1 experimental investigation on sooty flames at elavated pressures school of mechanical, aerospace...
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EXPERIMENTAL INVESTIGATION ON SOOTY FLAMES
AT ELAVATED PRESSURES
School of Mechanical, Aerospace and Civil Engineering
The University of Manchester
A first year PhD progress reportpresented by:
Hamidreza Gohari Darabkhani
Supervisor :Dr. Yang Zhang
20.09.2007
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Introduction
• Increasing efficiency and decreasing size in modern turbines and internal combustion engines requires higher operating pressures.
• At high pressure flames, the carbon (soot) particles are so dense that the flame is opaque to electromagnetic waves in the visible or near infrared.
• In the optical diagnostic methods, measuring the exact amount of combustion products is difficult but temperature and concentration of soot can be measured with high accuracy.
• The effect of pressure on thermo physical properties of laminar coflow diffusion flames (LCDF) was studied by optical diagnostic methods (Two-Colour Pyrometry) over the pressure range of 1 to 18 bar in ethylene-air and methane-air and 1 to 7 bar in propane–air LCDF.
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Objectives of this Research 1. Investigation on physical sooty flame’s properties at elevated pressures (The
changes in the height, diameter and shape of the flames…).
2. Applying emission imaging techniques (two-colour pyrometry) by using just one
CCD digital camera and two narrow bands filters (CH and C2).
3. Applying the IR infratherm pyrometry in order to measure soot temperature
profiles in high pressure sooty flames for comparison with two-colour results.
4. Thermo acoustic or thermo diffusivity flame’s instability observation due to
elevated pressures.
5. Chemilominescent emission measurement by using optical fibre system.
6. Terahertz time domain spectroscopy (THz-TDS) to study the combustion
reactions in regimes inaccessible to optical diagnostics (if equipments will be
ready).
7. Cross-correlating the obtained data in order to gain unique physical insights into
the flame’s properties under high pressure and sooty conditions.
4
Burner TypesThree types of laminar diffusion flame
burners are commonly used by soot researchers:
1. Coflow : Axisymmetric 2-D flames with demonstrated stability at high pressures.
2. Counterflow (opposed jet); 1-D flames with instability problems at elevated pressures flames and critical location of the stagnation point.
3. Wolfhard–Parker; 1 and 2-D Flames with instability problems at elevated pressures
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Measurement Method
Passive optical diagnostics (using light or laser sources)
Active optical diagnostics (uses natural flame
emission)
OPTICAL
Interferometry Holography Tomography Schelieren Shadowgraphy Rayleigh/Mie Scattering Laser Doppler Anemometry
(LDA) Particle Image Velocimetry
(PIV) Laser Induced Grating
Flame Photography High Speed
Photography Stereo Digital Imaging
SPECTROSCOPIC
Absorption Spectroscopy Laser Induced Fluorescence
(LIF) Coherent Anti Raman
Spectroscopy Raman Spectroscopy THz-time Domain
Spectroscopy
Flame Emission Spectroscopy
Narrow Band Photography
Summary of non-intrusive optical based combustion diagnostic techniques
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Refs.Pressure
range [bar]
Fuel and fuel flow rate [ml/min]
Diagnostic Method
Pressure exponent n in [soot]∝Pn
Fraction of fuel's carbon converted to
soot
Path integrated maximum soot
Local maximum soot (location)
Macfarlane el al. (1964) 1-20
C5 and C6
hydrocarbons (premixed)
Glass fibre filter paper
2.53 - -
McArragher and Tanon (1972)
Elevated Pressures
Hydrocarbon Fuels
(Diffusion and Premixed)
Review paper 13 - -
Flower and Bowman (1983) 1-25 Ethylene LOSA 1.52 1.52 0.5-1.0
Flower and Bowman (1986)
1-10Ethylene,
LDF, 91,129.5, 211
Line of sight integrated
1.2±0.1 - -
Lee and Na (2000)
1-4 Ethylene, 163
Two-colour method and
thermocouple 1.26
2(20 mm above)
(the burner)-
McCrain and Roberts (2005)
1-16 Ethylene, 54LOSA & LII
1.2 1.7 -
1-25 Methane, 92 1 1.2 -
Thomson et al.(2005)
5-20Methane, 46
SSE and LOSA
1.3 2 1
20-40 0.9 1.2 0.1
Fengshan Liu et al. (2006)
5-40 Methane, 46SSE, LOSA
and numerical1.3 2 1
Bento et al.(2006)
1-2Propane, 15
SSE and LOSA
3.4(requires further experiments for confirmation)
-3.3(requires
further experiments for confirmation)
2-7.3 1.4 1.8 1.1
High Pressure Soot Diagnostics (pressure dependence of soot)
7
Schematic diagram of apparatus used for Line of Sight measuring
the temperature of soot by Flower (1989)
8
Optical Layout of Spectral Soot Emission (SSE) Diagnostic
Optical Layout of the Line-of-Sight Attenuation (LOSA) diagnostic
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Two-Colour Soot Temperature Measurement Theory
1exp. 25
1
T
C
CI b
1exp. 25
1
T
C
CII b
)....36exp(1 LfF
v
22222 .42
.
