28H01
静電浮遊法を用いた高温融体粘性係数測定○石川 毅彦，岡田 純平（宇宙航空研究開発機構），渡邊 勇基（エイ・イー・エス）

Viscosity Measurement of High Temperature Melts using an Electrostatic Levitation Method○Takehiko ISHIKAWA, Junpei OKADA (JAXA), Yuki WATANEBE (AES Co., Ltd.)

1. Introduction
In the recent decade, levitation techniques have made asubstantial progress and have been utilized for many researches
in materials science. Levitation methods enable containerlesssample processing, with which problems associated withcrucibles (i.e. contamination from crucibles or chemical reaction
between samples and container walls) can be minimized.
Moreover, since nucleation from the crucibles is suppressed,
liquid samples can be brought to deeply undercooledtemperatures. Levitation methods are widely used forthermophysical property measurements of high temperaturemelts. Density, heat capacity, emissivity, thermal conductivity,
electrical resistivity, surface tension, and viscosity have beenmeasured with several kinds of levitators. Viscosity has beenmeasured by the drop oscillation method with bothelectromagnetic and electrostatic levitators. In this technique, alevitated melt is deformed from its spherical shape with an
external electric field superimposed on the levitation field toexcite drop oscillation. After stopping the excitation, theamplitude of sample oscillation decays due to its viscosity.
Knowing the density of the sample (), its radius (R0), theviscosity () can be obtained from the measured decay time ()and the following formula:
𝜌𝑅 2

η = 5τ0(1)

The Viscosities of refractory metals over 2000 K have beensuccessfully measured by this method. However, drop
oscillation method is not applicable for highly viscous samples
such as bulk metallic glass (BMG) alloys, since the drop
oscillation is hard, if not impossible, to excite.
An alternative method to measure the viscosity on anelectrostatically levitated sample has been proposed by Abe etal.,1) using sample rotation. In this method, a levitated sample isspun with vertical axis. When the rotation ratio excesses a
critical value, the sample shape transformed from axisymmetric
to non-axisymmetric. If the sample is spun more, the sample
shape becomes a dumbbells shape and finally breaks into twopieces. Abe et al. measured the terminal value of the maximum
sample length and determine the viscosity. They haveexperimentally proved this technique using propylene carbonate,glycerol, and mixture of glycerol and glucose; all the samples
are liquid at room temperature. However, there are a few
difficulties to apply this technique for high temperature melts,
including temperature homogeneity and experimental

repeatability.
Another method proposed by Ohsaka et al.2) also utilizes the
sample rotation. After spinning the levitated sample beyond its
bifurcation, they suddenly remove the rotation torque. Since thesample is levitated in gaseous atmosphere, the sample rotation
stops quickly. Then the shape of viscous sample gradually
returns from the dumbbells shape to sphere. They observe thisshape change as a function of time and determine the viscosity.
This technique can not apply to high temperature metals since a
vacuum condition is required to prevent oxidization.
A new method currently studied in this paper also use sample
rotation and bifurcation phenomena. In this study, a high speed
camera is equipped to observe the transformation fromaxisymmetric to non-axisymmetric shape in high vacuum
environment. This paper briefly describes the experimental
setup, analysis, and results of preparatory experiments.

2. Experimental Setup
2.1 Electrostatic Levitator
The electrostatic levitation system used in this study is similar
to the one developed by Rhim et al. 3) but includes several
modifications. A detailed description of the facility is given
elsewhere.4) It consists of a stainless steel chamber that isevacuated to a pressure of around 10-5 Pa. The chamber (Fig. 1)
houses a pair of parallel disk electrodes, typically 10 mm apartbetween which a positively charged sample is levitated using
Coulomb force. These electrodes are utilized to control thevertical position of the specimen, which has a typical diameterof about 2 mm. In order to levitate the sample against gravity, ahuge electric field of around 10 to 20 kV/cm is applied between
these electrodes. In addition, four spherical electrodes
distributed around the bottom electrode are used for horizontal
control. High speed feedback control is necessary to maintainstable sample levitation.
The levitated sample is heated by high power CO2 lasers, andthe sample temperature is measured by single color pyrometers.
The lower electrode is surrounded by four coils. These coils
create a horizontal rotating magnetic field that rotates at 400 Hz
around the vertical direction. The principle of the sample
rotation mechanism is the same as that of the asynchronous
induction motor. The four coils act as a stator while the levitatedsample serves as a rotor. The direction of the induced torque on
the sample can be controlled by selecting the direction of therotating magnetic field. Detailed explanation on this sample
rotation mechanism is found in elsewhere5).

Fig. 2 Sample images taken by the high speed camera
through a hole in the top electrode; (a) axisymmetric, and (b)non-axisymmetric.  indicates the rotation angle measured byimage analysis.
Fig. 1 Schematic side view of the electrode assembly andobservation system; (1) sample, (2) top electrode, (3) bottom
electrode, (4) four side electrodes, (5) four coils, (6) rotation
measurement system, (7) side view camera, and (8) high speed
camera.
An observation camera, equipped with a telephoto objective inconjunction with a background UV lamp, provides a magnified
side view of the sample. A rotation measurement systemdescribed later is also used. In addition, a high speed video
camera (HSV) is set above the top electrode so that the sample
rotation can be observed via the through the hole of the top
electrode (Fig.1).

2.2 Analysis
After stable levitation is achieved, deliberate sample rotation
in induced, and the levitated drop starts rotating around thevertical axis, its initial spherical shape changing to an oblate
shape due to the centrifugal force. When the sample rotation
frequency reaches a critical value (c), the sample shape
drastically changes from axisymmetric to non-axisymmetric(Fig.2). This change of shape is called bifurcation. The highspeed camera recorded the sample shape around the bifurcation
at 3000 fps for about 25 s. After the experiment, these images
are analyzed with homemade software. In this software, aspectratio (ratio between maximum and minimum length of drop
radius) and the angle of maximum radius (definition given in
Fig. 2(b)) were determined. From the analyses of more than
70000 images, the data array of as a function of time wascreated, from which the rotation frequency and was calculated.

Fig.3 Evolution of aspect ratio after bifurcation; low viscosity
sample (zirconium) shows higher evolution

Acknowledgement
This research was partially supported by a Grant-in-Aid for
Science Research (B) from the Japan Society for the Promotionof Science.

References
1)

Y. Abe, S. Matsumoto, T. Watanabe, K. Nishinari, H. Kitahata, A.
Kaneko, K. Hasegawa, R. Tanaka, K. Shitanishi, S. Sasaki: Int. J.
Microgravity Sci. Appl. 30 (2013) 42

2)

K. Ohsaka, A. Rednikov, S. S. Sadhal, E. H. Trinh: Rev. Sci.
Instrum. 73 (2002) 2091

3)

W. -K. Rhim, S. K. Chung, D. Barber, K. F. Man, G. Gutt, A.
Rulison, R. E. Spjut: Rev. Sci. Instrum. 64 (1993) 2961

4)

T. Ishikawa,P.-F. Paradis, T. Itami, S. Yoda: Meas. Sci. Technol.
16 (2005) 443.

5)W.-K. Rhim, T. Ishikawa: Rev. Sci. Instrum. 69 (1998) 3628

3. Experiment and Result
A zirconium (whose viscosity is about 4 mPa·s) and a glass
forming alloy (ZrCoAl; whose viscosity is about 40 mPa·s)
were selected for the preliminary experiment. Each sample waslevitated, molten, and spun. Figure 3 shows the change of aspectratio after the bifurcation, It is noticed that in the viscosity of thesample may affect the speed of shape transformation fromaxisymmetric to non-axisymmetric. Further experiments with avariety of samples are necessary to get secure conclusions.

28H02
静電浮遊炉を用いた回転変形による高温融体の表面張力測定○渡邊勇基（エイ・イー・エス），岡田純平，石川毅彦（宇宙航空研究開発機構）

Surface Tension Measurement of Molten Melts using Deformation by Rotation
using an Electrostatic Levitator○Yuki WATANABE (AES), Junpei OKADA, Takehiko ISHIKAWA (JAXA)
1. Introduction
Thermophysical properties of molten material at hightemperature are essential parameters for numerical simulation of
casting, or other industrial manufacturing. Recently, viscousmaterials at molten state such as bulk metallic glass (BMG) or
quasi-crystal have been investigated by many researchers.
Surface tension at high temperature, one of the important
properties, has been measured by oscillation method withlevitation techniques. But oscillation is not applicable to viscous
liquids because it is difficult to excite the sample oscillation. On
the other hand, there is a rotation method to measure surface
tension of viscous liquid with levitation, proposed by otherresearchers1). In this research, we apply a rotation method toelectrostatic levitation. Then, we check the rotation frequency
detected by laser power fluctuation reflected from sample
surface with high speed video camera (HSV). Finally, wemeasured surface tension of ZrCoAl (BMG material) throughthe rotation method.
2．Experimental Setup and Procedures
2.1 Electrostatic Levitator
The measurements were made using a high vacuum ESL
which can be evacuated to a ~10-5 Pa. Detailed information
about the ESL was found in elsewhere2,3). The levitated sample
was rotated using rotating magnetic field, which was generated
by four coils placed under the bottom electrode4).

3．Results
At first, we compared with rotation frequency of Zr melt
observation by HSC or detected by fluctuation of laser reflectedfrom sample surface. These were agreed well (Fig.2).

