Abstract

Two-photon excitation laser induced fluorescence (2p-LIF) is used here for imaging an optically dense atomizing spray. The main advantage of the approach is that very little fluorescence interference originating from multiple light scattering is generated. This leads to high image contrast and a faithful description of the imaged fluid structures. While point measurement 2p-LIF imaging is a well-known approach used in life science microscopy, it has, to the best of the authors’ knowledge, never been tested for analyzing liquid structures in spray systems. We take advantage of this process, here, at a macroscopic scale ($\sim 5\times 5$ mm field of view) by imaging the central part of a light sheet of 10 mm height. To generate enough 2p-LIF signal at such a scale and with single-shot detection, ultra-short laser pulses of 25 fs, centered at 800 nm wavelength and having 2.5 mJ pulse energy, have been used. The technique is demonstrated by imaging a single spray plume from a 6 hole commercial Gasoline Direct Injection (GDI) system running at 200 bar injection pressure. The proposed approach is very promising for detailed analysis of liquid breakups in optically dense sprays and can be used for other fluid mechanics related applications.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

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References

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  1. A. Coghe and G. Cossali, “Quantitative optical techniques for dense sprays investigation: A survey,” Opt. Lasers Eng. 50(1), 46–56 (2012). Advances in Flow Visualization.
    [Crossref]
  2. M. Linne, “Imaging in the optically dense regions of a spray: A review of developing techniques,” Prog. Energy Combust. Sci. 39(5), 403–440 (2013).
    [Crossref]
  3. T. D. Fansler and S. E. Parrish, “Spray measurement technology: a review,” Meas. Sci. Technol. 26(1), 012002 (2015).
    [Crossref]
  4. M. A. Linne, M. Paciaroni, E. Berrocal, and D. Sedarsky, “Ballistic imaging of liquid breakup processes in dense sprays,” Proc. Combust. Inst. 32(2), 2147–2161 (2009).
    [Crossref]
  5. C. F. Powell, S. A. Ciatti, S.-K. Cheong, J. Liu, and J. Wang, “X-ray absorption measurements of diesel sprays and the effects of nozzle geometry,” SAE Technical Paper, (SAE International, 2004).
  6. E. Berrocal, E. Kristensson, M. Richter, M. Linne, and M. Aldén, “Application of structured illumination for multiple scattering suppression in planar laser imaging of dense sprays,” Opt. Express 16(22), 17870–17881 (2008).
    [Crossref]
  7. E. Kristensson and E. Berrocal, “Crossed patterned structured illumination for the analysis and velocimetry of transient turbid media,” Sci. Rep. 8(1), 11751 (2018).
    [Crossref]
  8. Y. N. Mishra, E. Kristensson, M. Koegl, J. Jönsson, L. Zigan, and E. Berrocal, “Comparison between two-phase and one-phase slipi for instantaneous imaging of transient sprays,” Exp. Fluids 58(9), 110 (2017).
    [Crossref]
  9. C. Crua, M. R. Heikal, and M. R. Gold, “Microscopic imaging of the initial stage of diesel spray formation,” Fuel 157, 140–150 (2015).
    [Crossref]
  10. E. Berrocal, E. Kristensson, and L. Zigan, “Light sheet fluorescence microscopic imaging for high-resolution visualization of spray dynamics,” Int. J. Spray Combust. Dyn. 10(1), 86–98 (2018).
    [Crossref]
  11. P. T. So, Two-photon Fluorescence Light Microscopy (American Cancer Society, 2001).
  12. M. Pawlicki, H. A. Collins, R. G. Denning, and H. L. Anderson, “Two-photon absorption and the design of two-photon dyes,” Angew. Chem., Int. Ed. 48(18), 3244–3266 (2009).
    [Crossref]
  13. D. R. Richardson, S. Roy, and J. R. Gord, “Femtosecond, two-photon, planar laser-induced fluorescence of carbon monoxide in flames,” Opt. Lett. 42(4), 875–878 (2017).
    [Crossref]
  14. Y. Wang, A. Jain, and W. Kulatilaka, “CO imaging in piloted liquid-spray flames using femtosecond two-photon LIF,” Proc. Combust. Inst. (2018).
  15. M. Miranda, T. Fordell, C. Arnold, A. L’Huillier, and H. Crespo, “Simultaneous compression and characterization of ultrashort laser pulses using chirped mirrors and glass wedges,” Opt. Express 20(1), 688–697 (2012).
    [Crossref]
  16. C. Xu, W. Zipfel, J. B. Shear, R. M. Williams, and W. W. Webb, “Multiphoton fluorescence excitation: new spectral windows for biological nonlinear microscopy,” Proc. Natl. Acad. Sci. USA 93(20), 10763–10768 (1996).
    [Crossref]
  17. M. Gu, S. P. Schilders, and X. Gan, “Two-photon fluorescence imaging of microspheres embedded in turbid media,” J. Mod. Opt. 47(6), 959–965 (2000).
    [Crossref]

