Georgios Charalampous 1,*, Yannis Hardalupas...

17th International Symposium on Applications of Laser Techniques to Fluid Mechanics Lisbon, Portugal, 07-10 July, 2014

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Comparison between signal attenuation correction methodology for LIF

and scattered light intensity measurements in dense sprays

Georgios Charalampous 1,*, Yannis Hardalupas 1

1: Mechanical Engineering Department, Imperial College London, London, UK

* correspondent author: [email protected] Abstract An investigation is performed to comparatively examine the application of laser beam scanning and signal processing methodology on the measurement of Laser Induced Fluorescence (LIF) and scattered light intensities from droplets in sprays. The quantitative spray characteristics evaluated from measurements of LIF and scattered light intensity from spray droplets are examined before and after application of an attenuation correction procedure. The importance of the correction procedure is evaluated from the observed differences between the corrected and uncorrected spray profiles. The measured spray characteristics from LIF and scattered light intensity measurements are compared to determine the advantages and disadvantages of each approach. 1. Introduction A planar droplet sizing technique (also known as optical patternator) has been proposed for the measurement of the Sauter mean diameter (SMD) of spray droplets, based on combined laser-induced fluorescence and scattered light (LIF/Mie) intensity imaging on a plane of a spray determined by a laser sheet (Yeh, Kosaka et al. 1993, Kamimoto 1994, Le Gal, Farrugia et al. 1999, Sankar, Maher et al. 1999, Domann and Hardalupas 2001, Domann and Hardalupas 2003, Zimmer, Domann et al. 2003, Charalampous and Hardalupas 2011b, Charalampous and Hardalupas 2011a). The LIF/Mie technique has a significant advantage over other droplet sizing methods in that it is a planar technique that can size full planes of sprays, while the other methods are limited to “point” (Phase Doppler Velocimetry, PDV), line of sight (laser diffraction), or planes of small cross-sectional areas (Interferometric Laser Imaging Droplet Sizing, ILIDS) of sprays. In addition, this technique is applicable to dense spray regions, provided that appropriate compensation of multiple scattering effects and laser intensity attenuation along the sprays is included. The fundamental hypothesis of the LIF/Mie technique for droplet sizing (Yeh, Kosaka et al. 1993, Kamimoto 1994) is that when a spherical droplet doped with a fluorescing dye is illuminated with a laser, the intensity of the fluorescent light emitted from a droplet is proportional to the volume of the illuminated droplet while the intensity of the scattered light is proportional to the surface area of the illuminated droplet. However, it has been shown that the above assumption is not always valid (Domann and Hardalupas 2001, Domann and Hardalupas 2003, Charalampous and Hardalupas 2011b, Charalampous and Hardalupas 2011a) and there is a need to develop appropriate processing for droplet sizing (Domann and Hardalupas 2001). Recently, an extensive analysis of the operation of the LIF/Mie technique (Charalampous and Hardalupas 2011b, Charalampous and Hardalupas 2011a, Charalampous and Hardalupas 2012) has led to the development of a novel approach to improve the sizing accuracy of the technique. The application of the technique in dense sprays can lead to multiple scattering from spray droplets outside the illuminated plane (Czerwinski, Mroczka et al. 2001a, Czerwinski, Mroczka et al. 2001b, Berrocal, Meglinski et al. 2005). This may lead to a qualitative change of the measured spatial distribution of the droplets in sprays and uncertainties in the measurement of the droplet Sauter Mean Diameter. As a consequence, two methods have been proposed to correct for the effects of multiple scattering and laser incident beam intensity attenuation during propagation through the sprays (Brown, McDonell et al. 2002, Berrocal, Kristensson et al. 2008). The method (Berrocal, Kristensson et al. 2008) is more complicated to apply than the method of (Brown, McDonell et al. 2002), since it requires precise shaping of the incident intensity of the probing laser beam. The method (Brown, McDonell et al. 2002) relies on scanning the laser


