Burning and Suppression of Solids – II (BASS-II)
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.
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.
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.
- 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 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.
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.
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.
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.
- Dr. Sandra Olson, NASA Glenn Research Center, Cleveland, Ohio, United States
- Dr. Paul Ferkul, National Center for Space Exploration Research, Cleveland, Ohio, United States
- Prof. Carlos Fernandez-Pello, , University of California at Berkeley, Berkeley, California, United States
- Prof. Fletcher Miller, San Diego State University, San Diego, California United States
- Prof. Indrek Wichman, Michigan State University, East Lansing, Michigan, United States
- Prof. James Tien, Case Western Reserve University, Cleveland, Ohio, United States
- Prof. Subrata Bhattachjee, San Diego State University,San Diego, California, United States
- Robert Hawersaat, Glenn Research Center, Cleveland, Ohio, United States
- ZIN Technologies, Inc.