|Structure & Liftoff in Combustion Experiment (SLICE)|
About the SLICE Logo
Measured and computed temperature profiles of coflow laminar diffusion flames of 65% methane and 35% nitrogen in both normal gravity and microgravity.
See large image for a side-by-side comparison. (Yale University)
January 2015 – The first SLICE results have now been published in two papers in the Proceedings of the Combustion Institute.
The papers were both presented at the 35th International Symposium on Combustion (San Francisco, CA; 3-8 August, 2014), where preliminary versions had been presented at the 8th U.S. National Combustion Meeting (Park City, UT; 19-22 May, 2013). Although the analysis of the results is still continuing, a final report is now available for download. Additional information is available through the NASA/SLICE Facebook page.
Astronaut Don Pettit conducting a test in the Microgravity Science Glovebox (MSG) on the International Space Station (ISS) on March 9, 2012, where that day’s testing including both SLICE and SPICE tests (where both experiments use the same hardware). The MSG is covered so that the only experiment illumination is from the flame, (1) which Pettit is watching through a small gap in the stray light cover, and (2) which can also be seen on the upper monitor on Pettit’s left.
Coflow laminar diffusion flames are especially valuable for studies of combustion because of the availability of accurate numerical modeling with that flame configuration. In particular, excellent agreement can be achieved when the flow conditions are such that the flame detaches and lifts above (i.e., moves downstream of) the nozzle. A coupled experimental and numerical investigation can enable validation and improvements to combustion modeling. For example, the image to the right is not a photo, but a numerical simulation of a 40% ethylene flame. Enhanced modeling capability is important because it can reduce time and cost in the design of practical combustion devices. Furthermore, flame attachment to (or detachment from) a burner or condensed-fuel surface is of essential importance in both combustion systems and fire safety. The flame attachment point controls the stability of the entire trailing diffusion flame.
Microgravity testing allows for greater temporal and spatial scales and a broader range of flame characteristics than can be achieved in normal gravity. As one example of the NASA-recognized value of such studies, the Coflow Laminar Diffusion Flame (CLD Flame) experiment of Marshall B. Long and Mitchell D. Smooke (both of Yale U.) is currently in development for conduct in the Combustion Integrated Rack (CIR) on the International Space Station, as part of the Advanced Combustion via Microgravity Experiments (ACME) project.
The overall goal of the proposed study is to improve
our understanding of the physical and chemical processes controlling
diffusion (i.e., non-premixed) flame structure and lifting phenomena
(i.e., stabilization) and to provide for rigorous testing of numerical
models, including thermal radiation, soot formation, and detailed chemical
kinetics. As part of this aim, an important purpose of the SLICE
investigation is to conduct preliminary microgravity studies that will
maximize the scientific return of the subsequent CLD Flame experiment
and mitigate associated risks. In other words, SLICE is
a precursor to the CLD Flame experiment.
For diffusion flames of methane, ethylene, and selected
nitrogen dilutions of each fuel burning in a coflow of air:
(1) Characterize the structure of the flame, especially its base (i.e., stabilizing region), from attached through lifted conditions as a function of the fuel, burner diameter, and flow conditions.
(2) Identify the liftoff velocity limits as a function of the fuel and burner diameter.
The experimental hardware for the Smoke Points In Co-flow Experiment (SPICE), of David L. Urban (NASA Glenn) and Peter B. Sunderland (U. Maryland), which is currently onboard the International Space Station, was built to allow studies of coflow laminar diffusion flames. The SPICE hardware is within the ISS MSG in the image to the right. While the SPICE investigation has been specifically focused on a study of soot production and oxidation within flames, the hardware can be used without modification to conduct the SLICE experiment. In terms of the experimental hardware, the only additional requirements for SLICE are more fuel (i.e., gas bottles), recording media, and minor hardware elements such as new nozzle(s). The three existing SPICE nozzles are all smaller than the nozzle planned for the CLD Flame experiment. Of course, the SLICE testing could most benefit the CLD Flame experiment by bracketing and/or including the same nozzle size. It is also possible that screen(s) would be flown to alter the velocity profile of the coflow.
The SLICE operating procedures will have some differences
to the standard SPICE procedures given the differing objectives. However,
those changes are fully within the capabilities of the SPICE hardware,
as demonstrated by exploratory testing that has already been conducted
on orbit. As a simple example, the standard SPICE procedure calls
for a fixed air velocity and an increase of the fuel flow until the
smoke point is reached. In contrast, SLICE will include testing
where the fuel flow is fixed and the air velocity is incrementally
increased until the diffusion flame detaches and lifts off from the
nozzle. In all cases, still and video measurements of the flame
structure will be made for comparison with detailed numerical computations. Given
that the capture of the lifting processes in normal gravity is extremely
difficult, SLICE will provide valuable photographic observations on
the transient flame behavior.
Principal Investigator (PI): Prof.
Marshall B. Long, Yale University
Co-Investigators (Co-Is): Prof. Mitchell D. Smooke, Yale University
Dennis P. Stocker, NASA Glenn
Dr. Fumiaki Takahashi, NCSER @ NASA Glenn
NASA Technical Contact: Dennis P. Stocker, NASA Glenn
October 2013 – The SLICE combustion experiment operated on board the ISS from February 2012 to March 2012. The SLICE Principal Investigator Marshal Long is continuing analysis of the SLICE ISS flight data.