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beam system across the spray and post-processing the recorded spray images, which are easier to implement. The LIF and scattered light intensity measurements from droplets in dense sprays are hindered by multiple scattering noise, attenuation of the illuminating laser beam and attenuation of the collected signal from droplets between the probed spray region and the detector. A correction procedure was described by (Brown, McDonell et al. 2002) in order to address the attenuation of the incident and collected light intensity by a spray. It is the purpose of this investigation to evaluate the application of the above methodology to the scattered and the fluorescence light intensity signals from the droplets, which are representative of the droplet surface area and liquid volume densities, and quantitatively compare the results of the two approaches. 2. Experimental facility Instead of scanning the laser beam through the spray, here the spray was mounted on a motorised linear stage and traversed along a laser beam fixed in space (Figure 1). The spray traversing approach is equivalent to the beam scanning approach for the purposes of this experiment. The beam scanning approach has the disadvantage that is more complex to setup and that as the laser beam is scanned through the spray the distance between the laser beam and the camera changes. This requires constant refocusing of the camera lens during the duration of the experiment, which is both inconvenient and changes the magnification of the imaging system, which also needs to be accounted for. The camera can be mounted on a linear stage and move together with the scanning beam so that the focal distance and the system magnification remain constant but this approach is difficult to implement. The spray traversing approach has the advantage that the imaging system needs to be focused only once and the system magnification is always fixed while the system mechanics are simplified. For these reasons the spray traversing method was preferred for the current experiment.

Spray cross section

Imaging camera

Laser power meter

Direction of spray traversing

Laser beam

ZX

Figure 1 Traversing the spray through a fixed laser beam. The spray is the only moving component. The origin is

located at the centre of the spray nozzle For the purpose of this investigation, a flat spray air assist atomiser from Spraying Systems Model B1/4J-316SS-2SUE15B-316SS (Figure 2) was used. This allows for fine control of the spray droplet size and number density. For example, a greater number of smaller droplets is produced by increasing the air flow rate, while maintaining the same liquid flow rate, and vice versa. The overall spatial distribution of the spray is largely independent of the fluid flowrates. The atomiser was mounted vertically with the tip exhausting downwards, so that the injected liquid could be easily collected. The atomised liquid was distilled water doped with Rhodamine WT dye. A 9l vessel was utilised for the pumping of the water, where the contained water was kept under constant pressure of 4 bar stabilised by a pressure regulator. The large capacity of the vessel assured uninterrupted water flow for over 2 hours and the fixed pumping pressure guaranteed that the water flowrate did not fluctuate. The atomising gas was compressed nitrogen from a 200l cylinder, delivered at the system at a pressure fixed at 4 bar adjusted by a pressure regulator. The air and water flowrates were


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monitored by rotameters. The above arrangement guaranteed the continuous operation of the spray with stable characteristics over time periods sufficiently longer than the time required for complete characterisation of a full spray plane.

Atomiser

Spray centreline

Spray boundaries

Figure 2 Flat spray air assist atomiser mounted on the linear traverse. The spray centreline location is shown as a white

dashed line and the approximate location of the spray boundaries are shown in solid white lines. Spray measurements were performed along the horizontal plane at a distance of 20mm downstream of the atomiser nozzle. At that location, the spray is sufficiently dense for measurable attenuation of the illuminating beam and the collected signal. The illuminating beam was produced by a Nd:YAG laser operating at wavelength of 532nm. The diameter of the laser beam was 4.5mm. Absorption of light at this wavelength by water is minimal, so only the scattering of the illuminating light needs to be considered in the data processing method. Imaging of the scattered and fluorescent light intensities from the spray was performed by a 12bit CCD camera (Model PCO sensicam QE). The camera was fitted with a 105mm lens coupled with an interference filter (532±10nm) for the scattered light intensity measurements and a Schott OG590 long pass filter for the fluorescent light intensity measurements. The interference filter was centred at 532nm and had a bandwidth of 10nm, which suppressed ambient light noise for improved accuracy in the measurements. Monitoring the intensity of the laser beam before and after the spray was performed using a laser power meter. The motorised linear stage was acquired from Thorlabs (MTS50 model). The positioning accuracy of each stage is within 1µm. The travel range of each stage is 50mm, which is sufficient to traverse the full spray across the laser beam for many planes past the atomiser exit. The spray was traversed at increments of 5mm at a time. In this way, the speed of the measurements was maximised while the spray was fully resolved. The complete optical setup is presented in Figure 3. For each increment, 200-1000 images were acquired which are sufficient for the spray characteristics to converge.


