Burning and Suppression of Solids - II (BASS-II) - 11.22.16

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
The Burning and Suppression of Solids –II (BASS-II) investigation examines the burning and extinction characteristics of a wide variety of fuel samples in microgravity. The BASS-II experiment will guide strategies for materials flammability screening for use in spacecraft as well as provide valuable data on solid fuel burning behavior in microgravity. BASS-II results contribute to the combustion computational models used in the design of fire detection and suppression systems in microgravity and on Earth.
 
Science Results for Everyone
BASS-II tests produced data on how ambient oxygen, ventilation, and fuel affect combustion and burning. Theoretical formulas and data on flame spread do not always match in normal gravity. With data from microgravity, scientists determined thin and thick fuel spread rates and a formula for transition from thin to thick fuels. Models predict higher spread rates than observed, so need improvement. Data also allowed calculation of combustion completeness, heat release rates, and fuel-to-oxygen global equivalence ratios and supported theoretical models for quenching boundaries. Results will guide choice of materials for future spacecraft and advance fire detection and suppression in space and on Earth. 

The following content was provided by Sandra L. Olson, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom: BASS

Principal Investigator(s)
Sandra L. Olson, Ph.D., Glenn Research Center, Cleveland, OH, United States

Co-Investigator(s)/Collaborator(s)
Paul V. Ferkul, Ph.D., National Center for Space Exploration Research, Cleveland, OH, United States
Carlos Fernandez-Pello, Berkeley, CA, United States
James S. T'ien, Ph.D., Case Western Reserve University, Cleveland, OH, United States
Fletcher J. Miller, National Center for Space Exploration Research, Cleveland, OH, United States
Subrata Bhattacharjee, San Diego, CA, United States

Developer(s)
ZIN Technologies Incorporated, Cleveland, OH, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
NASA Research Office - Space Life and Physical Sciences (NASA Research-SLPS)

Research Benefits
Information Pending

ISS Expedition Duration
September 2013 - September 2014; March 2015 - September 2015; March 2016 - February 2017; March 2017 - September 2017

Expeditions Assigned
37/38,39/40,43/44,47/48,49/50,51/52

Previous Missions
ISS Expedition 23/24 was the first mission for the BASS experiment which utilizes the existing Smoke Point In Co-flow Experiment (SPICE) hardware on orbit aboard the ISS.

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Experiment Description

Research Overview

  • Burning and Suppression of Solids - II (BASS-II) tests the hypothesis that materials in microgravity, with adequate ventilation, burn as well if not better than the same material in normal gravity with other conditions being identical (pressure, oxygen concentration, temperature, etc.).NASA tests materials for flammability using an upward burning test, which is considered to be the worst-case geometry for flammability of the material on Earth.  One objective of the BASS-II tests is to identify what is the worst case for material flammability in spacecraft environments, and how does that compare to the terrestrial upward burning used to screen the materials for safe use aboard spacecraft.

  • The main variables to be tested are the effects of ambient oxygen concentration, ventilation flow velocity, and fuel type, thickness, and geometry.  Many of the tests will focus on finding a minimum oxygen concentration or flow velocity where a material will burn in space, to compare with the Earth-based limits.   Flame growth rates are also of interest, to determine how quickly a fire in space can grow and if the flames reach a finite size or continue to grow.  This has implications for firefighting strategies in spacecraft.

  • Detailed combustion models can be validated by data obtained in the simpler flow environment in microgravity. Once validated, they can be used to build more complex combustion models needed to capture the important details of flames burning in normal gravity. These models have wide applicability to the general understanding of many terrestrial combustion problems.

Description

Burning and Suppression of Solids - II (BASS-II) utilizes slightly modified Smoke Point In Co-flow Experiment (SPICE) hardware within the Microgravity Science Glovebox (MSG) for observations of burning solid materials on board the ISS.

BASS-II consists of 100 fuel samples and associated igniter wires. There are three categories of samples: flat samples, rod samples, and a section of a large solid sphere. Thin flat samples (10 cm long by 1 and 2 cm wide) yield concurrent or opposed-flow spread rates, limiting flame lengths, and extinction limits. The flat sample materials will include acrylic films and sheets of different thicknesses, and a cotton-fiberglass fabric blend Solid Inflammability Boundary at Low-Speeds (SIBAL) fuel which was previously tested in BASS. The rod samples are made of black or clear acrylic, and will provide solid fuel regression rates and extinction limits for both opposed and concurrent flow.  The large solid spherical section, also made of acrylic, will be used to study ignition of thick materials and flame growth over the thick material. 

