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EXPERIMENTAL INVESTIGATION OF THE LIQUID FUEL EVAPORATION IN A
PREMIX DUCT FOR LEAN PREMIXED AND PREVAPORIZED COMBUSTION
Michael Brandt
Institute for Propulsion Technology
German Aerospace Research Establishment
0-51140 Köln
111 1111111111111111 11111
Kay O. Qugel
Christoph Hassa
ABSTRACT
Liquid fuel evaporation was investigated in a premix duct,
operating at conditions expected for lean premixed and prevaporized
combustion. Results from a flat prefihning airblast atomizer are
presented. Kerosine Jet A was used in all experiments. Air pressure,
air temperature and liquid fuel flow rate were varied separately, their
relative influences on atomization, evaporation and fuel dispersion
are discussed.
The results show, that at pressures up to 15 bars and
temperatures up to 850 K, nearly complete evaporation of the fuel
was achieved, without autoignition of the fuel. For the configuration
tested, the fuel distributions of the liquid and evaporated fuel show
very little differences in their dispersion characteristics and were not
much affected by a variation of the operating conditions.
INTRODUCTION
Lean premixed and prevaporized combustion is a concept
designed for a significant decrease of nitric oxide emissions of gas
turbines (Tacina, 1990). As low combustion temperatures reduce the
thermal NOx formation, a lean homogeneous air - fuel mixture has to
be achieved at the combustor inlet. If liquid fuel is used, it has to be
atomized, evaporated and mixed homogeneously with the air in a
premix duct before autoignition of the fuel occurs. For typical engine
operating conditions this means a few milliseconds
(Spadaccini,1982). Since both atomization and evaporation depend on
the operating conditions, an experiment was designed that allows the
study of liquid fuel evaporation at conditions corresponding to cruise
conditions of aircraft engines (Dunker, 1993) or full load of industrial
gas turbines (Schulenberg, 1990). Optical access into the premix duct
enables the use of non-intrusive measurement techniques. Particle
size distributions, as well as liquid fuel concentrations are measured
with Phase Doppler Anemometry. The distribution of the evaporated
fuel is described by extinction measurements of infrared and visible
light along the line of sight of two laserbeams.
TEST FACILITY
All experiments were carried out in a test cell allowing three
way optical access into the rectangular premix duct. Inside the
premix duct, a quartz glass channel with a cross section of 25x40
mm, pressures up to 15 bars and temperatures up to 850K could be
achieved at air velocities above 120 rids. A sketch of the test cell is
shown in figure 1. The duct is surrounded by a cooling air flow.
Operating conditions in the duct were adjusted by a variation of the
mass fluxes of main and cooling air and the use of different throttles
at the air exit of the test cell. The air was heated by a 520kW
electrical air heater. Atomizers could be mounted at two axial
positions inside the duct. In previous studies (Eickhoff et al, 1983,
Brandt et a1,1994) a flat prefilming airblast atomizer showed
excellent atomizing qualities at operating conditions expected in a
premix duct In this type of atomizer the fuel is admitted to the free
surface by a thin slit, where the liquid spreads out as a thin film and
is atomized behind the atomizer edge by the forces of the high
velocity air flow.
In the present investigation two flat prefilming atomizers were
used. The small atomizer (fig 2a) was mounted horizontally in the
duct, allowing a good spatial resolution perpendicular to the atomizer
plane for the line of sight measurements. The large atomizer (fig 2b)
was a better approximation of a 2 dimensional atomizer with a more
practical slit height. It had to be mounted vertically in the duct.
