The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Lutz Mädler - One of the best experts on this subject based on the ideXlab platform.
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reference data set for three dimensional measurements of double Droplet Combustion of p xylene
Proceedings of the Combustion Institute, 2020Co-Authors: Lutz Mädler, Norbert Riefler, Thomas WriedtAbstract:Abstract In order to provide fundamental information for Droplet interactions in the versatile and promising flame spray pyrolysis (FSP) technique, double Droplet Combustion experiments of p-xylene have been conducted via an improved piezoelectric Droplet-on-demand generator. Using a steel nozzle plate with two laser-drilled nozzles, the generator can simultaneously generate two upwards-flying Droplets with initial diameters of around 100 µm. A three-dimensional (3D) measurement technique using two time-synchronized high-speed cameras has been developed to detect double Droplet Combustion processes. Droplet diameters, flame diameters, Droplet 3D trajectories, Droplet 3D velocities, and the center distances between the two burning Droplets are highly time-resolved measured, and then visualized via 3D videos and images. Flame spacing, as a new definition, is proposed to describe the interactions between the two flame fronts. The influences of the flame spacing and the oxygen concentration in the ambience on double Droplet Combustion were experimentally investigated. The obtained 3D data can serve as an ideal validation case for modeling and simulating Droplet interactions during Combustion as well as a highly time-resolved reference data set in the future.
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The gas-phase formation of tin dioxide nanoparticles in single Droplet Combustion and flame spray pyrolysis.
Combustion and flame, 2020Co-Authors: Suman Pokhrel, Marco Schowalter, Andreas Rosenauer, Johannes Kiefer, Lutz MädlerAbstract:Abstract Tin dioxide (SnO2) nanoparticles synthesized via flame spray pyrolysis (FSP) have promising applications for gas sensors. The formation of SnO2 nanoparticles in the gas-phase has been investigated using single Droplet Combustion and FSP. Precursor solutions of Tin (II) 2-ethylhexanoate dissolved in Xylene with varying Sn concentrations were selected as the precursor-solvent system. The selected precursor-solvent system has its stability and ability to synthesize homogeneous nanoparticles, compared to metal nitrate based precursor solutions. The precursor-solvent system was studied using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and thermogravimetric analysis (TGA). The SnO2 nanoparticles were characterized using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and transmission electron microscopy (TEM). Droplet surface micro-explosions were observed during the single Droplet Combustion of the precursor solutions. It is because of the heterogeneous vapor-phase nucleation, which is beneath the liquid Droplet surface and caused by precursor thermal decomposition. The results show that the size of nanoparticles obtained both from FSP and single Droplet Combustion increases with increasing metal-precursor concentration. The TEM images of the particles from such Droplet Combustion reveal two types of nanoparticles with different sizes and morphologies. The current work provides fundamental understanding of precursor decomposition and particle formation during single Droplet Combustion, which help in-depth understanding of the flame spray pyrolysis.
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single Droplet Combustion of precursor solvent solutions for nanoparticle production optical diagnostics on single isolated burning Droplets with micro explosions
Proceedings of the Combustion Institute, 2019Co-Authors: Christopher D Rosebrock, Thomas Wriedt, Lutz MädlerAbstract:Abstract In order to understand the Droplet micro-explosions occurring during single Droplet Combustion of the flame spray pyrolysis (FSP) precursor/solvent solutions, the optical techniques, such as, interferometric particle imaging (IPI) and standard rainbow refractometry (SRR), were applied to the single Droplet Combustion of Tin (II) 2-ethylhexanoate/Xylene. The changes of Droplet size and rainbow pattern were detected using IPI and SRR, respectively. A multicomponent diffusion limited model was developed to simulate the experimental changes of Droplet size and rainbow pattern, and to further estimate the mass and heat transfer inside the burning Droplets. The rainbow patterns of the precursor/solvent Droplets with micro-explosions show significantly different insights comparing to single component Droplets. The results demonstrate that the evolutions of rainbow patterns of the burning Droplets and the time needed for Droplet micro-explosions are strongly dependent on the concentration of the metal-organic precursor.