knkn
knF
bII 111 bII 222
2
2
1
1
21
2
252
11
1
251 1exp
1
1exp
1
FF
IC
T
C
IC
T
C
2
2
11
2
25
1
1
1exp1
1ln)(..36
.
F
v IC
T
C
FLf
1
2
5
1
221
122 )(
I
ILn
CT
(refractive index ) m=n-ik n,k from Lee and
Tien(1981) report
10
Test Setup Schematic
CCD Camera
Narrow Band Filter
Infratherm Pyrometer
Sooty Flame
Optical Windows
High Pressure Chamber
11
Experiment Arrangement
Olympus E-100RS Visible Windows Infrathem Pyrometer
Filters (C2 or CH)
High Pressure Chamber
12
CH filter (430 ± 5 nm) C2 filter (516 ± 2.5 nm)
Two-colour IR Pyrometer
Narrow band filters and IR Pyrometer
13
Camera calibration setup with tungsten ribbon lamp
Tungsten Lamp
Digital Camera
Digital Voltmeter
Rheostat
12V Battery
CH and C2 Filters
14
Test Results
Ethylene (100 ml/min)-Air (20 l/min) coflow diffusion flame
Ethylene(100 ml/min)-Air(20 l/min) Diffusion Flame(Flame Heights at Different Pressures)
0
5
10
15
20
25
0 2 4 6 8 10 12 14 16 18 20
Chamber Pressure (bar)
Fla
me
Hei
gh
t (m
m)
1 bar 2 bar 4bar 6 bar 8 bar 10 bar 14 bar 16 bar 18 bar
15
Flame Heights in Diffrent Pressures for Methan(120 ml/min)-Air(20 l/min) DF
0
5
10
15
20
25
30
0 2 4 6 8 10 12 14 16 18 20
Pressures (Bar)
Fla
mes
Hei
gh
t (m
m)
Propane (60 ml/min)-Air (20 l/min) DF
0
5
10
15
20
25
30
35
40
0 1 2 3 4 5 6 7 8
Pressures (bar)
Fla
me
, blu
e p
art
an
d s
oo
t lin
e
he
igh
ts in
fla
me
(m
m)
Blue Flame
Flame Heights
Soot Line
Flame Heights in Methane and Propane Flames
16
The cross-sectional area of the Propane flame
Propane (60 ml/min)-Air (20 l/min)
0
5
10
15
20
25
30
35
0 1 2 3 4 5 6 7 8
Chamber Pressures(bar)
Cro
ss
-Se
cti
on
al A
rea
of
Fla
me
(m
m^
2)
H=1 mm
H=5 mm
H=10 mm
H=15 mm
H=20 mm
H=25 mm
As the pressure was increased, axial flame diameters decreased, giving an overall stretched appearance to the flame.
In This Study: The cross-sectional area of the flame (Acs) inverse dependence on pressure to the power of 0.6±0.1
Glassman (1998): Acs inverse dependence on pressure to the power of 0.5
Thomson et al. (2006), Bento et al.(2006) and McCrain and Roberts(2005): Acs inverse dependence on pressure(1/P).
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Flame Visualisation:
1. The height of the flames increases gradually as pressure increases and then
decrease with further increases in pressure.
2. The shape of the flame changes dramatically with increasing pressure. At
atmospheric pressure, the flame has a bulbous appearance and is wider than
the exit diameter of the burner nozzle. By increasing the pressure the flame
changes in shape from wide and convex to slender and concave.
