Effect of hydrogen enrichment on the flame response to incompressible forcing
File(s)
Author(s)
Lim, Zhengli
Type
Thesis
Abstract
The principal objective of this work was to investigate the effect of hydrogen-enrichment of conventional methane/air premixed fuel on the resulting flame response to incompressible forcing. This was achieved for a laminar conical flame by numerically solving the G-Equation, and for a turbulent premixed flame using Large Eddy Simulation (LES) combined with the Wall-Adapting Local Eddy Viscosity (WALE) sub-grid scale model and the Partially-Stirred Reactor (PaSR) model for turbulence-chemistry interaction. The flame response was categorised by monitoring the instantaneous
heat release rate (thermal power) in the domain and comparing it against the inlet velocity
fluctuations. This relationship was mapped into corresponding Flame Transfer Functions (FTFs)
which show the associated gain and phase shift between the two signals. FTFs were constructed
for different premixed blends of increasing hydrogen content while constraining the mean thermal power as constant. For the turbulent premixed flame, the LES cases were run on a bluff body stabilised burner geometry at the Norwegian University of Science and Technology (NTNU), where experimental data was available for validation. Across both the laminar and turbulent flames, the key results showed that hydrogen enrichment increases the cut-off frequency associated with the
drop-off in gain, hence increasing the bandwidth over which the gain remains high, and increasing the propensity of the system toward thermoacoustic instability. Meanwhile, the magnitude of the phase lag decreased, corresponding to the lower convection time associated with the shorter hydrogen flames. The most significant factor driving the FTF shift was the base laminar flame speed, and to lesser extent, the preferential diffusion of hydrogen within the fuel, which became more important
to model as the hydrogen content of the fuel became relatively high.
heat release rate (thermal power) in the domain and comparing it against the inlet velocity
fluctuations. This relationship was mapped into corresponding Flame Transfer Functions (FTFs)
which show the associated gain and phase shift between the two signals. FTFs were constructed
for different premixed blends of increasing hydrogen content while constraining the mean thermal power as constant. For the turbulent premixed flame, the LES cases were run on a bluff body stabilised burner geometry at the Norwegian University of Science and Technology (NTNU), where experimental data was available for validation. Across both the laminar and turbulent flames, the key results showed that hydrogen enrichment increases the cut-off frequency associated with the
drop-off in gain, hence increasing the bandwidth over which the gain remains high, and increasing the propensity of the system toward thermoacoustic instability. Meanwhile, the magnitude of the phase lag decreased, corresponding to the lower convection time associated with the shorter hydrogen flames. The most significant factor driving the FTF shift was the base laminar flame speed, and to lesser extent, the preferential diffusion of hydrogen within the fuel, which became more important
to model as the hydrogen content of the fuel became relatively high.
Version
Open Access
Date Issued
2024-05
Date Awarded
2024-11
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Morgans, Aimee
Sponsor
Beit Trust
UK Research and Innovation
Engineering and Physical Sciences Research Council
Grant Number
EP/R029326/1
EP/X035484/1
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)