray has been an experimental lead at the German Aerospace Center DLR since January 2024. Previously, he was a postdoc at King Abdullah University of Science and Technology and subsequently at the Air Force Research Laboratory and Innovative Scientific Solutions, Inc., where his research focus was on detonations and nanosecond repetitively pulsed plasma discharges. Recently, his work has focused on high-pressure combustion for stationary and aviation gas turbine applications.

Authors:

Joshua A.T. Gray German Aerospace Center (DLR)
Oliver Lammel German Aerospace Center (DLR)
Holger Ax German Aerospace Center (DLR)
Rainer Lückerath German Aerospace Center (DLR)
Klaus Peter Geigle German Aerospace Center (DLR)
Gregory Boardman Pratt and Whitney Engineering
Wookyung Kim RTX Technology Research Center, Combustion & Propulsion Technology
Matthias Haeringer MTU Aero Engines AG