ISS: Collaborative Research: Spherical Cool Diffusion Flames Burning Gaseous Fuels

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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.