An experimental study on the spray behavior and fuel distribution of GDI

injectors using the entropy analysis and PIV method

K.H. Leea,*, C.H. Leea, C.S. Leeb

aDepartment of Mechanical Engineering, Hanyang University, 1271 Sa1-dong, Ansan-si, Kyungki-do 425-791, South KoreabDepartment of Mechanical Engineering, Hanyang University, 17 Hangdang-dong, Sungdong-gu, Seoul 133-070, South Korea

Received 4 February 2003; accepted 22 October 2003; available online 21 November 2003

Abstract

To improve the fuel consumption and exhaust emission for gasoline engines, Gasoline Direct Injection (GDI) system was spotlighted to

solve above requirements. Thus, many researchers have been studied to investigate the spray characteristics and the fuel formation of GDI

injector. In this study, we tried to study the characteristics of a direct injection gasoline spray by using entropy analysis and PIV methods. The

entropy analysis is based on the concept of statistical entropy, and it identifies the degree of homogeneity in the fuel concentration. The PIV

method was adopted to determine the fluid dynamics information at the spray. Also fuel formation within the cylinder in the case of early

injection timing greatly influences combustion characteristics. This study developed the analyzing system for the mixing fuel with air using

the Mie scattering method to visualize the fuel distribution. This technique was applied to a visualization single cylinder engine in order to

investigate the spray behavior and fuel distribution.

q 2004 Elsevier Ltd. All rights reserved.

Keywords: Entropy analysis; Particle image velocimetry; Vorticity strength; Gasoline direct injection

1. Introduction

As the environmental problems caused by vehicle

exhaust emissions become more severe, exhaust emission

standards and fuel economy regulations become more

stringent. For the gasoline engine, the emission of CO2 gas,

which is one of the main causes of global warming,

becomes a severe problem as well as the emission of toxic

gases such as CO, HC, NOx. Recently, the gasoline direct

injection (GDI) engine is spotlighted as a next generation

engine that can satisfy the Super Ultra Low Emission

Vehicle Super Ultra Low Emission Vehicle regulation and

can reduce the fuel consumption. Thus, the studies of high-

pressure vortex type injector, one of the key parts for the

development of GDI engine, have been performed by many

researchers [1,2]. Zhao et al. visualized the development

process of fuel spray of GDI injector by using a two-

dimensional Mie scattering method, and measured the

SMD and velocity of spray to investigate the evaporation

of fuel [3]. Yamauchi et al. performed a numerical analysis

for the fuel spray vortex of a high-pressure GDI injector by

using a Generalized Tank and Tube code, and compared

the results with those obtained by PDA [4]. Yamakawa

et al. developed a new fuel spray measuring technology of

LIF-PIV [5]. The velocity of airflow, which is induced by

the fuel spray, with the variation of the ambient pressure

was measured by using a LIF-PIV method. These studies

investigated particle diameter, velocity distribution, and

evaporation process of spray. However, the studies

experimentally investigated the fuel distribution within a

cylinder are very rare. Yuyama et al. developed a new

entropy analysis method that is based on the statistical

thermodynamics, and applied this method for the investi-

gation of propagation process of Diesel spray [6].

The present study developed a laser scattering image

detection system, and measured the macro scale fuel spray

characteristics such as spray penetration length, spray angle

and vorticity. An entropy analysis method based on the

concept of statistical thermodynamics has been developed,

and the fuel distribution was analyzed by this method.

0016-2361/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.fuel.2003.10.021

Fuel 83 (2004) 971–980

www.fuelfirst.com

* Corresponding author. Tel.: þ 82-31-400-5251; fax: þ 82-31-406-

5550.

E-mail addresses: hylee@hanyang.ac.kr (K.H. Lee); leemech@

ihanyang.ac.kr (C.H. Lee); cslee@hanyang.ac.kr (C.S. Lee).

2. Experimental apparatus and procedures

2.1. Entropy analysis method

The principle of entropy analysis that uses laser

scattering image is based on the concept of the statistical

thermodynamics Boltzmann studied a correlation of the

probability of particle distribution in the control volume and

the entropy. If particles of Ni are existed in energy level of

1i; the total energy E and the total number of particles N are

expressed as following equation

E ¼X

Ni1i; N ¼X

Ni

For convenience, let 10 is the lowest energy in system. And

assuming this value is zero relative to the other energy level.