MEASUREMENT TECHNIQUES
A sketch of the optical setup is shown in figure 3. The
evaporation of the liquid fuel was recorded by Phase Doppler
Anemometry (PDA) (DANTEC, 1992). The instrument is capable to
give particle size distributions, particle velocities and liquid volume
fluxes. To minimize drop sizing errors, caused by the temperature
dependence of the refractive index of the heating droplets, a
scattering angle near the brewsters angle is preferable ( Pitcher et. al,
1990). However, as optical streets was limited by. the test cell, a
scattering angle of 52° degrees was chosen, resulting in a systematic
drop sizing error below 5 % at investigated conditions. Other error
Presented at the International Gas Turbine and Aeroengine Congress & Exhibition
Birmingham, UK — June 10-13,1996
This paper has been accepted for publication in the Transactions of the ASME
Discussion of it will be accepted at ASME Headquarters until September 30, 1996
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sources like the non-linearity of the phase-dropsize correlation
resulted in drop sizing uncertainities of about Ima, the maximum
error due to misalignement was about 3% (Gugel, 1995).
The distribution of the evaporated fuel was determined by the
extinction measurement of an infrared laserbeam, as first described
by Chraplywy (1983). The infrared light extinction is based upon
strong absorption bands of most of the hydrocarbon fuels near 3.4 gm
wavelength. In an evaporating fuel spray the extinction of the
laserbeam is mainly a superposition of light scattered by droplets,
light absorbed by droplets and absorption of the gaseous fuel. If the
amount of the gaseous fuel is to be measured, light absorption and
scattering by particles have to be removed from the IR-extinction
measurements.
The amount of light scattered by particles was evaluated by a
method described by Winklhofer and Plimon (1990): the light
scattering is measured in the visible range, where light absorption can
be ignored. If the light detection apertures are adjusted according to
the different Mie parameter for the infrared and visible wavelengths,
the light scattered in the infrared can be measured with light scattered
in the visible range. The amount of light absorbed by particles was
neglected.
The technique was used with the aim to see relative values in
the gaseous fuel distribution. Absorption coefficients depend on the
ambient pressure and temperature, kerosine is a multicomponent fuel
with varying absorption coefficients and line of sight measurements
have a limited spatial resolution. Hence, to get absolute values at the
present state of the work was judged impractical and no attempt was
made to get vapour phase concentrations from these measurements.
As the evaporation rates of the spray bad to be determined by the
liquid volume flux measurements, the related uncertainties were
studied in detail. The liquid volume flux density has to be calculated
with the total droplet volume passing the cross section of the
measurement volume in a certain time.
One important error source is the correct determination of the
number of droplets passing the measurement volume. As the PDA
allows only one particle to be in the measurement volume at the same
time, signals of more than one particle in the measurement volume
will be rejected and not counted in the liquid flux measurements. The
measured liquid volume fluxes were corrected with an algorithm
suggested by Edwards and Marx (1991). Based on Poisson statistics
they gave a probability of the particle rejection. The probe volume of
the PDA with a gaussian measurement volume diameter of about 70
gm was limited by a slit in the receiving optics, which was set to 100
pm at high particle concentrations and 520 gm at locations where
particle concentrations were low. It turned out that, due to
extraordinary high particle concentrations at some conditions mainly
close to the atomizer lip the limits of this measurement instrument
were exceeded (data rates above 150 kHz and concentrations above
590' particles per cubic centimeter), making correct volume flux
measurements impossible. Edwards and Marx (1991) found, that the
rejection of particles is reasonably free of a particle size bias up to
rejection rates of 90%, such that for the measurements shown, an
influence on the SMD measurements can be neglected.
Another problem in the accurate measurement of the liquid
volume flux is the correct determination of the measurement volume
size, which is done by the PDA with a method first suggested by
Saffman (1987), for one dimensional flow. As optical limitations and
the orientation of the main flow direction forced a non - standard
optical setup, post processing of the liquid volume fluxes became
necessary. This post processing took into account the special form of
the measurement volume, limited by the slit in the receiving optics
and the orientation of the main flow direction. In a previous
publication (Brandt, 1995) this post processing is described in detail.
The error of the volume flux measurement was determined at
comparable operating conditions and found to be below ±15% of the
total liquid flux, if the particle concentrations are not too high. This is
the error margin of the liquid volume flux measurements presented
here.
