Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: P1.75 - Spray generator for the liquid fuel combustion
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 Material Information
Title: P1.75 - Spray generator for the liquid fuel combustion Industrial Applications
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Nowak, D.
Dobski, T.
Slefarski, R.
Magni, F.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: liquid fuel combustion
spray generator
nozzle design
 Notes
Abstract: Lower prices of crude oil as compared to costs of other fuels drive a common interest in its application. Regarding fuel flexibility, combustion of liquid fuels needs to follow the combustion criteria of other fuels, such as: - Stable flame for strong swirl in central flow - Low residence time of reactance in high temperature region of flame to lowering emission of thermal nitric oxides, - Strong entrainment of post flame gases similar to flameless technology to lowering fuel nitric oxides. These physical criteria generate particular technical challenges for the combustion of liquid fuels, which can be resolved experimentally. This paper presents experimental analyses of a spray generator dedicated to a gas turbine operating with liquid fuels. Properties of such fuels are different than the properties of a gas. Different droplets size and distribution of the droplets gives different spray cone angles. Crude oil, for example has similar physical properties compared to heating liquid fuels, but has crucial differences such as very low temperature of vaporization, low temperature of ignition and low viscosity. The atomization of the liquid fuels in a gas turbine is one of the most critical issues influencing the quality of the combustion process. Atomization has a significant impact on the stability of the combustion process and the decomposition process of the hydrocarbons. In this paper the experimental investigation of the modified simple pressure swirl atomizers used for the liquid fuels atomization is discussed. Based on the experimental results, the validation of the numerical model is presented.
General Note: The International Conference on Multiphase Flow (ICMF) first was held in Tsukuba, Japan in 1991 and the second ICMF took place in Kyoto, Japan in 1995. During this conference, it was decided to establish an International Governing Board which oversees the major aspects of the conference and makes decisions about future conference locations. Due to the great importance of the field, it was furthermore decided to hold the conference every three years successively in Asia including Australia, Europe including Africa, Russia and the Near East and America. Hence, ICMF 1998 was held in Lyon, France, ICMF 2001 in New Orleans, USA, ICMF 2004 in Yokohama, Japan, and ICMF 2007 in Leipzig, Germany. ICMF-2010 is devoted to all aspects of Multiphase Flow. Researchers from all over the world gathered in order to introduce their recent advances in the field and thereby promote the exchange of new ideas, results and techniques. The conference is a key event in Multiphase Flow and supports the advancement of science in this very important field. The major research topics relevant for the conference are as follows: Bio-Fluid Dynamics; Boiling; Bubbly Flows; Cavitation; Colloidal and Suspension Dynamics; Collision, Agglomeration and Breakup; Computational Techniques for Multiphase Flows; Droplet Flows; Environmental and Geophysical Flows; Experimental Methods for Multiphase Flows; Fluidized and Circulating Fluidized Beds; Fluid Structure Interactions; Granular Media; Industrial Applications; Instabilities; Interfacial Flows; Micro and Nano-Scale Multiphase Flows; Microgravity in Two-Phase Flow; Multiphase Flows with Heat and Mass Transfer; Non-Newtonian Multiphase Flows; Particle-Laden Flows; Particle, Bubble and Drop Dynamics; Reactive Multiphase Flows
 Record Information
Bibliographic ID: UF00102023
Volume ID: VID00466
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: P175-Nowak-ICMF2010.pdf

Full Text


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010



Spray generator for the liquid fuel combustion


D. Nowakl, T. Dobski2, R. Slefarski2, F. Magnil

LAlstom Power,
Brown Boveri 7, 5401 Baden, Switzerland
dariusz.nowak @power.alstom.com

2POznan University of Technology, Gas Technology Laboratory,
Piotrowo 3a, 60-965 Poznan, Poland
tomasz.dobski @put.poznan.pl