2018 (2)

E. Kristensson and E. Berrocal, “Crossed patterned structured illumination for the analysis and velocimetry of transient turbid media,” Sci. Rep. 8(1), 11751 (2018).
[Crossref]

E. Berrocal, E. Kristensson, and L. Zigan, “Light sheet fluorescence microscopic imaging for high-resolution visualization of spray dynamics,” Int. J. Spray Combust. Dyn. 10(1), 86–98 (2018).
[Crossref]

2017 (2)

Y. N. Mishra, E. Kristensson, M. Koegl, J. Jönsson, L. Zigan, and E. Berrocal, “Comparison between two-phase and one-phase slipi for instantaneous imaging of transient sprays,” Exp. Fluids 58(9), 110 (2017).
[Crossref]

D. R. Richardson, S. Roy, and J. R. Gord, “Femtosecond, two-photon, planar laser-induced fluorescence of carbon monoxide in flames,” Opt. Lett. 42(4), 875–878 (2017).
[Crossref]

2015 (2)

C. Crua, M. R. Heikal, and M. R. Gold, “Microscopic imaging of the initial stage of diesel spray formation,” Fuel 157, 140–150 (2015).
[Crossref]

T. D. Fansler and S. E. Parrish, “Spray measurement technology: a review,” Meas. Sci. Technol. 26(1), 012002 (2015).
[Crossref]

2013 (1)

M. Linne, “Imaging in the optically dense regions of a spray: A review of developing techniques,” Prog. Energy Combust. Sci. 39(5), 403–440 (2013).
[Crossref]

2012 (2)

A. Coghe and G. Cossali, “Quantitative optical techniques for dense sprays investigation: A survey,” Opt. Lasers Eng. 50(1), 46–56 (2012). Advances in Flow Visualization.
[Crossref]

M. Miranda, T. Fordell, C. Arnold, A. L’Huillier, and H. Crespo, “Simultaneous compression and characterization of ultrashort laser pulses using chirped mirrors and glass wedges,” Opt. Express 20(1), 688–697 (2012).
[Crossref]

2009 (2)

M. A. Linne, M. Paciaroni, E. Berrocal, and D. Sedarsky, “Ballistic imaging of liquid breakup processes in dense sprays,” Proc. Combust. Inst. 32(2), 2147–2161 (2009).
[Crossref]

M. Pawlicki, H. A. Collins, R. G. Denning, and H. L. Anderson, “Two-photon absorption and the design of two-photon dyes,” Angew. Chem., Int. Ed. 48(18), 3244–3266 (2009).
[Crossref]

2008 (1)

2000 (1)

M. Gu, S. P. Schilders, and X. Gan, “Two-photon fluorescence imaging of microspheres embedded in turbid media,” J. Mod. Opt. 47(6), 959–965 (2000).
[Crossref]

1996 (1)

C. Xu, W. Zipfel, J. B. Shear, R. M. Williams, and W. W. Webb, “Multiphoton fluorescence excitation: new spectral windows for biological nonlinear microscopy,” Proc. Natl. Acad. Sci. USA 93(20), 10763–10768 (1996).
[Crossref]

Aldén, M.

Anderson, H. L.

M. Pawlicki, H. A. Collins, R. G. Denning, and H. L. Anderson, “Two-photon absorption and the design of two-photon dyes,” Angew. Chem., Int. Ed. 48(18), 3244–3266 (2009).
[Crossref]

Arnold, C.

Berrocal, E.

