Successful combustion experiment in the Japanese Experiment Module, Kibo, aboard the International Space Station - Joint experiment by JAXA and Yamaguchi University: “Group Combustion” experiment (Principal investigator: Professor Masato Mikami) -

In the Japanese Experiment Module, Kibo, aboard the International Space Station (ISS), a joint experiment with JAXA, "Elucidation of Flame Spread and Group Combustion Excitation Mechanism of Randomly Distributed Droplet Clouds (Group Combustion)" , has recently begun, and has successfully carried out the first ever combustion experiment in Kibo. The principal investigator for the joint experiment is Professor Masato Mikami from the Graduate School of Sciences and Technology for Innovation (Engineering) at Yamaguchi University.

With regard to this news, we announced on our website in August of the year before last that the main unit of the experiment apparatus, GCEM, was going to be delivered to Kibo, and that preparations were under way for the first combustion experiment. This success, which has come after numerous checkout tasks of the GCEM functions, has delighted everyone involved. The principal investigator, Professor Mikami, expressed his happiness and his enthusiasm for future experiments, saying, "I am very pleased that the microgravity combustion research that originated from Japan over 60 years ago has got as far as an experiment in Kibo. I would like to express my gratitude to JAXA, all the joint researchers and other people involved who have worked on the preparations for the experiment, and the students who have kept the research going. The experiment is going to continue for the next several months, so please look forward to seeing more results."

 

[Background to the experiment]

Liquid fuel is used as the fuel for many vehicles, including automobiles and aircraft. In the engines in these, a liquid fuel is injected from a nozzle, which turns the liquid fuel into a mist (spray), and heat energy that is generated by the combustion of the atomized droplets becomes the driving power that makes vehicle move (spray combustion). Getting the sprayed liquid fuel to burn continuously and stably requires the "flame-spreading" of flames from droplets that are burning to droplets that are not burning, and a process called "group combustion", in which all of the spray droplets burn. However, the mechanism by which "group combustion" excited through "flame-spreading" between droplets is not clear. Numerical simulations of combustion processes is becoming more and more important in engine development, but a model that can properly handle flame-spreading between droplets and the process of excitation of group combustion still needs to be constructed.

 

[Overview of the experiment]

This experiment was the first combustion experiment to have been carried out in Kibo, and it was conducted using a droplet cloud combustion experiment apparatus developed by JAXA (GCEM*, see below). The main unit of the GCEM was delivered to the ISS's Japanese Experiment Module, Kibo, in August 2015 by Kounotori 5, one of the Japan Aerospace Exploration Agency (JAXA)'s an unmanned resupply spacecraft. Once all the constituent apparatus had arrived at Kibo in 2016, JAXA astronaut Takuya Onishi, who was in the middle of a long stay on the ISS, set them up on the experiment racks in the Kibo. The initial function checkout work for GCEM had been progressing up until then, and the experiment began on February 17, 2017.

In this experiment, the behavior and limiting distance of flame-spreading among droplets will be investigated under micro-gravity conditions using a small number of droplets, and what is understood in relation to these will be verified by means of the combustion of droplet clouds in which large numbers of droplets (up to 152) were randomly distributed. Through this, the mechanism for the excitation of group combustion will be clarified.

In the experiment this time, dynamic flame-spreading of 97 fuel droplets was successfully observed.

It is thought that this experiment will be able to theoretically connect what has been understood thus far in relation to the combustion of a few droplets as a result of short-time micro-gravity experiments, with droplet group combustion. Furthermore, if the mechanism by which group combustion is excited is clarified, it will become possible to make numerical simulations of spray combustion more advanced. It is therefore anticipated that it will make a significant contribution to the development of highly-efficient and environmentally-friendly engines.

 

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Image of flame-spreading (Provided by JAXA)

 

* JAXA International Space Station Japanese Experiment Module “Kibo”: The first combustion experiment in Kibo has begun (Includes a video of combustion)

* Engine System Engineering Lab., Department of Mechanical Engineering, Faculty of Engineering, Yamaguchi University

 

[Experiment apparatus]

Droplet could combustion experiment apparatus: GCEM (Group Combustion Experiment Module)

This is the first ever device from Japan to perform combustion experiments in orbit. It investigates the combustion mechanisms of fuel droplet clouds (a group of small fuel droplets for simulating states in which liquid fuel is injected in mist form). When combustion experiments are performed on the earth, strong natural convection occurs because of the temperature difference between the high-temperature flames and the air. However, natural convection resulting from heat does not occur in a micro-gravity environment, so detailed observations can be made with the focus on the phenomenon of combustion itself.

GCEM consists of a combustion chamber, a fuel supply device, observation devices, power and communication control devices, and air supply and exhaust devices. The combustion experiment is performed inside a combustion chamber by means of remote control from the earth. The experiment is filmed using high-speed cameras and digital cameras attached to the observation devices, and the images are sent to earth through the power and communication control devices.

 

 

                 Outline diagram of experiment method (Provided by JAXA)

 

[“Group Combustion” researchers] * PI: Principal investigator, CI: Co-investigator

 PI: Masato Mikami, Professor, Graduate School of Sciences and Technology for Innovation, Yamaguchi University

 CI: Hiroshi Nomura, Professor, College of Industrial Technology, Nihon University

 CI: Osamu Moriue, Associate Professor, Graduate School of Engineering, Kyushu University

 CI: Akira Umemura, Emeritus Professor, Nagoya University

 CI: Takehiko Sena, Associate Professor, Graduate School of Sciences and Technology for Innovation, Yamaguchi University

 CI: Yusuke Suganuma, Research Associate, College of Industrial Technology, Nihon University

 CI: Masao Kikuchi, Head Researcher and Developer, JEM Utilization Center, Japan Aerospace Exploration Agency (JAXA)

 CI: Daniel L. Dietrich, Researcher, Glenn Research Center, National Aeronautics and Space Administration (NASA)