Keywords: Liquid fuel combustion, spray generator, nozzle design

Abst ract

Lower prices of crude oil as compared to costs of other fuels drive a common interest in its application. Regarding fuel
flexibility, combustion of liquid fuels needs to follow the combustion criteria of other fuels, such as:
Stable flame for strong swirl in central flow
Low residence time of reactance in high temperature region of flame to lowering emission of thermal nitric oxides,
Strong entrainment of post flame gases similar to flameless technology to lowering fuel nitric oxides.
These physical criteria generate particular technical challenges for the combustion of liquid fuels, which can be resolved
experimentally. This paper presents experimental analyses of a spray generator dedicated to a gas turbine operating with liquid
fuels. Properties of such fuels are different than the properties of a gas. Different droplets size and distribution of the droplets
gives different spray cone angles. Crude oil, for example has similar physical properties compared to heating liquid fuels, but
has crucial differences such as very low temperature of vaporization, low temperature of ignition and low viscosity. The
atomization of the liquid fuels in a gas turbine is one of the most critical issues influencing the quality of the combustion
process. Atomization has a significant impact on the stability of the combustion process and the decomposition process of the
hydrocarbons. In this paper the experimental investigation of the modified simple pressure swirl atomizers used for the liquid
fuels atomization is discussed. Based on the experimental results, the validation of the numerical model is presented.


Nomenclature


fuel (Dobski 2010). The key parameters determining the
atomization quality are: spray cone angle, evaporation time,
Spray length and droplets size. The atomization process
generally consists of two separate processes: primary
atomization, in which the fuel stream is broken and
secondary atomization in which the fluid particles are
disintegrated into small droplets. The atomization process
depends on the fuel properties, as well on the injector
geometry, angular velocity inside the injector and injection
pressure. Various types of injectors have been tested for
years. Few references provide numerous computations and
measurements made on injectors (Kulshreshtha 2009,
Lacava 2004, Ommi 2009) for different structural
parameters and various fuels. Nevertheless the flow process
of the injectors cannot be modelled based on the commonly
available empirical equations (Lefebvre 1998, Jeng 1998).
For crude oil as the medium the paper presents the results of
studies on the most common design of the pressure swirl
atomizer. The design methodology described by Lefebvre
(1998) for this kind of swirl nozzle needs the consideration
of numerous experimental dependencies, because it is very
difficult to achieve the consistency between the test results
and the numerical simulations. This paper shows the
comparison of spray cone angle measured in the test rig
with analytical results based on the empirical equations for
pressure swirl atomizer. The paper also presents the concept
of a nozzle with a pin enabling the improvement of liquid
atomization parameters for high-density medium flows like


A, Total inlet ports area (m2)
do Discharge orifice diameter (m)
Do Discharge orifice diameter of new nozzle (m)
d, Inlet port diameter (m)
dpin Pin diameter (m)
D, Swirl chamber diameter (m)
L, Swirl chamber length (m)
ThMass flow rate (kg/h)
n Number of inlet holes
AP Pressure differential across nozzle (Pa)

a Spray angle (deg)
lu Kinematic viscosity (m2/S)
p Fluid density (kg/m3)



Introduction

Liquid fuel atomization in the burners of power generation
machines, such as gas turbines, or piston engines represents
a very important parameter affecting the combustion
process quality. The fuel atomization quality is responsible
for the production rate of a toxic compound, pulsations in
the combustion chamber in the case of gas turbines and
affects the combustion rate of hydrocarbons contained in the






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

The tested atomizer was also instrumented with pressure
measuring pipe directly before the swirler chamber, which
allowed finding the accurate characteristics of fluid flow
rate through the nozzle, depending on the injection pressure.
For the analysed nozzle of interest the measurements of
spray con angle was carried out upon processing of digital
pictures, which were taken during the experiment. The
liquid atomized was lit by means of a light knife obtained
through passage of a light beam through a rotating-mirror
system. A laser beam was used as the light source during the
tests. A sample picture of the liquid sprayed before and after
the numerical processing is presented in figure 2.