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Single Droplet Combustion of precursor/solvent solutions for nanoparticle production: Optical diagnostics on single isolated burning Droplets with micro-explosions
Proceedings of the Combustion Institute, 2019Co-Authors: Christopher D Rosebrock, Thomas Wriedt, Lutz MädlerAbstract:Abstract In order to understand the Droplet micro-explosions occurring during single Droplet Combustion of the flame spray pyrolysis (FSP) precursor/solvent solutions, the optical techniques, such as, interferometric particle imaging (IPI) and standard rainbow refractometry (SRR), were applied to the single Droplet Combustion of Tin (II) 2-ethylhexanoate/Xylene. The changes of Droplet size and rainbow pattern were detected using IPI and SRR, respectively. A multicomponent diffusion limited model was developed to simulate the experimental changes of Droplet size and rainbow pattern, and to further estimate the mass and heat transfer inside the burning Droplets. The rainbow patterns of the precursor/solvent Droplets with micro-explosions show significantly different insights comparing to single component Droplets. The results demonstrate that the evolutions of rainbow patterns of the burning Droplets and the time needed for Droplet micro-explosions are strongly dependent on the concentration of the metal-organic precursor.
Frederick L. Dryer - One of the best experts on this subject based on the ideXlab platform.
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n-Butanol Droplet Combustion: Numerical modeling and reduced gravity experiments
Proceedings of the Combustion Institute, 2015Co-Authors: Fahd E. Alam, C. T. Avedisian, Frederick L. Dryer, Yu Cheng Liu, Tanvir FaroukAbstract:Abstract Recent interest in alternative and bio-derived fuels has emphasized butanol over ethanol as a result of its higher energy density, lower vapor pressure and more favorable gasoline blending properties. Numerous efforts have examined the Combustion of butanol from the perspective of low dimensional gas-phase transport configurations that facilitate modeling and validation of Combustion kinetics. However, fewer studies have focused on multiphase butanol Combustion, and none have appeared on isolated Droplet Combustion that couples experiments with robust modeling of the Droplet burning process. This paper presents such an experimental/numerical modeling study of isolated Droplet burning characteristics of n -butanol. The experiments are conducted in an environment that simplifies the transport process to one that is nearly one-dimensional as promoted by burning in a reduced gravity environment. Measurements of the evolution of Droplet diameter ( D o = 0.56–0.57 mm), flame standoff ratio ( FSR ≡ D f / D ) and burning rate ( K ) are made in the standard atmosphere under reduced gravity and the data are compared against numerical simulation. The detailed model is based on a comprehensive time-dependent, sphero-symmetric Droplet Combustion simulation that includes spectrally resolved radiative heat transfer, multi-component diffusive transport, full thermal property variations and detailed chemical kinetic. The simulations are carried out using both a large order kinetic mechanism (284 species, 1892 reactions) and a reduced order mechanism (44 species, 177 reactions). The results show that the predicted burning history and flame standoff ratios are in good agreement with the measurements for both the large and reduced order mechanisms. Additional simulations are conducted for varying oxygen concentration to determine the limiting oxygen index and to elucidate the kinetic processes that dictate the extinction of the flame at these low oxygen concentrations.