RESULTS AND DISCUSSION
Kerosine Jet A was used in all experiments. If not explicitly
mentioned otherwise, all measurements were made at a constant air
velocity of 120 m/s, which was computed by the measured air mass
fluxes at operating conditions and the cross section of the duct. The
turbulence of the air in the duct, measured with Laser Doppler
Anemometry at atmospheric pressure and ambient temperature was
about 5-7%.
With respect to the autoignition limit of the fuel, the most
challenging operating conditions investigated were 15 bars, 750 K
and 9 bars, 850 K. The autoignition times for kerosine Jet A
calculated with the correlation of Spaddacini et al (1982) arc about 7
ms (at 15 bars, 750 K) and 1.1 ms (9 bars, 850 K). Although the
observable pathlength of 150 mm resulted in residence times of the
fuel of 1.25 ms ( computed with the mean air velocity), no
autoignition was observed.
In figure 4 the Sauter Mean Diameter of the total spray and the
relative liquid mass flux are presented for a variation of the ambient
air pressure at a constant air temperature of 750 K. Atomizer 1 was
used, the fuel loading ratio per atomizer width was Ir=125 g/s/m.
An increase of the ambient air pressure leads to a decreasing
Sauter Mean Diameter of the spray. As the air temperature was held
constant, the increase of the air pressure increases the pressure head
of the atomizing air. The influence found is about SMD — which
agrees with results obtained from other prefilming airblast atomizers
as reviewed by Lefebvre (1989), or Mellor (1990). The pressure
influence on atomization seems to decrease with increasing air
pressure. This is possibly when atomization approaches the 'prompt'
atomization for high momentum airstreams, as decribed by Lefebvre
(1991). Here no influence of the air density on atomization is
predicted.
The finer initial dropsize distribution at higher pressures leads
to a distinct increase of the evaporation rates of the fuel (fig 4b).
Measurements on the evaporating fuel were made at four axial
positions x downstream of the atomizer lip. Typically between 50 and
80 PDA measurements were made per measurement plane. Mean
diameters of the total spray were obtained from an addition of all
single point values, weighted with the local liquid mass fluxes.
Relative liquid mass fluxes of the total spray were obtained from an
integration over all measurement points, normalized with the inlet
liquid mass flux.
Usually 20000 particles were collected in one single point
measurement at acceptance rates above 90%. At conditions of high
evaporation rates, where data rates of only a few Hertz were
measured, sometimes only a few hundred particles were collected.
But, with the exception of the last measurement plane at 15 bars, 850
K. the condition with the highest evaporation rate where only 4000
particles have been collected, at least 10000 particles have been used
for the computation of the mean values of one measurement plane.
2
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diameter, but is not as drastic as the increase of the 90% Volume
Undersize Diameter of the spray might suggest
Wheras, with the exception of very high evaporation rates, for a
given operating condition the measured SMD of the spray remains
nearly constant (see fig 4.5,6), the 90% Volume Undersize Diameter
in figure 8 exhibits distinct differences. In the beginning of the spray
evaporation all droplet diameter start to diminish (a possible increase
of the diameter during beat-up is neglected), leading to a decrease of
the diameter of the biggest particles. This can be seen in figure 8 for
the 90% Volume Undersize Diameter of the highest fuel flow rates,
where evaporation rates are relativity small. On the other side: the
smallest particles evaporate completely very soon. Thus, depending
also on the initial dropsize distribution of the spray, the SMD of the
spray remains nearly constant When the evaporation of the spray is
very high (here typically above 98%) only a few of the initially
biggest particles 'survived', resulting in an increase of both the SMD
and the 90% Volume Undersize Diameter of the spray.
Whereas 150 mm behind the atomizer lip at 3 bars only 70% of the
liquid fuel was evaporated, at 15 bars evaporation rates of more than
99% were measured.