Fig.2 Comparing rotation frequency by two method.

Experimental value by rotational / oscillation methods withmolten Zr55Co20Al25 sample is shown in Fig.3. Viscosity of thissample rises up near melting point (Tm). By rotational method,
we could measure surface tension near Tm which we could not
apply the oscillating method.

2.2 Surface tension measurement with rotation
The shape of levitated droplet changes with increasing ofrotation speed. Surface tension is calculated from change ofsample diameter with change of rotation speed. With increasing
rotation speed, sample shape becomes spherical (axisymmetricwith vertical axis) to like a cigar (non-axisymmetric)5).
Therefore we can determine rotation frequency with the system
shown in Fig.1.
By ESL, it is possible to levitate the sample with various
viscosity, so we can observe the transition of sample shape(symmetrical - unsymmetrical) repeatedly. Theoretically,
rotation frequency of sample is determined by surface tension
and mass, so we can calculate the surface tension of the sample
by measuring rotation frequency at shape transition precisely.
Fig.3 Surface tension of Zr55Co20Al25 sample.

Fig.1

Detection of rotation frequency of the levitated sample.

4. Conclusion
In this paper, we tried to apply rotational method to surface
tension measurement with viscous sample at high temperature.
We confirmed that rotation frequency of Zr melt by HSC image
analysis and FFT analysis. Also, we applied rotation method at
Zr55Co20Al25, surface tension could be measured at various
temperature. We will study to apply rotation method for
viscosity measurement.

References
1)

W. -K. Rhim and T. Ishikawa, Rev. Sci. Instrum., 72 (2001),
3572-3575.
2) Paradis P-F, Ishikawa T, Lee G W, Holland-Moritz D, Brillo J,
RhimW-K, and Okada J T, Materials Science and Engineering R,
76 1-53 (2014).

3) T. Ishikawa et al. Rev. Sci. Instrum. 73 (2000), 2490.
4) P. -F. Paradis, T. Ishikawa, S. Yoda, J. Jpn Soc. Microgravity
Appl. Vol.20 No.3 (2003).
5)

R.A.Brown and L.E. Scriven, Proc. R. Soc. Lond. A 371 (1980),
331.

28H03超高温融体のコンプトン散乱測定〇岡田純平 1,2，P.H-L.Sit3，渡辺康裕 4，石川毅彦 1，B. Barbiellini5，伊藤真義 6，
櫻井吉晴 6，A.Bansil5，木村薫 4，七尾進 4

Compton Scattering Experiments on High-Temperature Liquids
1,2

J. T. OKADA , P. H.-L. Sit3, Y. WATANABE4, B. BARBIELLINI5, T. ISHIKAWA1, Y. J. WANG5, M. ITOU6,
Y. SAKURAI6, A. BANSIL5, R. ISHIKAWA4, M. HAMAISHI4, P. -F. PARADIS1, K. KIMURA4and S. NANAO1
1

ISAS/JAXA, 2PRESTO/JST, 3City University of Hong Kong, 4The Univ. Tokyo, 5Northeastern University,
6
JASRI/SPring-8

Levitation technique is extremely effective in studying thehigh temperature/undercooled liquid, since a sample vessel is
not required. Recently many remarkable studies on the
structural property of high temperature/undercooled liquid havebeen reported using the levitation technique. We applied thelevitation technique coupled with Compton scattering
measurements to study the electronic property of hightemperature liquid.
X-ray Compton scattering is an ideal technique for probing
wave functions in materials. The Compton profile J(pz) obtained
from the measurement isgiven within the impulse
approximation by

J ( pz ) =  ρ ( p) dpx dpy ,(1)

where p = (px, py, pz) and ρ(p) is the electron momentum density
given byρ ( p) =  n j  Ψ j ( r) exp ( −ip ⋅ r) dr

2

,

(2)

j

where nj is the electron occupation of j-state Ψj(r). The
Compton technique can also provide a novel spectroscopic
window on the liquid state. Since no charged particles enteringor leaving the sample are involved, the Compton technique is agenuinely bulk probe, which is not complicated by surface
effects present in photoemission or electron scatteringexperiments.
Compton profiles of high-temperature liquids were measured
by high-energy (116 keV) inelastic x-ray scattering at theBL08W beamline of SPring-8, Japan. The energy spectrum ofCompton scattered X-rays was converted to the Compton
profile with a momentum resolution of 0.16 a.u. The dataprocessing to deduce the Compton profile from the raw energy
spectrum consists of the following procedures: backgroundsubtraction and energy dependent corrections for the Compton
scattering cross section, the absorption of incident and scattered
x-rays in the sample, the efficiency of the analyzer and thedetector, and correction for double scattering event.

Backgrounds for the measured profiles are suppressed in thelevitation technique used since no material is present in theimmediate vicinity of the sample at the x-ray scattering center.
Car-Parrinello molecular dynamics (CPMD) simulations were
performed with the Quantum ESPRESSO package within theframework of the density-functional theory using thegeneralized gradient approximation. We employed ultrasoft
pseuopotentials with plane-wave expansion of the Kohn-Shamwave functions and charge density up to kinetic energy cutoff of
25 Ry and 200 Ry, respectively. The bonding character in thehigh temperature liquids obtained through CPMD simulation
was analyzed with the maximally-localized Wannier functions(MLWFs) method where the MLWFs are obtained through anunitary transformation of Kohn-Sham wave functions. The
spread is an indicator of the spatial extent of the MLWF. The
MLWFs with small spreads mostly correspond to the covalentbond pairs. The MLWFs with large spreads contribute to themetallic properties. We refer to such electron pairs as diffuse
pairs. The details of the experiments and analysis will be
discussed in the talk.

28H04「きぼう」搭載用静電浮遊炉の開発状況○田丸晴香，大熊隼人，柚木園諭，中村裕広，石川毅彦，岡田純平（JAXA），高田哲也，新井達也，
佐々木博，藤野直樹，酒井由美子（(株)IHI エアロスペース）

Current Status of Electrostatic Levitation Furnace (ELF) for KIBO in ISS○Haruka TAMARU, Hayato OHKUMA, Satoshi YUKIZONO, Yasuhiro NAKAMURA, Takehiko ISHIKAWA,
Junpei T. OKADA(JAXA), Tetsuya TAKADA, Tatsuya ARAI, Hiroshi SASAKI, Naoki FUJINO and Yumiko
SAKAI(IHI Aerospace Co. Ltd.)

1. Introduction
Three and a half years have passed since JAXA started thedevelopment of Electrostatic Levitation Furnace (ELF) for
Kibo/ISS. We already finished the development of Engineering
Model (EM), and improved the design of flight model in
response to the EM test result.
The objectives of the ISS mission using ELF are to measurethermophysical properties around high melting temperature, andto quest for new functional materials by solidification including
overcooling conditions. The first target sample is oxides. The
melt oxides cannot be levitated by electromagnetic force andalso it is difficult by Electrostatic Levitator on ground, because
the electric charge of nonconductor is much less than that of
conductor.
In 2012, JAXA selected one scientific experiment using ELF.
Next selection of ELF utilization research will be announced byearly 2015 and it is under preparation. Additionally, in August
2014, Electromagnetic levitator (EML) was launched by ATV5
and it is now assembled and is checked out for starting
experiment. The containerless processing with both equipments
will grow increasingly important in the future.

system. On the other hand, some commands which must be
performed quickly are transmitted and received using the laptop
in ISS. Ground operators control the laptop remotely withremote desktop function via Ku two-way communication.
This way will make it easier for users to conduct experiments.
For example, droplet oscillation starting, oscillation data autoanalyzing, and real-time graph displaying.

3. Countdown to ISS
Now we completed the flight model assembly, and then we
will start various tests to confirm whether all systems work
functionally. The tests include functional tesstings, off-gassing,
EMC, thermal cycling, noise check, MSPR (Multi-purpose
Small Payload Rack) / ELF interface check, and communication
testing.
We will hold the review to confirm whether the ELF is readyto flight by early 2015. The ELF will be launched in 2015. After
arriving to ISS, the ELF will be assembled by onboard
astronauts, then it will be set into the MSPR in Kibo. Fig. 2 and3 show the overview of ELF. Operations for users will be started
by the end of 2015.

2. Current Status of Development
2.1 Ground function Test
With the Engineering Model of ELF, we succeeded inlevitating and melting of zirconium. We also succeeded inmeasuring density changes, temperature changes, surface
tension, and viscosity. The high-voltage amplifier and electrodeinterval were different from flight configuration because ofgravity. We hope to get same or better data using flight model inthe function test. Fig. 1 shows a density change by Overview
Camera.

MSPR
Front DoorVideo
Compression
Record Unit

Sample Cartridge
ELF
DC converter

Fig. 2

Fig. 1

ELF in MSPR

density change image

2.2 Unique Operation of ELF
In the usual case, ELF will be controlled through the groundFig. 3

ELF Fight model image

28H05

鉄と酸化物メルトの界面張力測定－液滴振動法による界面張力測定の検討－
液滴振動法による界面張力測定の検討－○渡邉匡人（学習院大），上野翔也（東北大院工），小野寺健太（学習院大），田中敏宏（阪大院工），塚田隆夫（東北大院工），石川毅彦（JAXA），水野章敏（学習院大）

Interfacial Tension between Steel and Oxide Melts by Surface Oscillation Analysis- Interfacial Tension Measurement by Modified Surface Oscillation Technique Masahito WATANABE (Gakushuin Univ.), Toshihoro TANAKA (Osaka Univ.),
Takao TSUKADA (Tohoku Univ.), Takehiko ISHIKAWA(JAXA), Akitoshi MIZUNO (Gakushuin Univ.)

