Droplet Combustion Experiments Aboard the International Space Station

Published on Oct 1, 2014in Microgravity Science and Technology1.973
· DOI :10.1007/s12217-014-9372-2
Daniel L. Dietrich13
Estimated H-index: 13
(Glenn Research Center),
Vedha Nayagam15
Estimated H-index: 15
(Case Western Reserve University)
+ 9 AuthorsForman A. Williams54
Estimated H-index: 54
(UCSD: University of California, San Diego)
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.
  • References (26)
  • Citations (32)
📖 Papers frequently viewed together
73 Citations
59 Citations
70 Citations
78% of Scinapse members use related papers. After signing in, all features are FREE.
#1Tanvir Farouk (USC: University of South Carolina)H-Index: 18
#2Frederick L. Dryer (Princeton University)H-Index: 68
59 CitationsSource
#1Vedha NayagamH-Index: 15
#2Daniel L. DietrichH-Index: 13
Last. Forman A. WilliamsH-Index: 6
view all 4 authors...
The Flame Extinguishment (FLEX) experiment that is currently underway in the Combustion Integrated Rack facility onboard the International Space Station is aimed at understanding the effects of inert diluents on the flammability of condensed phase fuels. To this end, droplets of various fuels, including alkanes and alcohols, are burned in a quiescent microgravity environment with varying amounts of oxygen and inert diluents to determine the limiting oxygen index (LOI) for these fuels. In this st...
1 Citations
#1Vedha NayagamH-Index: 15
#2Daniel L. Dietrich (Glenn Research Center)H-Index: 13
Last. Forman A. Williams (UCSD: University of California, San Diego)H-Index: 54
view all 5 authors...
73 CitationsSource
#1Tanvir Farouk (Princeton University)H-Index: 18
#2Frederick L. Dryer (Princeton University)H-Index: 68
Abstract Quasi-steady burning and extinction of droplets are of interest from both fundamental and application viewpoints. The latter is related to combustor performance and fire safety issues in reduced gravity environments. Influences of diluent in the atmosphere on isolated droplet combustion characteristics including extinction provide insights to fire extinguishment phenomena and the effectiveness of various diluents as fire suppressants. Extinction of pure methanol and methanol–water dropl...
21 CitationsSource
#1Christopher L. Dembia (Cornell University)H-Index: 7
#2Yu Cheng Liu (Cornell University)H-Index: 11
Last. C. Thomas Avedisian (Cornell University)H-Index: 14
view all 3 authors...
A simple automated image analysis algorithm has been developed that processes consecutive images from high speed, high resolution digital images of burning fuel droplets. The droplets burn under conditions that promote spherical symmetry. The algorithm performs the tasks of edge detection of the droplet’s boundary using a grayscale intensity threshold, and shape fitting either a circle or ellipse to the droplet’s boundary. The results are compared to manual measurements of droplet diameters done...
16 CitationsSource
#1Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 13
#2Jingbin WeiH-Index: 1
Reduced and normal gravity combustion experiments were performed with fiber-supported methanol droplets with initial diameters in the 1 mm size range. Experiments were performed with air-diluent mixtures at about 0.101 MPa and 298 K, where carbon dioxide, helium, or xenon was separately used as the diluent gas. Results indicate that ambient gas transport properties play an important role in determining flammability and combustion behaviors including burning rates and radiant heat output historie...
3 CitationsSource
#1Tanvir Farouk (Princeton University)H-Index: 18
#2Frederick L. Dryer (Princeton University)H-Index: 68
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 incr...
22 CitationsSource
#1Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 13
#2J. B. Wei (UC Davis: University of California, Davis)H-Index: 4
Reduced gravity and normal gravity combustion experiments were performed with individual fiber-supported n-heptane and 1-propanol droplets with initial diameters in the 1-mm size range. Experiments were performed with air-inert mixtures at 0.1 MPa or 0.3 MPa and about 298 K, where helium, carbon dioxide, or xenon were separately used as inerts. The amount of inert gas required to suppress combustion was generally higher in reduced gravity than normal gravity, and higher mole fractions of xenon w...
7 CitationsSource
#1Craig MyhreH-Index: 1
10 CitationsSource
#1Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 1
#2Bret D. Clark (UC Davis: University of California, Davis)H-Index: 1
Last. Difei Wang (UC Davis: University of California, Davis)H-Index: 1
view all 3 authors...
Results are presented from experiments on reduced-gravity combustion of individual heptane/hexadecane droplets. Initial droplet diameters ranged from 0.25 to 5.2 mm, and initial hexadecane mass fractions in the droplets were 0.058, 0.10, 0.20, and 0.40. Most droplets were burned in cabin air on Spacelab with an ambient oxygen mole fraction of about 0.21 and a pressure of about 0.1 MPa. Data were also obtained for small (0.25-mm) droplets in a ground-based apparatus that provides simulated reduce...
9 CitationsSource
Cited By32
#1V.V. Tyurenkova (RAS: Russian Academy of Sciences)H-Index: 9
#2M. N. Smirnova (RAS: Russian Academy of Sciences)H-Index: 7
Last. V. F. Nikitin (RAS: Russian Academy of Sciences)H-Index: 20
view all 3 authors...