E. Kristensson and E. Berrocal, “Crossed patterned structured illumination for the analysis and velocimetry of transient turbid media,” Sci. Rep. 8(1), 11751 (2018).
[Crossref]

E. Berrocal, E. Kristensson, and L. Zigan, “Light sheet fluorescence microscopic imaging for high-resolution visualization of spray dynamics,” Int. J. Spray Combust. Dyn. 10(1), 86–98 (2018).
[Crossref]

Y. N. Mishra, E. Kristensson, M. Koegl, J. Jönsson, L. Zigan, and E. Berrocal, “Comparison between two-phase and one-phase slipi for instantaneous imaging of transient sprays,” Exp. Fluids 58(9), 110 (2017).
[Crossref]

M. A. Linne, M. Paciaroni, E. Berrocal, and D. Sedarsky, “Ballistic imaging of liquid breakup processes in dense sprays,” Proc. Combust. Inst. 32(2), 2147–2161 (2009).
[Crossref]

E. Berrocal, E. Kristensson, M. Richter, M. Linne, and M. Aldén, “Application of structured illumination for multiple scattering suppression in planar laser imaging of dense sprays,” Opt. Express 16(22), 17870–17881 (2008).
[Crossref]

Cheong, S.-K.

C. F. Powell, S. A. Ciatti, S.-K. Cheong, J. Liu, and J. Wang, “X-ray absorption measurements of diesel sprays and the effects of nozzle geometry,” SAE Technical Paper, (SAE International, 2004).

Ciatti, S. A.

C. F. Powell, S. A. Ciatti, S.-K. Cheong, J. Liu, and J. Wang, “X-ray absorption measurements of diesel sprays and the effects of nozzle geometry,” SAE Technical Paper, (SAE International, 2004).

Coghe, A.

A. Coghe and G. Cossali, “Quantitative optical techniques for dense sprays investigation: A survey,” Opt. Lasers Eng. 50(1), 46–56 (2012). Advances in Flow Visualization.
[Crossref]

Collins, H. A.

M. Pawlicki, H. A. Collins, R. G. Denning, and H. L. Anderson, “Two-photon absorption and the design of two-photon dyes,” Angew. Chem., Int. Ed. 48(18), 3244–3266 (2009).
[Crossref]

Cossali, G.

A. Coghe and G. Cossali, “Quantitative optical techniques for dense sprays investigation: A survey,” Opt. Lasers Eng. 50(1), 46–56 (2012). Advances in Flow Visualization.
[Crossref]

Crespo, H.

Crua, C.

C. Crua, M. R. Heikal, and M. R. Gold, “Microscopic imaging of the initial stage of diesel spray formation,” Fuel 157, 140–150 (2015).
[Crossref]

Denning, R. G.

M. Pawlicki, H. A. Collins, R. G. Denning, and H. L. Anderson, “Two-photon absorption and the design of two-photon dyes,” Angew. Chem., Int. Ed. 48(18), 3244–3266 (2009).
[Crossref]

Fansler, T. D.

T. D. Fansler and S. E. Parrish, “Spray measurement technology: a review,” Meas. Sci. Technol. 26(1), 012002 (2015).
[Crossref]

Fordell, T.

Gan, X.

M. Gu, S. P. Schilders, and X. Gan, “Two-photon fluorescence imaging of microspheres embedded in turbid media,” J. Mod. Opt. 47(6), 959–965 (2000).
[Crossref]

Gold, M. R.

C. Crua, M. R. Heikal, and M. R. Gold, “Microscopic imaging of the initial stage of diesel spray formation,” Fuel 157, 140–150 (2015).
[Crossref]

Gord, J. R.

Gu, M.

M. Gu, S. P. Schilders, and X. Gan, “Two-photon fluorescence imaging of microspheres embedded in turbid media,” J. Mod. Opt. 47(6), 959–965 (2000).
[Crossref]

Heikal, M. R.

C. Crua, M. R. Heikal, and M. R. Gold, “Microscopic imaging of the initial stage of diesel spray formation,” Fuel 157, 140–150 (2015).
[Crossref]

Jain, A.

Y. Wang, A. Jain, and W. Kulatilaka, “CO imaging in piloted liquid-spray flames using femtosecond two-photon LIF,” Proc. Combust. Inst. (2018).

Jönsson, J.

Y. N. Mishra, E. Kristensson, M. Koegl, J. Jönsson, L. Zigan, and E. Berrocal, “Comparison between two-phase and one-phase slipi for instantaneous imaging of transient sprays,” Exp. Fluids 58(9), 110 (2017).
[Crossref]

Koegl, M.

Y. N. Mishra, E. Kristensson, M. Koegl, J. Jönsson, L. Zigan, and E. Berrocal, “Comparison between two-phase and one-phase slipi for instantaneous imaging of transient sprays,” Exp. Fluids 58(9), 110 (2017).
[Crossref]

Kristensson, E.

