The Smoke Point In Co-flow Experiment (SPICE) determines the point at which gas-jet flames (similar to a butane-lighter flame) begin to emit soot (dark carbonaceous particulate formed inside the flame) in microgravity. Studying a soot emitting flame is important in understanding the ability of fires to spread and in control of soot in practical combustion systems space.Principal Investigator(s)
ZIN Technologies Incorporated, Cleveland, OH, United States
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)Research Benefits
Information PendingISS Expedition Duration:
October 2008 - October 2009Expeditions Assigned
18,19/20Previous ISS Missions
SPICE began experiments during Expedition 18.
The Smoke Point In Co-flow Experiment (SPICE) will continue the study of fundamental phenomena related to understanding the mechanisms controlling the stability and extinction of jet diffusion flames begun with the Laminar Soot Processes (LSP) on STS-94. SPICE will stabilize an enclosed laminar flame in a co-flowing oxidizer, measure the overall flame shape to validate the theoretical and numerical predictions, measure the flame stabilization heights, and measure the temperature field to verify flame structure predictions.
SPICE will determine the laminar smoke point properties of non-buoyant jet diffusion flames (i.e., the properties of the largest laminar jet diffusion flames that do not emit soot) for several fuels under different nozzle diameter/co-flow velocity configurations. Luminous flame shape measurements would also be made to verify models of the flame shapes under co-flow conditions. The smoke point is a simple measurement that has been found useful to study the influence of flow and fuel properties on the sooting propensity of flames. This information would help support current understanding of soot processes in laminar flames and by analogy in turbulent flames of practical interest.
Current NASA spacecraft materials selection is based upon a simplified test method that segregates material based upon behavior on Earth without real consideration of microgravity effects. A critical element of this understanding is the radiative heat emission from the flame. This heat emission is strongly influenced by the extent of soot formation. Improved understanding of soot formation and thereby the heat release from microgravity fires will allow more complete and effective utilization of the flammability test results. These results can be used in first-order models and predictions of heat release in spacecraft fires and as a means to extend heat release data from tests like the NASA cone-calorimeter test to microgravity fires to a performance based material selection process.Earth Applications
The smoke-point phenomena is a classical metric in the understanding of the heat release and spread rate of fires. It is commonly used in fire modeling on Earth and to understand the soot growth and emission by flames. The dominant characteristics of many flames of practical interest are nonbuoyant. SPICE seeks to extend our understanding by looking at the interaction of ambient flow with the smoke point, enabling us to better predict heat release from non-buoyant flames in practical combustors (e.g. jet engines and furnaces).
SPICE will be conducted inside the sealed MSG work volume. The crewmember is involved throughout the experiment to load fuel bottles, initiate tests, ignite the fuel, adjust flame to smoke point, monitor and record data, exchange burner tubes, exchange fuel bottles and replace the igniter. Six test sequences covering six different fuels with three different burner tubes, for a total of fifty-four (54) test points will be performed by the crewmember. Periodic repeat points are desired if time is available. Data will be downlinked via video during or immediately after each flame test. Digital photos are downlinked after selected flame tests for ground confirmation before proceeding. SPICE testing session must be conducted during periods when no major reboost or docking procedures are underway on the International Space Station.Operational Protocols
The crewmember installs the SPICE hardware in the MSG work volume. The SPICE hardware consists of a small flow duct with an igniter and a small nozzle. Outside the flow duct are 2 cameras, the fuel supply bottle and various electronic boxes. Each test is conducted by the crewmember who installs the correct diameter nozzle and sets the air flow rate through the duct before igniting the flame. When the flame is ignited, (it will look similar to a butane-lighter flame) the crewmember adjusts the flame size (by controlling the fuel flow rate) until the flame is just at the smoke point (the size where the flame just begins to emit a small stream of soot from the tip). After triggering the high resolution camera, the crewmember turns off the fuel and prepares for the next test. The science team on the ground will monitor the video downlink to assist the crewmember in determining the smoke point and will review the sensor data overlaid on the video image. Between test sessions the crew will change the fuel bottle to a different fuel (six will be tested). Upon completion of the tests the crewmember stows the hardware and the stored images and data are returned to Earth for analysis.
