Browsing by Author "Jomaas, Grunde"
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Item Effect of Flow Direction on the Extinction Limit for Flame Spread over Wire Insulation in Microgravity(47th International Conference on Environmental Systems, 2017-07-16) Nagachi, Masashi; Mitsui, Fumiya; Citerne, Jean-Marie; Dutilleul, Hugo; Guibaud, Augustin; Jomaas, Grunde; Legros, Guillaume; Hashimoto, Nozomu; Fujita, OsamuExperiments to determine the Limiting Oxygen Concentration (LOC) of a flame spreading over electric wire insulation were carried out in microgravity (parabolic flights) and in normal gravity, and the difference between the LOC in opposed and concurrent flows was evidenced under microgravity (μG). Polyethylene insulated Copper (Cu) wires and polyethylene insulated Nickel-Chrome (NiCr) wires with inner core diameter of 0.50 mm and insulation thickness of 0.30 mm were examined with external flow velocities ranging from 50mm/s to 200mm/s. The results for Copper wires show that with increasing external flow velocity, the LOC monotonically decreased in concurrent flow condition and the LOC first decreased and then increased (“U” trend) in opposed flow condition. These trends were similar to the results of the experiments with NiCr wires. Also, in terms of the minimum LOC value (MLOC), the MLOC for concurrent flow was about 1-2% lower in Oxygen concentration than that for opposed flow in both wires cases. Further, when comparing the MLOC of NiCr wires with the MLOC of Cu wires, it was found that the MLOC of the NiCr wires was close to that of Cu wires for concurrent flow conditions. However, the MLOC of the NiCr wires was about 1% lower in Oxygen concentration than that of Cu wires for opposed flow conditions. These results provide insight into the mechanism of extinction limit of flame spread over wire insulation, especially the effect of flow direction and core wire material, both of which will be useful for improving fire safety onboard spacecraft.Item Effect of flow direction on the extinction limit of spreading flame over wire insulation(46th International Conference on Environmental Systems, 2016-07-10) Nagachi, Masashi; Mitsui, Fumiya; Kizawa, Koki; Citerne, Jean-Marie; Dutilleul, Hugo; Jomaas, Grunde; Legros, Guillaume; Fujita, OsamuFire safety is one of the most important issues for manned space mission, because a fire in a spacecraft may results in irreversible alteration of the crew's environment. Electric wire is a major cause of fire accidents in spacecraft. So, it is very important to study the flammability of electric wire under microgravity conditions. In this paper experimental works to determine Limiting Oxygen Concentration (LOC) of spreading flame over electric wire insulation have been carried out and the difference between the LOC in opposed and concurrent flows has been evidenced under both normal gravity (1G) and microgravity (μG). Polyethylene (PE) insulated Nickel-Chrome (NiCr) wires with inner core diameter (dc) of 0.50 mm and insulation thickness (dp) of 0.30 mm are examined with external flow velocity ranging from 50mm/s to 200mm/s. Microgravity environment is provided along parabolic flights onboard the French A310 airplane. Results show that with increasing external flow velocity, the LOC in 1G first decreases and then increases (“U” trend) for both of opposed and concurrent cases. On the opposite the LOC in μG monotonically decreases with increasing external flow velocity. Furthermore the LOC in μG is lower than that at 1G because natural convection is vanished. Comparing opposed and concurrent flows in 1G condition, the LOC tendencies following the modification of the flow velocity are very similar and the minimum value is almost the same. On the other hand, in μG condition, the LOC value is almost the same within the low flow velocity region for both flow directions, but the LOC for concurrent flow is about 2% smaller in Oxygen concentration than that for opposed flow within the high flow velocity region. This research is supported by Japan Space Exploration Agency (JAXA) under the project of FLARE and the Centre National d'Etudes Spatiales (CNES) under contract #130615.Item Effect of the Ignition Method on the Extinction Limit for a Flame Spreading over Electric Wire Insulation(47th International Conference on Environmental Systems, 2017-07-16) Mitsui, Fumiya; Nagachi, Masashi; Citerne, Jean-Marie; Dutilleul, Hugo; Guibaud, Augustin; Jomaas, Grunde; Legros, Guillaume; Hashimoto, Nozomu; Fujita, OsamuExperiments for flame spreading over electric wire insulation were conducted in parabolic flights (microgravity) and on ground (normal gravity) to understand the effect of the ignition condition on the Limiting Oxygen Concentration (LOC) for electric wires under an external, opposed flow condition of 100 mm/s (typical flow velocity on ISS). Both the ignition power and the igniter heating time were varied ranging from 50 W to 110W and from 5 s to 15 s in order to investigate the ignition condition effect. Polyethylene-coated Nickel-Chrome wires with inner core diameter of 0.50 mm and insulation thickness of 0.30 mm were used as sample wires, and a 0.50 mm diameter coiled Kanthal wire was used as igniter. The experimental results show that the LOC assumes an almost constant value under normal gravity conditions once ignition occurred, whereas under microgravity conditions, the LOC gradually decreases as the ignition power or heating time increases and eventually it reaches an almost constant value. Thus, the