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Droplet Combustion Experiments Aboard the International Space Station
Microgravity Science and Technology, 2014Co-Authors: Daniel L. Dietrich, Benjamin D Shaw, Vedha Nayagam, Frederick L. Dryer, Michael C Hicks, Tanvir Farouk, Paul V. Ferkul, Hyun Kyu Suh, Mun Y. Choi, Yu Cheng LiuAbstract:This paper summarizes the first results from isolated Droplet Combustion experiments performed on the International Space Station (ISS). The long durations of microgravity provided in the ISS enable the measurement of Droplet and flame histories over an unprecedented range of conditions. The first experiments were with heptane and methanol as fuels, initial Droplet Droplet diameters between 1.5 and 5.0 m m , ambient oxygen mole fractions between 0.1 and 0.4, ambient pressures between 0.7 and 3.0 a t m and ambient environments containing oxygen and nitrogen diluted with both carbon dioxide and helium. The experiments show both radiative and diffusive extinction. For both fuels, the flames exhibited pre-extinction flame oscillations during radiative extinction with a frequency of approximately 1 H z . The results revealed that as the ambient oxygen mole fraction was reduced, the diffusive-extinction Droplet diameter increased and the radiative-extinction Droplet diameter decreased. In between these two limiting extinction conditions, quasi-steady Combustion was observed. Another important measurement that is related to spacecraft fire safety is the limiting oxygen index (LOI), the oxygen concentration below which quasi-steady Combustion cannot be supported. This is also the ambient oxygen mole fraction for which the radiative and diffusive extinction diameters become equal. For oxygen/nitrogen mixtures, the LOI is 0.12 and 0.15 for methanol and heptane, respectively. The LOI increases to approximately 0.14 (0.14 O _2/0.56 N _2/0.30 C O _2) and 0.17 (0.17 O _2/0.63 N _2/0.20 C O _2) for methanol and heptane, respectively, for ambient environments that simulated dispersing an inert-gas suppressant (carbon dioxide) into a nominally air (1.0 a t m ) ambient environment. The LOI is approximately 0.14 and 0.15 for methanol and heptane, respectively, when helium is dispersed into air at 1 atm. The experiments also showed unique burning behavior for large heptane Droplets. After the visible hot flame radiatively extinguished around a large heptane Droplet, the Droplet continued to burn with a cool flame. This phenomena was observed repeatably over a wide range of ambient conditions. These cool flames were invisible to the experiment imaging system but their behavior was inferred by the sustained quasi-steady burning after visible flame extinction. Verification of this new burning regime was established by both theoretical and numerical analysis of the experimental results. These innovative experiments have provided a wealth of new data for improving the understanding of Droplet Combustion and related aspects of fire safety, as well as offering important measurements that can be used to test sophisticated evolving computational models and theories of Droplet Combustion.
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tethered methanol Droplet Combustion in carbon dioxide enriched environment under microgravity conditions
Combustion and Flame, 2012Co-Authors: Tanvir Farouk, Frederick L. DryerAbstract:Abstract Tethered methanol Droplet Combustion in carbon dioxide enriched environment is simulated using a transient one-dimensional spherosymmetric Droplet Combustion model that includes the effects of tethering. A priori numerical predictions are compared against recent experimental data. The numerical predictions compare favorably with the experimental results and show significant effects of tethering on the experimental observations. The presence of a relatively large quartz fiber tether increases the burning rate significantly and hence decreases the extinction diameter. The simulations further show that the extinction diameter depends on both the initial Droplet diameter and the ambient concentration of carbon dioxide. Increasing the Droplet diameter and ambient carbon dioxide concentration both of them lead to a decrease in the burning rate and increase in the extinction diameter. The influence of ambient carbon dioxide concentration on extinction shows a sharp transition in extinction for larger size Droplets ( d o > 1.5 mm) due to a change in the mode of extinction from diffusive to radiative control. In addition predictions from the numerical model is compared against a recently developed simplified theoretical model for predicting extinction diameter for methanol Droplets, where the presence and heat transfer contribution of the tether is not taken into account implicitly. The numerical results suggest some limitation in the theoretical modeling assumptions for favorable comparisons with the experimental data.
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microgravity Droplet Combustion effect of tethering fiber on burning rate and flame structure
Combustion Theory and Modelling, 2011Co-Authors: Tanvir Farouk, Frederick L. DryerAbstract:Droplets tethering on fibers has become a well established technique for conducting Droplet Combustion experiments in microgravity conditions. The effects of these supporting fibers are frequently assumed to be negligible and are not considered in the experimental analysis or in numerical simulations. In this work, the effect of supporting fibers on the characteristics of microgravity Droplet Combustion has been investigated numerically; a priori predictions have then been compared with published experimental data. The simulations were conducted using a transient one-dimensional spherosymmetric Droplet Combustion model, where the effect of the supporting fiber was implicitly taken into account. The model applied staggered convective flux finite volume method combined with high-order implicit time integration. Thermal radiation was evaluated using a statistical narrow band radiation model. Chemical kinetics and thermophysical properties were represented in rigorous detail. Tether fiber diameter, Droplet di...
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Multi-User Droplet Combustion Apparatus - Flame Extinguishment Experiment
2009Co-Authors: Forman A. Williams, Frederick L. Dryer, Vedha Nayagam, Mun Young Choi, Benjamin D ShawAbstract:Multi-User Droplet Combustion Apparatus Flame Extinguishment Experiment (MDCA-FLEX) will assess the effectiveness of fire suppressants in microgravity and quantify the effect of different possible crew exploration atmospheres on fire suppression. The goal of this research is to provide definition and direction for large scale fire suppression tests and selection of the fire suppressant for next generation crew exploration vehicles.
