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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The Effect of Gravity on Premixed Flame Propagation and Extinction in a Vertical Standard Flammability Tube

The effect of gravity on the upward and downward flame propagation in lean methane/air and lean propane/air mixtures was studied using plexiglass flammability tubes with ignition at the open-end gravity levels which ranged from microgravity (0 + or - 0.1 g) to 1.77 g. The lean limits were found to be about 5.25, 5.25, and 5.85 percent methane in air; and about 2.15, 2.06, and 2.20 percent propane in air for 1 g upward propagation, 0 g, and 1 g downward propagation, respectively. The propane/air flames observed were stable, irrespective of the g level. On the other hand, lean methane/air flames were found to be sporadically unstable for upward propagation at g levels less than 0.5 g, and for donward propagation at g = 1.0. The extinction process observed was the same for both systems studied: at g = 0, the flame extinguished from the edge toward the center, while at g of 1 and above, the flame extinguished from the center toward the edge.

Strehlow, Roger A.↗
NASA NTRS1988

ASTM Committee G-4 metals flammability test program - Data and discussion

Results of metals flammability tests performed on twenty-six metals in the NASA/White Sands Test Facility are discussed together with the test systems. The promoted combustion and ignition characteristics of these metals are described, and the metals are ranked according to their suitability for use in oxygen systems. In general, alloys with high copper and nickel contents and low iron content were found to rank higher than those that had high iron content, while alloys that had high aluminum content were ranked the lowest.

Stoltzfus, Joel M.↗
NASA NTRS1990

Flammabilities Of Graphite-Reinforced Composites

Report describes tests and comparisons of flammabilities, thermal properties, and selected mechanical properties of composite materials made of epoxy and other matrices reinforced by graphite fibers. Composites also compared with baseline epoxy/fiberglass composite. Considers such properties as limiting oxygen index, smoke evolution, products of thermal degradation, total heat release, heat-release rate, loss of mass, spread of flames, resistance to ignition, and thermal stability.

Kourtides, Demetrius A.↗
NASA NTRS1992

Specimen Holder For Flammability Tests

Fixture holds sheet specimens for flammability tests. Frame and clamps designed to minimize local overstress on specimen. Heat capacity of fixture low, interfering less with interpretation of results of test by drawing less heat away from specimen. Accepts films, fabrics, foams, and other sheets, rigid or flexible. Specimens thin or thick, or of variable thickness. Bent to accommodate curved rigid specimens. Also used for such other tests as particle-impact tests.

Rucker, Michelle A.↗
NASA NTRS1992

Lean flammability limit of downward propagating hydrogen-air flames

Detailed multidimensional numerical simulations that include the effects of wall heat losses have been performed to study the dynamics of downward flame propagation and extinguishment in lean hydrogen-air mixtures. The computational results show that a downward propagating flame in an isothermal channel has a flammability limit of around 9.75 percent. This is in excellent agreement with experimental results. Also in excellent agreement are the detailed observations of the flame behavior at the point of extinguishment. The primary conclusion of this work is that detailed numerical simulations that include wall heat losses and the effect of gravity can adequately simulate the dynamics of the extinguishment process in downward-propagating hydrogen-air flames. These simulations can be examined in detail to gain understanding of the actual extinction process.

Patnaik, G.↗
NASA NTRS1994

Wire insulation degradation and flammability in low gravity

This view-graph presentation covers the following topics: an introduction to spacecraft fire safety, concerns in fire prevention in low gravity, shuttle wire insulation flammability experiment, drop tower risk-based fire safety experiment, and experimental results, conclusions, and proposed studies.

Friedman, Robert↗
NASA NTRS1995

The USML-1 wire insulation flammability glovebox experiment

Flame spreading tests have been conducted using thin fuels in microgravity where buoyant convection is suppressed. In spacecraft experiments flames were ignited in quiescent atmospheres with an elevated oxygen content, demonstrating that diffusional mechanisms can be sufficient alone to sustain flame spreading. In ground-based facilities (i.e. drop towers and parabolic aircraft) low-speed convection sustains flames at much lower concentrations of atmospheric oxygen than in quiescent microgravity. Ground-based experiments are limited to very thin fuels (e.g., tissue paper); practical fuels, which are thicker, require more test time than is available. The Glovebox Facility provided for the USML 1 mission provided an opportunity to obtain flame spreading data for thicker fuel Herein we report the results from the Wire Insulation Flammability (WIF) Experiment performed in the Glovebox Facility. This experiment explored the heating, ignition and burning of 0.65 mm thick polyethylene wire insulation in low-speed flows in a reduced gravity environment. Four tests were conducted, two each in concurrent flow (WIF A and C) and opposed flow (WIF B and D), providing the first demonstration of flame spreading in controlled forced convection conducted in space.