The important experimental observations from BASS-II with respect to the burning process include flame shape and appearance as a function of  ambient oxygen concentration, flow speed, flame spread rate (how fast the flame develops), and flame dynamics (pulsations, oscillations, etc.). With respect to extinction, the critical observations and data are the time to extinction as a function of fuel geometry, flow, and ambient oxygen concentration. The dynamics of the flame before extinction are also important for comparison to the modeling work.

The modeling effort includes:

  • Modeling flame spread over flat samples: For flat samples, the steady spread characteristics can be examined using the three-dimensional model currently available. Alterations are the new tunnel and sample geometry and the upstream boundary condition. For the flame growing phase, a transient model is currently being developed.
  • Modeling burning and extinction of PMMA spheres: Similar problem on modeling two-dimensional circular PMMA cylinder in cross flow has been performed. Some changes are needed for the sphere and the duct flow.

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Applications

Space Applications
A primary goal of BASS-II is improved spacecraft fire safety, improved understanding of combustion in space and how to avoid it. If you're on a mission far from Earth, a fire can be catastrophic. BASS-II helps engineers select the safest materials and improve firefighting methods on future space missions.

Earth Applications
In outer space, fuels burn as oval balls rather than with an upward pointed cone flame as they do on Earth. This simpler combustion process enables researchers to evaluate computer models of fuel burning. These models can then be used to more accurately study flames on Earth, such as in wildfires, building fires, energy recapture from waste recycling, and other combustion problems.
 

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Operations

Operational Requirements and Protocols

BASS-II is conducted inside the sealed MSG work volume. The crewmember is involved throughout the experiment to load fuel samples, adjust nitrogen gas (GN2) concentration in the working volume vitiation of the working volume, initiate tests, ignite the fuel,  monitor and record data, exchange fuel samples, and replace the igniter. Forty-one test samples will be burned in a variety of flow conditions for a total of 89 test points.

Data is downlinked via video during or immediately after each flame test. Digital photos are downlinked after selected flame tests for ground confirmation before proceeding. BASS-II testing session must be conducted during periods when no major reboost or docking procedures are underway on the International Space Station (ISS).


The crewmember installs the BASS-II hardware in the MSG work volume. The BASS-II hardware consists of a small flow duct with an igniter and a small nozzle along with exchangeable fuel samples. During BASS-II operations a fan produces a co-flow of air through the duct. An anemometer is used to measure the actual flow rate. The crewmember adjusts the airflow from 5 to 50 cm/s. Nitrogen vitiation of the working volume is then initiated using station GN2 at a flow rate of up to 500 cc/min for a prescribed time. The flame is ignited and allowed to burn for about a minute. A radiometer measures flame output. The crewmember conducts each test. They install the correct fuel assembly and set the air flow rate through the duct before igniting the flame. When the flame is ignited, the crewmember allows some time for the flame to stabilize then adjusts the flow of nitrogen suppressant through the nozzle until the flame goes out. After the test, the crewmember turns off the nitrogen flow and prepares for the next test. The science team on the ground monitors the video downlink to assist the crewmember in determining any peculiar flame behaviors and reviews the sensor data overlaid on the video image. Upon completion of the tests the crewmember stows the hardware and the stored images and data are returned to Earth for analysis.

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Decadal Survey Recommendations

CategoryReference
Applied Physical Science in Space AP6
Applied Physical Science in Space AP7
Applied Physical Science in Space AP8
Translation to Space Exploration Systems TSES8
Translation to Space Exploration Systems TSES9

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Results/More Information

They also found that how deep or thick the bed of fuel is does not affect the minimum speed of air required for flame-spread. However, the deeper or thicker the bed of fuel is, the slower the flame spread. Scientists consider a bed of fuel to be thin if the flame heats all the fuel. Otherwise, they consider the bed of fuel to be thick. In space, the critical thickness for the fuel poly-methyl methacrylate (PMMA), in ambient air, is 5.2 millimeters. Scientists also found that if the flame spreads faster if the fuel burns on two sides, compared to one.

Among the several fuel samples tested, the results included the observation that the vast majority of the oxygen consumed went into carbon dioxide. However, different fuel samples, depending which way the air was blown, had different ratios of carbon monoxide to carbon dioxide. Most of the flames had much higher rations of carbon monoxide to carbon dioxide, than flames on the Earth. That meant the flames were not as efficient as flames on the Earth.