A variation of the air temperature at a constant air pressure of 9
bar is shown in figure 5. With respect to the decrease of the air
density and thus the atomizing pressure bead, an increase of the SMD
should be expected with increasing air temperature, but the contrary
is found.
The authors assume that this decrease of the SMD is caused by a
decrease of the surface tension of the fuel, which flows through the
atomizer surrounded by the hot air. For airblast atomizers and low
viscosity fuels, the SMD of the spray is roughly inversely proportional
to the squareroot of the surface tension of the fuel (Lefebvre 1989,
Mellor 1990). Assuming a decrease of the surface tension of kerosine
with temperature as found in Vargaftik (1975), the results of this
study can be explained assuming an increase of the fuel temperature
of about dT=130 K, when the air temperature is increased from 550 K
to 850 K. The fuel temperature on the atomizer has not yet been
measured under running conditions, but such an experiment is
planned.
Both the higher temperature and the better atomization at
higher air temperatures lead to an increase of the evaporation rates of
the spray. At an air temperature of 850 K more than 99% of the fuel
was evaporated as early as 100 mm behind the atomizer. The boiling
range of kerosine let A is about 450 K - 550 K. hence at an air
temperature of 550 K 150 mm behind the atomizer lip an evaporation
rate of only 20% was found (for better comparison with other figures
it is not shown in figure 5b). Further increased air temperatures then
produce the dramatic rise of evaporation rates.
From the results presented so far, it should be noted that the
high evaporation rates of the kerosine are caused to a large extend by
the good fuel atomization, which in turn is caused by the high air
velocity of 120 m/s.
It turns out, that the relative velocity is the dominant factor for
airblast atomization in this operating range: a measurement was made
at P = 9 bar, T = 750 K and an air velocity of 80 m/s and exhibited an
initial SMD of the spray of about 25 pm and evaporation of about
50% of the fuel at the last measurement plane 150 mm behind the
atomizer lip. Compared with the evaporation of more than 95% at an
air velocity of 120 m/s, fuel evaporation rate is drastically decreased,
although the residence time of the fuel (computed with the mean air
velocity) increased by a factor of 1.5.
A variation of the fuel flow rate at a constant air pressure of 9
bar and an air temperature of 750 K was made with atomizer 2 (fig
6). For both atomizers the fuel velocities leaving the slit were about 2
m/s, so the relative velocity between the liquid and the air was nearly
equal to the main air velocity of 120 at/s. A comparison with the
results from atomizer 1 shows, that at comparable fuel loadings per
atomizer length, the same initial dropsize diameters were measured:
for this type of atomizer at the investigated operating conditions the
different heights of the slits don't have a dominant role on
atomization. Furthermore, since nearly the same evaporation rates
were measured in both cases, the absolute liquid mass flux doesn't
seem to have a dominant effect on evaporation, if the initial dropsize
distribution remains unchanged.
However, an increase of the liquid mass flux per atomizer
width leads to an increase of the SMD of the spray and thus to a
reduction of the evaporation rates. The increase of the SMD of the
dropsizt distribution might be an effect of the high local fuel
concentration in the gas field. In figure 7 mean velocities of the 6pm
(intervall from 5 to 7 pm) particles are shown. These mean velocities
were obtained for the total spray by weighting the mean velocities
with the liquid mass fluxes measured at each point. In a first
approximation they can be taken as a measure for the gas velocity
inside the spray.
Caused by the higher momentum loss of the air, accelerating
and atomizing a higher amount of fuel, the mean gas velocities are
reduced inside the spray. This results in a drastic increase of the 90%
Volume Undersize Diameter as seen in figure 8, which might also be
an effect of hindered secondary breakup of the large particles.