crude oil. The relationship of the spray cone angle to the
mass flow rate and the pressure drop on the nozzle were
determined experimentally. For the measured cone angles
the essential differences were found out with respect to the
well know Rizk & Lefebvre (1985) formula for viscous
liquid as

a= 6 o1 ~~2~2 1 i
do, p )


According to this equation, the spray angle depends on the
discharge orifice diameter, liquid density, injection pressure
and liquid viscosity. Benjamin (1998) validated this
equation using their database and modified the coefficients
for large-scale nozzle as given with


a=9.~ A -0 237 0P2 0067
Ao A~d2


Base on the obtained experimental results the Ritz &
Lefebvre (1985) formula is modified in this paper for the
analytical determination of the spray angle


Figure 2: Measured spray cone angle: left side-
experiment, right side spray angle after numerical
processing.



Results and discussion

The experimental tests of the fuel atomization process were
carried out to indicate the impact of the liquid density,
liquid viscosity, injection pressure and mass flow rate on the
spray cone angle. Crude oil of 866kg/m3 density and
1.62E-5m2/S kinematic viscosities was tested. In the
experimental set-up firstly standard pressure swirl nozzle
was designed in accordance with Lefebvre (1998) criteria.
Figure 3 shows the scheme of the standard nozzle, which
was used in tests.


Experimental Measurements


The test rig presented in figure 1 was designed and
constructed, in order to carry out the experimental analysis
of the spray generated for liquid fuels. The main purpose of
the experiment was to test the spray cone angle for crude oil
atomization with various geometric parameters of the
injector. In addition, the validation of the empirical equation
(1) defined by Rizk & Lefebvre (1985). The most important
elements of the measuring system are: adjustable tested
nozzle, nozzle feed system and visualization system
enabling the measurement of the tested spray cone angle.
The fuel was transported from the tank to the nozzle by
means of a high-pressure pump, through an electrical heater
and a mass flow meter. Owing to the application of the fluid
heater during the tests, it was possible to determine the
effect of fluid density and viscosity on the performance of
the atomization process.


Injection pressure


atomizer-


laser system


Figure 3: Geometry of the standard nozzle, where oc
denotes spray angle.

The measured spray cone angles for a standard nozzle are
shown in figure. 4 and 5. The variable parameters were the
number of inlets n (Figure 4) and orifice diameter do (Figure
5) while other parameters were kept unchangeable. In case
of reduction of fuel inlet numbers in the nozzle for the
constant flow intensity, the kinetic energy inside the swirl


| ~tank oil Ilquid

Data aquisition system


Figure 1: Experimental test rig for spray visualization and
spray cone angle measurements.





























m* a





*dp=1mm, do=0.9mm, n=3
m dp=1mm, do=0.9mm, n=2


*~*




o dp=1mm, do=0.9mm, n=3
m dp=1mm, do=1.5mm, n=3


For the new nozzle the identical tests were repeated to
validate an impact of the structural and flow parameters on
the crude oil spray cone angle. The measuring results are
presented in figure 7. It was observed that for the same
injection pressure value, higher flow rate through the nozzle
was obtained, which resulted in obtaining a larger spray
cone angle.

100




P.85


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

reduction of the boundary layer thickness and the desired
exit flow structure was obtained in the outlet zone. However,
the pressure increase has an impact on the increase of mass
flow, which in the case of a turbine increased the power.
Since the power must be become, the injector structure
should be changed in a way to generate a stream with an air
core in the exit section. This can be done by mounting a
special pin as shown in figure 6, which enforces to create
the demand flow structure of the fuel.


increases, what has an impact on a wider fuel spray cone
angle. This increase is noticeable only for the initial increase
period of mass flow rate through the swirl, then the angle
value settles on certain permanent level. In the case of
increasing the outlet diameter no significant change of the
spray cone angle was measured. The pressure increase of the
injected fluid just caused the higher mass flow rate through
the tested nozzle. The obtained test results proved that it was
impossible (for nozzles designed according to Lefebvre
(1998) theory with small outlet diameters do) to achieve fuel
spray cone angles in range of the injectors commonly used
for lighter fuels than the analysed here crude oil.