The oscillating drop technique with surface oscillation
analysis is useful for measurements of thermophysicalproperties of high-temperature liquid by using thelevitation technique. The conventional surface oscillation
analysis derives surface tension and shear viscosity ofliquid even on the ground conditions. Recently, modified
surface oscillation analysis of compound droplets has
been tried to measure the interfacial tension of immiscible
liquid system1). However, modified surface oscillation
analysis for compound droplets combined with levitation
method can be applied only in the microgravity
conditions because the density difference separates two
liquid parts under the ground. Therefore, we propose themeasurements of interfacial tension between steel melts
and molten oxides using the electrostatic levitation
furnace (ELF) in ISS with modified surface oscillation
analysis2). Interfacial tension between molten steel andmolten oxides is important thermophysical properties on
the industrial process control such as steel making
processes and/or welding processes, therefore interfacial
tension measurements without container and the substrate
have been required in order to obtain temperaturedependence of its without non-required elements inmolten iron and molten oxides.
Our proposal method to obtain interfacial tension isbased on the surface oscillation technique expanded to thecompound droplets cases. The modified surface
oscillation analysis method is as follows. We consider thenormal mode of compound droplets consisted two
incompressible fluids contacted each other withinterfacial tension (Fig.1). Each fluid droplet has anormal mode frequency characterized by surface tension.
For the case of compound droplet, two normal mode
frequencies are derived from the eigenvalue equation
same as a coupled harmonic oscillator. Two normal mode
frequencies are expresses as follows;

where,
is normal mode frequency of out side fluid of
surface tension of,is interfacial tension,isradius of out side or inside fluid,
is density of out
side or inside fluid, respectively. From these equations,
it is identified that normal mode frequency of compound
droplet depends on the density difference between outside
and inside fluids and the radius ratio of outside and inside
fluid. Thus, we examine the change of normal mode
frequency on the thickness of covered molten oxide layer
by numerical simulations. Most important problem is theeffect of viscosity of molten oxides. Because of, if highviscosity fluid covers on molten steel, the surface
oscillation easily damps with very short time. This case
we cannot measure the surface oscillation frequency.
Therefore, we also examine the dependence of normal
mode frequency on the viscosity by numericalsimulations. On presentation, we discuss about theanalysis of surface oscillation of compound droplet
consisted by molten steel and molten oxides andintroduce our current status of ISS experiments
preparations.

µ i , ρi

σ 12
Ri

σo

Ro

µo , ρoFig.1 System configuration of compound droplet for interfacial
tension measurements.

References
1) I. Egry et al., J. Mater. Sci., 45(2010) 1979.
2) M. Saffren et al., Proceedings of the 2nd international colloquium on
drops and bubbles, (1981) 7.
3) M. Watanabe, JASMAC-27 講演予稿集，講演番号 137

28H06
酸素雰囲気を制御した環境下における粘性を考慮した液滴振動解析○渡邉匡人，小野寺健太，水野章敏（学習院大），小澤俊平（千葉工大）

Surface Oscillation Analysis of Viscous Liquid Droplets in Various Oxygen Partial Pressure
Conditions
Masahito WATANABE, Kenta ONODERA, Akitoshi MIZUNO (Gakushuin Univ.) andShumpei OZAWA (Inst. of Chiba Tech.)

Thermophysical properties of high-temperature melts areindispensable for numerical simulations of materials processing.
Accurate data are necessary to improve the process modeling,which leads to cost-effective production of high-quality
products. From the requirements the levitation technique, which
provides containerless conditions during the measurements, isprogressed for accurate measurements of the thermophysicalproperties of high-temperature liquids. Therefore, we areplanning thermophysical properties of high-temperature melts in
the International Space Station (ISS) 1,2) using the materialsscience laboratory-electromagnetic levitator (MSL-EML)3).
Using levitation technique, thermophysical properties, surface
tension, viscosity and density, are obtained from the surface
oscillations of levitated liquid droplets, which is known as theoscillating drop method. Under microgravity, oscillating drop
method with levitation technique has advantage of precise
measurement of thermophysical properties high-temperatureliquids metals. However, the liquid metals easily reacts oxygenin the atmosphere. For the reason, the surface tension shows thedependence of oxygen partial pressure (Po2). Po2 dependence ofthe surface tension using reducing gas, H2, CO or CO2, has beenreported. For our ISS experiments using MSL-EML, these
reducing gases cannot be used for the reason of hazard in ISS.
Therefore, our OXYTHERM project for precise surface tension
measurements of high-temperature liquids under controlled
atmosphere in ISS must use the oxygen sensing and control
system (OSC) based on stabilized-zirconia (ZrO2) as the solidstate electrolyte. Using OSC,we can control Po2 in atmosphericgas, so Po2 at the sample surface can be controlled. However,since liquid metals have large solubility of oxygen at hightemperature, starting samples include much amount oxygen in
inside of samples. Almost initially containing oxygen diffusesout from samples, but remaining oxygen inside liquid metal
samples would affect on the viscosity. Therefore, we mustneed to know the effect of oxygen both inside and out side ofsamples on the surface oscillation for using droplet-oscillating
technique to measure the surface tension and viscosity. However,
the effect of oxygen inside the liquid droplets on the surface
oscillation has not be clarified. In order to clarify the effect ofdissolved oxygen on the surface oscillation, we observed thesurface oscillation of liquid Zr contained oxygen of 500 (ppm
mass oxygen: PMO) and 3000PMO3). These samples wereprepared by the ark melting of high-purity crystalline Zr
samples, which is purified by the directional crystallization
method, with ZrO2 powders. Using electrostatic levitator, weobserved the surface oscillation damping in the vacuum
conditions of 10-4Pa with the function of waiting time after
melting of the samples. Also, using electromagnetic levitator,
we observed the surface oscillation of the same samples under
the controlled Po2 conditions. From the observation, we foundthat the surface oscillation amplitude and damping weredifferent with the waiting time for the surface oscillation
generated after melting of the samples. The damping timedifference is caused by the out-diffusion of oxygen in liquid Zrfrom inside to the atmosphere. If oxygen completely diffusesout from inside of droplets, we will be able to obtain theviscosity value of pure liquid Zr. However, if oxygen still
remains inside droplets, the viscosity shows large value rather
than that of pure liquid Zr. In the case of large viscosity values,
the surface oscillation frequency showed also different values
from the samples without oxygen addition. This is attributed by
the surface segregation of oxygen at the surface areas. The
surface oscillation frequency changes with atmospheric oxygen
partial pressure Po24). Therefore, we must care of the surface
oscillation frequency analysis in different Po2 conditions
including the effect of out-diffusion of dissolved oxygen into thesamples. We are planning to clarify the effect of out-diffusion ofdissolved oxygen on the surface oscillation frequency underlong time microgravity conditions using MSL-EML of ESA
facility in ISS with oxygen dissolved Zr samples.
This work was supported by JAXA-WG and also by JSPS
KAKENHI Grant Number 24360316.
References
1) H.-J. Fecht et al., Europhysicsnews, 39 (2008)19.
2) I. Egry and D. Voss, J. Jpn. Soc. Microgravity Appl., 27(2010) 178.
3) T. Harada et al., MRS Online Proceedings, Vol. 1528(2013)
Paper No.426.
4)

S. Ozawa et al., J. Appl. Phys., 107 (2010) 014910.

28A01
微小重力場での過電流による難燃被覆導線の着火○小松賢史，藤田修（北海道大学）

Ignition of Overloaded Electric wire Insulated by Fire Retardant Material in Microgravity○Yoshifumi KOMATSU, Osamu FUJITA (Hokkaido Univ.)

1. Introduction
One of the causes of fire in spacecraft is ignition of electric
wire. The wire ignition is generally started with short circuit oroverloading. Therefore, it is important to know the ignition
characteristics of electric wire by overloading in microgravity.
In the previous research1, 2), we clarify that ignition limit ofelectric wire is extended in microgravity than normal gravity.
We also clarified the influence on ignition limit and ignition
delay time by oxygen concentration, pressure, and so on. In thestudies we used single PE-NiCr wire to investigate thephenomenon. However, single PE wire is not practical one
because PE has high flammability and practical shape in actual
use is not single wire but two or more twisted wires.
In this study, therefore, we investigate the difference ofchange in ignition limit by gravitational condition (1G andmicro G) between PE wire and ETFE (fire retardant material)
wire in the shape of twisted wire.