effect of ignition condition on LOC is stronger in microgravity than in normal gravity. The difference in oxygen concentration between the maximum and the minimum LOC was about 2% within the tested range of ignition conditions. This means that additional heating is required after ignition occurs to obtain the correct LOC. Finally, the results suggest that there exists a minimum ignition power and heating time to obtain the correct LOC values for electric wire combustion, especially in microgravity. This result has the potential to improve safety aspects associated with the development of a fire safety standard for spacecrafts, and consequentially also to improve spacecraft fire safety in general.Item Experimental Results on the Effect of Surface Structures on the Flame Propagation Velocity of PMMA in Microgravity(47th International Conference on Environmental Systems, 2017-07-16) Eigenbrod, Christian; Hauschildt, Jakob; Meyer, Florian; Urban, David L.; Ruff, Gary A.; Olson, Sandra L.; Ferkul, Paul; Jomaas, Grunde; Toth, BalazsMaterials foreseen for the design of manned spacecraft must pass the NASA-STD 6001B Test 1 regarding its fire hazard. During this qualification test in 1g conditions, a flat sample with fire protected edges is placed vertically in a quiescent environment, and ignited at its lower end. To pass the test, it must extinguish within 150 mm propagation length. Even though PMMA does not pass this test, it is extensively used for scientific investigations because of its repeatability and use in previous studies. Systematic ground tests of generic geometries have revealed that almost any realistic machined geometry like sharp or rounded edges, fins or grooves may lead to a rise in flame propagation velocity up to a factor of four related to the flat standard sample. For the first time, the flamed spread over a structured, thick PMMA sample of 290 x 50 mm was examined in microgravity (3x10-5g0) under concurrent flow of 0.20 m/s onboard Orbital ATK’s re-supply spacecraft Cygnus. The results were compared to the behavior of a similarly-sized flat sample. Just as in 1g, it was found that vertical structures promote faster flame spread compared to a flat sample but to a lesser degree than what is observed in 1g. While the structured sample burned 70% faster than the flat sample in 1g, this difference was reduced to only 32% in microgravity. Both samples burned drastically slower in microgravity: 23 times slower for the structured sample and 18 times slower for the flat sample. In 1g the pyrolysis front rapidly spreads along the surface and takes advantage of improver in depth heat transfer afforded by edges but, in microgravity, the burning mostly confined to the leading edge which has the best supply of oxygen. Finally, the microgravity flames produced more smoke and exhibited a larger preheat area.Item Fire Safety Implications of Preliminary Results from Saffire IV and V Experiments on Large Scale Spacecraft Fires(50th International Conference on Environmental Systems, 7/12/2021) Urban, David; Ruff, Gary; Ferkul, Paul; Easton, John; Owens, Jay; Olson, Sandra; Meyer, Marit; Fortenberry, Claire; Brooker, John; Graf, John; Casteel, Michael; Jomaas, Grunde; Toth, Balazs; Eigenbrod, Christian; T'Ien, James; Liao, Ya-Ting; Fernandez-Pello, Carlos; Meyer, Florian; Legros, Guillaume; Guibaud, Augustin; Smirnov, Nikolay; Fujita, OsamuThe spread and growth of flames over large solid fuel samples and their effect on the pressurized spacecraft were studied inside Cygnus spacecraft while in orbit after departing the International Space Station. These experiments were developed by NASA�s Advanced Exploration Systems Division in the Human Exploration and Operations Mission Directorate. The ignited materials consisted of poly-methyl methacrylate (PMMA), cotton fabric and a cotton/fiberglass fabric blend. The samples were all 40 cm wide and with various lengths ranging from 18 cm for the PMMA samples to 50 cm for the fabrics. The overall results from these tests and their impact on the spacecraft are presented with emphasis on the fire safety implications of the results. The experiments included, a post-fire cleanup system, vehicle internal volume measurements, and transport of acid gases (HCl and HF). Measurements included video images, flame spread rate, flame temperatures and radiant heat output; energy release through oxygen calorimetry; distributed measurements of CO2 concentration and temperature at six locations in the spacecraft; CO2, CO, O2, HF and HCl concentrations; vehicle pressurized volume; and aerosol concentrations. Details of the flame growth and spread are discussed in other papers as are details of the post-fire cleanup system performance. The fire events had a measurable impact on the vehicle pressure, temperature, and carbon dioxide concentration. However, despite having heat release rates up to 10 kW, the average vehicle conditions did not rise to unacceptable levels. The combined results of the experiments provide significant new understanding of the impact of sample and flow duct height on flame spread and growth in addition to an improved perspective of the impact of a fire event on a spacecraft.Item Opposed flame spreading along a structured PMMA sample in exploration atmosphere under microgravity(50th International Conference on Environmental Systems, 7/12/2021) Eigenbrod, Christian; Meyer, Florian; Jomaas, Grunde; Olson, Sandra; Ferkul, Paul; Urban, David; Ruff, Gary A.; Toth, BalazsAs part of SAFFIRE V experiments