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Atomiser

Energy meter

Linear traverse

Beam steering optics

Laser beam path

Probe laser beam

Figure 3 Experimental arrangement showing the mounted atomiser, the laser energy meter, the beam steering optical arrangement and the beam path (dashed green line). The location of measurement is the solid green line just below the

spray. 3. Image processing When considering processing the dense spray images, attenuation effects of the incident laser beam have to be taken into account. There is: • Attenuation of the laser beam intensity as it traverses through the spray. • Attenuation of the scattered light intensity as it traverses from the illuminated droplets to the detector

and multiple scattering of the signal Both have been considered by many researchers and various approaches have been proposed to address them as the measurement accuracy of the LIF/Mie technique (Yeh, Kosaka et al. 1993, Sankar, Maher et al. 1999) is sensitive to the scattered light intensity (Charalampous and Hardalupas 2011b, Charalampous and Hardalupas 2011a, Charalampous and Hardalupas 2012). Approaches for addressing the first effect include bidirectional illumination (Su, Drake et al. 1998), measurement of the amount of attenuation of the LIF signals by means of a laser dye cuvette and compensation for the attenuation (Sick and Stojkovic 2001), sequential illumination by opposed laser sheets (Douglas, Verdieck et al. 1996). In order to address the latter issue, multiple imaging of the spray under structured illumination methods have been proposed (Berrocal, Kristensson et al. 2008, Kristensson, Araneo et al. 2011, Kristensson, Berrocal et al. 2011a, Kristensson, Berrocal et al. 2011b, Berrocal, Kristensson et al. 2012). However these methods are complex and require substantial investment of resources and effort, especially when instantaneous


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measurements are required. A simpler yet efficient method that addresses both effects has been proposed by (Brown, McDonell et al. 2002). Instead of using a laser sheet to illuminate the spray a laser beam is used. Since a smaller number of droplets are illuminated with the laser beam rather than the laser sheet at a time, there are less multiple scattering affects and the collected light is inherently substantially less affected by noise. The quantitative description of the attenuation effects of the light collected by the spray is considered as detailed by Eq. (1) below: 0( , ) ( ) ( , ) ( , ) ( , )CCD b cI x z K z I e x z x z e x zσ= ⋅ ⋅ ⋅ ⋅ (1) where: I0 is the intensity of the laser beam before it enters the spray eb(x,z) is the relative decrease of the laser beam intensity as it traverses the spray σ(x,z) is the scattering cross section of the droplets ec(x,z) is the relative decrease of the droplet light intensity as it traverses the spray K is a constant that translates the intensity signal detected by the camera to the physical signal intensity The procedure for the reconstruction of the spray is applied in steps which reconstruct the spray one layer at a time. The method begins with the evaluation of the constant K which is estimated as:

( )

( , )( , )

1 ( , )

CCDx

c

b

I x z dxe x zK ze z

+∞

=−∞⋅

=− +∞

∫ (2)

For the first scanned beam, there is no attenuation of the scattered light signal on the droplets. Hence Eq. (2) reduces to:

( )( ,0)

01 ( ,0)

CCDx

b

I x dxK

e

+∞

=−∞⋅

=− +∞

∫ (3)

and is completely solvable from the measured quantities. Once K is estimated, it is possible to estimate eb(x,z) as:

( ) 0

( , )1( , ) 1( , )

x x CCDb x

c

I x ze x z dxK z e x z

=

== − ⋅ ⋅∫ (4)

For the first scanned beam the above equation becomes

( ) 0

1( ,0) 1 ( ,0)0

x x

b CCDxe x I x dx

K=

== − ⋅ ⋅∫ (5)

Subsequently σ(x,z) is evaluated as:

( )( )

( , ),, ( , ) ( , )

CCD

b c

I x zx zK x z e x z e x z

σ =⋅ ⋅

(6)


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and as before, for the first scanned beam, Eq. (6) reduces to:

( )( )

( ,0),0,0 ( ,0)CCD

b

I xxK x e x

σ =⋅

(7)

In order to determine the spray quantities for the first scanned beam, all the information needed is available. However, for scanned beams inside the spray where attenuation of the scattered light from the spray droplets is present, consequential knowledge of ec(x,z) is required. This is obtained from:

0( , )

( , )x z

zx z dz

ce x z eσ

=

=− ⋅∫= (8)

following the Beer-Lampert law. Therefore, all the required information for the evaluation of the spray characteristics from one scanned beam further inside the spray is available and can be obtained by following equations (2) to (8). 4. Results & discussion By applying the procedure that is described in the previous section the attenuation of the laser beam was measured as it traversed the spray. Due to the attenuation of the laser beam as it traverses the spray it can be observed that its intensity can decrease up to 10%. The attenuation is small at the edges of the spray but increases at the spray centre where the droplet density is high.

