Advanced Instability Methods (AIM) Network
Experiments workshop, 2nd November 2010,
University College London
Low Emission GT Combustors
R. Balachandran
r.balachandran@ucl.ac.uk
Department of Mechanical Engineering, University College London,
Torrington Place, London, United Kingdom, WC1E 7JE
Ultra Low Emission Engines
• Renewables gaining importance: Fossil fuels will
continue to be the main stay.
• Options to achieve low emissions:
– Lean Burn technology
– Carbon Capture (Pre-Combustion and PostCombustion)
– Efficiency improvements through novel
component/system designs
– Future fuels: Renewables, fuel flexibility, synthetic
future fuels
Low emission GT engines
• Ultra Low emission in aero/industrial GT combustors:
– Lean premixed combustion: common approach
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Low flame temperature
High fuel efficiency
Susceptible to combustion oscillations, resulting in complete plant meltdown
Flame blowout
• Low emission option for land based power generation:
– Integrated Gasification Combined Cycle (IGCC)
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Coal, Biomass utilisation (reducing Natural gas dependence)
Fuel flexibility
CCS capability
Flame behaviour changes due to change in fuel properties (Hydrogen enriched
fuels) resulting in unsteady combustion
• Initial and operational cost
Overview of GT combustion research @UCL
• Turbulent combustion
– Unsteady Combustion
• Fundamental flame behaviour in the presence and absence of flow
perturbations
• Hydrogen enrichment for combustion dynamics control
• Fuel flexible combustor
– Sustainable fuel (Biogas, Syngas, H2 )
– Ignition, Flame stabilisation and stability
– Emission characteristics
• Development of sensors and laser diagnostics techniques
for flow and flame
– Multi-scalar imaging to investigate local heat release
– Fuel LIF, IR and chemiluminescence sensors to study mixing field
– 3D PIV, Highspeed imaging for flow field characterisation
Combustion Oscillations in GT
combustors: Feedback Mechanism
mreactants
Flame area, Heat
of reaction,
Flame speed
Q’
p’
Rayleigh
criteria
Combustion
Chamber
u’, ’
Fuel properties

Amplification or attenuation of the pressure oscillation by heat addition would
occur if the periodic heat release occurs in or out of phase with the pressure
oscillation, respectively.
T
T
  p ( x, t ) Q ( x, t ) dt dV     L ( x, t ) dt dV
V
V
where,
0
0
p - pressure
Q - heat addition
x - location
t - time
T - period of the oscillation
V - volume of interest
Li - i-th wave energy dissipation process
i
i
Putnam & Dennis
(1953)
Model GT Combustor @UCL
80 mm
Based on RB12 (Rolls-Royce combustor)
Diameter of the Air passage =35 mm
Bluff body diameter = 25 mm
Diameter of Enclosure =70 mm
• Choked fuel injection
through central pipe to
achieve partial
premixing
• Acoustic velocity
determined using the twomicrophone technique and
calibrated against hotwire
measurements under cold
flow conditions
Key features:
High Reynolds number,
High Swirl (Vane and
Tangential flow induced)
Fuel flexibility,
Combustion modes:
premixed, partially-premixed, nonpremixed
• Fuel sensitivity to flow
perturbations
Multi-scalar Imaging for combustion
• Schematic and picture of the
laser imaging facility used for
PLIF measurements
• For sequential OH PLIF, both
the laser were tuned near 283
nm
• The double exposure option of
ICCD was used to capture
OH* chemiluminescence
Heat-release Imaging: Premixed combustion
OH
OH
CH2O
CH2O
HR
(a)
OH
CH2O
HR
(b)
HR
(c)
• Spatially and temporally resolved heat release images
• Investigation of flame vortex interaction in a fully
premixed flame applicable to Lean Prevaporised
Premixed GT combustors
(d)
Phase averaged PLIF imaging
• Capture periodic variation in flame behaviour
– Appearance of vortex decreases the global heat release estimate from this
technique suggesting flame annihilation
• The flame behaviour mimics self-excitation in practical combustors
Non-linear Flame response
• Nonlinear response to inlet perturbations
Sequential OH PLIF capability
t=0
t = 1 ms
t = 2 ms
t = 3 ms
•Four laser pulses illuminated premixed flame of  =0.55 separated by 1 ms; resulting time
resolved OH PLIF realisations shows flame surface annihilation; U =9.9 m/s, A~0.5
•These results enable better flame dynamics modelling for combustion instability prediction
Future Low Emission Micro-engines
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Increased interest in milli-to-watt range power generation due to increased
demand for MEMS (Micro Electro Mechanical Systems).
The potential of exploiting the high specific energy of hydrocarbon fuels,
typically 50 - 100 times that of top range batteries currently in the market, [1],
by means of micro combustion.
Versatility of combustion based, integrated systems in providing heat
generation and power (Combined Heat and Power) and fuels (hydrogen from
reforming)
Potential application
•
Personal power pack for rescue workers in disaster zone where use of battery is
limited
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Military application, particularly for soldiers
•
Laptops
Issues hindering development
•
high surface area to volume ratio characteristic of micro-combustors unfavourably
enhances heat loss to the combustor walls, increasing near-wall destruction of
radical species
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Lack of efficient power generation at this scale
Micro combustor development at UCL
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First operational micro-combustion in UK
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Dimension of the combustion channel: 1 mm x 3 mm x 27 mm.
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Cold start capability, no preheating required
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Wide operating range and good optical access
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Further research underway to develop integrated combustion systems for heat and
power generation
SProp [m/s]
3
L1
L2
2
L3
1
0
0.7
0.9
1.1
1.3
Equivalence Ratio, 
Flame speed measured
between different
locations
1.5
My Interests
• Non-linear/non-normal growth of instabilities
• Flame – flow interactions >> extinction/blowout
• Dynamics of flames with heat loss
Sponsors
Acknowledgements
• Prof Ladommatos of UCL, Prof. E.
Mastorakos, Prof. A. P. Dowling, Dr N.
Swaminathan, Dr. R. S. Cant, Dr. B.O.
Ayoola, Dr G. Hartung & Dr. C.F. Kaminski,
University of Cambridge.
Thank you!