on the ISS supply spacecraft CYGNUS, flame propagation along different surface structures on a PMMA sample was investigated in opposed flow. The sample was 200 x 400 mm (length x width) with a thickness of 10 mm and contained ribs of different widths (1-10 mm), each 3 mm high, on both sides, arranged in the flow direction. The total thickness of the specimen was thus 16 mm for the ribs. For the first 360 s after ignition with a Kanthal wire, the flow velocity was 20 cm/s in the opposed direction. Then the flow velocity was reduced to 5 cm/s for a duration of 300 s before it was switched off to terminate the experiment. The experimental pressure was 761 hPa and the oxygen concentration was 26.9 vol %. These conditions correspond to atmospheric conditions envisioned for future exploration missions. It was found that the flames ignited downstream propagated forward along the rib edges surprisingly fast with up to 0.88 mm/s (1 mm rib width). Also, it was observed that the wider the rib, the slower the propagation. The widest rib (10 mm) already showed two largely independent edge flames. Unintentionally, the experiment showed how sensitive the flames are to small perturbations of the flow field, as remnants of a preceding and upstream experiment disturbed the incoming flow stratification partially.Item Results of Large-Scale Spacecraft Flammability Tests(47th International Conference on Environmental Systems, 2017-07-16) Ferkul, Paul; Olson, Sandra; Urban, David; Ruff, Gary; Easton, John; T'Ien, James; Liao, Ya-Ting; Fernandez-Pello, A. Carlos; Torero, Jose; Eigenbrod, Christian; Legros, Guillaume; Smirnov, Nickolay; Fujita, Osamu; Rouvreau, Sebastien; Toth, Balazs; Jomaas, GrundeThe preliminary results for two flights of the Spacecraft Fire Experiment (Saffire), conducted on an orbiting spacecraft, are presented. These experiments directly address the risks associated with our understanding of spacecraft fire behavior at practical length scales and geometries. The result of this lack of experimental data has forced spacecraft designers to base their designs and safety precautions on 1-g understanding of flame spread, fire detection, and suppression. However, low-gravity combustion research has demonstrated substantial differences in flame behavior in low-gravity. Over the past several years, NASA and an international team of investigators have worked to address open issues in spacecraft fire safety. NASA’s Spacecraft Fire Safety Demonstration Project was developed with a goal to conduct a series of large-scale experiments in true confined spacecraft environments that represent practical spacecraft fires. The first two flights are complete and examined spread over a large thin sheet of flammable fuel (cotton/fiberglass 41 x 94 cm) and over 9 samples (5 x 30 cm) of various materials (silicone (4), PMMA (2), cotton/fiberglass (2) and Nomex®) that addressed the conditions of NASA STD 6001 Test 1 (material flammability). These experiments were performed on two separate unmanned ISS re-supply spacecraft after they had delivered their cargo and had begun their return journeys to Earth (destructive reentry). Preliminary flame spread rates and flammability assessments are presented for the conditions studied with comparison to prior data. A computer modeling effort is underway to complement the experimental effort. In addition, conceptual development has begun for three more flights that will include fire detection and suppression objectives to the program.Item Spacecraft Fire Experiment (Saffire) Development Status(44th International Conference on Environmental Systems, 2014-07-13) Ruff, Gary A.; Urban, David L.; Fernandez-Pello, A. Carlos; T'ien, James S.; Torero, Jose L.; Legros, Guillaume; Eigenbrod, Christian; Smirnov, Nickolay; Fujita, Osamu; Cowlard, Adam J.; Rouvreau, Sebastien; Minster, Olivier; Toth, Balazs; Jomaas, GrundeThe status is presented of a spacecraft fire safety research project that is under development to reduce the uncertainty and risk in the design of spacecraft fire safety systems for exploration missions. The Spacecraft Fire Safety Demonstration Project is developing three Spacecraft Fire Experiments (Saffire-I, -II, and -III) to conduct a series of material flammability tests at a length scale that is realistic for a serious spacecraft fire in low-gravity. The objectives of these experiments are to (1) determine how rapidly a large scale fire grows in low-gravity and (2) investigate the low-g flammability limits compared to those obtained in NASA’s normal gravity material flammability screening test. The experiments will be conducted in Orbital Science Corporation’s Cygnus vehicle after it has deberthed from the International Space Station. Although the experiment will need to meet rigorous safety requirements to ensure the carrier vehicle does not sustain damage, the absence of a crew removes the need for strict containment of combustion products. The tests will be fully automated with the data downlinked at the conclusion of the test before the Cygnus vehicle reenters the atmosphere. A computer modeling effort will complement the experimental effort. An international topical team is collaborating with the NASA team in the definition of experiment requirements and performing supporting analysis, experimentation and technology development. The status of the overall experiment are summarized in this paper along with a brief look at future experiments that could further enhance NASA’s approach to spacecraft fire safety.