Fig.3 Comparison the ignition
limit between single and twisted
wire at 1G (PE)Fig.4 Comparison the ignition limit
between PE and ETFE wire at 1G(twisted wire)

Table 1 Ignition delay time at each situation (twisted wire)
Insulation

O2 concentrationmaterial (1G or(%)

Current value(A)Ignition delay time(s)µG)
PE (1G)

40

17

2.40

PE (µG)40

17 (ignition limit)

2.23

ETFE (1G)

40

21(ignition limit)

2.17

ETFE (µG)

40

21 (ignition limit)

2.17

2. Experimental method

Fig.1 Outline of experimental
chamber

0.15mm

Di=0.5 mm

Do=0.8 mm

Fig.1 shows the outline of experimental chamber. It is
composed of a combustion chamber with sample wire, DV
camera, and Current source.
Two types of wire shape, single and twisted wire as shown in
Fig.2, are compared in terms of ignition limit with PE insulation
wire and, then, flammability of PE and ETFE insulated wires intwisted shape are compared to know their flammability
difference.
To obtain microgravity environment, we use the HASTIC
drop tower (“COSMOTORRE”, Akabira, Hokkaido, µG: 2.5s).

Fig.2 Outline of sample wire

3. Result and discussion
First, we consider the effect of wire shape. Fig.3 shows theignition limit of single wire and twisted wire at 1G by using PE.
From Fig.3, it seems that the twisted shape has an effect toextend the ignition limit.

Second, we investigate the effect of materials. Fig.4 shows
the ignition limit of PE and ETFE wire at 1G (twisted wire).
From the results, the ignition limit of PE wire is wider than of
ETFE wire. Table 1 shows the comparison between 1G and µG.
According to the table, difference by the difference of gravity
condition is unclear for both of PE and ETFE. This is because(1) µG time is too short to discuss the difference of ignition
limit, and (2) twisted of wire may lead to smaller difference ofignition limit. Therefore, we need to make more research about
the difference using longer microgravity time.

4. Conclusion
1. The shape of twist has an effect to extend the ignition limit.
2. The effect of microgravity is small with twisted ETFE wire,
which may be caused by the reduced microgravity effect intwisted shape.

Acknowledgement
The authors appreciate JAXA for their support in conducting
the research on “Solid Combustion” and “FLARE”.

References
1)

H. Noda et al., JSME, MECHJ-5, vol 5, pp459-460, (2005)

2)

K. Agata et al., International Journal of Microgravity Science andApplication, vol25, No.1, pp11-16, (2008)

28A02微小重力下で対向流を受ける薄い平板試料の可燃限界○高橋周平，坪井寛大，井原禎貴（岐阜大）

Flammability Limit of a Thin Flat Material with an Opposed Flow in Microgravity○Shuhei TAKAHASHI, Kandai TSUBOI, Tadayoshi IHARA (Gifu Univ.)

1. Introduction
The flammability test for materials used in space environmenthas been checked by the so called NASA STD-6001, which is apass/fail test conducted in normal gravity [1]. On the other
hand, it has been reported that the flammability limit or limiting
oxygen concentration in microgravity environment may expand
in a certain condition [2, 3]. Many materials has been tested it
flammability on ground, like as LOI method (JIS K7201) andthe accumulated database are valuable. Therefore, it is very
important to clarify the difference between the flammability
limits in normal gravity and microgravity.
In the Solid Combustion and FLARE projects [4], ISS Kibo
module experiments, supported by JAXA, we are discussing
new criteria of fire safety for solid materials used in spaceenvironment. For flat materials, we first have obtained theflammability map of a PMMA sheet with an opposed flow topropose an extinction model in various conditions. In thisarticle, we show the obtained flammability map by parabolic
experiments and compare the extinction limit with theprediction by the model.

2. Experimental Setup and Scale Modeling

-4

-3

-2

-1

0

1

2

3

4

5 [cm]

32

2.2 Scale Analysis
We built up scale modeling of heat transfer in the flame
spread over a thermally thin material [5]. Figure 2 shows theschematic of the flame used. Since the radiation loss and the
kinetic effect were considered as the suppression factors offlame spread, the heat balance equation is expressed as follows,V f  s c sW (T  T )   (1  aabs ) (T4  T4 ) LsxW

Sampleguide(1)(T f  T )1 ~ 1 
LgxW  gDa
LgyIn this equation, the second term of left hand side and thefactor appears in the right hand side are the radiation loss andthe kinetic effect, respectively. Non-dimensionalizing Eq. (1)by the flame spread rate in thermal regime [6], we obtained asimple equation,  1/ DaR  1/ Da  1
DaR ~2.1 Experimental Apparatus for Parabolic Flight
The flammability limit of a thermally thin PMMA sheet(Acryplen: Mitsubishi Rayon Co., Ltd.) was investigated in
microgravity. The thickness of the sample was 125μm. The
width and the length are 2cm and 12cm, respectively. The
sample was put between metal guide plates and set in a small
wind tunnel with a suction fan, rectifying honeycomb meshes,
and a Ni-Cr igniter (see Fig. 1). The microgravity environment
was attained by parabolic flight by DAS for 20s. The sample-5

was ignited at the onset of microgravity environment, and theflame spread rate and the surface temperature are measured by avisible CCD camera and an infrared camera. The opposed
flow velocity and the oxygen concentration were varied asparameters.

Da ~

(2)

 g cgVr (T f  T )(3)

 (1  aabs) (T4  T4 )gVr2

 g YO A exp( E / RT f )(4)where DaR is the radiation (fourth) Damköhler number [5] andDa is the first Damköhler number, respectively. In Eq. (2), we
assumed that the extinction occurs at η~0.

3. Results and Discussion
The obtained flammability map is shown in Fig. 2. The
number beside the symbol means the spread rate in mm/s. The
limiting Oxygen Index (LOI) was found to be 17.0% by theground downward spread tests. In microgravity environment,1y

V r=V g+V f

0

L gx

Igniter-1

Pyrolysis zone

x
Lsy



Preheat zone-3

Fig. 1

Gas (g)L gy-2

Test section of the experimental apparatus.

Fig. 2

Environment
esr ser(e)

L sx

Flame spread over a thin material.

gsr

gsc

sfc

Solid (s)the flame spread was possible even below the LOI. The
minimum limiting oxygen concentration (MLOC) was 14.7%,
which was 2.3% lower than the LOI. The opposed flow
velocity near the MLOC condition was observed was about
6~10cm/s. The predicted flammability limit by Eq. (2) is also
shown in Fig. 2. The model underestimated the MLOC about
1.7%, but reproduced the profile of the limiting line properly.
The predicted opposed flow velocity at the MLOC condition
was 8cm/s, which agreed with the experimental result.
We also conducted the flammability test changing the diluent
gas from nitrogen to carbon dioxide as well. Carbon dioxide
has large specific heat and small temperature diffusivity;
therefore, it was predicted that the flame spread was possible atvery low opposed flow and the difference between the LOI and
the MLOC became large. Figure 3 shows the flammability
map and the predicted limiting line. It is found that flame
spread was possible when the opposed flow velocity was very
low, 2cm/s, whereas extinction occurred at the same opposed
flow velocity in nitrogen balance condition. The LOI was
24.3%, and the MLOC was 19.2%. It is found that the margin
between the LOI and the MLOC was 5.1%, which was larger
than that in nitrogen balance condition. Thus, the trend in
carbon dioxide balance condition was captured by the model.
Although the developed model underestimated the MLOC, it
could predict the effect of ambient gas properties correctly.
Bhattacherjee et al. reported that the non-dimensional spreadrate η become 0.5 at extinction condition [7]. Hence, theassumption η~0 may be too strong. For more accurate
prediction, the extinction assumption should be modified.

4. Summary
The flammability limit of thin PMMA sheet was obtained andthe effect of the diluents gas was clarified. The developedmodel could capture the trend of extinction near MLOC and theeffect of ambient gas properties, but it still under estimate theMLOC. The modification of the extinction assumption may beneeded.

Acknowledgment
This study was supported by JAXA and JSF as Solid
Combustion and FLARE projects.

References
1)

NASA-STD-6001
B:
Flammability,
Offgassing,Compatibility Requirements and Test Procedures (2011).

2)

O. Fujita, M. Kikuchi, K. Ito, S. L. Olson, T. Kashiwagi and T.
Sakurai: J. Jpn. Soc. Microgravity Appl., 14, 1(1997) 25 (inJapanese).

3)

A. Kumar, H. Y. Shih and J. S. T'ien, Combustion and Flame 132(2003) 667.

4)

O. Fujita, J. Combustion Society Japan 56, 176 (2014) 117 (inJapanese).

5)

S. Takahashi, M. Kondou, K. Wakai, S. Bhattacharjee, Proc.
Combustion Institute, 29 (2002) 2579.

6)

S. Bhattachrjee, J. West, and R. A. Altenkirch, Proc. Combust.
Inst. 26 (1996) 1477.

7)

S. Bhattacharjee, K. Wakai, S. Takahashi, Combust. and Flame,
132 (2003) 523.

30

21
2.09

1.70
1.10

28

1.62

Oxygen level (%)

19
1.00

18

0.49

LOI

17

1.15

16

0.50
0.45

MLOC

15

0.26

0.81
0.67

0.38

0.79
0.78
0.80
0.63
0.50

1.19

0.83
0.83
0.63

14
MLOCPrediction

12
11
2

4

6

8 10

Oxygen level (%)

20

13

and

26

0.65

18

14

Fig. 3
Flammability map and the predicted extinction
limit for nitrogen balance condition.