Greenberg, Paul S.↗
NASA NTRS1998

Flammability of Heterogeneously Combusting Metals

Most engineering materials, including some metals, most notably aluminum, burn in homogeneous combustion. 'Homogeneous' refers to both the fuel and the oxidizer being in the same phase, which is usually gaseous. The fuel and oxidizer are well mixed in the combustion reaction zone, and heat is released according to some relation like q(sub c) = delta H(sub c)c[((rho/rho(sub 0))]exp a)(exp -E(sub c)/RT), Eq. (1) where the pressure exponent a is usually close to unity. As long as there is enough heat released, combustion is sustained. It is useful to conceive of a threshold pressure beyond which there is sufficient heat to keep the temperature high enough to sustain combustion, and beneath which the heat is so low that temperature drains away and the combustion is extinguished. Some materials burn in heterogeneous combustion, in which the fuel and oxidizer are in different phases. These include iron and nickel based alloys, which burn in the liquid phase with gaseous oxygen. Heterogeneous combustion takes place on the surface of the material (fuel). Products of combustion may appear as a solid slag (oxide) which progressively covers the fuel. Propagation of the combustion melts and exposes fresh fuel. Heterogeneous combustion heat release also follows the general form of Eq.(1), except that the pressure exponent a tends to be much less than 1. Therefore, the increase in heat release with increasing pressure is not as dramatic as it is in homogeneous combustion. Although the concept of a threshold pressure still holds in heterogeneous combustion, the threshold is more difficult to identify experimentally, and pressure itself becomes less important relative to the heat transfer paths extant in any specific application. However, the constants C, a, and E(sub c) may still be identified by suitable data reduction from heterogeneous combustion experiments, and may be applied in a heat transfer model to judge the flammability of a material in any particular actual-use situation. In order to support the above assertions, two investigations are undertaken: 1) PCT data are examined in detail to discover the pressure dependence of heterogeneous combustion experiment results; and 2) heterogeneous combustion in a PCT situation is described by a heat transfer model, which is solved first in simplified form for a simple actual-use situation, and then extended to apply to PCT data reduction (combustion constant identification).

Jones, Peter D.↗
NASA NTRS1999

Experimental Verification of Material Flammability in Space

The flammability in microgravity of three US-furnished materials, Delrin, polymethylmethacrylate (PMMA), and high-density polyethylene, was determined using a Russian-developed combustion tunnel on Mir. Four 4.5-mm-diameter cylindrical samples of each plastic were ignited under concurrent airflow (in the direction of flame spread) with velocities from no flow to 8.5 cm/s. The test results identify a limiting air-flow velocity V(sub lim) for each material, below which combustion ceases. Nominal values are V(sub lim) < 0.3 cm/s for Delrin, 0.5 cm/s for PMMA, and 0.3 to 0.5 cm/s for polyethylene. These values are lower than those obtained in prior ground testing. Nevertheless, they demonstrate that flow shutoff is effective for extinguishment in the microgravity environment of spacecraft. Microgravity test results also show that the plastic materials maintain a stable melt ball within the spreading flame zone. In general, as the concurrent flow velocity V decreases, the flame-spread rate V(sub F) decreases, from an average (for all three materials) of V(sub F)= 0.5-0.75 mm/s at V = 8.5 cm/s to V(sub F)= 0.05-0.01 mm/s at V = 0.3-0.5 cm/s. Also, as V decreases, the flames become less visible but expand, increasing the probability of igniting an adjacent surface.

Ivanov, A. V.↗
NASA NTRS2000

Model of ASTM Flammability Test in Microgravity: Iron Rods

There is extensive qualitative results from burning metallic materials in a NASA/ASTM flammability test system in normal gravity. However, this data was shown to be inconclusive for applications involving oxygen-enriched atmospheres under microgravity conditions by conducting tests using the 2.2-second Lewis Research Center (LeRC) Drop Tower. Data from neither type of test has been reduced to fundamental kinetic and dynamic systems parameters. This paper reports the initial model analysis for burning iron rods under microgravity conditions using data obtained at the LERC tower and modeling the burning system after ignition. Under the conditions of the test the burning mass regresses up the rod to be detached upon deceleration at the end of the drop. The model describes the burning system as a semi-batch, well-mixed reactor with product accumulation only. This model is consistent with the 2.0-second duration of the test. Transient temperature and pressure measurements are made on the chamber volume. The rod solid-liquid interface melting rate is obtained from film records. The model consists of a set of 17 non-linear, first-order differential equations which are solved using MATLAB. This analysis confirms that a first-order rate, in oxygen concentration, is consistent for the iron-oxygen kinetic reaction. An apparent activation energy of 246.8 kJ/mol is consistent for this model.