E. Berrocal, E. Kristensson, and L. Zigan, “Light sheet fluorescence microscopic imaging for high-resolution visualization of spray dynamics,” Int. J. Spray Combust. Dyn. 10(1), 86–98 (2018).
[Crossref]

E. Kristensson and E. Berrocal, “Crossed patterned structured illumination for the analysis and velocimetry of transient turbid media,” Sci. Rep. 8(1), 11751 (2018).
[Crossref]

Y. N. Mishra, E. Kristensson, M. Koegl, J. Jönsson, L. Zigan, and E. Berrocal, “Comparison between two-phase and one-phase slipi for instantaneous imaging of transient sprays,” Exp. Fluids 58(9), 110 (2017).
[Crossref]

E. Berrocal, E. Kristensson, M. Richter, M. Linne, and M. Aldén, “Application of structured illumination for multiple scattering suppression in planar laser imaging of dense sprays,” Opt. Express 16(22), 17870–17881 (2008).
[Crossref]

Kulatilaka, W.

Y. Wang, A. Jain, and W. Kulatilaka, “CO imaging in piloted liquid-spray flames using femtosecond two-photon LIF,” Proc. Combust. Inst. (2018).

L’Huillier, A.

Linne, M.

Linne, M. A.

M. A. Linne, M. Paciaroni, E. Berrocal, and D. Sedarsky, “Ballistic imaging of liquid breakup processes in dense sprays,” Proc. Combust. Inst. 32(2), 2147–2161 (2009).
[Crossref]

Liu, J.

C. F. Powell, S. A. Ciatti, S.-K. Cheong, J. Liu, and J. Wang, “X-ray absorption measurements of diesel sprays and the effects of nozzle geometry,” SAE Technical Paper, (SAE International, 2004).

Miranda, M.

Mishra, Y. N.

Y. N. Mishra, E. Kristensson, M. Koegl, J. Jönsson, L. Zigan, and E. Berrocal, “Comparison between two-phase and one-phase slipi for instantaneous imaging of transient sprays,” Exp. Fluids 58(9), 110 (2017).
[Crossref]

Paciaroni, M.

M. A. Linne, M. Paciaroni, E. Berrocal, and D. Sedarsky, “Ballistic imaging of liquid breakup processes in dense sprays,” Proc. Combust. Inst. 32(2), 2147–2161 (2009).
[Crossref]

Parrish, S. E.

T. D. Fansler and S. E. Parrish, “Spray measurement technology: a review,” Meas. Sci. Technol. 26(1), 012002 (2015).
[Crossref]

Pawlicki, M.

M. Pawlicki, H. A. Collins, R. G. Denning, and H. L. Anderson, “Two-photon absorption and the design of two-photon dyes,” Angew. Chem., Int. Ed. 48(18), 3244–3266 (2009).
[Crossref]

Powell, C. F.

C. F. Powell, S. A. Ciatti, S.-K. Cheong, J. Liu, and J. Wang, “X-ray absorption measurements of diesel sprays and the effects of nozzle geometry,” SAE Technical Paper, (SAE International, 2004).

Richardson, D. R.

Richter, M.

Roy, S.

Schilders, S. P.

M. Gu, S. P. Schilders, and X. Gan, “Two-photon fluorescence imaging of microspheres embedded in turbid media,” J. Mod. Opt. 47(6), 959–965 (2000).
[Crossref]

Sedarsky, D.

M. A. Linne, M. Paciaroni, E. Berrocal, and D. Sedarsky, “Ballistic imaging of liquid breakup processes in dense sprays,” Proc. Combust. Inst. 32(2), 2147–2161 (2009).
[Crossref]

Shear, J. B.

C. Xu, W. Zipfel, J. B. Shear, R. M. Williams, and W. W. Webb, “Multiphoton fluorescence excitation: new spectral windows for biological nonlinear microscopy,” Proc. Natl. Acad. Sci. USA 93(20), 10763–10768 (1996).
[Crossref]

So, P. T.

P. T. So, Two-photon Fluorescence Light Microscopy (American Cancer Society, 2001).

Wang, J.

C. F. Powell, S. A. Ciatti, S.-K. Cheong, J. Liu, and J. Wang, “X-ray absorption measurements of diesel sprays and the effects of nozzle geometry,” SAE Technical Paper, (SAE International, 2004).

Wang, Y.

Y. Wang, A. Jain, and W. Kulatilaka, “CO imaging in piloted liquid-spray flames using femtosecond two-photon LIF,” Proc. Combust. Inst. (2018).

Webb, W. W.