0.48

MLOC

12

0.56
0.48

1.17

0.75
0.46
0.35

Flammable
Extinct

Opposed flow velocity, Vg (cm/sec)

1.13
0.97

22

16

40

1.17
1.06

20

0.96
0.88

1.42

LOI

24

1/ DaR  1/ Da  1

20

1.44
1.88

1.13
0.80
0.46

0.31

1/ DaR  1/ Da  1

Flammable
Extinct

MLOCPrediction

1

2

4

6 8 1020

40

Opposed flow velocity, Vg (cm/sec)
Fig. 4
Flammability map and the predicted extinction
limit for carbon dioxide balance condition.

28A03
LOI に与える重力影響に関する考察○中村祐二（豊橋技科大），細貝亜樹（JAXA），若月薫（消防研究センター）

A Study of Potential Gravity Effect on LOI○Yuji NAKAMURA (Toyohashi Univ. Tech.), Aki HOSOGAI (JAXA), Kaoru WAKATSUKI (NRIFD)

1. Introduction
1.1 Do We Have a Problem in Selection of Fire SafenessMaterial in Space?
To ensure the fire safeness in space, the material to bring into
ISS (International Space Station) must be passed thequalification test. Currently NASA-STD-60011) is the major
protocol for this purpose based on the pass/fail criteria for
upward flame propagation process. Since the upward flame
propagation is believed to always give the most hazardous fire
scenario, this test is widely recognized as “conservative” one(namely it should adopt the fire in any gravity environment).
Because NASA-STD-6001 was originally designed to thespecific environment as ISS, NASA recently proposed theextended methodology based on “ULOI (Upward Limiting
Oxygen Index)” to adopt various type of space habitants. Thisis the test to check whether the material could continuously
burns under which oxygen concentration in upward propagation
system. Again, upward propagation is the most conservative
test, oxygen concentration below ULOI should be safe in fire.
However, what happens if the “conservative” assumption is not
valid (in other word, say, minimum oxygen concentration
becomes much lower when the exposed gravity is reduced)?
Unfortunately, at very near the extinction limit, it is suspectedthat the judgment with upward propagation system undernormal gravity does really give the most “dependable (i.e.,
conservative)” limit.
Consider that oxygen concentration decreases gradually tofind the extinction point under normal gravity. One expects
that the flame becomes very weak and be so sensitive to theambient flow. Eventually, flame shall be experienced theblow-off because of the relatively strong buoyancy-induced flow.
In this sense, the limit must be given always as blow-off
criterion. On the contrary, as the buoyancy-induced flow
decreases (i.e., most likely the imposed gravity is reduced), theflame could potentially stay there since there is little flow
disturbance. Instead, under such condition, diffusive transport
starts to play a role and extinction will be somehow triggered byconductive (or radiative) loss in the system. In other word,
conductive/radiative heat balance will determine the limit under
low gravity.
Considering altogether, to know the“conservative” limit under microgravity environment,
conductive/radiative heat balance in either concurrent/opposed
flow system must be properly modeled and examined.

1.2 Objective in this Study
Research target is now clear and all we need to study is how
much we could find the “largest” difference between the limit
under normal gravity and the one obtained under low gravity
environment. To examine this issue, we must select the mostappropriate experimental design, namely, what kind of test
condition could give the most sensitive to the gravity. This isobjective and motivation in this study.
Meanwhile, in this work, we only consider about the very low
gravity since the limit under normal gravity in upward flame
propagation system could be obtained by elsewhere (e.g.,NASA). Because the target condition is the very low gravity,
at which diffusive transport is dominant, flowing direction
against the spreading direction of the flame does not matter.
Thus the test is performed with opposed-flow system and thequantity to be compared is LOI (Limiting Oxygen Index).

2. Experiment
In this study, LOI is obtained by the protocol described in
ISO4589-22). Facility, procedure of the test and typical flame
obtained are shown in Fig.1.

Fig.1 LOI test facility: (top) test system, (bottom left)
specimen, (bottom center) ignition procedure, (bottom right)
typical flame spreading toward the downward.

According to the ISO protocol, the top surface of thespecimen (10mm width and 4mm thickness) is heated by the
propane burner flame to achieve flaming. The candle-likeflame is established over the specimen and moves down as thematerial is consumed. During the burning event, specimen
tends to melt (if it is the melting material) and the molten layer
is formed surrounded the top surface.

3. Results and discussion
3.1 Limiting Flame Configuration for 4mm-thickness Sample
Fig. 2 shows the representative of the limiting flame formed
over the standard PMMA specimen followed by ISO protocol(namely, the thickness of the specimen is 4 mm).

It is rather obvious that the flame is elongated toward the
upstream (which is bottom direction in the figure) and theregression of the specimen is not likely 1-D as suggested by
Fig.2. Moreover it seems that two side flame covers the
specimen side-by-side. In this sense, this flame systemremains the dimensional feature (not likely 1-D).
3.3 Effect of Thickness on Limiting Flame and Their
Dependency on Gravity
Let us consider the very thick limit and very thin limit of thesample and what kind of flame system would be appropriate toassume. It is understood that the thicker sample tends to lessdimension and thinner sample does not (rather 2-D like flamesappears).
Thus the applicable flame system would besummarized as following figures (Fig3)

Fig.2 Candle-burning test of PMMA (whose LOI is 17.34)
under different oxygen atmosphere (17.4% and 18%). Flameat 17.4% O2 is the very near the extinction condition (sufficient
to call “limiting flame”)3)
As indicated in the figure, flame becomes shorter when thelimiting condition is approached. Moreover, as found in theright pics, edge of the flame is close to flat. It is understoodthat the small flame is attached over the surface and the fuelregression is continuously done along the specimen. The latterfeature reminds us that the combustion system would show“less-dimension” feature and it is approached to most likely 1-D
flame system.
3.2 Limiting Flame Configuration for 1mm-thickness Sample
Fig. 3 shows the another representative of the limiting flame
formed over the “thinner” PMMA specimen whose thickness is
1 mm (quarter of the standard one).

Fig.3 Applicable flame model depending on the sample
thickness
If this consideration is valid, gravity effect must be more
pronounced in thinner sample so that effect of the gravity must
appear to such specimen. In other word, it is less-pronounced
the gravity effect on standard sample described by ISO protocol
to measure LOI. We will continuously work on this issue in
future under the monitoring the FLARE project.

Acknowledgments
This work is conducted as part of the study of prioritizedresearch proposals of JEM utilization (FLARE project).

References1)

2)

Fig.3 Flame at 0.2%-higher-than-extinction-O2 formed over
1mm thickness PMMA sample. Front image is enbedded in
the figure with backrigh image (side view)3)NASA-STD-6001;Flammability,
Odor,
Offgassing,andCompatibiliyy Requirements and Test procedures for Materials in
Environments that Support Combustion, NASA (Feb. 9, 1998)
ISO4589-2 Plastics-Determination of burning behaviour by
oxygen index Part 2: Ambient-temperature test
K. Kizawa: Bachelor Thesis approved by Hokkaido University(supervisor: Y. Nakamura), 2014.3.

28A04
ISS「きぼう」における固体材料燃焼実験(Solid Combustion)

第二報○水島隆成，菊池政雄，高柳昌弘（JAXA），鳥飼宏之，伊藤昭彦（弘前大），
高橋周平（岐阜大），藤田修（北大）

Overview of "Solid Combustion" Experiment in the ISS/KIBO○Takanari MIZUSHIMA, Masao KIKUCHI , Masahiro TAKAYANAGI (JAXA), Hiroyuki TORIKAI,
Akihiko ITO (Hirosaki Univ.), Syuuhei TAKAHASHI (Gifu Univ.), Osamu FUJITA (Hokkaidou Univ.)
1. Introduction
A lot of astronauts have been staying in the International
Space Station(ISS) for long term. They have carried out many
scientific experiments in the microgravity environment. To
secure their safety, the protection against fire is a particularly
important issue. However, the current material flammability
tests for fire safety in space are performed in the normal gravity,and it is known that the material flammability could be enlarged
in microgravity in some conditions[1]-[4] .Therefore it isnecessary to understand the impact of gravity on the the material
flammability.
In JASMAC-26, we introduced the main objectives of Solid
Combustion. In this report, we will introduce the contents ofeach experiment.

2.4 Experiment 3
We quantify the spreading speed and the preheated sizes of the
PMMA sheets. Then we clarify the extinction limit conditions
and review the prediction obtained from scale analysis.
Fig.2 shows the concept of the experiment. With two metalframes, PMMA sheet and ignition wire are sandwiched.
With the ignition wire, forced ignition is carried out. Then we
observe the flame which is spreading on the sheet.
2.5 Experiment 4
Experimental content is same as experiment 3. We utilize thefilter paper which is the charring sample instead of PMMA
sheet.
In this experiment, we clarify the effect of the existence of thechar and the deference of the width on flammability limit.