Steinberg, Theodore A↗
NASA NTRS1994

Wire Insulation Flammability Experiment: USML-1 One Year Post Mission Summary

Herein we report the results from the Wire Insulation Flammability (WIF) Experiment performed in the Glovebox Facility on the USML-1 mission. This experiment explored various aspects of electrically induced fire scenarios in a reduced gravity environment. Under quiescent microgravity conditions, heat and mass transfer are dominated by diffusive and radiative transport; while in normal-gravity buoyancy induced convection often dominates. Of considerable scientific and practical interest is the intermediate situation of combustion occurring in the presence of imposed gas flows, with lower characteristic velocities than those induced by buoyancy in noma1 gravity. Two distinct cases naturally arise: flow direction opposed to, or concurrent with, the flame spread direction. Two tests of each kind were conducted in the WIF experiment, providing the first controlled demonstration of flame spreading in forced convection ever conducted in space. Four test modules were flown. The wire insulation, 1.5 mm in diameter, was polyethylene, extruded onto nichrome wire. Temperatures of the wh3 cores and insulation heated in quiescent and flowing environments were measured. Video and still-camera images of the samples, burning in air flowing at approximately 10 cm/sec, were recorded to obtain flame characteristics including spread rate, structure and temperature. Flame spread rates in concurrent flow were approximately twice those in opposed flow. In concurrent and opposed flow regimes, the spreading flames stabilized around a bead of molten insulation material, within which bubble nucleation was observed. An ignition attempt without flow mated a quiescent cloud of vaporized fuel which ignited dramatically yet failed to sustain normal flame spread. Finally, all tests produced substantial soot agglomerates, particularly the concurrent flow tests; and the collected soot has a morphology very distinct from soot formed in normal gravity flames. Several unexpected and unique microgravity combustion phenomena were observed.

Greenberg, Paul S.↗
NASA NTRS2003

Upward Flammability Testing: A Probabilistic Measurement

Examination of NASA-STD-6001 Test 1 data suggests burn length outcome for a given environment has a large statistical variation from run to run. Large data sets show that burn length data form cumulative probability distribution curves, which describe a material's characteristic to burn in a specific environment, suggesting that the current practice of testing three samples at specific conditions is inadequate. Sufficient testing can establish material characteristics probability curves to provide the probability that a material will sustain a burn length of at least 15.24 cm (6.0 in.) or will sustain burning until all material is consumed. A simple pasdfail criterion may not be possible or practical. Future application of flammability data for some material classes may require the engineer to assess risk based on the probability of an occurrence and the probable outcome with different materials as characterized with cumulative burn length distributions for specific use conditions.

Davis, Samuel E.↗
NASA NTRS2003

An Earth-Based Equivalent Low Stretch Apparatus to Assess Material Flammability for Microgravity and Extraterrestrial Fire-Safety Applications

The objective of this project is to modify the standard oxygen consumption (cone) calorimeter (described in ASTM E 1354 and NASA STD 6001 Test 2) to provide a reproducible bench-scale test environment that simulates the buoyant or ventilation flow that would be generated by or around a burning surface in a spacecraft or extraterrestrial gravity level. This apparatus will allow us to conduct normal gravity experiments that accurately and quantitatively evaluate a material's flammability characteristics in the real-use environment of spacecraft or extra-terrestrial gravitational acceleration. The Equivalent Low Stretch Apparatus (ELSA) uses an inverted cone geometry with the sample burning in a ceiling fire configuration that provides a reproducible bench-scale test environment that simulates the buoyant or ventilation flow that would be generated by a flame in a spacecraft or extraterrestrial gravity level. Prototype unit testing results are presented in this paper. Ignition delay times and regression rates for PMMA are presented over a range of radiant heat flux levels and equivalent stretch rates which demonstrate the ability of ELSA to simulate key features of microgravity and extraterrestrial fire behavior.

Olson, S. L.↗
NASA NTRS2004

Flammability Configuration Analysis for Spacecraft Applications

Flight hardware configuration flammability assessment will: a) evaluate the overall hardware configuration; b) evaluate the way in which the hardware will be used; c) identify the major materials to be assessed; d) determine fire propagation paths; and e) evaluate ability of containers to contain fire.

Hirsch, David↗
NASA NTRS2004

A New Test Method for Material Flammability Assessment in Microgravity and Extraterrestrial Environments

The objective of this research is to modify the well-instrumented standard cone configuration to provide a reproducible bench-scale test environment that simulates the buoyant or ventilation flow that would be generated by or around a burning surface in a spacecraft or extraterrestrial gravity level. We will then develop a standard test method with pass-fail criteria for future use in spacecraft materials flammability screening. (For example, dripping of molten material will be an automatic fail.)

Olson, S. L.↗