80

75




cn 60
o
55

50


Figure 6: Geometry of
(Nowak et al, 2010).


the nozzle with the special pin


20 25 30 35 40 45 50 55 60
mass flow rate [kg/s]


Figure 4: Measured spray cone angles for two and three
injection holes in the standard nozzle design.


so I


75

S70



55 5


50


--


30 35 40 45 50 55 60 65 70 75 80 85
mass flow rate [kg/s]

Figure 5: Spray cone angle measured for two different
orifice diameters.

The reason of those differences is in the fluid behaviour of
the oil by flowing through the orifice exit section. As crude
oil is characterized with high surface tension and the size of
the orifice exit is very small, the boundary layer in the
central part of the injector orifice grows, which in turn
causes blocking of the outlet. Further on, the liquid behaves
in the same way like the plain jet. Therefore, all the
considerations on calculating the spray cone angle by means
of the equation proposed by Rizk & Lefebvre (1985) and
other authors are wrong for high viscous fluid e.g. crude oil.
To avoid such situation, the injection pressure was enlarging
to increase the angular velocity in the injector's chamber
(Figure 4 and 5). A higher angular velocity caused a


ddp=1mm, do=3mm, dpin=2,
mdp=1mm, do=3mm, dpin=2,


n=3 -I
n=2 _


40 45 50 55 60 65 70 75 80 85 90 95 100
mass flow rate [kg/s]

Figure 7: Spray cone angle measured for the nozzle with a
pin and different number of the inlet holes.

The photographs of the spray cone are presented in figure 8.
For an injector constructed in such a way, the mass flow rate
change may take place through the change of the total jet
inlet area port cross-section. The reduction of the number of
the inlets affects the reduction of the mass flow rate and
increase of the fuel spray cone angle. The presented
experimental results provided an answer to the question of
how to modify the nozzle in order to obtain the desired
spray cone angle. For small orifice diameter the application
of the pin enables the control of the mass flow rate and the

























Figure 8: Photographs of crude oil stream atomized in an
injector with a pin.

The references provide numerous examples and empirical
equations. Figure 9 shows spray cone angle measured in the
test rig for different mass flow rate compared to the
analytical calculation for the standard nozzle with two and
three injection holes. It is noticeable that the measured spray
cone angle is on the similar level whereas the calculated
spray cone angle increases along with the growing mass
flow rate. The change of the angular velocity inside the
injector (two inlet holes instead of three with the same mass
flow rate) also causes the spray cone angle increase only.


dp = 1 mm; do=1.5 mm, n=3
80




S65 **
S60 -- Rizk & Lefebvre
~55~ --Experiment


45 *
40
35 40 45 50 55 60 65 70 75 80 85
mass flow rate [kg/s]

Figure 9: Spray cone angle for crude oil calculated with
equation (1) for three injection holes compared to the
measurement in the test rig.

The measurements for two and three injection holes show
the same trend, i.e. scarce changes of the spray cone angle.
Figure 10 shows the results of measurement and
computation of a new structure with a pin of diameter
d,,,,=2mm and d,=1 mm, d,,=3 mm, n=3 (numbers of
injection holes). Spray cone angle grows along with the
mass flow rate, which was expected. However, comparing
the spray cone angle calculations made by equation (1) to
the experimental results, we can see that the inclinations of
the two curves are comparable to each other, although the
spray cone angle values are different. It means that equation
(1) in the form proposed by Rizk & Lefebvre (1985) cannot
be applied to the injector with a pin.


***


spray angle. However, we should consider how the spray
angle for given geometric parameters of the injector could
be computed.


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010



dp = 1 mm, do=3 mm, dpin=2, n=3
100
95 --I -Rizk & Lefebvre
90 -C Experiment
u.85

S80

c 75
70 ,. *


60
40 45 50 55 60 65 70 75 80 85 90 95 100 105
mass flow rate [kg/s]


Figure 10l: Spray cone angle for crude oil calculated with
equation (1) for three injection holes compared with
measurement in the test rig for nozzle with pin.