2. Overview of the Experiment
2.1 Objectives
Our research entitled “Quantitative Description of Gravity
Impact on Solid Material Flammability as a base of Fire Safetyin Space(Solid Combustion)“ will be carried out in the JapaneseExperiment Module/KIBO in the ISS. The main target of theresearch is to clarify the impact of gravity on the the material
flammability.
In this research, we will carry out four kinds of experiment toobtain the ignition map of overloaded wire and flammability
map of spreading flame.
Table 1 shows the sample and the expected data map in eachexperiment.
2.2 Experiment 1
We define the marginal condition in which the wire covering is
ignited. Then we clarify the mechanism which define themarginal condition for the case that an over-current flows into
the polyethylene insulated wire.
Fig.1 shows the experimental apparatus. It has the reals andmotors to wind the wire. The wire is electrified with the electricpole. Then we will investigate the presence or absence ofignition.
2.3 Experiment 2
We define the marginal condition that the flame spreading on
the wire covering maintain the oneself. Then we clarify themechanism which the marginal condition is determined.
The experimental apparatus is similar as the experiment 1.
Although, the ignition wire is utilized instead of electric pole.
Forced ignition is carried out to the wire. After that, theapparatus controls the speed to maintain the flame and melting
sphere in one position. Then we will observe the flame andsphere with the camera such as high-speed camera and IR
camera.

Table 1 Experiment in Solid Combustionsolid material
polyethylene
insulated wirepolyethylene
insulated wire

Experiment 1
Experiment 2
Experiment 3

plastic sheet

Experiment 4

filter paper

Fig. 1

expected data map
ignition map ofoverloaded wire

flammability map of
spreading flame

Experimental apparatus for experiment 1

Ignition wire

Metal
frame

Slit of theframe

Fig. 2Concept of experiment 3 and 4

PMMAsheet or
Filter paperReferences
1)
2)

K.agata, et al., J.Jpn.Soc.Microgravity Appl., VOL.25 No.1,
pp.11-16,2008.1.
O.Fujita, J.Jpn.Soc.Microgravity Appl., VOL.28 No.3, pp.9095,2011.

3)
4)

Y. Onishi, et al., Transactions of the Japan Society for
Aeronautical and Space Sciences, Vol.8, pp.Ph_19-Ph_24, 2010.
O.Fujita, et al., Proc.Combustion Institute, VOL.33, Issue2,
pp.2617-2623,2011.

28A05微小重力環境を利用した微燃性冷媒の燃焼性評価○滝澤賢二，徳橋和明，近藤重雄（産総研）

Flammability Evaluation of Mildly Flammable Refrigerants using Microgravity Environment○Kenji TAKIZAWA, Kazuaki TOKUHASHI, Shigeo KONDO (AIST)

1. Introductionin g will abstract the intrinsic flammability characteristics that

In recent years, development of new alternative refrigerants
having low global warming potentials (GWP) have beenaddressed. In general, to shorten atmospheric lifetime, which
results in reduction of GWP, leads to an increase in reactivity
with air, and consequently increases flammability. To develop
environmentally friendly materials, we should consider suchtradeoff relationships, that is, to minimize environmental impact
without compromising fire safety for practical use. Accordingly,
the demand for evaluating flammability of mildly flammablecompounds has been increased.
We have reported on burning velocity (Su) measurement offluorinated compounds using the closed vessel methods 1). As
the first method we directly measured the flame radius (rf)-timedevelopment in the prepressure period of combustion by theschlieren photography (SP) technique. As the second one, weused the spherical-vessel (SV) method, in which we measured
pressure-time development and obtained Su by employing a
spherical flame propagation model. The model was originallyestablished for small hydrocarbons 2,3) and we applied the model
to hydrofluorocarbons. However, for mildly flammablecompounds with Su below 5 cm s-1, the flame propagated soslowly that it moved upwards and was distorted by buoyancy, as

is not perturbed by the effect of the gravity. Fig. 2 shows Su for
R-32 (CH2F2) and R-1234yf together with literature data.
According to Saburi and Wada 4), flame front of R-32 kept
smooth during propagation in 1000 mm diameter vessel forequivalence ratio (φ) in the range 0.9-1.2. Wrinkling due tohydrodynamic instability was not observed for mildly
flammable compounds. We also obtained quenching distance of
mildly flammable compounds. Using these data, we obtained agood relationship between Su and quenching distance for highly
to only mildly flammable compounds, which will be presented
in the conference.

Fig. 1

Direct flame image of R-1234yf at φ=1.32 in(a) 1G and (b) g. Su is ca. 1.5 cm s-1

shown in Fig. 1(a). Since the flame propagation was different
from the spherically propagating flame of highly flammablecompounds, it is necessary to check the validity of the obtained
data. We added experiments in g environment, where thebuoyancy does not work and Su from the spherically
propagating flame will be obtained.

2. Experiments using a 10-m drop tower
The g experiments were performed using a 10-m drop tower
in AIST Hokkaido center. We carried out the g experimentusing the same vessel, ignition system, and recording system as
the 1G experiment. Accordingly, all the differences in the results
will come from the effects of gravity. To reduce the effects ofignition spark and curvature (stretch) on the flame, relatively
large vessel was used (inner diameter of 155 or 200 mm).
Because the SP method system was difficult to be set in thecurrent falling capsule, the flame images were recorded directlywith a high-speed video camera.

3. Results
Fig.

1(b)

shows

flame

propagationof

R-1234yf(CH2=CFCF3)/air in g. Different from the data in 1G, the data

Fig. 2

Su of R-32 and R-1234yf as a function of φ.

4. Future work
We are planning to set up a 15-m drop tower in AIST
Tsukuba center. We will utilize the facilities not only for further
development of evaluation of low flammable materials but also
for collaboration with institutes and companies.

References
1)

K. Takizawa, A. Takahashi, K. Tokuhashi, S. Kondo and A.
Sekiya, Combust. Flame, 141 (2005) 298.

2)

M. Metghalchi and J. C. Keck, Combust. Flame, 38 (1980) 143.

3)

P. G. Hill and J. Hung, Combust. Sci. Technol., 60 (1988) 7.

4)

T. Saburi and Y. Wada, JSRAE 2013 Progress Report (inJapanese) (2014) 68.

28A06
列方向移動可能液滴間を燃え広がる火炎が液滴の運動に及ぼす影響○菅沼祐介，野村浩司（日本大学），三上真人（山口大学），菊池政雄（JAXA）

Motion of Movable Droplets Induced by a Flame Spreading between Movable Droplets○Yusuke SUGANUMA, Hiroshi NOMURA (Nihon Univ.), Masato MIKAMI (Yamaguchi Univ.),
Masao KIKUCHI (JAXA)

1. Introduction
Spray combustion is widely employed for industrial
combustors such as diesel, jet engines, and industrial furnaces.
Because spray combustion is a complicated phenomenon, there
are still unknown areas in the spray combustion mechanism.
Therefore various approaches have been applied to investigate
spray combustion. In most of investigations focusing on fueldroplet array combustion, the droplet array consists of fixed
droplet. During real spray combustion, fuel droplets movefreely, relative to other droplets. Droplet motion caused byflame spreading, and the influence of the droplet motion on
flame spreading, are also important areas for research. In thepresent work, a fuel droplet array with plural movable droplets
is employed to investigate flame spreading between movable

Fig. 1

Experimental model.

Microgravity experiments will be conducted withthe group combustion experiment module (GCEM) installed
into the multi-purpose small payload rack (MSPR) on theinternational space station (ISS). n-decane is employed as a
droplets.

low-volatile fuel, in contrast to the FLEX-2J NASA experiments
1)
in which n-heptane is examined as a high-volatile fuel. In
this report, the ground-based experimental apparatus and theresults obtained under normal gravity conditions were presented.

2. Experimental Apparatus and Procedure
Figure 1 illustrates the employed experimental model of alinear fuel droplet array. Four fixed droplets and two movable
droplets were dispensed along a horizontal thin fiber. The
droplet closest to the igniter was referred to as the first fixeddroplet. The four fixed droplets were employed in order tosuppress the influence of disturbance due to the ignition processof the first fixed-droplet on the motion of movable droplets.
Movable droplets were suspended directly on the thin fiber to beallowed to move freely in the direction of the thin fiber.
The ground-based experimental apparatus consists of thedroplet-array suspension system, a droplet-array slider, a droplet
generator, an igniter, a high speed camera, and a sequencer asshown in Fig. 2. Behavior of movable droplets and a
spreading flame were observed with the high-speed video
camera.

The horizontally-fixed fiber of 78 m in diameter and

30 mm in length allows us to suspend droplets of 0.8 mm indiameter. Movable droplets were very weakly anchored at
predetermined locations. One anchor point consists of two

Fig. 2Ground-based experimental apparatus.

slightly-thinner zones etched by a CO2 laser. Experiments
were performed at atmospheric pressure, room temperature, andnormal gravity. As a liquid fuel, n-decane was employed.
Each center-to-center distance of the fixed droplets was set at
1.6 mm ± 10% for all tests.
The initial spacing between the fourth fixed-droplet and thefirst movable droplet and the initial spacing between the two
movable droplets were varied. Initial diameter of all droplets
used for the calculation of averaged initial diameter was
regulated within the range of 0.8 mm ± 5%.