The effects of the higher fuel flow rate lead to a decrease of the fuel
evaporation, which is mainly caused by the larger initial dropsize
With respect to lean premixed and prevaporized combustion not
only complete evaporation, but also the homogeneity of the air fuel
mixture at the combustor inlet are important factors for a reduction of
the nitric oxide emissions. Measurements of the optical thickness of
the gaseous fuel, which is proportional to the integration of the fuel
concentration along the line of sight of the laserbeams are shown in
figure 9 for a variation of the ambient air pressure. Presented are the
limits of the fuel distribution perpendicular to the atomizer plane,
containing 68.3% of the totally measured fuel. As early as 30 mm
behind the atomizer lip, the measured profiles exhibited a reasonable
Gaussian distribution. Hence the 68.3% width equals twice the
standard deviation. These measurements are compared with the fuel
distribution of the liquid phase. For the comparison the point
measurements of the liquid mass fluxes were integrated over the line
of sight of the laser of the extinction measurements.
The differences between the evaporated and liquid fuel
distributions are small. Due to the good atomization, the spray
produced is very fun and follows the streamlines of the gasflow quite
well. Measurements show that 30 mm behind the atomizer edge even
particles with a mean diameter of 30 pm (intervall from 25 -35 pm)
have reached more than 80% of the mean gas velocity. This means, as
for the most part of the spray the acceleration is nearly finished 30
mm behind the atomizer, the mixing and penetration of the particles
is dominated by the velocity fluctuations of the main flow. In the
present air flow, which was not modified by i.e. turbulence
generators, the turbulent length- and timescales of the gas flow allow
a good response of the spray to the gas motion.
There is only a weak influence of the ambient air pressure, air
temperature and the fuel flow rate on the penetration and mixing of
3
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the liquid, as well as the gaseous fuel. A very slight tendency of a
weaker fuel penetration for higher air densities was found. The
mixing of the liquid with the air is relatively poor and leads to the
next step in further investigations: a modification of the main air flow
by turbulence generators upstream the atomizer, allowing the study of
the effects of an increased air turbulence on fuel mixing and
evaporation.
Edwards, C.F. and Marx, K.D., 1991,"Application of Poisson
Statistics to the Problem of Size and Volume Flux Measurements by
Phase Doppler Anemometry", ICLASS-91, Gaithersburgh, U.S.A
Eickhoff, H., Granser, D. and Krockow, W., 1983, "Liquid Fuel
Atomization and Mixing in a High Velocity Airstream*,
AGARD-CP-353,Paper 14
Gugel, K. 0., "Experimentelle Untersuchung der ZweiPhasen-StnSmung in ether Vormischstrecke fur die magere
vorgemischte und vorverdampfte Verbrennung", 1995, University of
Karlsruhe
CONCLUSION
Evaporation rates and mixing qualities of liquid fuel have been
investigated for a flat prefilming airblast atomizer, at conditions
expected in a premix duct for lean premixed and prevaporized
combustion. The results show, that at high atomizing air velocities
complete evaporation of the fuel can be achieved without autoignition
of the fuel.
Evaporation rates are strongly influenced by the initial dropsize
distribution, which is dominated by the air velocity and depending on
the fuel loading ratio and the air pressure.
For this type of atomizer and the investigated flow conditions
the differences between the distributions of the liquid and the
evaporated fuel are small. The mixing of the fuel with the air is not
much affected by ambient air pressure, air temperature and the fuel
flow rate.
Lefebvre, A.H., 1989, "Atomization and Sprays", Hemisphere
Publishing Corporation, Washington D.0
Lefebvre, AR., 1991, "Twin Fluid Atomization - Factors
Influencing Mean Drop Size", ICLASS-91 Gaithersburg, U.S.A
Mellor, A. M., 1990, "Design of Modern Turbine Combustors",
Academic Press, ISBN 0-12490055-0
Pitcher G., Wigley, G. and Saffman. M. , 1990, "Sensitivity of
Dropsize Measurements by Phase Doppler Anemometry to Refractive
Index Changes in Combusting Fuel Sprays", 5th Int. Symp.
