Browsing by Author "Easton, John"
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Item Development and Validation of a Model to Account for Gaseous HCl and Aluminum Surface Interactions for Spacecraft Fire Safety Applications(49th International Conference on Environmental Systems, 2019-07-07) Niehaus, Justin; Gokoglu, Suleyman; Mazumder, Sandip; Berger, Gordon; Easton, JohnExperiments and modeling were performed to determine the surface kinetics of gaseous hydrogen chloride (HCl) with aluminum surfaces subjected to various treatments. HCl and other acid gases are a spacecraft fire safety concern as they are commonly found in products from electrical wire pyrolysis. Three types of aluminum surfaces were considered: surface with chromate conversion coating (iridite), anodized, and untreated. A test cell made of Teflon was used to measure the difference in HCl from the inlet to the outlet. Inlet and outlet sensors were used to measure HCl concentrations. A simple one-step global surface reaction model was proposed, and an Arrhenius surface kinetics expression that accounts for active surface sites was employed. The kinetic constants were determined (calibrated) using the measured data. The calibrated model was validated against experiments with different flow rates and HCl inlet concentrations. The results showed that anodized aluminum had the most HCl uptake, followed by the iridite and then the untreated aluminum. The amount of HCl uptake seems to correlate well with the thickness of the oxide layer on aluminum. The relevance of these findings are discussed with respect to the design of large-scale fire safety experiments in space and various fire safety application scenarios.Item Effect of Humidity on Surface Interactions of Gaseous HCl and Aluminum for Spacecraft Fire Safety Applications(2020 International Conference on Environmental Systems, 2020-07-31) Niehaus, Justin; Gokoglu, Suleyman; Mazumder, Sandip; Berger, Gordon; Easton, JohnExperiments were performed to understand the interaction of gaseous hydrogen chloride (HCl) with aluminum surfaces in the presence of water vapor. The results show that increasing levels of relative humidity, tested for 10, 25, and 50 percent in air, increase the capacity of HCl adsorption compared to results previously published with dry air flow. A series of tests were performed on individual aluminum samples after they had been saturated with a fixed concentration of HCl in dry air conditions with the goal of determining how their HCl uptake capacity change after various treatments with water relative to the original saturation run. HCl-saturated aluminum samples subjected to a second dry air flow at the same HCl concentration as the original test had an uptake of 23.5% of the original sample. Saturated aluminum samples subjected to an in-between clean-up relative humidity of 90% air flow had an uptake of 35.6% of the original. Saturated aluminum samples submerged in distilled water for 12 hours had an uptake of 82.2% of the original sample. Saturated aluminum subjected to 50% humid air resulted in similar uptake characteristics in multiple repeated tests. These small-scale tests were run in parallel to a large-scale ground duct test used to mimic the stand-off in the Cygnus spacecraft during a Saffire experiment. Conclusions of this testing will be used in the design of large-scale spacecraft fire safety experiments and to develop a model to account for the interactions of HCl and aluminum surfaces in the presence of water in those tests.Item Evaluation of Combustion Products from Large-Scale Spacecraft Fires during the Saffire-IV and Saffire-V Experiments(50th International Conference on Environmental Systems, 7/12/2021) Fortenberry, Claire; Casteel, Michael; Graf, John; Easton, John; Niehaus, Justin; Meyer, Marit; Urban, David; Ruff, GaryThe aim of the spacecraft fire safety series of experiments (Saffire) is to investigate the behavior of large-scale fires in microgravity. During these experiments, materials are ignited within the Northrop Grumman Cygnus resupply vehicle following its departure from the International Space Station. Saffire-IV and Saffire-V introduced a far-field diagnostics (FFD) unit to house sensors for smoke characterization, including gas monitors and particle detectors. The FFD also housed a prototype �smoke eater� device and a CO2 scrubber, which are designed to remove combustion products from a spacecraft atmosphere. Remote sensors installed at six locations throughout the Cygnus cabin measured CO2 concentrations and temperature, allowing evaluation of smoke plume transport. In this work, we report on gas and particle measurements from the Saffire-IV and Saffire-V experiments, presenting the first effort to comprehensively characterize combustion products from large-scale microgravity fires. We evaluate the transport of key species throughout the spacecraft cabin. Finally, we address post-fire cleanup methods and discuss remaining science questions to be targeted in future work.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 Modeling the Uptake of Hydrogen Chloride onto Interior Spacecraft Materials(50th International Conference on Environmental Systems, 7/12/2021) Niehaus, Justin; Mazumder, Sandip; Gokoglu, Suleyman; Berger, Gordon; Easton, JohnHydrogen chloride (HCl) is a major combustion product from the pyrolysis of polyvinyl chloride (PVC) insulated electrical wires, a common spacecraft fire safety concern. Models at two different scales were developed to predict HCl uptake on anodized, chromate conversion coated (Iridite), and bare aluminum surfaces, as well as on Nomex fabric: a macroscopic one-step global surface reaction model where all the active sites are on the exterior surface, and a pore model where the interior active sites deeper into the oxide layer can also be accessed by HCl. Experiments were performed to calibrate kinetic and diffusion constants in the models. A cast acrylic test cell was used to measure the differences between the inlet and outlet concentration of HCl after inserting a sample rod of the test material. For the materials with a thin (< 200 �m) or no oxide layer, the macroscopic surface reaction model adequately predicts the experimental measurements. For the anodized aluminum with a thicker oxide layer, the pore model provided a better match to experimental results. The results will be discussed with respect to the spacecraft fire safety project (Saffire).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 Smoke Detector Characterization with Reference and Smoke Aerosols(2020 International Conference on Environmental Systems, 2020-07-31) Wang, Xiaoliang; Chow, Judith; Watson, John; Meyer, Marit; Ruff, Gary; Easton, John; Berger, Gordon; Mudgett, PaulPerformance testing of consumer smoke detectors requires specific facilities and experiments with smoldering and flaming emissions from different fuels. Smoke detectors for use in spacecraft are tested using similar setups with representative fuel materials. To simplify smoke detector testing, this study explored the use of laboratory-generated reference aerosols as transfer standards to evaluate smoke detector performance. Among the three tested reference aerosols, mineral oil particles were reproducibly generated with a Gemini smoke detector tester, dioctyl sebacate (DOS) particles were generated with a wide concentration range and flexible size distributions using an atomizer, while polystyrene latex (PSL) particles were difficult to produce with the high concentrations needed for smoke detector testing. Reference aerosols generated from 1.5%–100% DOS solutions and mineral oil covered the response range of six types of smoke aerosols generated by oxidative pyrolysis of spacecraft-relevant materials. Although no single reference aerosol can be used to simulate the response of different smoke detection technologies to different smoke aerosols within ±10% error, the relationship between reference and smoke aerosols derived from this study can be used to predict smoke detector responses to combustion aerosols.