3. Experimental Results and Discussion
Flame-spread between the first and the second movable
droplets was observed with varying the initial spacing between
the movable droplets. The initial spacing between the fourth
fixed-droplet and the first movable droplet was set at 1.38 mm
or 1.42 mm (1.40-1.44 mm), which are below the initial droplet

spacing of the flame-spread-limit from a fixed droplet to a
movable droplet. It was found that behaviors of spreading flame
were classified into four patterns. Figure 3 shows four typical
histories of the positions of the first and second movable
droplets. Flame spread pattern changes from the pattern 1 to 4
as the increase in the initial spacing between two movable
droplets.
Pattern 1 (Fig. 3a): This pattern was observed when theinitial spacing between two movable droplets was narrow.
When a spreading flame reached the fourth fixed-droplet, thefirst movable droplet started to move in the positive direction.
At 0.058 s, the flame spread to the first movable droplet. The
first movable droplet in the group-flame continued to move inthe positive direction and collided against the second movable
droplet. The flame around the first movable droplet was
extinguished by the collision. It is supposed that the sudden
temperature drop due to the coalescence with the cold second
droplet led to the flame extinction of the first movable droplet.
After the flame extinction, the coalesced droplet continued tomove in the positive direction.
Pattern 2 (Fig. 3b): Flame extinction did not occur after the
coalescence of the first and second movable droplets. The
duration between the ignition of the first droplet and thecoalescence was longer than in the case of the pattern 1. Afterthe collision, the coalesced droplet continued combustion andstopped moving.
Pattern 3 (Fig. 3c): Flame spread from the first movable
droplet to the second movable droplet without collision. Afterthe flame-spread, the both movable droplets continued
combustion and stopped moving.
Pattern 4 (Fig. 3d): Flame did not spread from the firstmovable droplet to the second movable droplet and the second
movable droplet escaped from the burning first movable droplet.
The first movable droplet stopped moving after the second
movable droplet started moving. The second movable droplet
kept moving after the first movable droplet stopped moving.
At narrow initial spacing between the fourth Fixed-droplet
and the first movable droplet, another flame spread pattern wasobserved, which was shown in Fig. 4. The behavior of the newflame spread pattern was the same as the pattern 2 until collisionof the first and second movable droplets occurred. However,the coalesced droplet accelerated towards the fixed droplets.
In the case of the pattern 2, the flame of coalesced droplet was
isolated. On the other hand, in this case, the coalesced droplet
was surrounded by the group combustion flame together withthe fixed droplets. This fact means that the coalesced droplet
was heated by the group combustion flame mainly from theother side of the fixed droplet.
It was supposed thatasymmetric evaporation of the coalesced droplet generated thethrust towards the fixed droplet.

(a) Flame-spread pattern 1.

(b) Flame-spread pattern 2.

(b) Flame-spread pattern 3.

(b) Flame-spread pattern 4.

Fig. 3Fig. 4

Histories of movable-droplet position [1].

Histories of movable-droplet position at movable
droplet spacing of 1.70 mm (new flame-spreadpattern).

4. Conclusions
The interaction between flame-spread and droplet motion wasinvestigated under normal gravity conditions. Initial spacings
between the fourth fixed-droplet, the first movable droplet andthe second movable droplet were varied. Five flame-spreadpatterns were observed.

Acknowledgments
This study was carried out as a part of “Research Working
Group Activity of Space Environment Science” supported by
ISAS-JAXA.

References1)

Hiroshi NOMURA, Masato MIKAMI, Masao KIKUCHI, Daniel
L. DIETRICH, Proceedings of the 27th Journal of the Japan
Society of Microgravity Application, 2013

28A07
大気球を利用した微小重力燃焼実験の実施結果について○菊池政雄，石川毅彦（JAXA），山本信（IHI 検査計測），澤井秀次郎，丸祐介，橋本樹明，
坂井真一郎，坂東信尚，清水成人，小林弘明，吉光徹雄，菅勇志，水島隆成（JAXA），
福山誠二郎（AES），岡田純平，依田眞一，福家英之，梯友哉（JAXA）

Result of Microgravity Combustion Experiment by Using Balloon Operated Vehicle○Masao KIKUCHI, Takehiko ISHIKAWA (JAXA) , Shin YAMAMOTO (IIC), Shujiro SAWAI, Yusuke MARU,
Tatsuaki HASHIMOTO, Shinichiro SAKAI, Nobutaka BANDO, Shigehito SHIMIZU, Hiroaki KOBAYASHI,
Tetsuo YOSHIMITSU, Yuji KAN, Takanari MIZUSHIMA (JAXA), Seijiro FUKUYAMA (AES),
Junpei OKADA, Shinichi YODA, Hideyuki FUKE, Yuya KAKEHASHI (JAXA)

1. Introduction
The usefulness of the high-altitude balloon operated vehicle
as a microgravity experiment method with high quality
microgravity level was demonstrated by Hashimoto et al.1-4). It
was shown that the experimental system could provide lowgravity environment in the order of 10-4 G for around 30 s bydrag-free control of the payload, which is accommodated inside
the outer structure of the free falling vehicle. However,maximum payload size was very limited in previous system.
In order to enlarge the allowable payload size with sustaining
microgravity level, development of new drag-free control
method was performed by Ishikawa et al.5). For technicaldemonstration of the new system, a flight experiment using thehigh-altitude balloon was planned. Preparation effort of theflight experiment at the JAXA’s Taiki Aerospace Research Field(TARF) , located in the Taiki town in Hokkaido, was performedin the summer of 2012 at first. However, the flight experiment
was not achieved due to bad weather condition in 2012.
Although flight experiment was also tried in the spring of 2013
and 2014, it resulted in postponement of the experiment due tobad weather conditions. Finally, the flight experiment was
performed in the summer of 2014 as the 4th trial at the TARF.
This paper briefly reports the outline of the experiment andits result.

2. Overview of the Experiment
The primary objective of the flight experiment isdemonstration and verification of the new drag-free experiment
system. As described detail in later, the new system wasdesigned to accommodate a payload whose size is as large asthat of European TEXUS sounding rocket. Since experimental
apparatus called DCU (Droplet Array Combustion Unit),
employed for the droplet array combustion experiment by
TEXUS 46 in 20096), was available, it was employed for the
payload of this flight experiment. For the flight experiment,
engineering model (EM) of the DCU was modified so that itmeets flight operation by the balloon operated vehicle. It wasalso intended to obtain scientific data on flame spread along alinear fuel droplet array with pre-vaporization in microgravity7).

Fig. 1 shows schematic concept of the combustion
experiment. Same as previous TEXUS rocket experiment,
observation of flame spread phenomena along n-decane droplet
array in 500 K air was planned in the current experiment. In the
TEXUS rocket experiment, flame spread with relatively large
degree of pre-vaporization was observed 3 times by varying prevaporization time during 6 minutes microgravity6). On the other
hand, 1 time observation of flame spread with relatively small
degree of pre-vaporization during about 30 s microgravity was
intended in the current experiment. It was expected that dataobtained by the balloon experiment would fill the gap between
those by short duration drop tower/shaft experiments and by
longer duration TEXUS rocket experiments.

Flame Spread

IgnitionFig. 1 Schematic concept of the combustion experiment

3. Experimental System
The differences of drag-free control methods in previous andcurrent system are indicated in Fig. 2. In previous system (a),the three dimensional (3D) relative position of the inner capsule(payload of the microgravity experiment) was measured fromouter capsule, and the cold gas jets in the outer capsuleproduced forces to cancel the disturbances and kept the distance
between the inner and outer capsule constant. Although the 3D
control method realized high quality microgravity environment
during free falling of the balloon operated vehicle, it was almost
impossible to accommodate larger size payload.
In the current system (c), a one dimensional (1D) drag-freecontrol system using a linear slider mechanism was adopted.
The payload and the outer capsule (balloon operated vehicle) ismechanically connected by a linear slider. When the verticaldistance between the payload and inner wall of the vehicle
decreases by drag force to the vehicle, longitudinal cold gas jets

thrusters at the rear end of the vehicle are activated so that they
cancel disturbances and maintain appropriate distance between
the payload and the inner wall of the vehicle. Better low gravity
environment by this system was expected than the system
without any drag-free control system (b).
As a result, allowable payload size was enlarged to 400 mm
in diameter and 600 mm in height, from spherical shape in 280
mm diameter by previous system.

batteries for the payload were provided by the rocket side in the
TEXUS experiment, whole system shall be prepared by the
payload itself in the current experiment by the balloon operated
vehicle. Therefore, control devices and batteries wereadditionally installed in the experimental apparatus. Also,
observation devices including a high-speed video camera were
replaced to new one.

Linear Slider(a) Previous Type (b) Type A(c) Type B (current type)
3D control
No drag-free control 1D control
Small payload
Large payload
Relatively large payload

Fig. 2 Comparison of drag-free control methods of the
payloadWing (x4)Middle body

Nose coneFig. 4 Photo of the modified EM of the DCU

The whole experimental system for microgravity experimentby the balloon operated vehicle consists of the high altitude
balloon system, the balloon operated vehicle, and the payload
inside the vehicle. Configuration of these systems is
Aft body

Access hatch (x2)Fore bodyschematically shown in Fig. 5. It is possible to lift scientificpayloads with 700 kg to an altitude of 40 km, by the highFig. 3 Appearance of the balloon operated vehicle
Fig. 3 shows a photo of the balloon operated vehicle on the
ground. The shape of the vehicle (outer capsule for the payload)
is almost identical to the previous system. Total length of thevehicle is about 4.1 m and outer diameter of the body is about
0.6 m. The weight of the vehicle including the payload
described in detail later is about 310 kg. The vehicle consists ofnose cone, fore body, middle body, and aft body with 4 wings.
The fore body and the middle body accommodate system
devices of the vehicle as well as the payload. The aft bodyaccommodates parachute of the vehicle and cold gas jets
thrusters. The fore body and the middle body are airtightstructures, so that inner pressure is kept at atmospheric pressure(about 1 atm) even at higher altitude. Also, the structures protect
inner devices from sea water after splashdown in the sea.
Fig. 4 shows a photo of the modified EM of the DCU,
employed as the payload of the current experiment. The weightof the payload is about 50 kg. Although the control device andHigh Altitude
BalloonParachute(for Gondola)

GondolaSeparation
Mechanism

Balloon Operated
Vehicle (BOV)

Fig. 5 Schematic of the whole configuration of the balloon
experiment systemaltitude balloon filled with helium gas. The balloon operated
vehicle is lifted up by the balloon via the gondola. Control
devices, electrical batteries, communication devices, and othersystem devices for the balloon system are accommodated in the
gondola. Maximum height of these systems is beyond 150 m.