C. Xu, W. Zipfel, J. B. Shear, R. M. Williams, and W. W. Webb, “Multiphoton fluorescence excitation: new spectral windows for biological nonlinear microscopy,” Proc. Natl. Acad. Sci. USA 93(20), 10763–10768 (1996).
[Crossref]

Williams, R. M.

C. Xu, W. Zipfel, J. B. Shear, R. M. Williams, and W. W. Webb, “Multiphoton fluorescence excitation: new spectral windows for biological nonlinear microscopy,” Proc. Natl. Acad. Sci. USA 93(20), 10763–10768 (1996).
[Crossref]

Xu, C.

C. Xu, W. Zipfel, J. B. Shear, R. M. Williams, and W. W. Webb, “Multiphoton fluorescence excitation: new spectral windows for biological nonlinear microscopy,” Proc. Natl. Acad. Sci. USA 93(20), 10763–10768 (1996).
[Crossref]

Zigan, L.

E. Berrocal, E. Kristensson, and L. Zigan, “Light sheet fluorescence microscopic imaging for high-resolution visualization of spray dynamics,” Int. J. Spray Combust. Dyn. 10(1), 86–98 (2018).
[Crossref]

Y. N. Mishra, E. Kristensson, M. Koegl, J. Jönsson, L. Zigan, and E. Berrocal, “Comparison between two-phase and one-phase slipi for instantaneous imaging of transient sprays,” Exp. Fluids 58(9), 110 (2017).
[Crossref]

Zipfel, W.

C. Xu, W. Zipfel, J. B. Shear, R. M. Williams, and W. W. Webb, “Multiphoton fluorescence excitation: new spectral windows for biological nonlinear microscopy,” Proc. Natl. Acad. Sci. USA 93(20), 10763–10768 (1996).
[Crossref]

Angew. Chem., Int. Ed. (1)

M. Pawlicki, H. A. Collins, R. G. Denning, and H. L. Anderson, “Two-photon absorption and the design of two-photon dyes,” Angew. Chem., Int. Ed. 48(18), 3244–3266 (2009).
[Crossref]

Exp. Fluids (1)

Y. N. Mishra, E. Kristensson, M. Koegl, J. Jönsson, L. Zigan, and E. Berrocal, “Comparison between two-phase and one-phase slipi for instantaneous imaging of transient sprays,” Exp. Fluids 58(9), 110 (2017).
[Crossref]

Fuel (1)

C. Crua, M. R. Heikal, and M. R. Gold, “Microscopic imaging of the initial stage of diesel spray formation,” Fuel 157, 140–150 (2015).
[Crossref]

Int. J. Spray Combust. Dyn. (1)

E. Berrocal, E. Kristensson, and L. Zigan, “Light sheet fluorescence microscopic imaging for high-resolution visualization of spray dynamics,” Int. J. Spray Combust. Dyn. 10(1), 86–98 (2018).
[Crossref]

J. Mod. Opt. (1)

M. Gu, S. P. Schilders, and X. Gan, “Two-photon fluorescence imaging of microspheres embedded in turbid media,” J. Mod. Opt. 47(6), 959–965 (2000).
[Crossref]

Meas. Sci. Technol. (1)

T. D. Fansler and S. E. Parrish, “Spray measurement technology: a review,” Meas. Sci. Technol. 26(1), 012002 (2015).
[Crossref]

Opt. Express (2)

Opt. Lasers Eng. (1)

A. Coghe and G. Cossali, “Quantitative optical techniques for dense sprays investigation: A survey,” Opt. Lasers Eng. 50(1), 46–56 (2012). Advances in Flow Visualization.
[Crossref]

Opt. Lett. (1)

Proc. Combust. Inst. (1)

M. A. Linne, M. Paciaroni, E. Berrocal, and D. Sedarsky, “Ballistic imaging of liquid breakup processes in dense sprays,” Proc. Combust. Inst. 32(2), 2147–2161 (2009).
[Crossref]

Proc. Natl. Acad. Sci. USA (1)

C. Xu, W. Zipfel, J. B. Shear, R. M. Williams, and W. W. Webb, “Multiphoton fluorescence excitation: new spectral windows for biological nonlinear microscopy,” Proc. Natl. Acad. Sci. USA 93(20), 10763–10768 (1996).
[Crossref]

Prog. Energy Combust. Sci. (1)

M. Linne, “Imaging in the optically dense regions of a spray: A review of developing techniques,” Prog. Energy Combust. Sci. 39(5), 403–440 (2013).
[Crossref]

Sci. Rep. (1)

E. Kristensson and E. Berrocal, “Crossed patterned structured illumination for the analysis and velocimetry of transient turbid media,” Sci. Rep. 8(1), 11751 (2018).
[Crossref]

Other (3)

Y. Wang, A. Jain, and W. Kulatilaka, “CO imaging in piloted liquid-spray flames using femtosecond two-photon LIF,” Proc. Combust. Inst. (2018).