Based on the experimental tests and calculations, the
authors suggest the following modifications of the
exponents in equation (1) for the injector with a pin.


-0163 O12
a= A, Pd,, p (3)
(d,,D,) p


The suggested change is the result of series of experiments
done on more than a dozen of injectors with a pin differing
by geometric parameters and injection pressure for water
and crude oil. Figure 11 presents the comparison of the
measured spray cone angle for crude oil injection (the same
injector as in figure 10) with calculation using equation 3.


dp = 1 mm, do=3 mm, dpin=2, n=3
100
95 -C Equation 3
90 -C Experiment


40 45 50 55 60 65 70 75 80 85 90 95 100 105
mass flow rate [kg/s]


Figure 11: Spray cone angle for crude oil calculated with
equation 3 compared with measurement in the test rig for
nozzle with pin.






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Conclusions


& Exhibition, Stockholm, Sweden, 1998


The experimental investigation of the pressure swirl
atomizers used for the liquid fuels atomization has been
discussed. More than a dozen of injectors differing by
geometric dimensions were tested on the test rig. Crude oil
was used as the medium. Due to the fact that the obtained
results were not satisfactory, i.e. the spray cone angle was
on a similar level for different injector geometries, a new
structure of an injector with a pin has been developed. The
pin forced a stream with air core in the exit section. Further
on, the spray cone angle based on the empirical equation
proposed by Rizk & Lefebvre (1985) was calculated for the
tested cases. A comparison of the experimental and
computational results for the standard and new designed
swirl nozzle shows that empirical equation proposed by
Rizk & Lefebvre (1985) for spray cone angle calculation is
not sufficient. Based on the experimental results, the authors
proposed new exponent coefficients in equation (1) for the
spray cone angle calculated for a nozzle with a pin. Finally,
the validation of the new empirical model for the swirler
with a pin has been successfully completed.


References

Lefebvre A., Gas Turbine Combustion, Second Edition,
Taylor & Francis, USA (1998)

Ommi F., Nejofar K., Movahednejad E., Designing and
experimental investigation of characteristics of a double
base swirl injector in a liquid rocket propellant engine,
Journal of applied sciences research 5(8), 955-968, (2009)

Jeng S.M., Jog A.A., Benjamin M.A., Computational and
experimental study of liquid sheet emanating from simplex
fuel nozzle, AIAA Journal, Vol. 36, No.2, (1998)

Dobski T., Nowak D., Chmielewski J., Jankowski R., Magni
F., Experimental experiences with crude oil combustion in
strong swirl flow, Proceedings of ASME Turbo Expo, 14-11
June Glasgow, Scotland, (2010)

Kulshreshtha D.B., Dikshit S., Channiwala S.A, Variation of
spray cone angle and penetration length of pressure swirl
atomizer designed for micro gas turbine engine,
International Journal of Dynamics of Fluid, Vol. 5, pp.
165-172, November (2009)

Lacava P.T., Bastos-Netto D., Pimenta A.P., Design
procedure and experimental evaluation of pressure-swirl
atomizers, 24th International Congress of The Aeronautical
Sciences, 29.08-03.09 Yokohama, Japan, (2004)

Rizk N. K., Lefebvre A. H., Prediction of velocity
coefficient and spray cone angle for simplex swirl atomizer,
Proc. 3rd. Int. Conf. Liquid atomization and spray systems,
London, 1985

Benjamin M. A., Mansour A., Samant U. G., Jha S., Liao Y.,
Harris T., Jeng S. M., Film thickness, droplet size
measurements and correlation for large pressure-swirl
atomizer, International Gas Turbine & Aeroengine Congress


Nowak D., Dobski T., Slefarski R., Magni F., Injection
nozzle for gas turbine combustion chamber, Patent,
B09/182-0, Alstom, Switzerland, 2010.




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