For example, if all of it is existed in 10 state, possible

particle array is expressed like this {N;O;O;…}(case A).

And {N;22;22; 0;…}(case B) is that 10 state is the number

of N 2 2; 11 state is the number of 2. Generalized each

energy level 1i is the particle number of Ni; the number of

possible combination of the total particles number of N is

distinguished in this system, W is

W ¼N CN1£ðN2N1Þ

CN2£ · · · £NM

CNM

¼N!

N1!N2!N3!· · ·NM!¼

N!QNi!

ð1Þ

It is obvious that occurrence possibility of case B is higher

than that of case A.

The entropy might be expressed in the natural

logarithm of W combination according to the concept of

the Boltzmann statistics. It becomes a following equation

when Stirling approximation is applied for the case of

N q 1

ln n! < n ln n 2 n ðn q 1Þ

ln W ¼ ln N!2X

ln Ni

¼ N ln N 2 N 2X

Ni ln Ni þX

Ni

¼ N ln N 2X

Ni 2X

Ni ln Ni ð2Þ

S ¼ k lnðWÞ ¼ k½N lnðNÞ2X

{Ni lnðNiÞ}� ð3Þ

where k is a Boltzmann constant.

If we assume that the particle number of Ni in each cell

ðMÞ of the image is in proportion to image intensity IðiÞ of the

cell

S ¼ aXM

i

IðiÞ

( )ln a

XMi

IðiÞ

( )2

XMi

½aIðiÞ ln{aIðiÞ}�

¼ aXM

i

IðiÞ

( )ln

XMi

IðiÞ

( )2 a

XMi

½IðiÞ ln{IðiÞ}� ð4Þ

where a is the constant including a Boltzmann constant and

the coefficient of proportion between the number of particle

and image intensity.

IðiÞ is an image intensity corresponding to the number of

particle within the cell divided the number of M: If we think

that the particle is uniformly scattered, the average intensity

is

IðiÞ ¼1

M

XMi

IðiÞ ¼It

Mð5Þ

where It is the integrated value of the luminance over the

whole space. The entropy of a homogeneous divergence is

then

S1 ¼ aIt lnðMÞ ð6Þ

Beside, the total sum of luminance over the whole space is

constant and entropy S0 divided the image distribution to 0

and 255 is indicated as following, if P is the number of sell

that fluorescent light 255 occupy

S0 ¼ a½It lnðItÞ2 PIMAX lnðIMAXÞ�

¼ a½It lnðItÞ2 It lnðIMAXÞ� ð7Þ

Using S1 and S0; when entropy is a maximum value, that is

one, and when entropy is a minimum value, that is zero,

Nomenclature

E total energy

I the intensity of an individual pixel

M the number of meshs

N the total number of particles

S entropy

u X-directional velocity

v Y-directional velocity

W the number of a case for groups

a a proportionality factor

1 specific energy

k Boltzmann’s constant

v vorticity

F correlation coefficient

V the number of microscopic state

Subscripts

i ith state

z interrogation area (A, B, C)

t total

K.H. Lee et al. / Fuel 83 (2004) 971–980972

normalized entropy Sp is defined as

Sp ¼S 2 S0

S1 2 S0

¼

It lnðIMAXÞ2XM

i

{IðiÞ lnðIðiÞÞ}

It{lnðMÞ2 lnðItÞ þ lnðIMAXÞ}ð8Þ

The value of Eq. (8) writes directly a program from a

luminosity distribution in pictures and we can analyze

homogeneity degree of a spray and a diffusion phenomenon.

2.2. Experimental apparatus for spray behavior

Fig. 1 shows a schematic diagram of the experimental

apparatus for the entropy analysis of GDI spray. In order to

simulate the spray behavior in the engine combustion

chamber with different engine operation condition, the

ambient pressure and the temperature in the high-pressure

chamber controlled by nitrogen gas and a heater. The spray

chamber is pressured by high-pressure nitrogen gas and fuel

is injected to the high-pressure chamber. An Nd:YAG laser

(200 mJ, 532 nm) is used as a light source. It generates two

times sequentially laser beam with short time interval by

using a double pulse option (DPO). The laser beam passes

through the cylindrical lens and is introduced to the

observation area as a form of sheet with the thickness of

2–3 mm. The exposure times of CCD camera and laser

beam and the injection time of fuel spray are controlled by a

timing board (PC-TIO-10) and the LabView program. By

controlling the laser trigger signal and delay time, the

scattering image of the formation of fuel spray can be

obtained. The image obtained by a high resolution CCD

camera (1008 £ 1008, Kodak, Megaplus ES 1.0) is recorded

as a digital form by an image board (frame grabber,

metoerll/digital) in a PC. Fig. 2 shows the definition of

injector attached angle and specification of test injectors,

and Table 1 shows the experimental conditions.

