Browsing by Author "Meyer, Florian"
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Item Analysis of Saffire II two-sided concurrent flame spread over a thick PMMA slab(48th International Conference on Environmental Systems, 2018-07-08) Olson, Sandra; Urban, David; Ruff, Gary; Ferkul, Paul; Toth, Balazs; Eigenbrod, Christian; Meyer, FlorianThis paper reports the results of the microgravity flame spread over a 10 mm flat slab sample and a 4-10 mm structured sample. The samples were 50 mm wide and 290 mm long. They were ignited for 30 seconds in a constant air flow rate of 200 mm/s at one atmosphere pressure. The flame over the structured sample grew faster and was much more luminous than the flat sample. Interestingly, it was also quite non-symmetric on the two sides of the fuel card based on the radiometer readings. This non-symmetry affected the flow in the duct, implying the flame significantly affected the local flow field even in microgravity. The total radiometric output increased for the entire test time, indicating that the overall flame strength was increasing. Both flames over the samples grew to be 80-100 mm long, with soot streaming out the tip of the flames. Compared to normal gravity tests, the microgravity pyrolysis front spread rates were 18 to 24 times slower, but the fuel burnout rates were only 1.6 to 3 times slower. This resulted in a significant difference in overall flame size, with the microgravity flames being much smaller. Vapor jetting of bubbles of MMA monomer rupturing at the surface caused violent perturbations in the flame that got progressively worse as the test progressed. Both tests set off the vehicle smoke detector at levels well above the background reading of the sensor. The highest smoke detector reading occurred after the flow was turned on at the start of the flat sample test, as the residual smoke in the flow duct was flushed out. This may be due to soot agglomeration and/or the generation of a cloud of condensed fuel vapor.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 Sooting Behavior in Concurrent and Upward Burning of Cylindrical PMMA-samples(2023 International Conference on Environmental Systems, 2023-07-16) Eigenbrod, Christian; Meyer, Florian; Ries, Hans-Christoph; Heissmeier, JanIR videography has proven useful for tracking the position of the pyrolysis front under a flame propagating upward in 1g. Since PMMA burns with low soot formation in 1g conditions, the radiation density of the gases above the sample is very low and the flame is hardly visible. As a result, the surface can be easily followed and the temperature at the pyrolysis front can be determined. The phenomenological definition of the pyrolysis front remains difficult. In experiments on concurrent propagation along cylindrical PMMA samples under µg conditions during the Sounding Rocket flight TEXUS 57, it was shown that the drastically increased soot production compared to terrestrial conditions leads to a significantly increased radiation fraction by the gas phase above the sample. Here, pyrolysis front temperatures were determined to exceed 450 °C and include a significant radiative fraction of soot formed between the flame and the sample. This also sheds light on the significantly elevated local temperatures under µg conditions, which can lead to self-sustaining burning of some materials in microgravity that are inflammable or extinguishing on ground– this despite the overall reduced mass burn rate observed in microgravity. The paper compares pyrolysis front velocities in upward configuration (1g) along cylindrical PMMA samples with diameters of 5, 20, and 25 mm with concurrent propagation (µg) of the same samples. Both the 1g and µg experiments were performed in hypoxic exploration atmosphere (70 kPa, 26.5% O2). While the 1g experiments were subjected to buoyant convection only with a typical but averaged flow velocity of 20 to 30 cm/s, a forced inflow between 20 and 30 cm/s was set for the µg experiments. Soot formation was also analyzed in the microgravity tests.Item UB-FIRE Experiment Results on Upward Flame Propagation along Cylindrical PMMA Samples in Reduced Gravity(47th International Conference on Environmental Systems, 2017-07-16) Meyer, Florian; Schwenteck, Tim; Ruhe, Maximilian; Bihn, Patrick; Freier, Alex; Eigenbrod, ChristianAiming for improvements on fire safety in human spaceflight, upward flame propagation is examined on three different cylindrical PMMA rods during the REXUS 20 sounding rocket mission within the UB-FIRE project. The rods are of identical diameter of 15 mm with a reference sample of a smooth surface, one sample featuring vertical grooves and one sample exhibiting two vertical ribs. The concurrent flow of air is identical for all three samples with 18 cm/s velocity which is comparable to air conditioning flow velocities in space habitats like the International Space Station. The advantage of the cylindrical shape is that no border effects occur. The leading edge of the pyrolysis front is observed by means of an infrared camera centrally mounted between the surrounding wind tunnels alternately looking to the individual samples. The UB-FIRE experiment, flown on REXUS 20 in a reduced gravity environment (~0.094 g), reveals a reduced pyrolysis front propagation velocity up to a factor of 0.28 compared to ground-based experiments with an identical test setup (NASA-STD-6001B test 1). However, the corrugation effect which affects the propagation velocity is different in a reduced gravity environment compared to 1g. Possible reasons for this behavior along with a detailed evaluation of each sample are discussed in this paper. The 1g results are used to develop and validate an empirical model for the flame propagation along structured surfaces of several shapes.