Application of Laser Techniques to Fluid Mechanics, Lisbon
NOMENCLATURE
90% Volume Undersize Diameter - diameter such, that 90% of the
total liquid volume of the spray is in drops below this diameter
(Ftm)
lit - infrared light, here: 3.14 pm wavelength
P - air pressure [bar]
Saffman, M., 1987, "Automatic Calibration of LDA
Measurement Volume Size", Applied Optics, Vol. 26, No. 13
Schulenberg, T., 1990, "Elbersichtsvortrag zum 2. Stataisseminar
der Arbeitsgemeinschaft Hochtemperatur-Gasturbine", 22. 23. Nov.
1990, DLR Koln - Porz, published by Sekretariat AG TURBO, DLR,
0-51140 Köln
SMD - Sauter Mean Diameter [pm], SMD = E
T - air temperature [K]
VIS - visible light, here: 632 nm wavelength
Ir - liquid loading ratio [g/s/m], liquid mass flux per atomizer width
w - mean axial bulk air velocity [m/s]
Spadaccini, L. J. and TeVelde, J.A., 1982, "Autoignition
Chraracteristics of Aircraft-Type Fuels", Combustion and Flame 46:
283-300 (1982)
Tacina, R.R., 1990, "Combustor Technology for Future
Aircraft", AIAA-90-2400, Orlando, Florida
ACKNOWLEDGEMENTS
This work was sponsored by the CEC BR1TE/EURAM "Low
Emissions Combustor Technology - Phase If"
Vargaftilc, N. B, 1975, "Tables on the thermophysical properties
of liquids and gases", Hemisphere Publishing Corporation, ISBN
0-470-90310-4, p 692
REFERENCES
Brandt, M. , Hassa, C., Kallergis, IC and Eickhoff, H., 1994,
"An Experimental Study of Fuel Injectors for Premixin g Ducts",
ICLASS-94 Rouen, France
Winklhofer
E.. and Plimon A., 1990, "Monitoring of
Hydrocarbon Fuel-Air Mixtures by Means of a Light Extinction
Technique in Optically Accessed Research Engines", Optical
Engineering
Brandt, M., 1995, "Liquid and Gaseous Fuel Measurements in a
Premix Duct", ILASS-95 Niimberg, Germany
FIGURES
Chraplywy, A., 1981, "Nonintrusive Measurements of Vapor
Concentration Inside Sprays", Applied Optics, Vol. 20, No. 15
DANTEC, 1992, PDA User's Manual, Tonsbakken 18, OK 2470 Skovlunde, Denmark
Dunker, R., 1993, "Advances in Engine Technology", Wiley, EC
Areonautics Research
4
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topview
5 mm
18mm
21 mm
0.1
2 mm
tuumnr K.
w
f-.
sidcview
sa
' ./
lip
4
, Az
.,:r--fil
re,:rn,,,n;
.,,,...
a) Atomizer
2 mm
0.3
Pressure Window
topvicw
22 mm
25 mm
30 mm
Pressure Housing
sid eview
a) cross section
to) Atomizer II
Cooling Air
Figure 2: Flat prefilming airblast atomizer
Turbulence Grid Holder
Pressure Window
I. PDA - Transmittin g Optics
2. He Ne Laser (633 run)
A.
.d,
Il i
la IIIIR
Attr4
----.0.7
3.' He Ne Laser (3.39 pm)
, I
s rnsissamensmose
.:&tneeetarte
Wt.