2.3. Experimental apparatus for PIV system

The PIV method measures the particle velocity by

analyzing CCD camera particle images that are exposed by

sequentially double exposure laser beams. Usually, the

particle images have been obtained by a single frame-

double exposure method, and the images have been

analyzed by an auto-correlation. However, this method

had a difficulty in determining the direction of the velocity

vector. The image shifting process which uses a rotating

mirror or the two-color PIV method have been developed to

determine the direction of velocity vector more clearly [7],

but these methods require complicate experimental

apparatus.

This PIV is a well established technique for the

measurement of instantaneous planar velocity fields and

has been reviewed by a number of authors [8–13].

Especially, Adrian developed a PIV algorithm and optical

systems to obtain velocity vectors in the flow field [9].

However, it is hard to purchase the PIV because the

commercial PIV is very expensive. Thus, the Q-switch is

installed to the single pulse Nd:YAG laser in order to add

the double pulse function to the laser source and the control

Fig. 1. Experimental apparatus.

Fig. 2. Definition of injector attached angle and specification of test

injectors.

Table 1

Experimental condition

Ambient temperature (K) 298, 373

Ambient pressure (MPa) 0.1, 1

Spray

Swirl injector

A Offset (208)

B Non-offset

Fuel Gasoline

Fuel pressure 10 MPa

Injection period 3 ms

K.H. Lee et al. / Fuel 83 (2004) 971–980 973

unit is developed to synchronize the laser pulse interval with

the expose timing of CCD camera.

The PIV system used in this study is composed of the

laser source, image storage and control unit. In case of laser

source, the DPO, which could be controlled by the time of

pulse separation and Q-switch delay, is installed to the

Nd:YAG laser to generate the double pulse function and the

DPO can control the interval time between primary pulse

and main pulse. In case of image storage, the image

controller adjusted the exposure timing of double exposure

CCD and Q-switch timing to synchronize the primary frame

and main frame. Finally, the control unit is operated by the

laser and CCD trigger based on the injection timing and

crank angle signal of visualization engine. In addition, the

PIV algorithm is made by using a cross-correlation method

and the accuracy of the developed PIV algorithm is

evaluated with the standard images suggested by JPIV

[14]. From this validating procedure, we found that the

developed PIV algorithm has a good agreement with the

standard flow image.

The present study recorded particle images exposed by

each sequential laser beam at separate frames by using a

CCD camera and calculated velocity vector by a cross-

correlation PIV algorithm. The direction of particle velocity

vector could be determined clearly because the particle

images of each laser pulse were recorded at the separate

frames. Fig. 3 shows the ‘frame-straddling’ method, which

aligns laser pulse at each sequential CCD camera frame.

Fig. 4 shows the cross-correlation PIV algorithm using fast

Fourier transform, which is programmed to obtain the

velocity by calculating the coordinates of location of the

maximum cross-correlation parameter.

2.4. Measurements of fuel distribution

in the visualization engine

The fuel distribution and the process of mixing fuel with

air in a single cylinder visualization engine have been

observed. A schematic diagram of the laser beam system is

shown in Fig. 5. The sheet type laser beam is induced into

the cylinder either through a cylinder liner or through a

mirror under the piston and a transparent piston crown. A

rotary encoder is mounted at the camshaft, and the injection

timing and the ICCD are synchronized with the encoder

signal. The spray images with the crankshaft angle at the

intake stroke are obtained with this apparatus.

3. Experimental results and discussion

3.1. Analysis of fuel distribution by using the entropy

analysis algorithm

It is well known that the Mie scattering light intensity is

generally affected by the droplet diameter and the number

density. The droplet diameter of test injector is measured by

using PDPA. From the experimental result, the distribution

of droplet size is uniform and the spray droplet diameter is

Fig. 3. Schematic diagram of frame straddling and timing chart.

Fig. 4. Schematic diagram of cross-correlation PIV algorithm.

Fig. 5. The laser sheet method for observing the spray pattern.