The Smoke Point in Co-flow Experiment (SPICE) started operations inside the microgravity science glove box (MSG) on board the ISS in April, 2009, and finished operations in March, 2012. SPICE successfully completed over 250 combustion tests with gaseous fuel mixtures of ethane, ethylene, propane, propylene, and propylene with nitrogen. More than 70 smoke points were found, and these are helping researchers understand the effects of microgravity and co-flowing (flowing in the same direction as fuel gas flow) air speed on smoke points.
The smoke point measurements yielded estimates of soot-forming conditions and flame dimensions. Flames of propylene and propylene mixtures were generally more luminous than the others, attributed to increased soot volume fractions. Periodic flame motion was observed in some flames, especially those with high air velocity, large burners, and long flames, and is attributed to unsteady co-flow air stream causing slight increase in the uncertainties in smoke points under these conditions. Smoke points for propane and ethylene were generally identified by the onset of gradual dimming, reddening, and rounding of the luminous flame tip. The brightest flames, generally for propylene and propylene mixtures, normally did not display significant dimming and reddening near their tips except when much longer than their smoke points. Smoke points for these flames were identified by the rapid transition to open-tipped flames. Open-tipped flames are common in both normal gravity and microgravity when smoke points are far exceeded and are generally associated with local flame extinguishment along the centerline and soot emission in an annular shell. For conditions sufficiently above the smoke points a glowing stream of particles could be seen leaving the flame. Smoke-point lengths in coflow generally increase with decreasing burner diameter and increasing coflow velocity in agreement with normal-gravity results. This is expected because a decrease in burner diameter ? or an increase in coflow velocity ? decreases the residence time (the time a fuel molecule takes to pass through the entire flame) available for soot formation and decreases the radiative heat loss fraction making the flame shorter and narrower.
Microgravity smoke points are of interest to spacecraft fire safety. Microgravity allows improved control over residence time and provides better understanding of the different mechanisms responsible for smoke points in normal gravity and microgravity (Dotson et al. 2011).
Dotson KT, Sunderland PB, Yuan Z, Urban DL. Laminar Smoke Points in Coflow Measured Aboard the International Space Station. 48th Aerospace Sciences Meeting and Exhibit, Orlando, FL; 2010
Urban DL, Yuan Z, Sunderland PB, Lin KC, Dai Z, Faeth GM. Smoke-Point Properties of Nonbuoyant Round Laminar Jet Diffusion Flames. Proceedings of the Combustion Institute. 2000; 28: 1965-1972.
Sunderland PB, Mendelson BJ, Yuan Z, Urban DL. Shapes of Buoyant and Nonbuoyant Laminar Jet Diffusion Flames. Combustion and Flame. 1999; 116: 376-386.
Lin KC, Faeth GM, Sunderland PB, Urban DL, Yuan Z. Shapes of Nonbuoyant Round Luminous Hydrocarbon/Air Laminar Jet Diffusion Flames. Combustion and Flame. 1999; 116: 415-431.
Sunderland PB, Mortazavi S, Faeth GM, Urban DL. Laminar Smoke Points of Nonbuoyant Jet Diffusion Flames. Combustion and Flame. 1994; 96: 97-103.
Urban DL, Yuan Z, Sunderland PB, Linteris GT, Voss JE, Lin KC, Dai Z, Sun K, Faeth GM. Structure and Soot Properties of Nonbuoyant Ethylene/Air Laminar Jet Diffusion Flames. 38th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Orlando, FL; 1998
Aalburg C, Diez FJ, Faeth GM, Sunderland PB, Urban DL, Yuan Z. Shapes of nonbuoyant round hydrocarbon-fueled laminar-jet diffusion flames in still air. Combustion and Flame. 2005; 142: 1-16.