Introduction

The experiment...

1. "What's a diffusion flame?"
2. "What are the effects of gravity on a flame?"
3. "What's the interest of an electric field?"
   

The equipment...

Conclusion

Links

Introduction

The ESA (European Space Agency) organizes the 4th campaign for European students, giving them an opportunity to carry out the experiment of their choice in microgravity, in July 2001. The A-300 Zero-G (photo) flies along a parabolic path, creating microgravity conditions on top of parabolas. The parabolic flight program includes 25 to 30 parabolas. Each og period lasted about 20s and was preceded and followed by an acceleration of about 2g. The residual microgravity during the period of weightlessness was of about 0.001g.

This year, we (Hedwige Tourmente, Mikhaïl Stepanov, Bruno Coriton, Franck Richecoeur) participate in this campaign, intending to carry out an experiment on the effects of an electrical field on a diffusion flame in microgravity..
This adventure is an exceptional opportunity to carry out a scientific project under unique conditions: to work like astronauts in zero-gravity.

Sponsored by Jean-Michel Most (LCD, Laboratoire de Combustion et Détonique, CNRS, Poitiers) and supported by Jacques Baillargeat ("Thanks Jacques!!!"), we have created an experimental protocol, specific to zero-gravity conditions. They accepted to help us scientifically and technically, thanks to their knowledge in parabolic flight.

The experiment we wish to make is first of all visual: a flame will be filmed in a closed box. Some experiments studying flames in microgravity have already been made, bringing to the fore the difficulties in maintain the shape of the flame and its exploitation in these conditions.Using an electrical field might solve this fundamental issue.

The experiment...

1. "What's a diffusion flame?"

A flame results from the combination of 3 elements: fuel, oxygen, heat.

lighter tilted

If the lighter is tilted, the flame revetsto its natural vertical position. Why does this phenomenon exist?
Flame shape is determined by various parameters, for instance::

• buoyancy effects;
• convection;
• gas diffusion;
• gravity...

More precisely:

The combined action of gravity and convection at the flame periphery allows the mixting of oxygen and diffused gas (fuel), consequently chemical reactions specific to combustion (a complex phenomenon involving intermediary molecules: H+, OH-, O...) can happen

So, gravity is a determining factor of the flame shape, end perhaps of its creation...

 

2. "What are the effects of gravity on a flame?"

Let's see the Navier-Stokes equation:

This equation, characterizing the fluid flow, comprises a viscosity term, a pressure term and forces applied to the fluid.
Among the forces, gravity plays an essential role.

Here are the results of an experiment, made in microgravity, studying the behaviour of a candle flame:

a candle flame in normal gravity	a candle flame in microgravity

Buoyancy effects can be compared to the Archimed thrust in air. Combined to the gravity force, they are at the origin of convection, supplying the flame in oxygen.
In microgravity, these forces don't exist anymore. The Oxygen supply is ensured by molecular diffusion, but in smaller quantity. So combustion is limited, heat emission is reduced as well. The flame has a spherical shape.

Convection has to be recreated so as to maintain the flame shape and its calorific efficiency.

3. "What's the interest of an alternative electric field?"

As we saw it previously, chemical reactions cause the formation of charged particles. Given convection movement doesn't exist in microgravity, the particles are almost static.

Could the application of an alternative electrical field recreate such movement?
Indeed, an alternative electrical field may make it possible for these charged particles to move again in microgravity conditions. For rebuilding a body force, the flame should submit to an uniform electrical field. The radicals of the flame are oriented and moved by the electrical field, inducing a flow motion suffiicient to allow a good feeding of the flame by the reactants. The flame is then deflected and oriented in the direction of the electrical field by a body force F=neE, where ne is the electrical charges contained in this volume.

The equipment...

This is a plan of the experimental device:

We use a candle flame. The candle has a fibreglasses wick

the candle

In order to film the behaviour of the flameduring the parabolic flight, the candle is placed in an airtight box. It has to permit the exhaust of burnt gases and the supply of fresh gases. So, two sluices are situated on the top of the box.

the box

Box - Right view

 

The equipment vill be fix on a support.

 

Conclusion...

We hope to have an opportunity to carry out this experiment aboard the A-300 Zero-G, and to check if our suppositions concerning the efficiency of electrical field, giving back its main features (shape and heat emission) to the flame, are funded.

Links:

• ESA web site: http://www.esa.int/export/esaCP/index.html
• About the 4th student campaign for parabolic flight: http://www.estec.esa.nl/outreach/pfc/