K.H. Lee et al. / Fuel 83 (2004) 971–980974

approximately 20–30 mm. Therefore, the droplet diameter

effect is negligibly small. The details of the result are

described elsewhere [15], so they will not be discussed here.

Since it is assumed that the particle number density could be

linearly correlated to the local luminance light of an image,

the Mie scattering light intensity in this paper is only

affected by the number density.

The laser scattering images of the fuel distribution

obtained by the system are shown in Fig. 1. The images are

divided to small interrogation area of the size of 40 £ 40

pixels, and the entropy of each measuring area is calculated

by Eq. (8). Figs. 6 and 7 show the isentropic lines of the

scattering images. The main mechanisms of fuel distribution

are the momentum exchange due to viscous friction of air

and fuel and the direct diffusion due to fuel evaporation. As

shown in Figs. 6 and 7, at the downstream, the fuel spray

spreads widely and shows high entropy value. The

development of fuel spray is more progressed as time goes

on. Especially, the entropy increases clearly at the whole

area of fuel spray at a temperature of 373 K which is above

the fuel evaporation temperature. As shown in this figure,

the entropy value of the region near the injector tip showed

lower value than that of other region. This reason can be

explained by the fact that the droplet breakup does not occur

in the region close to the nozzle tip. Thus, the diffusivity of

fuel in this region could not be fully developed. On the other

hand, the entropy increased at the measuring points far from

downstream from the injector tip. An explanation could be

that the vortex is generated at the edge of spray due to higher

momentum of droplets. Since the air entrained by the vortex

pulls the smaller droplets towards the centerline, the vortex

enhanced mix the fuel with ambient air. The other reason for

high entropy value is that the viscosity is decreased by the

higher temperature (373 K), which helps the fuel to

evaporate. The region of high entropy, which represents

the uniform fuel formation, is distributed widely neat the

end of the cone region. The reason of these phenomena is

believed that the momentum change between the fuel spray

and the airflow induced by fuel spray increase mixing of two

components. To compare entropies for the ambient

Fig. 6. Comparison of spray pattern and entropy analysis at 4 ms after injection start.

K.H. Lee et al. / Fuel 83 (2004) 971–980 975

temperature of 298 K which is below the evaporating

temperature of fuel and for the temperature of 373 K, which

is above the evaporating temperature, the entropies for the

temperature of 373 K show higher values than those for the

temperature of 298 K. These phenomena can be observed

more clearly at the region near the injector tip. The direct

diffusion is believed to be more dominant mechanism than

the momentum change near the injector tip. Comparing the

analysis results for the ambient pressure of 1 MPa and those

for the ambient pressure of 0.1 MPa, the spray is less

propagated at high ambient pressure. A region of hetero-

geneous particle distribution of round shape is shown at the

edge of cone region of high ambient pressure, which is not

shown at the results of low ambient pressure. The reason of

formation of heterogeneous region at the edge of cone

region is believed that the fuel particles at the boundary of

cone go into the center of the spray because of the vortex at

the end of spray and the pressure decrease at the center

region of spray due to high velocity of spray flow.

3.2. Correlation between entropy and vorticity strength

The vorticity from the velocity fields obtained PIV

system is calculated by grid coordinate as following Fig. 8.

The vorticity is basically calculated on the left term of Eq.

(9) but is calculated by the circulation using the stoke theory

like the right term

vz ¼1

2

›v

›x2

›u

›x

� �¼ lim

A!0

G

Að9Þ

The vorticity which is basically obtained on the circulation

as following the grid coordinate of Fig. 8 is like Eq. (11).

Where Dx (mm) and Dy (mm) is corresponding to the spatial

resolutions of flow fields which are obtained from the PIV

system

þu dL ð10Þ

Fig. 7. Comparison of spray pattern and entropy analysis at 4 ms after injection start.

