1. Numerical Model on the Effects of Gravity on Diffusion Flames
By: Crisen McKenzie

2. Introduction Motivation Project Goal Objectives Approach
Understanding how flames are effected by gravity
Spacecraft safety
Better understanding of the combustion process
Project Goal
Perform calculations to see flame shape and behavior in a microgravity environment.
Objectives
Understanding how gravity affects flame behavior
Better understanding of Flame shape
Species ratio though the combustion process
Approach
Literature review
Physical model
Non premixed flame model
Gravitational model / Microgravity model
Results

3. Literature Search Turns Glassman Paul D Ronney
Good theoretical knowledge of diffusion flames
No numerical analysis calculation
Glassman
Theoretical knowledge of diffusion flames
No numerical analysis
Paul D Ronney
Uses Roper model to calculate flame shape
Experimentation analysis done on flames in microgravity (SOFBALL)
NASA Glenn Research Center
Understanding of what research is being done for flame under microgravity condition and why it is so important
S.S.Krishnan
Analyzed Roper model for flame shape.
Performed experimental analysis of flames in microgravity

4. Non premixed diffusion flame
Combustion occurring with fuel and air mixing together through diffusion.

5. Normal Gravity
9.81 m/s2
Buoyancy - the upward force on an object or fluid when immersed in another fluid.
In diffusion flame buoyancy causes upward motion of heated less dense gases.
Convection occurs due to the mass
transfer of heated gases up towards
regions of unheated gas

6. Microgravity State of receiving minute gravitational effects
Pure diffusion and initial mass flow rate govern the momentum equation
Ignore buoyancy forces
Very slow convection

7. Convection Inside the Flame
Convection occurs as the Paraffin
gas combusts with air. The products heat
and rise in the air caused by buoyancy forces since the heated air is less dense than the cooler air around it. As the heated products rise, they start to cool due to heat transfer with the cooler air around it. As the products leave the flame cooler air takes it place. This cycle keeps the flame burning. If not then the flame will not get its
supply of oxygen and die

8. Governing Equations Conservation of mass Conservation of momentum
Axial
Radial
Species Conservation
Conservation of energy
Buoyancy term- with
greater acceleration of
gravity of less dense
gas the buoyancy
increases

9. Numerical Model Candle Flame Model Products, Air, and, Unburned gas
Porous Wick OX OX F
Candle Flame Model

10. Numerical Model Fluent 6.3 Reacting Flows non-premixed flame model
Steady State
Axisymmetric flame
Fuel – methane
NOTE: methane was used instead of paraffin wax because it was not available in fluent
MFR = 0.3 grams/sec
Fuel inlet mixture fraction of 1
Oxidizer – Air
MFR = 0.1 grams/sec
23% oxygen 77% nitrogen
Oxidizer mixture fraction of 0

11. Candle Flame Temperature
Normal Gravity
Microgravity
Effects of Buoyancy on temperature profile. Heated gases are
lifted up do to buoyancy and cooled down through convection.

12. CO2 Distribution Normal Gravity Microgravity
From the gravity side one can see that the heated products are
convecting outward away from the flame, while in microgravity the
products are more contained by the entrance of the fuel. This will result
in the choking of the flame from lack of oxygen. If oxygen is not supplied
due to convection the flame will die.

13. Exaggerated Candle Flame Model
Heated gas 1g
100g
This exaggerated model shows what the candle flame profile would look
like after being exposed to 100 times earth’s gravity. This model allows for
a clear view of how buoyancy affects candle flame profiles. One cane also see
the light region on top of the flame to show heated gas escaping to flame profile.

14. Conclusion
Flames are deeply affected by buoyancy forces. Without it a flame could die. Buoyancy helps gives the flame its needed supply of oxygen. This type of information is needed for when we have combustion in space or for fire prevention here on earth. When dealing with combustion in space it is better to use premixed flames rather than diffusive, since oxygen is readily supplied to the pre-mixed flames.

15. Improvements
Next step is to model the soot formation in the surrounding air.
Extend my study using varying mixture fractions coming from the wick
Do an unsteady case showing the production of the products and how they dissipate over time.
Also with the unsteady case show the time it takes for the flame in microgravity to go out do to choking from lack of oxygen
Find a way to model paraffin wax from solid state, to liquid, to gas in order to fully see the candle flame characteristics. Because we used a simple gas as methane this model would not be an accurate model on describing candle flames.