X (mm)

Z (m

m)

Extinction coefficient eb

-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.7

0.75

0.8

0.85

0.9

0.95

1

Figure 4 Distribution of the extinction coefficient as the laser beam passes the spray

The attenuation of the signal intensity, emitted from the illuminated droplets, during its propagation through the spray towards the location of the camera is more significant and can be as high as 15%. This parameter is highest at the location directly behind the spray axis where the droplet signal needs to travel through the full length of the spray to be imaged by the camera.


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X (m)

Z (m

)

Attenuation coefficient ec

-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.7

0.75

0.8

0.85

0.9

0.95

1

Figure 5 Distribution of the attenuation coefficient as the light from the droplets travels to the imaging camera

The scattering coefficient is calculated using only the attenuation of the laser beam as it traverses through the spray and is presented in Figure 6. The distribution of the scattering coefficient is characteristic of that of a flat spray with maximum attenuation at the centre and diminishing attenuation at the edges. However, the quantitative interpretation is incorrect, since the attenuation of the droplet scattered light intensity on the way to the camera is not considered in this case.

X (m)

Z (m

)

Scattering coefficient js (m-1)

-0.02 -0.01 0 0.01 0.02-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0

5

10

15

20

Figure 6 Distribution of the uncorrected scattering coefficient of the spray

The correction of the scattering coefficient error shown in Figure 7 demonstrates a quantitative increase in the value of the scattering coefficient, which for the considered spray is of the order of 20%. The maximum error is not centred along the centreline of the spray, but is rather offset closer to the region of the spray further from the camera, which is affected more by the attenuation of the collected light during the interaction with other droplets.


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X (m)

Z (m

)

Scattering coefficient js error (m-1)

-0.02 -0.01 0 0.01 0.02-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0

0.5

1

1.5

2

2.5

3

3.5

4

Figure 7 Distribution of the error of the scattering coefficient

When considering the distribution of the collected scattered light intensity, Figure 8, an oval shape is observed. The scattered light intensity is high along the spray central axis and decreases with the distance from the centreline. This is demonstrative of a high amount of surface area on the spray centreline

X (m)

Z (m

)

Mie

-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0

50

100

150

200

250

300

350

400

Figure 8 Distribution of the uncorrected scattered light intensity signal from the droplets

By applying the correction procedure to the scattered light, Figure 9, while there is no significant qualitative difference, the intensity of the signal is corrected in accordance to the correction of the scattering coefficient in Figure 7.


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X (m)

Z (m

)

Corrected Mie

-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0

50

100

150

200

250

300

350

400

Figure 9 Distribution of the corrected scattered light intensity signal from the droplets

The distribution of the fluorescent intensity emitted from the spray droplets is presented in Figure 10. As in the case of the scattered light, the highest intensity is found along the centreline of the spray. This indicated that the mass density is greatest there. The distribution of the intensity also has an oval shape as the distribution of the scattered light, but in this case there is a contraction close to the centreline. This shows that the mass distribution does not follow exactly the same pattern as the droplet surface area distribution. The constriction is most likely caused by the gas jets that are responsible for the atomisation of the liquid jet and the oval spray of the pattern. It appears that at the location where the gas jets meet there is a depletion of liquid volume. This is not observed in the scattered light images of the spray where there is no dimple in the pattern at the same location. As a consequence, spray patternation using the scattered light intensity and the fluorescent intensity signals might result to different observations in some cases. This possibility should be taken into account when measuring sprays and the imaging wavelength should be selected according to the spray property that is of importance.

X (m)

Z (m

)

LIF

-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0

10

20

30

40

50

60

70

80

Figure 10 Distribution of the uncorrected fluorescent intensity signal emitted from the droplets

By applying the correction procedure to the fluorescent light intensity of Figure 11, there is an increase of the fluorescent intensity in the region of the spray furthest from the camera, where the attenuation of the fluorescence signal is greatest.