(a)

(b)

(c)

(d)

4. Result of the Experiment
Final ground operation at the TARF for the flight experiment
was started at about 23:30 on August 21. Power system, control
system, and communication system of the vehicle were turned
on. Also, every access hatches of the vehicle body were closed.
Confirmations on transmission and reception conditions of thetelemetry signals and telecommands were performed between
the vehicle and the ground system. After every preparation of
the vehicle was completed, injection of helium gas to the highaltitude balloon was started at around 03:00 on August 22.
Finally, the balloon with the vehicle was released to air ataround 04:30. Photos of the balloon and the vehicle during final
preparation phase are shown in Fig. 6 and Fig. 7. Also,
sequential photos of the vehicle at the moment of the balloon
release are shown in Fig. 8.

Gondola & Balloon Operated Vehicle

Fig. 8 Sequential photos of the balloon operated
vehicle after the release of the balloon

During ascent of the balloon, several telecommands forexperiment preparation were sent to the vehicle from the ground.
Heating of the combustion chamber of the payload was started
at around 5:50. Temperature inside the combustion chamberincreased to 500 K within 45 minutes, same as nominal groundtest. 5 minutes prior to the release of the vehicle from the
gondola, automatic timer sequence of the experiment procedures
was started. The vehicle was released from the gondola at 7:11.
Sequential photos of the vehicle after the release, obtained byvideo camera at the gondola, are shown in Fig. 9.

(a)

(b)

VehicleVehicle(c)(d)

VehicleVehicleHigh Altitude Balloon

Fig. 6 Whole view of the high altitude balloon, the gondola
and the balloon operated vehicle before the release

Fig. 9 Sequential photos of the vehicle after the release fromthe gondola

Fig. 7 Photo of the gondola and the balloon operated vehicle
before the release

During free fall of the vehicle, experiment sequences of the
payload such as generation of n-decane droplet array on thearray holder, insert of the array holder into the combustion
chamber, activation of igniter after 3 s pre-vaporization time inthe chamber, recording of high-speed video camera and backlit
camera et al. were automatically performed. About 35 s after the
release of the vehicle, pilot parachute at the rear end of thewell as microgravity level, were successfully retrieved. Fig.10
shows the history of the measured data of the payload
acceleration in 3-axis direction during free falling of the vehicle.
Z-axis means the longitudinal direction along the vehicle body,and X and Y-axis mean the lateral directions. In Fig. 10, the freefalling of the vehicle starts at around 8 s of the horizontal axis.
By 22 s of the horizontal axis (14 s after the start of free falling),
some spike-like disturbances of gravity level are indicated forall 3-axis. These disturbances are attributed to the motion ofexperimental devices of the payload, such as movement of thedroplet generation device, opening the shutter of the combustion
chamber, and insert of the array holder into the combustion
chamber. After this phase, relatively calm gravity level ismaintained by around 33 s of the horizontal axis. The timing of
igniter activation for droplet ignition corresponds to this stablegravity duration. After 33 s, spike-like disturbances appear again
due to motion of experimental devices, followed by large
disturbances at around 40 s due to deployment of the parachuteof the vehicle. Apart from the disturbances induced by the
motion of experimental devices, it was confirmed that theballoon operated vehicle successfully provided good low gravity
condition for more than 20 s.
.

1

Acceleration (G)vehicle was deployed and free fall of the vehicle was completed.
Also, about 320 s after the release of the vehicle, main
parachute was deployed from the vehicle. The vehicle splasheddown the sea at around 7:27. Finally, the vehicle in addition to
the gondola and balloon were retrieved by ships.
After the retrieval of the vehicle, experimental data including
high-speed video camera and backlit camera were normally
retrieved. Also, measurement data of ambient condition of the
payload inside the vehicle, including temperature, humidity as

0.1
Measured level in 3-axis

0.01
1E-03

SSP 41000 level

1E-04
1E-05

1E-06

SSP 50036 level

1E-07
0.1

1

10

100

1000

Frequency (Hz)Fig. 11 Comparison of the measured gravity level in 3-axis
with microgravity level of the ISS

Fig. 11 shows the comparison of the measured gravity levelin 3-axis during 30 s after the start of free falling, with required
microgravity level of the ISS. According to the result, thegravity level of the payload is less than 10-3 G in low frequency
region (less than 100 Hz), though it exceeds 10-3 G in highfrequency region (more than 100 Hz). It means gravity level
achieved by the new drag free system is still high level even theaccommodated payload size is significantly enlarged. In
addition, it should be noted that gravity level in low frequency
region was lower than that of the ISS.
As for the combustion experiment by the payload, activationof the igniter (Fe-Cr wire) was confirmed by the obtained video
image at nominal timing. However, ignition of the n-decane
droplet was not occurred. Fig. 12 shows the igniter which is
glowing by electric current during the experiment. The
brightness of the igniter was lower than that observed in the
ground tests. Also, the time length of glowing was shorter thanthat measured in the tests. It could be possible that dew
condensation on the igniter surface due to temperature variation
during the flight experiment may cause this trouble, thoughdetail investigation is underway, at present.

Deployment of
the parachute

IgniterStart of free fall

Z-axis(longitudinal)
X-axisY-axis(a) balloon experiment(b) ground test

Fig. 12 Comparison of the glowing igniter

5. Summary
Disturbances by the experiment
sequence of the payload

Fig. 10 Measurement data of the payload acceleration in
3-axis direction during free falling

The flight experiment by the balloon operated vehicle was
performed at the JAXA’s Taiki Aerospace Research Field(TARF) in the summer of 2014. The primary objective of theflight experiment was demonstration and verification of the new
drag-free experiment system for microgravity experiment. Also,
combustion experiment on flame spread of n-decane droplet

array was intended. The whole flight experiment including theretrieval of the vehicle was successfully performed. According
to the obtained data, it was confirmed that the vehicle with new
drag-free system successfully realized low-gravity environment
in the order of 10-3 G for more than 20 s. Regarding the
combustion experiment, ignition of the fuel droplet was notoccurred due to insufficient glowing of the igniter.

References
1)

Ishikawa, T., Inatomi, Y., Hashimoto, T., Sawai, S., Saito, Y.,
Yoshimitsu, T., Sakai, S., Kobayashi, H., Fujita, K., Bando, N.,
Goto, M.: J. Jpn. Soc. Microgravity Appl., 25, (2008), pp. 3-10.

3)Sawai, S., Hashimoto, T., Sakai, S., Bando, N., Kobayashi, H.,
Yoshimitsu, T., Ishikawa, T., Inatomi, Y., Fuke, H., Kamata, Y.,
Hoshino, S., Tajima, K., Kadooka, S., Uehara, S., Kojima, T.,
Ueno, S., Miyaji, K., Tsuboi, N., Hiraki, K., Suzuki, K.,
Matsushima, K., and Nakata, T.: JSASS 56, (2008), pp.339-346.

Ishikawa, T., Hashimoto, T., Sawai, S., Saito, Y., Inatomi, Y.,
Yoshimitsu, T., Sakai, S., Kobayashi, H., Fujita, K., and Bando,
N.: Transaction of JSASS Space Tech. Japan 7 (2009), pp.29-33.

5)Ishikawa, T., Kikuchi, M., Yamamoto, S., Sawai, S., Maru, Y.,
Hashimoto, T., Sakai, S., Bando, N., Shimizu, S., Kobayashi, H.,
Yoshimitsu, T., Kan, Y., Tazaki, A., Fukuyama, S., Okada, J.,
Yoda, S., Fuke, H., and Kakehashi, Y.: Proc. FY24 Balloon
Symposium (in Japanese), 2012, isas-12-sbs-023.

6)

Kikuchi, M., Yamamoto, S., Mikami, M., Nomura, H., Moriue, O.,
and Umemura, A.: Proc. 49th Combustion Symposium (Japanese),
2011, pp.108-109.

7)

Kikuchi, M., Ishikawa, T., Yamamoto, S., Maru Y., Bando, N.,
Kan, Y., Tazaki, A., Fukuyama, S., Okada, J., and Fuke, H.:

Hashimoto, T., Sawai, S., Sakai, S., Bando, N., Kobayashi, H.,
Ishikawa, T., Inatomi, Y., Fujita, K., Yoshimitsu, T., Saito, Y., andFuke, H.: J. Jpn. Soc. Microgravity Appl., 26, (2009), pp. 9-14.

2)

4)Transaction of JSASS Space Tech. Japan 12 (2014), to be
published.