Thomas Wriedt - One of the best experts on this subject based on the ideXlab platform.
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reference data set for three dimensional measurements of double Droplet Combustion of p xylene
Proceedings of the Combustion Institute, 2020Co-Authors: Lutz Mädler, Norbert Riefler, Thomas WriedtAbstract:Abstract In order to provide fundamental information for Droplet interactions in the versatile and promising flame spray pyrolysis (FSP) technique, double Droplet Combustion experiments of p-xylene have been conducted via an improved piezoelectric Droplet-on-demand generator. Using a steel nozzle plate with two laser-drilled nozzles, the generator can simultaneously generate two upwards-flying Droplets with initial diameters of around 100 µm. A three-dimensional (3D) measurement technique using two time-synchronized high-speed cameras has been developed to detect double Droplet Combustion processes. Droplet diameters, flame diameters, Droplet 3D trajectories, Droplet 3D velocities, and the center distances between the two burning Droplets are highly time-resolved measured, and then visualized via 3D videos and images. Flame spacing, as a new definition, is proposed to describe the interactions between the two flame fronts. The influences of the flame spacing and the oxygen concentration in the ambience on double Droplet Combustion were experimentally investigated. The obtained 3D data can serve as an ideal validation case for modeling and simulating Droplet interactions during Combustion as well as a highly time-resolved reference data set in the future.
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single Droplet Combustion of precursor solvent solutions for nanoparticle production optical diagnostics on single isolated burning Droplets with micro explosions
Proceedings of the Combustion Institute, 2019Co-Authors: Christopher D Rosebrock, Thomas Wriedt, Lutz MädlerAbstract:Abstract In order to understand the Droplet micro-explosions occurring during single Droplet Combustion of the flame spray pyrolysis (FSP) precursor/solvent solutions, the optical techniques, such as, interferometric particle imaging (IPI) and standard rainbow refractometry (SRR), were applied to the single Droplet Combustion of Tin (II) 2-ethylhexanoate/Xylene. The changes of Droplet size and rainbow pattern were detected using IPI and SRR, respectively. A multicomponent diffusion limited model was developed to simulate the experimental changes of Droplet size and rainbow pattern, and to further estimate the mass and heat transfer inside the burning Droplets. The rainbow patterns of the precursor/solvent Droplets with micro-explosions show significantly different insights comparing to single component Droplets. The results demonstrate that the evolutions of rainbow patterns of the burning Droplets and the time needed for Droplet micro-explosions are strongly dependent on the concentration of the metal-organic precursor.
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Single Droplet Combustion of precursor/solvent solutions for nanoparticle production: Optical diagnostics on single isolated burning Droplets with micro-explosions
Proceedings of the Combustion Institute, 2019Co-Authors: Christopher D Rosebrock, Thomas Wriedt, Lutz MädlerAbstract:Abstract In order to understand the Droplet micro-explosions occurring during single Droplet Combustion of the flame spray pyrolysis (FSP) precursor/solvent solutions, the optical techniques, such as, interferometric particle imaging (IPI) and standard rainbow refractometry (SRR), were applied to the single Droplet Combustion of Tin (II) 2-ethylhexanoate/Xylene. The changes of Droplet size and rainbow pattern were detected using IPI and SRR, respectively. A multicomponent diffusion limited model was developed to simulate the experimental changes of Droplet size and rainbow pattern, and to further estimate the mass and heat transfer inside the burning Droplets. The rainbow patterns of the precursor/solvent Droplets with micro-explosions show significantly different insights comparing to single component Droplets. The results demonstrate that the evolutions of rainbow patterns of the burning Droplets and the time needed for Droplet micro-explosions are strongly dependent on the concentration of the metal-organic precursor.
Christopher D Rosebrock - One of the best experts on this subject based on the ideXlab platform.
