1. Methanol Droplet Extinction in Oxygen/Carbon-dioxide/Nitrogen
Mixtures in Microgravity: Results from the
International Space Station Experiments
Vedha Nayagam1, Daniel L. Dietrich2, Paul Ferkul1, Michael C. Hicks2
and
Forman A. Williams3
1National Center for Space Exploration Research
2NASA Glenn Research Center
3University of California, San Diego
Eastern States Section of the Combustion Institute, Fall Technical Meeting
October 9-12, 2011, University of Connecticut, Storrs, CT

2. Flame Extinguishment Experiments (FLEX)
BACKGROUND
FLEX experiments are microgravity droplet combustion experiments, currently underway in the International Space Station (ISS).
Objectives of these experiments are to study fire safety aspects of microgravity . Alcohol (methanol) and alkane (n-heptane) fuel droplets are burned in diluent substituted environments.
Carbon dioxide and helium are used to replace nitrogen.
The Limiting Oxygen Index (LOI) is determined experimentally for different diluents at selected pressures.
Preliminary results for methanol droplets burning in carbon dioxide substituted environments are presented along with simplified theories to explain the observed behavior.

3. FLAME EXTINGUISHMENT EXPERIMENT (FLEX)
Investigator Team
PI: Prof. Forman A. Williams, UCSD
Co-Is: Prof. Mun Y. Choi, UConn
Prof. Frederick L. Dryer, Princeton
Mr. Michael C. Hicks, NASA GRC
Dr. Vedha Nayagam, NCSER/CWRU
Prof. Benjamin D. Shaw, UC Davis
PS: Dr. Daniel L. Dietrich, NASA GRC
Dr. Paul V. Ferkul, NCSER/GRC
Ms. Victoria M. Bryg, NCSER/GRC
PM: Mr. J. Mark Hickman, NASA GRC

4. FLEX Experiment Operations
International Space Station
TDRS
Satellite
POIC, NASA/MSFC
Combustion Integrated Rack
(Destiny Module of the ISS)
Multi-User Droplet Combustion
Apparatus (MDCA)
TSC, NASA/GRC
Cleveland

5. Experiment Videos FLEX-TEST-161:
Methanol droplet burning in 16%O2 - 59%N2 - 25%CO2 at 1 atm pressure: d0=2.8 mm
Back-lit droplet imaging camera view
Color camera view
Primary Diagnostics: Droplet-view, color-camera flame view, UV-camera flame view
Setup: Partial-pressure mixing on-board from compressed gas bottles (95 liters, free volume)
Operations: Remote operations with crew assistance for setup an trouble shooting. Data stored
digitally and down liked

6. Data Reduction FLEX-TEST-161:
Methanol droplet burning in 16%O2 - 59%N2 - 25%CO2 at 1 atm pressure: d0=2.8 mm
igniter retraction
UV camera
K=d(d2)/dt
color camera df
flame extinction
Backlit view camera images are used to obtain burning rate constant K, and the color and UV-camera (310 nm) images are used to obtain flame position history. (Cameras run at 30 frames per second)

7. Burning Rate Constants
Burning rate constant K increases (almost linearly) with ambient oxygen concentration, and slightly decreases with increasing carbon dioxide concentration

8. Burning Rate Constants
Deviations from quasi-steady values
At low oxygen concentrations burning rate deviates substantially from quasi-steady predictions

9. Flame Stand-off Ratio d df
*V. Nayagam, Combustion and Flame, 2010

10. Droplet Extinction Diameter
Droplet extinction diameter as a function of initial droplet diameter

11. Droplet Extinction Diameter
Zhang and Williams Theory of Methanol Droplet Extinction Induced by Water Evaporation:
Quasi-steady, spherically symmetric combustion with water absorption
Flame-sheet approximation and unity gas-phase Lewis number
Initially, water produced in the flame diffuses back to the droplet surface and gets absorbed
Water concentration gradually builds up and eventually the water begins to vaporize
Diluted mixture leads to a drop in flame temperature
When the adiabatic flame temperature falls below a critical value flame extinguishes
This theory leads to a pair of non-linear ODEs for liquid temperature and water concentration as a function of droplet diameter. These ODEs are integrated numerically for the specific atmospheres corresponding to the experimental conditions.
*B.L. Zhang, J.M. Card and F.A. Williams, Combustion and Flame, 1996

12. Zhang and Williams’ Theory of Droplet Extinction
Text=1800K
dl(m)
Tf(K)
de(mm)=1.4mm
Tl (K)
dl(m)
d0(mm)=3mm
evaporation
water flux fraction
water absorbed
dl(m)
*B.L. Zhang, J.M. Card and F.A. Williams, Combustion and Flame, 1996

13. Droplet Extinction Diameters

14. Concluding Remarks
Experimental results for methanol droplets burning in carbon dioxide diluted
environments in microgravity are presented
Simplified theoretical models explain many aspects of the observations reasonably well
Methanol droplet extinction is controlled by water absorption for high oxygen concentrations ( > 18%) below a critical initial droplet diameter.
Radiative extinction occurs at low ambient oxygen levels above a critical initial droplet diameter
Transient, ignition driven combustion may occur at low oxygen concentrations (~13-14%)
The limiting oxygen index (LOI) for methanol at atmospheric pressure lies close
to ~13% oxygen

15. QUESTIONS?

16. Concluding Remarks
Test FLEX161: t= 8s
UV-image
Color camera image