K.H. Lee et al. / Fuel 83 (2004) 971–980976

vzði; jÞ ¼1

4DxDyuði; j 2 1ÞDx þ 1

2ðuði þ 1; j 2 1ÞDx

nþ vði þ 1; j 2 1ÞDyÞ þ vði þ 1; jÞDy

2 12ðuði þ 1; j þ 1ÞDx 2 vði þ 1; j þ 1ÞDyÞ

2 uði; j þ 1ÞDx 2 12ðuði 2 1; j þ 1ÞDx

þ vði 2 1; j þ 1ÞDyÞ2 vði 2 1; jÞDy

þ 12ðuði 2 1; j 2 1ÞDx 2 vði 2 1; j 2 1ÞDyÞ

oð11Þ

As we investigated in Section 3.1, the main mechanisms to

increase entropy are the viscous friction due to velocity

gradient and the vaporization. Because the velocity gradient

can be referred as the vorticity, this study quantifies the

velocity gradient as the vorticity strength. The vorticity

strength in this study is defined as the absolute vorticity

value at each interrogation area (A, B and C) divided by

their total value, as shown in Eq. (12)

vz ¼

Xi

lvz;ilPXi

lvz;ilð12Þ

where Z is interrogation area of the A, B and C region, i

mean the image number at each interrogation area.

Fig. 9 shows the interrogation areas of the region A, B

and C which is the location apart from injector tip. The

locations of the A, B and C are, respectively, 15, 30 and

45 mm at the downstream from the injector tip.

Fig. 10 shows the comparison of the entropy value and

the vorticity strength at the location of the region A, B and

C. The correlation between entropy and vorticity strength

were investigated in order to clarify the mixing process. And

we analyzed the relationship between entropy, vorticity and

effect of vaporization. The vorticity measured in this study

is a macro scale movement of particle because the spatial

resolution of the PIV system has a limitation. On the other

hand, the entropy is based on a micro scale movement.

Therefore, the each value represents different scale move-

ment. Generally, these values show larger values at the

downstream, but it may be changed according to the

experimental conditions.

As can be seen in Fig. 10, the correlation between

entropy and vorticity strength in the lower temperature case

is stronger than that of high temperature case. From these

observations, it can be concluded that viscous friction due to

velocity gradient is less dominant than the evaporation at the

downstream of spray.

3.3. Characteristics of fuel distribution with the variation

of injector attached angle

The fuel distributions in the visualization cylinder are

measured with the variation of injector attached angle.

Fig. 11 shows the fuel distribution with the variation of

crank angle. As the crank angle increases, the more fuel

sprays moves with the tumble flow induced by intake

airflow. The fuel spray of the large injector attached angle is

more distributed at the center of the cylinder than those of

the small injector attached angle. The movement of fuel

spray of the large injector attached angle has a tendency to

curve toward the center of the cylinder liner. This result can

be obtained because injected droplet is influenced by intake

flow and injector attached angle is large.

Fig. 8. Sketch of data grid with notation of vectors.

Fig. 9. Interrogation areas.

Fig. 10. Relation between entropy and vorticity strength.

K.H. Lee et al. / Fuel 83 (2004) 971–980 977

3.4. Analysis of fuel distribution in the visualization cylinder

by using of the entropy analysis

In order to analyze the propagation of fuel particles and

the process of mixing fuel with air, the development process

and the homogeneity degree of fuel spray in the visualiza-

tion cylinder are analyzed quantitatively by using the

entropy analysis. Fig. 12 shows the normalized entropy

distribution calculated by the Eq. (8). Fig. 12(a) shows that

the fuel particles are concentrated near the injector tip at the

beginning of the injection, and they are propagated as

the crank angle increases. At the end of the injection, the

mixture shows the homogeneous distribution. The spray

angle of injector B is larger than that of injector A. In Fig.

12(b), we are able to know that actively diffusion

phenomenon is occurred by increasing a contact area of

intake flow because of spray angle addition in the early of

injection. When crank angle is 4758, the end of injection and

the left of injection center are shown that non-dimension

entropy value is small. The reason of non-dimension

entropy value is large in the end of injection because of

the union of droplet by loss of momentum and distribution

of relatively large droplet.

4. Conclusion

A new entropy analysis method based on statistical

thermodynamics has been developed. By applying the

methods to the fuel spray of GDI injector, following

conclusions are obtained.

(1) The entropy analysis shows that the fuel spray

propagates more widely to the downstream direction

as time passes. When the ambient temperature is above

the fuel evaporation temperature, the entropies of

whole area of spray are higher than those obtained

when the ambient temperature is below the evaporation

Fig. 11. Fuel distribution in cylinder for attached angle according to crank angle.

K.H. Lee et al. / Fuel 83 (2004) 971–980978

temperature. When the ambient pressure is increased,

fuel spray shows a macro scale heterogeneous

distribution.