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single Droplet Combustion of precursor solvent solutions for nanoparticle production optical diagnostics on single isolated burning Droplets with micro explosions
Proceedings of the Combustion Institute, 2019Co-Authors: Christopher D Rosebrock, Thomas Wriedt, Lutz MädlerAbstract:Abstract In order to understand the Droplet micro-explosions occurring during single Droplet Combustion of the flame spray pyrolysis (FSP) precursor/solvent solutions, the optical techniques, such as, interferometric particle imaging (IPI) and standard rainbow refractometry (SRR), were applied to the single Droplet Combustion of Tin (II) 2-ethylhexanoate/Xylene. The changes of Droplet size and rainbow pattern were detected using IPI and SRR, respectively. A multicomponent diffusion limited model was developed to simulate the experimental changes of Droplet size and rainbow pattern, and to further estimate the mass and heat transfer inside the burning Droplets. The rainbow patterns of the precursor/solvent Droplets with micro-explosions show significantly different insights comparing to single component Droplets. The results demonstrate that the evolutions of rainbow patterns of the burning Droplets and the time needed for Droplet micro-explosions are strongly dependent on the concentration of the metal-organic precursor.
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Single Droplet Combustion of precursor/solvent solutions for nanoparticle production: Optical diagnostics on single isolated burning Droplets with micro-explosions
Proceedings of the Combustion Institute, 2019Co-Authors: Christopher D Rosebrock, Thomas Wriedt, Lutz MädlerAbstract:Abstract In order to understand the Droplet micro-explosions occurring during single Droplet Combustion of the flame spray pyrolysis (FSP) precursor/solvent solutions, the optical techniques, such as, interferometric particle imaging (IPI) and standard rainbow refractometry (SRR), were applied to the single Droplet Combustion of Tin (II) 2-ethylhexanoate/Xylene. The changes of Droplet size and rainbow pattern were detected using IPI and SRR, respectively. A multicomponent diffusion limited model was developed to simulate the experimental changes of Droplet size and rainbow pattern, and to further estimate the mass and heat transfer inside the burning Droplets. The rainbow patterns of the precursor/solvent Droplets with micro-explosions show significantly different insights comparing to single component Droplets. The results demonstrate that the evolutions of rainbow patterns of the burning Droplets and the time needed for Droplet micro-explosions are strongly dependent on the concentration of the metal-organic precursor.
Vedha Nayagam - One of the best experts on this subject based on the ideXlab platform.
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Partial-Burning Regime for Quasi-Steady Droplet Combustion Supported by Cool Flames
AIAA Journal, 2016Co-Authors: Vedha Nayagam, Daniel L. Dietrich, Forman A. WilliamsAbstract:A simplified model for Droplet Combustion in the partial-burning regime is applied to the cool-flame regime observed in Droplet-burning experiments performed in the International Space Station with normal-alkanes fuels resulting in expressions for the quasi-steady Droplet burning rate and for the flame standoff ratio. The simplified predictions are found to produce reasonable agreement with the experimentally measured values of burning-rate constants but not with their apparent dependencies on pressure or on the initial Droplet diameter. Good agreement is found, however, with newly measured and numerically calculated flame standoff ratios in this Droplet Combustion supported by cool flames.