Overall, the flames did not receive enough air to burn all of the fuel. Some fuel ended up as soot, some as carbon monoxide, and some as unburned hydrocarbons.
Another team used a composite cotton-fiberglass fabric blend as a fuel. When they decreased the air speed during some of the tests, the flame would go out when the air had more oxygen in it. This happened when the air was moving in a range of 1 and 5 centimeters per second. The higher the speed of air, the lower the amount of oxygen was at when the flame would go out. When the team graphed their results, the found that the shape of the boundary, where air speed and oxygen amount matched with the flame going out, supported the prediction made by earlier theoretical models.

In addition to finding the limits at which the flame would go out, they team recorded the sequence of sample ignition, flame growth, steady spread, and final decay.
Also as part of the BASS-II experiment, ground teams burned cylindrical rods of PMMA. They found that the flames would go out when the speed of moving air became sufficiently slow that the flame could no longer generate enough heat. The flame had to generate enough heat to make up for the heat lost to conduction into the PMMA rod, and radiation. The team also found that when the flame blew out, the temperature of the flame was constant. This was the case regardless of the oxygen concentration or of how much the flame stretched. They determined that the temperature was critical in determining whether the flame quenched.

The understanding of burning and combustion is crucial for future long-duration missions beyond low Earth orbit. Testing how materials ignite and smolder in microgravity is essential for choosing everything for future spacecraft, from windowpanes to wire insulation, which will travel on longer-term missions to Mars or other destinations. The BASS-II results contribute to the combustion computational models used in the design of fire detection and suppression systems in microgravity and on Earth.
 

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Results Publications

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Ground Based Results Publications

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ISS Patents

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Related Publications

    Wichman I, Olson SL, Miller FJ, Hariharan A.  Fire in microgravity. American Scientist. 2016 January-February; 104(1): 44. DOI: 10.1511/2016.118.44.

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Related Websites

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Imagery

image NASA Image: ISS038E049143 - Image taken during a BASS-II (Burning and Suppression of Solids - II) experiment flame test.
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image NASA Image: ISS038E049159 - Image taken during a BASS-II (Burning and Suppression of Solids - II) experiment flame test.
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image NASA Image: ISS038E047576 - NASA astronaut Rick Mastracchio works with the Burning and Suppression of Solids (BASS-II) experiment in the Microgravity Science Glovebox (MSG).
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image NASA Image: ISS040E088798 - ESA astronaut Alexander Gerst removes hardware for the combustion experiment known as the Burning and Suppression of Solids (BASS-II) from the Microgravity Science Glovebox (MSG) while NASA astronaut Reid Wiseman, flight engineer, looks on.
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This image sequence from the BASS investigation shows a flame igniting (top left) and spreading upward across a  1-cm wide flat cotton-fiberglass sample with a 10 cm/s concurrent air flow (flow direction is also up in images).  The images are just over 1 second apart.  The flame reaches a steady size by 10 seconds, and burns the entire sample (bottom right).  As the flame spreads, some smoldering of the fuel residue (glowing orange spots) continues.   


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These two images from the BASS investigation are of ceramic encased candles burning in a very low velocity flow (flow is blowing upward in both images).  On the left is a ‘normal’ candle where the flow is up and the candle is up.  On the right, the candle is ‘inverted’.  In normal gravity, the flames would be very different, but in microgravity with very low speed flow, the shapes are fairly similar and the primary difference is how the candle stabilizes around the candle.  In the ‘normal configuration, the flame starts near the ceramic base and is primarily next to and above the wick, where the fuel starts.  In the ‘inverted’ configuration, the flame starts below the wick where the air and fuel first meet, and the flame wraps downstream around the ceramic housing as the air and fuel continue to mix.  Soot is formed in both geometries, with the maximum sooting (brightest yellow color) indicating the hottest part of the flame.  The maximum sooting is on opposite ends of the candle in the two cases.  The blue is chemiluminescence from the burning fuel.  Rod samples to be tested in BASS-II will be functionally similar to these candle samples. 


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The results of a Burning and Suppression of Solids (BASS) experiment demonstrates that in zero-gravity—where heat doesn’t rise—a candle flame burns in a uniform oval (NASA Image).

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Drop tower results and modeling of a 2-cm-diameter PMMA sphere burning in 17% oxygen, 1 atm. pressure, at 2 cm/s forced convective flow. Experiment images are overlaid with computer simulations, which can capture the flame response as it transitions from 1-g to 0-g. Left-side contours show reaction rate (kgmol/m3/s); right side contours show temperature (K)
(NASA Glenn Image).

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