(2) By comparing the entropy and the vorticity strength, it

can be concluded that viscous friction due to velocity

gradient is less dominant than the evaporation at the

downstream of spray.

(3) The spray of the large injector attached angle is more

distributed at the center of the cylinder than those of the

small injector attached angle. This means that the spray

behavior of the large injector attached angle has a

tendency to curve toward the center of the cylinder

liner.

(4) The droplets are concentrated near the injector tip at

the beginning of the injection, and they are propagated

as the crank angle increases. At the end of the injection,

the mixture shows the homogeneous distribution.

(5) From the entropy analysis results, it is known that the

spray is widely distributed according to the elapsed

time after injection. Especially, in vaporization con-

dition (373 K), entropy value is increased in a whole

spray area. Besides, as ambient pressure increases, the

fuel distribution becomes heterogeneous condition.

(6) According to compare entropy value with vorticity

strength, a velocity gradient by viscosity fraction does

not affect uniform mixing process of fuel spray than

entropy increase by evaporation of the spray.

Acknowledgements

We would like to thank Combustion Engine Research

Center (CERC) for financial support for this work.

Fig. 12. Fuel distribution I cylinder about two injectors using the entropy analysis.

K.H. Lee et al. / Fuel 83 (2004) 971–980 979

References

[1] Zhao F-Q, Yoo J-H, Lai M-C. Spray dynamics of high pressure fuel

injectors for DI gasoline engines. SAE technical paper, No. 961925;

1996.

[2] Yamauchi T, Wakisaka T. Computation of the hollow-cone sprays

from a high-pressure swirl injector for a gasoline direct-injection SI

engine. SAE technical paper, No. 962016; 1996.

[3] Yamakawa M, Isshiki S, Yoshizaki T, Nishida K. Measurement of

ambient air motion of D.I. gasoline spray by LIF-PIV. COMODIA

2001;499–504.

[4] Preussner C, Doring C, Fehler S, Kampmann S. GDI: interaction

between mixture preparation, combustion system and injector

performance. SAE paper No. 980498; 1998.

[5] Yuyama R, Chikahisa T, Kikuta K, Hishinuma Y. Entropy analysis of

microscopic diffusion phenomena in diesel sprays. COMODIA 2001;

542–50.

[6] Lee K-H, Woo Y-W, Park S-C, Lee C-S. An analysis of intake flow in

a 5-valve gasoline engine by two color PIV. A volume of D of the

KSME 2001 Spring Papers; 2001.

[7] Lee K-H, Lee C-h, Woo Y-W, Lee C-S. A study on the spray

characteristics for a gasoline direct injector by using entropy analysis

and PIV method. KSME 2002;1047–54.

[8] Hinsch KD. Particle image velocimetry. In: Rajpal SS, editor. Speckle

metrology. New York: Marcel Dekker; 1993.

[9] Keane RD, Adrian RJ. Theory of cross-correlation analysis of PIV

images. J Appl Sci Res 1992;49:191–215.

[10] Lecordier B, Mouqallid M, Trinite M. Simultaneous 2D measure-

ments of flame front propagation by high-speed tomography and

velocity field by cross correlation. Proceedings of the Eighth

International Symposium on Application of Laser Techniques to

Fluid Mechanics Lisbon, Portugal; 1994.

[11] Stolz W, Kohler J, Lawrenz W, Meier F, Bloss WH, Maly RR,

Herweg R, Zahn M. Cycle resolved flow field measurements using

a PIV movie technique in a SI engine. SAE International Fuels

and Lubricants Meeting and Exposition, San Francisco, Paper

922354; 1992.

[12] Wormell DC, Sopchak JL. A particle image velocimetry system using

a high resolution CCD camera. Conference on Optical methods and

Data Processing in Heat and Fluid Flow, City University, London,

UK; 1994. IMechE C485/014.

[13] Stereoscopic WC. Digital particle image velocimetry for appli-

cation in wind tunnel flows. Meas Sci Technol 1997;8(12):

1465–79.

[14] Stanislas M, okamoto K, Kaher C. Main results of the first

international PIV challenge. Meas Sci Technol 2003;14:63–89.

[15] Lee K, Reitz RD. Investigation of spray characteristics from a low-

pressure common rail injection system for use in a HCCI engine.

ILASS Americas, 16th Annual Conference on Liquid Atomization

and Spray Systems, Monterey, CA; 2003.

K.H. Lee et al. / Fuel 83 (2004) 971–980980