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X (m)

Z (m

)

Corrected LIF

-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0

10

20

30

40

50

60

70

80

Figure 11 Distribution of the corrected fluorescent intensity signal emitted from the droplets

The LIF/Mie ratio is presented in Figure 12. The ratio was calculated at regions of the spray, where the fluorescence signal was at least 20% of the maximum value. This is because as the density of the spray decreases, the signal to noise ratio of the LIF/Mie ratio also decreases and the spatial distribution of the relative values of the droplet SMD becomes noisy. The filtering out of the low signal to noise regions does not affect the characterisation of the spray significantly, since these regions are only at the outer edge of the spray. The LIF/Mie ratio shows that the Sauter Mean Diameter of the examined spray is close to the centre and decreases with radial distance away from the axis. This qualitative behaviour of the droplet diameters in the spray is expected for this type of atomiser. A small asymmetry is observed in the spatial distribution of the SMD, which may be present in the spray. The application of the correction procedure on the fluorescent and scattered light intensities does not have an effect on the resulting distribution of the SMD. This is because the LIF/Mie technique relies on a ratio of intensities and the same corrections are applied to both intensity signals. As such, the ratio remains unchanged. Therefore, while the correction procedure offers significant quantitative improvement of the individual measurements of the droplet scattered and fluorescent light intensities, which correspond to the surface area and volume of the measured droplets, the measurement of the droplet size is not improved. Another uncertainty in the measurement of dense sprays is the contribution of secondary scattering. The beam scanning method addresses this issue by illuminating one line of the spray droplets at a time. Therefore, the contribution of ‘noise’ due to secondary scattering on the measured intensities is reduced, because the size of the illuminated spray volume is reduced in comparison to planar illumination. The quantitative difference between the two approaches however has not been quantified. Therefore, measurements of the scattered and fluorescent light intensities from spray droplets need to be performed with the scanning method and the planar approach, in order to assess the relative advantages and shortcomings of each approaches. This will be the focus of a future investigation.


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X (m)

Z (m

)

Relative SMD

-0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015 0.02-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0

0.2

0.4

0.6

0.8

1

Figure 12 Spatial distribution of the LIF/Mie intensity ratio, indicative of the Sauter Mean Diameter of the spray,

normalised to the maximum value. 5. Conclusions An investigation was conducted to examine the application of a laser beam scanning methodology on the measurement of the time-averaged spatial structure of a spray. This approach can directly reduce secondary light scattering effects from spray droplets and can take into account probe laser beam and signal intensity attenuation in order to reduce associated uncertainties on spray characteristics. The probing beam and the imaging optics were fixed in space, while the spray was traversed across the laser probe volume. This approach has the benefit of avoiding the constant refocusing of the imaging system to the probed region and is thus more appropriate for the purpose of our investigation. In addition, the imaging resolution is maintained which is not the cases in the scanning beam approach where the distance between the probe laser beam and the imaging optics is constantly changing. Therefore, the signal correction methodology can be applied directly. Scattered and fluorescent light intensity measurements were acquired close to the nozzle along the long dimension of the spray so that attenuation is more profound. The attenuation of the laser beam along the spray was found to be as high as 10% while the attenuation of the collected signal intensity could exceed 15%. Corrections can be made to address the attenuation effects and in the investigated spray the measurement error was found in the region of 20% especially at the further regions of the spray where attenuation is strongest. This highlights the need for accounting for attenuation effects of the laser beam and scattered light intensity for quantitative spray measurements. Another finding is that the evaluated spray pattern from the scattered and the fluorescent intensities gives different results. In the case of scattered light, which is the method most commonly used, an oval spray cross section was observed. In the case of the fluorescent light an oval spray cross section was also observed, but this time a dimple was found close to the centreline. These findings demonstrate the need for the appropriate selection of the droplet imaging wavelength in order to characterise the desirable spray property. The correction procedure was found not to have an effect on the evaluation of the spatial distribution of the droplet size using the LIF/Mie intensity ratio approach. This is because by taking the ratio of the two signal intensities the attenuation effects are cancelled out. However, there is still the question of the contribution of the secondary scattering on the detected fluorescence and the scattering intensities. The differences in the characterisation of droplet sizes in sprays using a beam scanning approach and a planar imaging approach will be the topic of a future investigation.