March 29, 2012 – SLICE testing was completed on March 23 and the hardware has now been reconfigured for the Burning and Suppression of Solids (BASS) experiment. After restoring the video overlay, astronaut Don Pettit conducted SLICE tests twice per week for a seven-week period in February and March. In the thirteen sessions (i.e., days) of testing, all twelve bottles of gaseous fuel were consumed, during which approximately 120 flames were ignited and about 4,000 high-resolution photos were taken at roughly 700 flow conditions. Preliminary estimates have been made of flame liftoff limits for ten fuel and burner tube combinations. With testing complete, the focus is on analyzing the acquired data and using it to enhance the computational modeling of the flames, extending our ability to accurately predict a broader range of flame conditions. The improved modeling capability will lead to design tools enabling improved fuel efficiency and reduced pollutant emission in practical combustion on Earth. The analysis and modeling activity is being led by Profs. Marshall Long and Mitchell Smooke at Yale University as described in the online story, “Space Station Research Comes Back to Earth.” To view additional photos and learn more about the experiment, visit the NASA/slice Facebook page - which is simply a web page and doesn’t require registration with Facebook or special software.
In this photo taken on Feb. 24, astronaut Don Pettit is in the U.S. Laboratory on the International Space Station conducting a smoke point test using 100% propane as the fuel. The Microgravity Science Glovebox (MSG), in which the test is being conducted, is covered with its stray light cover so that the only light in the photography is from the propane flame. As such, Pettit is watching the flame on a video monitor on his left while adjusting the fuel and air coflow using the tethered control box.
In this SLICE test conducted on March 15, 20% ethylene diluted with nitrogen (where that mixture is a gaseous fuel) flows upward at a fixed rate from a 0.8-mm inner diameter burner, which is centered within a small duct. A fan-driven and upward-pointing air coflow is gradually increased over time, where the results are shown from left to right in the composite image sequence. Initially the flame is non-premixed, where the ethylene and oxygen are separated by the burner and flame. The blue flame becomes smaller in both length and diameter as the air coflow increases. The distance between the flame’s base and the burner gradually increases until the flame abruptly separates from the burner and stabilizes downstream. When the flame lifts from the burner (where that distance increases with the coflow), air is able to mix with the fuel and the flame becomes increasingly premixed and therefore shorter. The flame eventually flattens into a disk-like shape and later blows out, i.e., extinguishes, at a sufficiently high coflow.
Example of preliminary SLICE results prepared by the project team at Yale University, under the leadership of Prof. Marshall Long. It shows an attached flame of 100% methane from a test conducted on Feb. 9, where it was photographed through a blue-green (BG7) filter to prevent saturation in the red from the bright soot. Hydrocarbon flames are naturally blue (because of the chemistry, i.e., chemiluminescent emission of excited species, especially CH*), whereas the yellow, orange, and red coloring is from broadband radiation from the hot soot particles. The flame color was then reconstructed and preliminary estimates were made of the soot concentration and the soot temperature. The temperature was determined by a color-ratio process using the individual RGB (red/green/blue) planes of the digital still photo, based on a blackbody calibration of the camera conducted prior to its launch.
January 18, 2012 – On the ISS, astronaut Don Pettit is scheduled to unstow and set up the SLICE experiment on Jan. 19 and 20, respectively. Testing is expected to begin on Jan. 31 and be conducted twice per week in eleven sessions over a period of 5.5 weeks. For more information about the SLICE status, see the experiment’s Facebook page.
December 2011 – The SLICE team in Cleveland has been busy preparing for the experiment’s start with planning, practice in the lab, and training activities including participation in a Multilateral Joint Multi-Segment Training (JMST) simulation on Dec. 8. As planned, astronaut Don Pettit and fellow crew members launched from Kazakhstan on Dec. 21 and arrived at the space station on Dec. 23 returning the crew size to its normal six. You can learn more about Pettit and his space station activities from his preflight interview and Letters to Earth blog. You can also follow what’s happening through the daily reports of the crew activities. The MSG glovebox failed to power up on Dec. 19, but this was corrected with hardware replacement on Dec. 28. With this short delay, set up of the SLICE experiment is now planned for January 20.
November 2011 – While the MSG glovebox is currently being used for the Selectable Optical Diagnostics Instrument (SODI), it is expected that those tests will be completed in time for SLICE to begin in mid January 2012. Astronauts Ron Garan and Mike Fossum have both returned to Earth (in September and November, respectively) so SLICE is waiting for the launch of astronaut Don Pettit which is planned for December 21. Unless there is an unexpected delay, Pettit will conduct the SLICE experiment. This is his second time as an ISS crew member; Dr. Pettit previously served as Expedition 6’s Science Officer and may be best known for his Saturday Morning Science.
October 2011 – The Capillary Channel Flow (CCF) experiment has been completed and the Microgravity Science Glovebox (MSG) is now being used for investigations using the Selectable Optical Diagnostics Instrument (SODI). SLICE operations will follow both SODI and the launch of astronaut Don Pettit and are still expected to occur in January-February 2012 (during Increment 30).
September 2011 – SLICE operations are approaching, and will follow (in order) the CCF, SODI-Colloid, and SODI-DSC experiments in the Microgravity Science Glovebox (MSG). It is currently anticipated that SLICE will begin in January 2012, in which case the experiment will be conducted by astronaut Don Pettit. Final SLICE operations (tentatively in February 2012) will include some tests for the Smoke Point In Coflow Experiment (SPICE).
July 2011 - The SLICE hardware launched in February 2011 on STS-133/ULF-5 and is currently on board the International Space Station (ISS). Astronauts Joe Acaba, Mike Fossum, Ron Garan, Don Pettit, and Suni Williams have been trained for the experiment. Although Garan and Fossum are both now on the ISS, the facility in which SLICE will be conducted, i.e., the Microgravity Science Glovebox (MSG), is being used for other experiments. It is currently expected that SLICE operations will begin in early 2012 (or perhaps late 2011) where that timing will determine which astronaut(s) conduct the experiment. SLICE operations should last approximately two months, after which the MSG will be used for the Burning And Suppression of Solids (BASS) experiment.