OR2‐3
TEXUS ロケットを用いた微小重力下での複数液滴冷炎点
火実験 ―液滴の蒸発および点火―
Multiple Droplet Cool Flame Ignition Experiment under
Microgravity using TEXUS Rocket‐Droplet evaporation and ignition‐
菅沼祐介 1, 齊藤允教 1, Meyer Florian 2, Eigenbrod Christian2, 野村浩司 1, 田辺光昭 1
Yusuke SUGANUMA1, Masanori SAITO1, Florian MEYER2, Christian EIGENBROD2, Hiroshi
NOMURA1 and Mitsuaki TANABE112

日本大学，Nihon University,ZARM

1. Introduction
Atomization of fuel droplets, evaporation, and flame spreading along the droplets have been studied as
basic research for elucidating the group combustion mechanism of spray combustion. The cool flame is a low‐temperature oxidization that precedes the high‐temperature flame and plays an important role in the ignition
process. This project aims to elucidate the dynamics of cool flames in multiple droplets1). The cool flame
ignition phenomena near the ignition limit temperature were observed and the ignition delay, ignition
position, etc. were investigated in detail. Experiments were also conducted by varying the droplet spacing toinvestigate droplet spacing and cool flame ignition. Since the experimental conditions required a microgravity
environment for a long duration, the experiment was conducted using a TEXUS rocket under an international
collaboration between Japan and Germany. This paper reports on the evaporation and ignition of the droplets.
2.

Experimental Apparatus and Conditions
The experimental apparatus consists of a combustion chamber with a shutter, a droplet array suspension

system, a droplet array generator, a fuel feed pump, a droplet array elevator, CMOS video cameras, a high‐speed video camera, and LED backlights. A droplet array is generated outside the combustion chamber andinserted into the combustion chamber through the slit at the bottom of the combustion chamber by the droplet
array elevator just before observation. Liquid fuel is supplied from a Micro syringe to the droplet arraygenerator by a stepper motor. For details on the experimental equipment, please refer to the previous report2).
The backlit images required for droplet diameter analysis were acquired using a high‐resolution CMOS video
camera (Imaging Source, DMK33UJ003). The resolution was 14.9 pix/mm, and the frame rate was 14 fps. To
obtain sufficient resolution for droplet diameter analysis, two cameras were arranged side‐by‐side to capture
the entire droplet array.
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The experimental apparatus was equipped with two combustion chambers, with the internal temperaturesof Unit 1 set to 570 K and Unit 2 set to 590 K. However, since Unit 2 did not work, the data presented in thisreport are only for Unit 1 (570 K).

Figure 1. 3D model of experimental apparatus2).

3.

Results and Discussion
Figure 2 shows a backlit image of the droplet array. Droplet spacing was 8 mm, and the array was anarrangement of two droplet pairs. The droplet diameter was measured from this image. Figure 3 shows thedroplet diameter history. The origin of the horizontal axis is the time when the droplet array came to stopped
at the experimental position in the combustion chamber. Normalized times from 0 to 2 s/mm2 represent theinitial heating period. Normalized times from 2 to 5 s/mm2 represent the evaporation period, and the slope of
the plot for this period indicates that the evaporation rate constant is K= 0.15 mm2/s. In the graph on the rightside of Figure 3, the droplet diameter decrease rate increases after normalized time 5.5 s/mm2, suggesting thatthe droplet ignited with a cool flame. The slope of the normalized time from 5.5 to 6.5 s/mm2 indicates that theburning‐ rate constant with cool flame is K= 0.35 mm2/s. Nayagam et al. conducted combustion experimentswith single 4 mm n‐decane droplets and reported that the evaporation rate constant with cool flame after theradiative extinction of hot flame was K= 0.39–0.40 mm2/s3). Since the intersection of the evaporation period andthe combustion period is the time of cool flame ignition, under these conditions, 5.5 s/mm2 was cool flameignition.

The ignition time of the cool flame could be confirmed from the droplet diameter history.

Figure 2. Backlit image of droplet array. (S= 8 mm)
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Figure 3. Histories of squared nondimensional droplet diameter.

4.

Conclusion
Microgravity experiments were conducted using the TEXUS rocket to obtain data for clarifying cool flamedynamics. The droplet diameter history analysis confirmed that a cool flame was generated, and the time of
the cool flame ignition was estimated.

References1)

M. Tanabe, M. Saito, Y. Suganuma, M. Mikami, M. Kikuchi, Y. Inatomi, O. Moriue and H. Nomura: Scope ofPHOENIX‐2 Sounding Rocket Experiment, “Cool Flame Dynamics in Multi‐droplet Ignition”, Int. J. Sci. Appl. 37 (4)(2020) 370401‐1, DOI: 10.15011/jasma.37.4.370401.

2)

Y. Suganuma, M. Saito, Y. Goto, S. Yamamoto, M. Nokura, M. Mikami, M. Kikuchi, Y. Inatomi, O. Moriue, H. Nomura
and M. Tanabe: Hardware Development for Cool Flame Combustion Experiment of Fuel Droplets using SoundingRocket, Int. J. Sci. Appl. 37 (4) (2020) 370403‐1, DOI: 10.15011/jasma.37.4.370403.

3)

V. Nayagam, D.L. Dietrich, M.C. Hicks, F.A. Williams, Cool‐flame extinction during n‐alkane droplet combustion inmicrogravity, Combust. Flame 162 (2015) 2140–2147, DOI: 10.1016/j.combustflame.2015.01.012

Acknowledgements
This study was supported by ISAS‐JAXA as The Front‐Loading Project and Small‐Scale Project, byKAKENHI Grant Number JP19K04843 and JP21K14347, and by Nihon University President Grant Initiative.
The experimental apparatus and its integration for the TEXUS rocket were supported by IHI Inspection &Instrument Co., Ltd. and Airbus Defense and Space. On the German side, this experiment was funded by theGerman Space Agency at DLR.

© 2024 by the authors. Submitted for possible open access publication under theterms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/li censes/by/4.0/).

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