| NSF Org: |
CBET Division of Chemical, Bioengineering, Environmental, and Transport Systems |
| Recipient: |
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| Initial Amendment Date: | July 21, 2017 |
| Latest Amendment Date: | June 9, 2022 |
| Award Number: | 1740490 |
| 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: | September 1, 2017 |
| End Date: | February 28, 2023 (Estimated) |
| Total Intended Award Amount: | $238,354.00 |
| Total Awarded Amount to Date: | $286,023.00 |
| Funds Obligated to Date: |
FY 2020 = $47,669.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
3112 LEE BUILDING COLLEGE PARK MD US 20742-5100 (301)405-6269 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
3104 J.M. Patterson Bg. College Park MD US 20742-5103 |
| 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, Special Initiatives |
| Primary Program Source: |
01002021DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.041 |
ABSTRACT
Spherical cool diffusion flames are remarkable flames with unusually low temperatures. They offer valuable insight into combustion processes in practical combustion devices, such as engines. These flames were discovered in 2012 aboard the International Space Station (ISS), and since then this has been the only platform for observing them. To date all the ISS cool flames have involved liquid droplet fuels. This has limited the number of fuels to be observed and the ability to observe truly steady flames. For this project, experiments aboard the ISS will be performed using gaseous hydrocarbon fuels burning as nearly steady spherical flames. These flames will be supported by spherical porous burners. Their observation, with the most advanced combustion diagnostics available aboard the ISS, will allow the development of new chemical kinetics mechanisms and computational tools for combustion research. The improved understanding of cool diffusion flames gained by these experiments will lead to improved designs of practical combustion devices.
The discovery of cool diffusion flames has spawned a rapidly growing research field, but only a few measurements at limited conditions are available. Consequently, cool flame chemical kinetics mechanisms cannot be adequately tested or advanced, but such knowledge is needed to design cleaner and more efficient internal combustion engines. The objectives of this project are to observe diverse cool diffusion flames aboard the ISS, to simulate the tests with advanced computational models, and to advance chemical kinetics mechanisms that can accurately model these flames. The ISS is the only platform for observing spherical cool diffusion flames because they require about 20 s of microgravity to establish and even longer to reach steady state. The flames will be supported by a 6-mm spherical burner fed with propane, n-butane, or n-pentane. Normal and inverse flames will be considered, including a broad range of dilution conditions and pressures. The burners, gas delivery system, and diagnostics will be those used by the previous ISS flight experiments. The diagnostics will support color video, imaging of excited CH* and CH2O*, and measurements of gas temperatures, radiative emissions, optical emissions from H2O and OH, and ambient gas compositions. The research will be disseminated widely to the combustion research community and to industry. There will be outreach activities to attract secondary school students to engineering. This project will advance the state-of-the-art in cool flame kinetics mechanisms, which in turn should lead to cleaner, more efficient internal combustion engines.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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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.
An improved understanding of cool diffusion flames could lead to improved engines. These flames were investigated using a spherical porous burner with gaseous fuels in the microgravity environment of the International Space Station. Normal and inverse flames burning ethane, propane, and n-butane were explored with various fuel and oxygen concentrations, pressures, and flow rates. The diagnostics included an intensified video camera, radiometers, and thermocouples. Spherical cool diffusion flames burning gases were observed for the first time. However, these cool flames were not readily produced and were only obtained for normal n-butane flames at 2 bar with an ambient oxygen mole fraction of 0.39. The hot flames that spawned the cool flames were 2.6 times as large. An analytical model is presented that combines previous models for steady droplet burning and the partial-burning regime for cool diffusion flames. The results identify the importance of burner temperature on the behavior of these cool flames. They also indicate that the observed cool flames reside in rich regions near a mixture fraction of 0.53.
Additionally, until now the study of cool diffusion flames has been hindered by the high cost of the experimental systems used to observe them. A method is presented here for observing cool diffusion flames inexpensively using a pool of liquid n-heptane and parallel plates heated so as to produce a stably stratified stagnation flow. The flames were imaged with a color camera and an intensified camera. Measurements included gas phase temperatures, fuel evaporation rates, and formaldehyde yields. These are the first observations of cool flames burning near the surfaces of fuel pools. The measured peak temperatures were between 705 and 760 K and were 70 K above the temperature of the surrounding air. Autoignition first occurred at 550 K.
Last Modified: 06/28/2023
Modified by: Peter B Sunderland
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