| NSF Org: |
CBET Division of Chemical, Bioengineering, Environmental, and Transport Systems |
| Recipient: |
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| Initial Amendment Date: | August 24, 2012 |
| Latest Amendment Date: | August 24, 2012 |
| Award Number: | 1233728 |
| Award Instrument: | Standard Grant |
| Program Manager: |
song kong
CBET Division of Chemical, Bioengineering, Environmental, and Transport Systems ENG Directorate for Engineering |
| Start Date: | September 1, 2012 |
| End Date: | August 31, 2016 (Estimated) |
| Total Intended Award Amount: | $326,998.00 |
| Total Awarded Amount to Date: | $326,998.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
160 ALDRICH HALL IRVINE CA US 92697-0001 (949)824-7295 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
5171 California Ave, Suit 150 Irvine CA US 92617-3067 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
CFS-Combustion & Fire Systems, GOALI-Grnt Opp Acad Lia wIndus |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.041 |
ABSTRACT
This project develops and demonstrates a unique, gated, picosecond, digital holography system for imaging the detailed structure of dense sprays of liquid droplets. Dense sprays are commonly found in diesel and gas turbine engines, and in spray drying processes for food and pharmaceutical production. Understanding the governing behaviors in spray systems depends heavily on identifying the processes occurring at the core of the spray where the bulk liquid is breaking up into ligaments and droplets. Dense sprays make identifying those processes tremendously challenging because they are optically thick making it difficult to obtain any image information from deep within the spray. The innovation in this project is to employ a combination of digital holography and picosecond gating to limit the amount of optical noise sufficiently to enable high resolution, 3D imaging through an optically dense medium. The approach effectively generalizes existing pseudo-ballistic imaging systems, where photons that pass through the spray with relatively few near-forward scattering interactions are selectively collected while those scattered multiple times at wide angles are rejected. Digital holography further enhances the photon selection by coherence filtering. To combine ballistic photon and holographic imaging we utilize a laser pulse short enough to enhance the ballistic photon detection and long enough to allow holographic recording with acceptable spatial resolution. The laser output is split into three different beams: 1) a beam that controls a Kerr-cell optical switch, 2) an object beam, and 3) a reference beam for the hologram. The Kerr cell provides the photon timing selectivity. It is adjusted to open just before the holography pulse arrives. The overlap time of these two pulses determines the effective gating time. When the Kerr gate is open, the object and reference waves pass through and are recorded on the digital camera. An imaging approach of this form can provide a detailed look at the structure of all of the particles in a three-dimensional sample volume. Results will aid in identification of the diagnostic limitations and will produce data useful for comparisons to spray modeling. The remainder of the effort will be dedicated to system refinement via the application of design rules to quantify tradeoffs and optimization for future field measurements.
This new diagnostic will allow three-dimensional imaging of dense sprays unachievable with existing techniques. This new measurement capability has the potential to produce much needed data on spray formation and ligament breakup essential for understanding and modeling of spray physics. For example, spray behavior of heavy fuels is a controlling process determining combustion efficiencies of many devices. While spray physics has been researched for decades, significant limitations still exist in accurate modeling of spray breakup and fuel distribution near the nozzle. Very little near field imaging data exists. This work combines the noise rejection aspects of ballistic imaging with digital holography to produce a demonstrated instrument capable of addressing the need for near field, three-dimensional imaging data in dense sprays. The university?industry collaboration with Metrolaser, Inc. that is included in this project will greatly enhance the research by refining its focus while simultaneously broadening it beyond a purely academic exercise. The result will be useful for leveraging towards the development of a commercially viable diagnostic instrument that is desired and needed by the spray and combustion communities.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Intellectual Merit: Liquid fuel injection in combustion systems involves multi-phase flows generated by fuel sprays. Studying how these sprays behave as they break up into small droplets can benefit from experimental approaches for imaging them. The images can help with design choices to improve the spray and thereby control stability and increase the efficiency of combustion systems. However, the high optical scattering from the cloud of small droplets obscures traditional imaging methods. That is, the light scattered from the mist makes it difficult to see what is happening at the liquid sheet. In addition, conventional imaging does not provide depth information that is often critical in spray understanding. Digital holography (DH) is a well-established and powerful technique for high-resolution 3D imaging. This project examined the use of ultra-short laser pulses for digital holography in multi-phase flows of combustion interest. Using this system creates the opportunity for coherence filtering and time-gating filtering, which improved signal-to-noise ratio. Experimental results showed high potential of ultra-short pulse DH for microscopic imaging though highly scattering media. The technique can potentially image in 3D any intact liquid core of diesel sprays, even when veiled behind the optically deep cloud of droplets, a capability never achieved before.
The most significant finding of the project, in addition to demonstrating that ultra-short pulse digital holography holds great promise for imaging in densely scattering media, is that the coherence filtering effect of the hologram is automatically a good way to reduce scattering noise without resorting to more complex approaches. In addition, putting an iris in the system as a spatial filter often itself can assist in improving image quality.
Broader Impacts: The technical contribution of imaging through highly scattering media has implications for improved engine performance in terms of better fuel economy and lower emissions. In addition, the method may be useful for medical imaging applications. The project also supported two graduate student researchers, one to their Ph.D.; it provided the groundwork for further development in a industry collaboration with our GOALI partner; it provided a research environment and project for two visiting intern students as well as for undergraduates from underrepresented groups. These students aided in the design and construction of the experiment.
Last Modified: 09/24/2016
Modified by: Derek Dunn-Rankin
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