| NSF Org: |
CBET Division of Chemical, Bioengineering, Environmental, and Transport Systems |
| Recipient: |
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| Initial Amendment Date: | August 28, 2015 |
| Latest Amendment Date: | August 28, 2015 |
| Award Number: | 1552074 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Harsha Chelliah
hchellia@nsf.gov (703)292-7281 CBET Division of Chemical, Bioengineering, Environmental, and Transport Systems ENG Directorate for Engineering |
| Start Date: | August 1, 2015 |
| End Date: | August 31, 2018 (Estimated) |
| Total Intended Award Amount: | $193,738.00 |
| Total Awarded Amount to Date: | $193,738.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
500 S LIMESTONE LEXINGTON KY US 40526-0001 (859)257-9420 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
500 South Limestone Lexington KY US 40526-0001 |
| 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 |
| 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
1336184
Renfro
In many practical combustors, heat is released by chemical reactions in relatively thin flame sheets. Turbulence in the flow of fuel and air in the combustor lead to fluctuations in velocity that perturb the flame sheet and increase the transfer of heat away from the flame. When these fluctuations are sufficiently large, the heat loss can be too high compared to the heat released by the flame resulting in local extinction. A local extinction event leaves a hole in the flame sheet that can lead to complete extinction of the flame. In many applications extinction is a significant limitation to the operation of the combustor, while in other applications extinction can be desired to quench a flame. In either case, physical understandings of the mechanisms that cause extinction are needed. This project seeks a fundamental understanding of the interactions of velocity and flame sheets that cause local extinction such that more accurate models of flame limits and the response of flame holes can be generated. The intellectual merit of the work focuses on a detailed understanding of the impact that velocity fluctuations in turbulent flames have on heat transfer from flames sheets as well as the impact of these changes to the flame's chemical heat release. The experimental and computational project will utilize an optically-accessible combustor that has been designed to create local extinction in a flame sheet enabling a detailed study using laser diagnostics. The measurements will be used to develop models describing extinction that can have broader impact on industrial design tools. The research will involve the participation of graduate and undergraduate students, who will be trained in fundamental combustion theory and application of optical measurements.
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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.
Turbulent flow in the combustors of modern engines can significantly interact with the surface of flames leading in some cases to local quenching of the reactions and the formation of an extinction hole in the flame sheet. These local extinction regions can close and reform a fully burning flame, or they can grow leading to loss of power and increased emissions of pollutants and unburned fuel. Thus, to improve engine designs, it is necessary to better understand the speed at which flame edges grow or shrink under conditions relevant to engines. This project used two laboratory combustors to provide new experimental data on the speed of extinction flame edges. In one burner, developed under a previous NSF project, new measurements were taken of laminar extinction flame edges to quantify the relationship between the flame?s speed and the rate of heat loss through the edge. Detailed velocity measurements at the edge were used to show a linear relationship between the heat loss and the propagation velocity. Numerical simulations of this same flame were also used to assess how the flame?s velocity responds to oscillations in the flow around the flame. It was discovered that for slow oscillations of the flow, the flame?s response was sufficiently fast such that the dynamic response was quasi-steady; that is, the flame?s velocity was only a function of the instantaneous conditions at the flame edge and not dependent on the rate of oscillation. For sufficiently fast oscillations, the extinction flame edge had limited response to the flow oscillation. A response map for the flame was measured as a function of oscillation frequency, and for the conditions studied displayed a transition in flame behavior around 50 Hz.
The second laboratory combustor used in this work was designed as part of this project to better understand how the edges of flame holes interact with turbulent flow. The new combustor stabilized a planar flame, similar to prior work, but used turbulent jets to impinge on the flame surface and generate local extinction holes that propagated along the flame sheet. Measurements of the local flame propagation were conducted as a function of parameters of the flow including the total velocity, the intensity of the turbulence, and the fuel mixture. It was discovered that, like for the oscillating laminar flames, the turbulent flame response was limited to the low frequency portion of the turbulent flow. Thus, the overall velocity of the flame edge has a dependence on both the average flow velocity and the turbulent intensity, but this relationship depends on details of the turbulence. These measurements will provide fundamental information for better modeling of flame propagation.
Last Modified: 01/11/2019
Modified by: Michael W Renfro
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