C. F. Powell, S. A. Ciatti, S.-K. Cheong, J. Liu, and J. Wang, “X-ray absorption measurements of diesel sprays and the effects of nozzle geometry,” SAE Technical Paper, (SAE International, 2004).

P. T. So, Two-photon Fluorescence Light Microscopy (American Cancer Society, 2001).

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Figures (10)

Fig. 1.
Fig. 1. Comparison between single-photon (a) and two-photon (b) excitation processes for a beam crossing a water solution containing diluted fluorescein dye. In (a), the dye is excited at 450 nm using a CW diode laser. In (b) femtosecond pulses generated by a titanium-sapphire femtosecond laser are used to excite the water solution. In this example the incident beam is focused by a cylindrical lens of +50 mm focal length.
Fig. 2.
Fig. 2. Effect of the focal distance of a converging cylindrical lens on the generation of two-photon excitation fluorescence signal. Here, the focal distance corresponds to 50 mm, 100 mm and 150 mm in (a), (b) and (c) respectively. By using longer focal distances a more homogeneous two-photon fluorescence signal is generated.
Fig. 3.
Fig. 3. Comparison between (a) single-photon and (b) two-photon excitation processes applied in a spray system consisting of a cloud of droplets. The fluorescence from two-photon excitation is only generated along the light sheet reducing a significant part of unwanted fluorescence outside of the light sheet.
Fig. 4.
Fig. 4. Spectra of the one-photon excitation at 400 nm, the fuorescein emission and the two-photon excitation centered at 800 nm. To generate the 400 nm excitation pulse, the 800 nm laser beam is frequency doubled by inserting a BBO crystal.
Fig. 5.
Fig. 5. Description of the optical arrangement for each detection configuration. The detection corresponding to shadowgraphy imaging, two-photon fluorescence, elastic light scattering and one-photon fluorescence are shown in (a), (b), (c) and (d) respectively.
Fig. 6.
Fig. 6. Image results comparison between shadowgraphy in (a) and 2p-LIF light sheet imaging in (b) for a 6 holes GDI spray injected at 200 bars liquid pressure and recorded at 200 µs. The two images have been recorded with the exact same camera system and operating conditions. While the shadowgraph image shows blurred liquid structures; the droplets, liquid blobs, ligaments and voids are clearly observable in the ×2 zoomed areas of the 2p-LIF image.
Fig. 7.
Fig. 7. Light sheet imaging comparison between elastic scattering in (a) and 2p-LIF light sheet imaging in (b) for the 6 holes GDI spray injected at 200 bars liquid pressure and recorded at 200 µs. The two images have been recorded with the same camera system but corresponds to independent injection events. It is seen from the ×3 zoom areas that 2p-LIF provides images with limited blur allowing the visibility of liquid structures which are not observable with the elastic scattering scattering scheme.
Fig. 8.
Fig. 8. Optical signals comparison between elastic scattering and 2p-LIF light sheet imaging. The area of interest is located at 4 mm below the nozzle tip as shown in the image on the right. Each image corresponds to independent injection events. It is observed here that the Mie scattering image is locally affected by strong reflections that saturate the 14 bit camera. On the contrary the 2p-LIF signal does not show those unwanted intensity peaks.
Fig. 9.
Fig. 9. Light sheet imaging comparison between 1p-LIF in (a) and 2p-LIF light sheet imaging in (b) for the 6 holes GDI spray injected at 200 bars liquid pressure and recorded at 200 µs. The two images have been recorded with the same camera system but corresponds to independent injection events. It is seen from the ×3 zoom areas that 2p-LIF provides images with limited blur allowing the visibility of liquid structures which are not observable with the 1p-LIF scheme.
Fig. 10.
Fig. 10. Optical signals comparison between 1p-LIF and 2p-LIF light sheet imaging. The area of interest is located at 4 mm below the nozzle tip as shown in the image on the right. Each image corresponds to independent injection events. It is observed here that the 1p-LIF does not show high contrast signal levels between the imaged droplets and their surrounding. On the contrary the 2p-LIF signal is strongly increased where droplets are imaged, indicating clearly their presence.

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