The second flight of microgravity experiment system using a free fall capsule from a high altitude balloon was conducted in May 2007. Using a drag free control, around 10-4G gravity conditions were obtained for 30 seconds. Results of a combustion experiment with Japanese sparker conducted inside the microgranity experimental unit were also reported

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Ignition phenomenon of polyethylene insulated wire with excess electric current was observed in normal and microgravity. Microgravity experiments were conduted by HASTIC 50m drop tower in Hokkaido and MGLAB (Microgravity Laboratory of Japan） in Gifu. The experimental parameters were electric current value, surrounding oxygen concentration and pressure.The results showed that the limit of electric current to cause ignition dramatically extended to lower current value in microgravity in comparison with normal gravity. Further, it was shown that the longer microgravity time led to lower current limit of wire ignition. Oxygen concentration and pressure had impoetant effect on ignition delay time; namely, the higher oxygen and higher pressure resulted in shorter ignition delay time under the condition applied in the present study.

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his paper deals with the numerical study of the enhancement of droplet combustion of ethanol fuel under a uniform electric field. The predicted burning rate constant is compared with experimental results and a good qualitative agreement is obtained. The increase in the rate of vaporization depends on the amount of droplet heat absorption. The vaporization rate might change with distance from the flame and a combustion enhancement will occur due to flame deformation using a uniform electric field. Flame deformation, electric field and charge density are investigated in order to reveal the mechanism of combustion enhancement. The results show that a change in the local electric field via a charge density profile causes the flame deformation and increases the rate of vaporization

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Microgravity experiments were curried out to investigate the effect of fuel vapor concentration of ambient gas on flame spread along a fuel droplet array. Ten decane droplets were simultaneously generated in astraight line and suspended at crossing points of Ⅹ-shaped suspenders. Decane vapor-air mixture was filled in a conmbustion chamber. At onset of microgravity condition, the droplet at the one end gas equivalence ratios. It was found that the flame spread speed increases with the gas equivalence ratio.The flame spread speed at 0.7 in gas equivalence ratio is almost twice as large as that at 0.1 in gas eqyivalence ratio. Size effect on the flame spread speed at 10 in nondimensional spacing is almost negligible in the range of initial droplet diameter from 0.48 to 1.02mm.

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The flame spread over a thin PMMA film is measured in microgravity condition with varying the ambient flow velocity, the diluent gas, the ambient pressure and the sample width. In order to find out the impact of these factors, we build up a simple flame scheme with a scale analysis. We set the oxygen level at 30％, and use N2 CO2, Ar, and He as a diluent gas. The ambient flow is varied from 0cm/s to 28cm/s. The result shows that the flame spread near a quiescent condition is suppressed due to mainly two heat losses; one is a radiative loss and the other is a conductive heat loss sideward. The scale analysis is very helpful to decouple these sffects and it is found that the radiative loss is dominant in N2 O2 or Ar-O2 condition, and the side loss is dominant in He-O2 condition.　Reducing ambient pressure and/or sample width increases the side loss significantly and causes extinction especially in He-O2 condition. In CO2-O2 condition, both the radiative loss and the side loss are small even with very low ambient flow, that leads robust flame near a quiescent condition in microgravity. Keyword(s)

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JAXA has already developed the multi-user facilities to conduct the microgravity experiments in KIBO, ISS Japanese Experiment Module, such as Fluid Physics Experiment Facility, Cell Biology Experiment Facility and Image Processing Unit. Those facilities are waiting for launch at KSC, NASA Space Shuttle launch site at Florida.On the other hand, to meet various demands for space environment utilization, JAXA is now planning to develop the Multi-Purpose Utilization Rack (MPUR) . Its launch target year is around 2010 and it will be used on-orbit for about 5 years. As one of the mission definition of the MPUR, the MPUR should accommodate the combustion experiment equipment

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　Preparation for Japan – Europe cooperative microgravity combustion experiment by using TEXUS sounding rocket, which would be launched in the spring of 2009, is on-going in JAXA. The TEXUS experiment is established based on cooperation between Japanese droplet combustion research working group and European CPS (Combustion Properties of Partially Premixed Spray Systems) research team. In this cooperative project, JAXA prepares experimental plan of the flight experiment and develops experimental apparatus while ESA provides flight opportunity of the TEXUS rocket. In the flight experiment, flame spread and combustion behaviors of partially pre-vaporized n-decane droplet array would be observed 4 times with different degree of pre-vaporization during 6 minutes microgravity duration. Also, combustion gas samples of the array would be collected for subsequent gas composition analysis on the ground.

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Microgravity experiment may provide breakthrough impacts on the understanding of liquid ligament breakup mechanism in turbulent atomization. In the present paper, how various difficulties and misunderstandings present in the conventional atomization theory can be overcome in the light of new concepts derived from micro-gravity experiment results is described in detail in order to demonstrate a scientific significance of microgravity experiment.

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In spray combustors, the group combustion of fuel spray is required to attain stable combustion. The group combustion follows some transient processes, such as ignition and flame spread after local mixing of fuel spray and air. The fuel spray/air mixture is termed the premixed spray. It is important to conduct systematic researches on combustion of premixed sprays to elucidate the occurrence of group combustion. Recently, there have been many microgravity experiments which are fundamental researches of some elementary processes appearing in the premixed-spray combustion. The present paper shows some results from these microgravity experiments and premixed-spray combustion experiments. Characteristics of the premixed-spray combustion are discussed based on knowledge from microgravity researches.

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