3. As the pressure was increased, axial flame diameters decreased, giving an
overall stretched appearance to the flame. The cross-sectional area of the
propane flame was observed to decrease with pressure as AcsP-n , where ,
n=0.6±0.1
4. The flame can be considered as a laminar axisymmetrical coflow diffusion
flame.
18
Ethylene-Air DF soot temperatures along centre line at different pressures
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
Flames Heights (mm)
So
ot T
em
pe
ratu
re (
ºC)
1 bar
2 bar
4 bar
6 bar
8 bar
10 bar
12 bar
16 bar
Soot temperatures along the centre line at different pressures
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Soot Temperature Measurement
1. In atmospheric pressure most centre parts of flames was blue and the
presence of soot is limited to the region near the tip of the flame.
2. By increasing the chamber pressure the overall soot temperature was
decreased.
3. Temperature increment by increasing the flame height from nozzle tip and
temperature drop after a certain height was observed for all flames.
4. The temperature trend line plots show steep radial temperature gradients
across the soot annulus and a general axial increase in temperature.
5. It is found that at lower pressures the temperature of soot annuals are more
than centreline soot temperature and after a critical pressure this trend will
be changed.
6. It is shown that rate of temperature dropping are more in lower pressures
in compare with higher pressures.
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Two-Colour Soot Temperature Results (Ethylene-Air)
Ethylene (100 ml/min)-Air (20 l/min)Flame Centre Line
P=1 bar
1300
1350
1400
1450
1500
1550
1600
1650
4 5 6 7 8 9 10 11 12 13 14 15 16
Flame Heights (mm)
So
ot
Tem
per
atu
re (
ºC)
Pyrometery
Two-Colour Method
Ethylene (100 ml/min)-Air (20 l/min)Flame Centre Line
P=2 bar
1000
1100
1200
1300
1400
1500
1600
1700
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Flame Heights (mm)
So
ot
Tem
per
atu
re (
ºC)
Pyrometry
Two-Colour Method
Ethylene (100 ml/min)-Air (20 l/min)Flame Centre Line
P=4 bar
1000
1100
1200
1300
1400
1500
1600
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Flame Heights (mm)
So
ot
Tem
per
atu
re (
ºC)
Pyrometry
Two-Colour Method
Ethylene (100 ml/min)-Air (20 l/min)Flame Centre Line
P=6 bar
1260
1280
1300
1320
1340
1360
1380
1400
1420
1440
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Flame Heights (mm)
So
ot
Tem
per
atu
re (
ºC)
Pyrometry
Two-Colour Method
21
Propane (60 ml/min)-Air (20 l/min)P=2 bar, H=15 mm
1200
1250
1300
1350
1400
1450
1500
1550
1600
1650
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
Radial Distance (mm)
So
ot
Tem
per
atu
re (
ºC)
Two-Colour Method
Pyrometry
Trend Line
Propane (60 ml/min)-Air (20 l/min) P=4 bar , H= 15 mm
1000
1100
1200
1300
1400
1500
1600
1700
1800
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
Radial Distance (mm)
So
ot
Te
mp
era
ture
(ºC
)
Two-Colour MethodPyrom etryTrend Line
Propane (60 ml/min)-Air (20 l/min) P=7 bar , H=15 mm
1315.0
1320.0
1325.0
1330.0
1335.0
1340.0
1345.0
1350.0
1355.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Radial Distance (mm)
So
ot
Te
mp
era
ture
(ºC
)
Two-Colour Method
Pyrom etry
Two-Colour Soot Temperature Results (propane-Air)
22
Soot Concentration Results by Applying Two-Colour Method(Ethylene-Air)
Ethylene (100 ml/min)-Air (20 l/min)Soot Concentration (fv .L ) in flame centre line
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
0 2 4 6 8 10 12 14 16 18
Flame Heights (mm)
fv.L
P=1 bar
P= 2bar
p=4 bar
P=6 bar
p=16 bar
Ethylene (100 ml/min)-Air (20 l/min)Soot volume fraction profile
0
20
40
60
80
100
120
140
160
180
200
220
240
0 2 4 6 8 10 12 14 16 18
Flame Heights (mm)
fv-S
oo
t V
olu
me
Fra
cti
on
(p
pm
) P=1 bar
P=2bar
P=4 bar
P=6 bar
p=16 bar
23
Soot volume fraction Results by Applying Two-Colour Method(Propane-Air)
Propane (60 ml/min)-Air (20 l/min)P=2 bar, H=15 mm
0
50
100
150
200
250
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
Radial Distance (mm)
So
ot
Vo
lum
e F
rac
tio
n, f
v (
pp
m)
Propane (60 ml/min)-Air (20 l/min) P=4 bar , H=15 mm
0
50
100
150
200
250
300
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
Radial Distance (mm)
So
ot
Vo
lum
e F
rac
tio
n, f
v (
pp
m)
Propane (60 ml/min)-Air (20 l/min) P=7 bar , H=15 mm
0
50
100
150
200
250
300
350
400
450
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Radial Distance (mm)
So
ot
Vo
lum
e F
ract
ion
, fv
(mm
)
24
Soot Formation
1. It is found that the methane-air diffusion flame is less sooty in compare
with ethylene and propane diffusion flames.
