Session: 04-21: Combustion Dynamics - Flame Transfer Functions

Paper Number: 83298

83298 - Flame Transfer Functions for Turbulent, Premixed, Ammonia-Hydrogen-Nitrogen-Air Flames 

Ammonia is a promising energy carrier but a challenging fuel to use in gas turbines, due to its low flame speed, limited flammability range, and the production of NOx from fuel bound nitrogen. Previous experimental and theoretical work has demonstrated that partially dissociated ammonia (ammonia-hydrogen-nitrogen mixtures) can match many of the laminar flame properties of methane flames such as the laminar flame speed and adiabatic flame temperature. Among the remaining concerns pertaining to the use of ammonia-hydrogen-nitrogen blends in gas turbines is their thermoacoustic behavior. This paper presents the first measurements of flame transfer functions (FTFs) for turbulent, premixed, ammonia-hydrogen-nitrogen-air flames and compares them to methane-air flames that have a similar laminar flame speed and adiabatic flame temperature. FTFs for ammonia-hydrogen-nitrogen blends were found to have a lower gain than methane at low  frequencies. However, the cut-off frequency was found to be greater than that of methane flames, due to a shorter flame length. The results suggest that ammonia-hydrogen-nitrogen blends may excite different thermoacoustic modes in gas turbines. Furthermore, the linearity of the flame response up to high forcing amplitudes suggests that particularly high-amplitude limit cycles may occur. For both methane flames and ammonia/hydrogen/nitrogen flames the confinement diameter was found to have a strong influence on peak gain values and the FTF phase. However the cut-off frequency is relatively unaffected, except in the case of extreme confinement. Chemiluminescence resolved along the longitudinal direction show a suppression of fluctuations when the flame first interacts with the wall followed by a subsequent recovery, but with a significant phase shift. Nevertheless, simple Strouhal number scalings based on the flame length and reactant bulk velocity at the dump plane result in a reasonable collapse of the cut-off frequency and phase curves.

Presenting Author: Samuel Wiseman NTNU

Presenting Author Biography: Samuel Wiseman is currently a postdoctoral research fellow in the Department of Energy and Process Engineering at the Norwegian University of Science and Technology. His research areas include combustion dynamics, sound generation in reacting flows, flame stabilization, combustion emissions, and the combustion properties of low carbon fuels.

Authors:

Samuel Wiseman NTNU
James Dawson Norwegian University of Science and Technology
Andrea Gruber SINTEF