NIM N'tt."1.
v / :
-0C23 \ s?...:\
t HI ,
''''
re s
r
r
-
. !Au
-r.pp. ”...‘tcs
S. IR Detector (PbS Detector)
(Aperture Diameter 400 pm)
6 VIS Detector (Si Diode)
(Aperture Diameter 150 pm)
7 Mirror.
•:=Mil
10
// /
(4
Aril
Au ,
Glass Duct
4. PDA Receiving Optics
8. Lens (Ca F, few 400 mm)
9. Lens (fa 300 mm)
10.Bearn Splitter
11.Lens (CaF, P= 50 mm)
12. Lens( fa 100 mm)
13. Chopper
Throttle
Space for Atomizer Mountin g
b) longitudinal section
Figure 3: Sketch of tbe optical setup
Figure 1: Test cell
5
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30
SMD (pm)
30
25
25
20
20
15
15
SMD (pm)
29--
10
10
o
o
30
•
60
90
120
Position x (mm
30
150
60
90
120
150
Position x (mm)
T= 550 K T= 650 K T= 750 K T= 850 K
S
•
•
P=3 bar P=6 bar P=9 bar P=12 bar P=14.5 bar
•
Atomizer .1=750K. w=120 m/s. Ir=125 g/s/m
Atomizer I. P= 9bar, w= 120 m/s, Ir= 125 g/s/m
a)
a)
Relative Liquid Mass Flux (%)
Relative Liquid Mass Flux (%)
50
50
40
30
20
10
30
60
90
120
150
30
Position x (mm)
60
90
120
150
Position x (mm)
P=3 bar P=6 bar P=9 bar P=12 bar P=14.5 bar
•
•
•
h. 650 K 1-= 750 K 1.= 850 K
•
Atomizer I. T= 750K, w= 120 m/s,11= 125 g/s/m
Atomizer I P= 9 bar, w= 120 m/s, Ir= 125 g/s/m
b)
b)
Figure 4: Sauter Mean Diameter a) and relative liquid volume
flux b) at different air pressures
Figure 5: Sauter Mean Diameter a) and relative liquid volume
flux b) at different air temperatures
6
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SMD (pm)
30
Mean Axial Velocity (m/s)
140
25
120
1C0
20
83
15
60
10
40
5
20
00
30
120
90
60
Position x (mm)
o
150
Ir= 83 g/s/rrir=167 g/s/rrir=250 g/s/rrir=333 g/s/m
A
•
•
30
120
60
90
Position x (mm)
150
ir=83 g/s/mIr=167 g/s/mIr=250 g/s/rrir=333 g/s/m
A
•
•
Atomizer II, P= 9 bar, Tin 750 K, w= 120 m/s
Atomizer II, P=9 bar, Is 750 K. w=120 m/s
a)
Figure 7: Mean axial velocities of 6pm particles at different fuel
loadings
Relative Liquid Mass Flux (%)
90% Volume Undersize Diameter (pm)
50
50
40
40
30
30
20
20
10
10
60
90
120
o
150
Position x ( mm) •
o
30
60
90
120
150
X-Position (mm)
Ir=83 g/s/rrir=167 g/s/rrir= 250 g/s/rrir=333 g/s/m
•
Ir=83 g/s/rrir=167 g/s/rrIr=250 g/s/rrir=333 g/s/m
•
A
•
Atomizer II. P= 9 bar, Tr, 750 K. w= 120 m/s
Atomizer II, P=9 bar, T= 750 K. w= 120 m/s
Figure 8: 90% Volume Undersize Diameter at different fuel
Figured: Sauter Mean Diameter a) and relative liquid volume
flux b) at different fuel loadings
loadings
7
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Dispersion Width of the Liquid Fuel (mm)
12
10
a
6
47
4
2
0
0
30
120
60
90
Position x(mm)
150
P=3 bar P=6 bar P=9 bar P=12 bar P=15 bar
•
Atomizer I, T=750 K, w= 120 m/s, Ir= 125 g/s/m
Dispersion Width of the Gaseous Fuel (mm)
12
10
6
4
2
30
60
90
120
Position x(mm)
150
P=3 bar P=6 bar P=9 bar P=12 bar P=15 bar
•
Atomizer I, T=750 K, w=120 m/selr=125g/s/m
Figure 9: Comparison of the 68% dispersion width of liquid and
gaseous fuel at different air pressures
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