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6. Acknowledgements Support from the European Office of Aerospace Research and Development (EOARD) under contract number FA8655-12-1-2011 is acknowledged. We would like to thank Dr. Doug Talley and Prof. Vince McDonell for useful discussions. 7. References Berrocal, E., E. Kristensson, P. Hottenbach, M. Alden and G. Grunefeld (2012). "Quantitative imaging of a non-combusting diesel spray using structured laser illumination planar imaging." Applied Physics B-Lasers and Optics 109(4): 683-694. Berrocal, E., E. Kristensson, M. Richter, M. Linne and M. Alden (2008). "Application of structured illumination for multiple scattering suppression in planar laser imaging of dense sprays." Optics Express 16(22): 17870-17881. Berrocal, E., I. Meglinski and M. Jermy (2005). "New model for light propagation in highly inhomogeneous polydisperse turbid media with applications in spray diagnostics." Optics Express 13(23): 9181-9195. Brown, C., V. McDonell and D. Talley (2002). Accounting for laser extinction, signal attenuation, and secondary emission while performing optical patternation in a single plane. Proceeding of the 15th ILASS-America, Madison, USA. Charalampous, G. and Y. Hardalupas (2011a). "Method to reduce errors of droplet sizing based on the ratio of fluorescent and scattered light intensities (laser-induced fluorescence/Mie technique)." Applied Optics 50(20): 3622-3637. Charalampous, G. and Y. Hardalupas (2011b). "Numerical evaluation of droplet sizing based on the ratio of the fluorescent and scattered light intensities (LIF/Mie technique)." Applied Optics 50(9): 1197-1209. Charalampous, G. and Y. Hardalupas (2012). "Estimation of the droplet size spread with the laser induced fluorescence/Mie technique." Optics Letters 37(11): 2040-2042. Czerwinski, M., J. Mroczka, T. Girasole, G. Gouesbet and G. Grehan (2001a). "Light-transmittance predictions under multiple-light-scattering conditions. I. Direct problem: hybrid-method approximation." Applied Optics 40(9): 1514-1524. Czerwinski, M., J. Mroczka, T. Girasole, G. Gouesbet and G. Grehan (2001b). "Light-transmittance predictions under multiple-light-scattering conditions. II. Inverse problem: particle size determination." Applied Optics 40(9): 1525-1531. Domann, R. and Y. Hardalupas (2001). "A study of parameters that influence the accuracy of the Planar Droplet Sizing (PDS) technique." Particle & Particle Systems Characterization 18(1): 3-11. Domann, R. and Y. Hardalupas (2003). "Quantitative measurement of planar droplet Sauter Mean Diameter in sprays using Planar Droplet Sizing." Particle & Particle Systems Characterization 20(3): 209-218. Douglas, T., J. Verdieck, S. Lee, V. McDonell and G. Samuelsen (1996). Accounting for laser sheet extinction in applying PLLIF to sprays. 34th Aerospace Sciences Meeting and Exhibit, American Institute of Aeronautics and Astronautics. Kamimoto, T. (1994). Diagnostics of Transient Sprays by Means of Laser Sheet Techniques. COMODIA 94. Yokohama, Japan: 33-41. Kristensson, E., L. Araneo, E. Berrocal, J. Manin, M. Richter, M. Alden and M. Linne (2011). "Analysis of multiple scattering suppression using structured laser illumination planar imaging in scattering and fluorescing media." Optics Express 19(14): 13647-13663. Kristensson, E., E. Berrocal and M. Alden (2011a). "Extinction coefficient imaging of turbid media using dual structured laser illumination planar imaging." Optics Letters 36(9): 1656-1658. Kristensson, E., E. Berrocal, R. Wellander, M. Ritcher, M. Aldén and M. Linne (2011b).


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"Structured illumination for 3D Mie imaging and 2D attenuation measurements in optically dense sprays." Proceedings of the Combustion Institute 33(1): 855-861 Le Gal, P., N. Farrugia and D. A. Greenhalgh (1999). "Laser Sheet Dropsizing of dense sprays." Optics and laser technology 31(1): 75-83. Sankar, S. V., K. E. Maher and D. M. Robart (1999). "Rapid characterization of fuel atomizers using an optical patternator." Journal of Engineering for Gas Turbines and Power-Transactions of the ASME 121(3): 409-414. Sick, V. and B. Stojkovic (2001). "Attenuation effects on imaging diagnostics of hollow-cone sprays." Applied Optics 40(15): 2435-2442. Su, J., M. Drake, T. Fansler and D. Harrington (1998). Towards Quantitative Characterization of Transient Fuel Sprays Using Planar Laser Induced Fluorescence Imaging. ILASS - Americas '98. Sacramento, CA. Yeh, C. N., H. Kosaka and T. Kamimoto (1993). A fluorescence / scattering imaging technique for instantaneous 2-D measurements of particle size distribution in a transient spray. Proceedings of the 3rd Congress on Optical Particle Sizing. Yokohama, Japan: 355-361. Zimmer, L., R. Domann, Y. Hardalupas and Y. Ikeda (2003). "Simultaneous laser-induced fluorescence and Mie scattering for droplet cluster measurements." AIAA Journal 41(11): 2170-2178.

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