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Droplet Combustion Experiments Aboard the International Space Station
Microgravity Science and Technology, 2014Co-Authors: Daniel L. Dietrich, Benjamin D Shaw, Vedha Nayagam, Frederick L. Dryer, Michael C Hicks, Tanvir Farouk, Paul V. Ferkul, Hyun Kyu Suh, Mun Y. Choi, Yu Cheng LiuAbstract:This paper summarizes the first results from isolated Droplet Combustion experiments performed on the International Space Station (ISS). The long durations of microgravity provided in the ISS enable the measurement of Droplet and flame histories over an unprecedented range of conditions. The first experiments were with heptane and methanol as fuels, initial Droplet Droplet diameters between 1.5 and 5.0 m m , ambient oxygen mole fractions between 0.1 and 0.4, ambient pressures between 0.7 and 3.0 a t m and ambient environments containing oxygen and nitrogen diluted with both carbon dioxide and helium. The experiments show both radiative and diffusive extinction. For both fuels, the flames exhibited pre-extinction flame oscillations during radiative extinction with a frequency of approximately 1 H z . The results revealed that as the ambient oxygen mole fraction was reduced, the diffusive-extinction Droplet diameter increased and the radiative-extinction Droplet diameter decreased. In between these two limiting extinction conditions, quasi-steady Combustion was observed. Another important measurement that is related to spacecraft fire safety is the limiting oxygen index (LOI), the oxygen concentration below which quasi-steady Combustion cannot be supported. This is also the ambient oxygen mole fraction for which the radiative and diffusive extinction diameters become equal. For oxygen/nitrogen mixtures, the LOI is 0.12 and 0.15 for methanol and heptane, respectively. The LOI increases to approximately 0.14 (0.14 O _2/0.56 N _2/0.30 C O _2) and 0.17 (0.17 O _2/0.63 N _2/0.20 C O _2) for methanol and heptane, respectively, for ambient environments that simulated dispersing an inert-gas suppressant (carbon dioxide) into a nominally air (1.0 a t m ) ambient environment. The LOI is approximately 0.14 and 0.15 for methanol and heptane, respectively, when helium is dispersed into air at 1 atm. The experiments also showed unique burning behavior for large heptane Droplets. After the visible hot flame radiatively extinguished around a large heptane Droplet, the Droplet continued to burn with a cool flame. This phenomena was observed repeatably over a wide range of ambient conditions. These cool flames were invisible to the experiment imaging system but their behavior was inferred by the sustained quasi-steady burning after visible flame extinction. Verification of this new burning regime was established by both theoretical and numerical analysis of the experimental results. These innovative experiments have provided a wealth of new data for improving the understanding of Droplet Combustion and related aspects of fire safety, as well as offering important measurements that can be used to test sophisticated evolving computational models and theories of Droplet Combustion.
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Quasi-steady flame standoff ratios during methanol Droplet Combustion in microgravity
Combustion and Flame, 2010Co-Authors: Vedha NayagamAbstract:Abstract Recently, Aharon and Shaw developed a simplified analytical expression to predict quasi-steady flame stand-off ratios for alkane fuels. Their analysis is strictly valid only for alkane-type fuels where there is no reabsorption of flame generated species back into the Droplet. In this note we show that Aharon and Shaw’s analysis can be extended to methanol Droplet Combustion where water generated at the flame-sheet is absorbed back into the Droplet. The model predictions are shown to compare well with available experimental results.
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Multi-User Droplet Combustion Apparatus - Flame Extinguishment Experiment
2009Co-Authors: Forman A. Williams, Frederick L. Dryer, Vedha Nayagam, Mun Young Choi, Benjamin D ShawAbstract:Multi-User Droplet Combustion Apparatus Flame Extinguishment Experiment (MDCA-FLEX) will assess the effectiveness of fire suppressants in microgravity and quantify the effect of different possible crew exploration atmospheres on fire suppression. The goal of this research is to provide definition and direction for large scale fire suppression tests and selection of the fire suppressant for next generation crew exploration vehicles.
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Fiber-Supported Droplet Combustion
2004Co-Authors: Frederick L. Dryer, Vedha Nayagam, John B. Haggard, Forman A. Williams, Ben D. Shaw, Daniel L. DietrichAbstract:Individual Droplets with diameters ranging from about 2 mm to 5 mm were burned under microgravity conditions in air at 1 bar with an ambient temperature of 300 K. Each Droplet was tethered by a silicon carbide fiber of 80 mm or 150 mm diameter to keep it in view of video recording, and, in some tests, a forced air flow was applied in a direction parallel to the fiber axis. Methanol, two methanol-water mixtures, two methanol-dodecanol mixtures, and two heptane-hexadecane mixtures were the fuels. Droplet diameters were measured as functions of time and compared with existing theoretical predictions. The prediction that methanol Droplets extinguish at diameters that increase with increasing initial Droplet diameter is verified by these experiments. In addition, the quasi-steady burning rate constant of the heptane-hexadecane mixtures appears to decrease with increasing Droplet diameter; obscuration consistent with very heavy sooting, but without the formation of soot shells, is observed for the largest of these Droplets. Forced convective flow around methanol Droplets was found to increase the burning rate and to produce a ratio of downstream-to-upstream flame radius that remained constant as the Droplet size decreased, a trend in agreement with earlier results obtained at higher convective velocities for smaller Droplets having larger flame standoff ratios. There are a number of implications of the experimental results regarding Droplet-Combustion theory.
