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Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
MUSCLES
Modelling of UnSteady Combustion in Low Emission Systems
G4RD-CT-2002-00644R&T project within the 5th Framework program of the European Union
1 June 2002 to January 2006
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Motivation
Lean burn combustors inherently prone to instabilities; large potential for amplification > rich-burn combustors as heat release very sensitive to equivalence ratio close to lean extinction
Practically, this limits NOx levels attainable as customers will not accept an environmentally friendly engine which is perceived to be less safe.
Need to fundamentally understand unstable combustion in order to design combustors which avoid these phenomena
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Objectives
To investigate the mechanisms by which acoustic coupling can occur in combustors
To devise methods which capture the important mechanisms in a way which can be incorporated in CFD codes
To demonstrate that unsteady combustion phenomena can be predicted in both frequency and amplitude
Where possible to recommend design practices to reduce the impact of such unsteadiness
→ more fundamental understanding of unsteady phenomena
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Project StructureWP1 management and exploitationWP2 Prediction of unsteady reacting flow and validation
• ITS – near blowout (LBO) study• EBI – mixing/reaction effects at LBO• IST – Radiation/vaporisation interaction• Uni Genoa - Modelling and experimental studies of prevaporisor
WP3 Advanced diagnostics in two-phase flow field• ONERA/CORIA/LEMTA develop unsteady 2 phase measurements.• Uni Naples Measurements of fluctuations of kerosene swirled flame
WP4 Analysis of pressure/acoustic waves• Cambridge – measure transfer functions in real combustor• LU – measure injector response, and aerodynamic response, • to a pressure wave.• CORIA/ EM2C - Influence of acoustic waves on spray vaporisation and
combustion • Uni Naples – characterisation of jet in crossflow
Plus industrial implementation and integration of methods (RR/MTU/SNECMA/Turbomeca/Avio)
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Main AchievementsExperimental• Characterisation of behaviour of fuel injector subject to pressure fluctuations• Improved understanding of the design of premixers• Characterisation of jet in crossflow• Effects of radiative heat transfer on droplet evaporation quantifiedMeasurement techniques• Coupling of different laser based techniques to allow simultaneous measurements
of diameter and temperature, droplet temperature and gas vapour concentration and gas temperature and species concentration
• Generation of databases for model validationNumerical• Model capable of capturing lean blow-out• Methodology for the modelling and improvement of premix ducts• DNS database of droplet evaporation for model validation• New model for mixture fraction variance source term due to droplet evaporation
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Highlights - Measurements of effect of pressure oscillations on spray formation
•Particle size unaffected by fluctuations•Large variations in droplet number density•Will lead to large variations in local mixture fraction and hence heat release, thus providing a feed back mechanism
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Main Achievements – Measurements of LPP injector
Liquid fuel displacement within combustion chamber
Liquid fuel release from premixing duct exit lip
Instantaneous axial velocity distribution
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Measurements of flow instabilities in combustor
Frequency (Hz)P
ower
Spe
ctra
lDen
sity
(u'2 /H
z)100 101 102 103 10410-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
N=1600rpmExcited
Frequency (Hz)
Pow
erS
pect
ralD
ensi
ty(u
'2 /Hz)
100 101 102 103 10410-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
N=800rpmExcited
Frequency (Hz)
Pow
erS
pect
ralD
ensi
ty(u
'2 /Hz)
100 101 102 103 10410-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
N=800rpmNon- Excited
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Main Achievements – Characterisation of jet in cross-flow
Averaged image Intensity FluctuationszD
= 2 .27 q 0.44 W eaero−0.012
xD
⎛⎝⎜
⎞⎠⎟
0 .367
Generalized trajectory
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Highlights – simultaneous measurements of droplet temperatureand gas phase vapour concentration
Finj=12 kHzC=3.5
Finj=24 kHz C=2.2
Fluorescence Fluorescence SignalsSignals VapourVapour Phase ConcentrationPhase Concentration
Data Data ProcessingProcessing
LiquidLiquid PhasePhase
VapourVapour PhasePhase
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Highlights - Evaluation of temperature gradients within combusting droplets in linear stream using two colors laser-induced fluorescence
-100 -50 0 50 100
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t= 5.3 ms
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t=6.9 ms
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t= 9.6 ms
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t = 8.6 ms
Droplet temperature evolves in 2 phases• Heating phase → wet bulb temperature• Constant temperature evaporation
Internal measurements show the presence of an internal recirculation, consistent with Hill vortex
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Highlights - Extension of two colors LIF to polydisperse sprays
Thermocouple
Liquid reservoir
Pressurizedair
réservoirFlow heater
Sprayer
z
T injection : 50°CT ambient : 23°C
* amb
inj amb
T TT TT −
−=
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Highlights – Prediction of Lean Blow-out
measured stability limits
Stability Diagram
Flame Wall Breakup (FWB)
Lean Blow Out (LBO)• Lack of a definite stability criterion, deducible from both, experiment and CFD
open problem, actual work at EBI beyond the scope of MUSCLES
Perspectives
• More exact modeling of radiative heat losses
coupling of extended JPDF-reaction-model with a radiation model by means
of the Monte-Carlo-Method within FW6-project: INTELLECT D.M.
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Highlights - Limit-cycle prediction with low-order thermoacoustic model
Experiment80mm enclosure → no instability.350mm enclosure → 350 Hz mode, velocity amplitude 0.74.
Enclosure
pressure tappings
Plenum
Air
Loudspeakers
Air
Flowstraightener
Nonlinear flame transfer function measured for 80mm enclosure byforcing with loudspeakers at a range of amplitudes and frequencies.This is used in low-order model to give linear/nonlinear predictions.
Model results80mm enclosure → stable linear mode at 353 Hz.350mm enclosure → unstable linear mode at 342 Hz,
limit cycle at 357 Hz, velocity amplitude 0.80.
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Highlights - First 3D DNS database of droplet transportDNS« Exact » resolution of the fullycompressible Navier-Stokes equations
analysis of physical phenomenadevelopment of models
Dispersed phase• Lagrangian modeling
• Evolution of the properties of each droplets(position, velocity, size, temperature)
→ validation database & new model for source term in mixture fraction variance due to droplet evaporation
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
Highlights – measurements and predictions of unsteadygaseous and two-phase jet flames
General objective: Evaluate the capability of numerical simulations to capture spray flames/acoustic modulations
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
GAS EM2CModulated flames (200 Hz)
Aeronautics Days 2006 / 19-21 June 2006 / Vienna Austria
ConclusionsImproved understanding of the underlying physics of
unsteady phenomena has been achieved → potential for major improvements in combustor design for instabilities
Important advances in experimental techniques made → improved understanding of droplet evaporation and hence modelling
Improved numerical methods have been developed Transfer of technology to industry has already begun;
further benefits will become manifest as the methodologies become embedded in design processes