Abstract Using multicomponent and multi-phase fuels is one of the methods for increasing effectiveness of rocket engines. In developing different compositions one should guarantee a stable fuel burning process in weightlessness. The present study is aimed at developing physical and mathematical models, allowing to consider the effect of multiphase fuel (hydrocarbon liquid + solid combustible material) on the conditions of ignition and modes of propagation of combustion in poly-dispersed non-unif...
#1Yiguang Ju (Princeton University)H-Index: 57
#2Christopher B. Reuter (Princeton University)H-Index: 8
Last. Sang Hee Won (USC: University of South Carolina)H-Index: 3
view all 5 authors...
Abstract Cool flames play a critical role in ignition timing, burning rate, burning limits, engine knocking, and emissions in conventional and advanced combustion engines. This paper provides an overview of the recent progress in experimental and computational studies of cool flames. First, a brief review of low-temperature chemistry and classical studies of cool flames is presented. Next, the recent experimental and computational findings of cool flames in microchannels, microgravity droplet co...
2 CitationsSource
#1V.V. Tyurenkova (RAS: Russian Academy of Sciences)H-Index: 9
Abstract This paper is devoted to the burning of an isolated n-heptane droplet in microgravity and analysis of the experimental data presented by FLEX experiment. Developing the classical analytical research methodology, proposed by Forman A. Williams, and using our obtained analytical solutions for the problem of droplet equilibrium evaporation and combustion, the analytical solutions to solve the problem of two regimes of droplet burning were found. To explain the presence of the radiative fla...
#1Forman A. Williams (UCSD: University of California, San Diego)H-Index: 54
#2Vedha Nayagam (Case Western Reserve University)H-Index: 15
Two steady-state chemical-kinetic approximations are introduced into the apparently most relevant five cool-flame steps of the latest San Diego mechanism for n-heptane, supplemented by a sixth step...
#1A.E. Saufi (Leonardo)H-Index: 1
#2Alessio Frassoldati (Leonardo)H-Index: 35
Last. Alberto Cuoci (Leonardo)H-Index: 30
view all 4 authors...
Abstract This paper aims at presenting the DropletSMOKE++ solver, a comprehensive multidimensional computational framework for the evaporation of fuel droplets, under the influence of a gravity field and an external fluid flow. The Volume Of Fluid (VOF) methodology is adopted to dynamically track the interface, coupled with the solution of energy and species equations. The evaporation rate is directly evaluated based on the vapor concentration gradient at the phase boundary, with no need of semi...
2 CitationsSource
#1Masato Mikami (Yamaguchi University)H-Index: 14
#2Yasuko Yoshida (Yamaguchi University)H-Index: 2
Last. Yuji Kan (JAXA: Japan Aerospace Exploration Agency)
view all 7 authors...
#1Tanvir Farouk (USC: University of South Carolina)H-Index: 18
#2Daniel L. Dietrich (Glenn Research Center)H-Index: 13
Last. Frederick L. Dryer (Princeton University)H-Index: 68
view all 3 authors...
Abstract Transient, isolated n-alkane droplet combustion is simulated at elevated pressure for helium-diluent substituted-air mixtures. We report the presence of unique quasi-steady, three-stage burning behavior of large sphero-symmetric n-alkane droplets at these elevated pressures and helium substituted ambient fractions. Upon initiation of reaction, hot-flame diffusive burning of large droplets is initiated that radiatively extinguishes to establish cool flame burning conditions in nitrogen/o...
5 CitationsSource
#1Fahd E. Alam (USC: University of South Carolina)H-Index: 4
#2Ali Charchi Aghdam (USC: University of South Carolina)H-Index: 1
Last. Tanvir Farouk (USC: University of South Carolina)H-Index: 18
view all 4 authors...
Abstract This paper reports simulation results of oscillatory cool flame burning of an isolated, submillimeter sized n-heptane (n-C7H16) droplet in a selectively ozone (O3) seeded nitrogen-oxygen (N2-O2) environments at atmospheric pressure. An evolutionary one-dimensional droplet combustion code encompassing relevant physics and detailed chemistry was employed to explore the roles of low-temperature chemistry, O3 seeding, and dynamic flame structure on burning behaviors. For XO2= 21% and a rang...
2 CitationsSource
#1C. L. Vang (UC Davis: University of California, Davis)
#2B. D. Shaw (UC Davis: University of California, Davis)
Combustion experiments on heptane–hexadecane mixture droplets were conducted onboard the International Space Station. The ambient consisted of oxygen mixed with either helium or nitrogen at 1 atm. Initial droplet diameters were in the 1.7–4.8 mm range with initial heptane mass fractions of 0.95 or 0.80. Because of limitations on resources, only fiber-supported experiments were possible. Vaporization of the more volatile fuel component (heptane) was favored during the droplet combustion process, ...
#1Changxiao Shao (ZJU: Zhejiang University)H-Index: 5
#2LUOKun (ZJU: Zhejiang University)H-Index: 24
Last. Jianren Fan (ZJU: Zhejiang University)H-Index: 29
view all 5 authors...
Abstract A computational framework for interface-resolved direct numerical simulations (DNS) of simultaneous atomization, evaporation and combustion process is proposed. The present work utilizes a level set method to implicitly capture the gas–liquid interface and the ghost fluid method (GFM) to accurately address jump conditions across the interface. Specific care has been devoted to the discretization of the convective term and diffusive term for the species and energy equations. The level se...
1 CitationsSource