2. It was observed that by increasing the pressure the soot concentration and
proportionally soot volume fraction dramatically increased.
3. Soot formation at lower pressures was occurred mainly at the tip of the
flame and in an annular band near the burner rim, as the pressure was
increased, the luminous carbon zone moved downward, filling an
increasingly large portion of the flame.
4. It is found that the more sooty flame the less soot temperature. In our
measurements for example in 4 bar the maximum temperature which was
recorded for methane-air diffusion flame is 1552 ºC, however for same
pressure in ethylene-air diffusion flame the maximum recorded soot
temperature is 1444 ºC and for propane-air diffusion flame 1400 ºC.
25
Two-Colour Pyrometry
1. The values of soot volume fraction measured using two-colour method are
coupled to the measured soot temperatures, any errors in measured
temperatures will lead to errors in soot volume fractions.
2. The main problem in applying two-colour method in our experiments was
spectrum region of two selected narrow band filters.
3. Also in separate pictures of flame by CH and C2 filters it is inherently difficult to
find exactly the same points in two pictures of flame, for intensity evaluation.
4. The sensitivity of the main equation was tested on all the parameters and was
found that F1 and F2 have the less effect; however the I1 and I2 show
maximum change.
5. calibration of two colour optical setup (camera with filters) was performed on a
certified tungsten ribbon lamp.
6. The maximum average error that is recorded in our temperature measurement in
two-colour calculation was about 10%.
26
Instability Observations
1. Pressure is very influence on stability behaviour of different gaseous flame.
2. The ethylene flames with fuel flow rates of 100ml/min and 115ml/min exhibited good, long term stability at all pressures up to 16 bars.
3. In Methane flame from 8 bar flame dramatically changed to an unstable flame.
4. It was observed that propane presented more stable flame in comparison with ethylene and methane.
5. Fuel and air flow rates play an important role in instability behaviour of gaseous flames.
Methane (120 ml/min)-Air (20 l/min) at 18 bar Ethylene(300 ml/min)–Air(20 l/min) at P=16 bar)
27
Future Works (1)
Applying Modified and Specified Two-Colour Pryometry
Filters (Two-colours and natural density)
Tungsten Ribbon Lamp
CCD Camera
Anti-Heat Filter
Infratherm Pyrometer
Optical Windows
High Pressure Chamber
Roof PrismQuartz Plate
28
Future Works (2)
Chemilominescent Emission Measurement (evaluation of flame dynamic)
Collection Lens
Fibre Optic Cable
3D-Traverse gear
Digital CCD Camera Infrathem Pyrometer
Maas Flow Meters
29
Terahertz Time-Domain Spectroscopy of Sooty Flames at High-Pressure Future Works (3)
•Removing the effects of ambient water vapour• Improving dynamic range and measurable bandwidth •Reducing thermal lensing effects to increase THz transmission
30
Thermo-Acoustic Instability Simulation at Elevated Pressures
• Combustion instability is the main problem in developing new low
emission combustors and burners.
• In our experiments instability was observed for ethylene flame in
higher flow rates and in methane flame after 8 bar flame started
flicking and in higher pressures it became totally unstable.
• Feasibility study of thermo aquatic simulation in this high pressure
burner by using Gambit and Fluent software.
• It means in addition with Chemilominescent emission measurement,
we can predict and discussed the effect of pressure on flame
instabilities, flame buoyancy and Reynolds number
Future Works (4)