Rangwala thesis defense

A Variable B-Number for Modeling Laminar Flame Propagation : 

A Variable B-Number for Modeling Laminar Flame Propagation Ali S. Rangwala Department of Mechanical and Aerospace Engineering University of California, San Diego Committee: Professor Steven G. Buckley (Chair) Professor Massimo Franceschetti Professor Alex Groisman Professor Kalyanasundaram Seshadri Professor Forman A. Williams

Fire : 

Fire An interesting phenomena that has allured researchers for a long time “…there is not a law under which any part of this universe is governed which does not come into play and is touched upon in this phenomena…” – The Chemical History of a Candle by Michael Faraday (1860) An amalgamation of various fields of study such as thermodynamics, fluid mechanics, heat transfer, chemistry Properly controlled - an excellent energy source Uncontrolled - can lead to severe material damage and loss of life

Uncontrolled Fires : 

Uncontrolled Fires Improved understanding of mechanisms by which fires spread is needed This requires knowledge of material properties, environmental considerations, geometry and scale – A complicated problem!

Fire Safety in Space : 

Fire Safety in Space “Mir Prompts New Effort to Quench Threat of Fire in Space” …… For space exploration, Dr. Ross said, a new focus is Mars, where NASA would like to send astronauts early in the next century. The long trip, with no possibility of quick escapes back to Earth, would require much new thinking about fire safety. New York Times Oct 14, 1997

NASA’s Fire Research Objectives : 

NASA’s Fire Research Objectives Many cases of fires aboard space shuttles have been reported Current drive is to send space missions for extended periods (10 -20 years) Need to better understand material flammability in space Are current test methods used by NASA adequate?

NASA’s Material Flammability Test NASA-STD-6001 : 

NASA’s Material Flammability Test NASA-STD-6001

Limitations of the Current Test : 

Limitations of the Current Test Over-simplification Pass/fail screening criterion Worst-case scenario? Poor repeatability No quantifiable data that connects material flammability with the test results

OUTLINEWhat are the main objectives of this dissertation? : 

OUTLINEWhat are the main objectives of this dissertation? Develop a methodology to extract meaningful data from the current NASA test set up Experimental determination of the standoff distance A variable B-number formulation Test this methodology on a solid fuel sample (PMMA) Apply the theory and experimental data to predict flame propagation in microgravity

Flame Propagation : 

Flame Propagation

Flat Plate Flame Propagation : 

Flat Plate Flame Propagation What is a flame? Why does it exist? What causes the flame to propagate?

A Diffusion Flame : 

Fuel Molecule Oxygen Molecule Diffusion Flame Xp A Diffusion Flame

Parameters Involved : 

Parameters Involved x Pyrolysis Temperature Flame Temperature Ambient Temperature

A Brief History of the B-Number : 

A Brief History of the B-Number Formulated by D. B. Spalding in 1950 to describe the burning of a liquid droplet (D2 law) Used by Howard Emmons in 1956 to develop a model for solid fuel burning x y solid fuel burning

The Emmons Classical Solution(1956) : 

XP The Emmons Classical Solution(1956) X Y

Typical B-Number Values : 

Typical B-Number Values * A. Murty Kanury, “Introduction to Combustion Phenomena,” 1975

What Causes the Flame to Propagate Flame Length SolutionPagni and Shih (1978) : 

XP XF Excess Pyrolyzate Combusting Plume Region What Causes the Flame to Propagate Flame Length SolutionPagni and Shih (1978) Flame Heat Flux

Validation of Theory : 

Validation of Theory

Free Convective Burning of PMMA(Theory vs. Experiment) : 

t (s) Xp (cm) Pello Orloff Current work * Annamalai and Sibulkin (1979) Theory* Free Convective Burning of PMMA(Theory vs. Experiment)

Burning of PMMA in Microgravity(Forced Convection) : 

Burning of PMMA in Microgravity(Forced Convection) XF /XP Theory (Pagni) Experimental Data (Torero et al., 2002) (mm/s)

What is novel about this work : 

What is novel about this work

What makes the B-Number variable : 

What makes the B-Number variable A Closer Look at:

Slide 22: 

Y X

The Change of Q with x : 

X Y The Change of Q with x

Variation of the B-Number with x (Theory) : 

Variation of the B-Number with x (Theory) B x (cm) 0 1 0.5 5 10 15

Is there an elegant way to measure a variable B–Number? : 

Is there an elegant way to measure a variable B–Number?

Standoff Distance and the B-Number : 

XP XF Standoff Distance and the B-Number A. Rangwala, S. Buckley, and J. Torero, “An Analysis of Upward Burning Utilizing Experimentally Measured Stand-off Distances,” Paper 05F-16, Fall Technical Meeting of the Western States Section of the Combustion Institute, Stanford University, Stanford, October 17-18, 2005

Flame Location Expressed as a Function of B : 

fuel surface Flame Location Flame Location Expressed as a Function of B

Obtaining a B-Number from the Standoff Distance(Theory) : 

Obtaining a B-Number from the Standoff Distance(Theory) A B-Number

What We Have Done so Far : 

What We Have Done so Far What causes the over-prediction? Could it be due to an incorrect estimate of the B-Number? Can we measure a variable B-Number? Yes! Exploit the relation between standoff distance and B

Experimental Apparatus : 

Experimental Apparatus PMMA Digital camera 50 cm 5 cm

Stand-Off Distance Measurement (PMMA) : 

Raw image from camera Edge detection Stand-Off Distance Measurement (PMMA)

Standoff Distance as a function of streamwise direction(Experimental data) : 

Standoff Distance as a function of streamwise direction(Experimental data) (cm) x (cm) t = 10s t = 30s t = 50s t = 40s t = 60s t = 70s

Variation of the B-Number with x(Experimental) : 

Increasing Flame Height B-Number x (cm) Edge Effects Variation of the B-Number with x(Experimental)

The variation of B with timeNormalization : 

XP The variation of B with timeNormalization X/XP = 0.2 Trailing edge Leading edge

Progress of the B-Number with time : 

Time (s) B Progress of the B-Number with time XF > 25cm

Other Materials Tested : 

Other Materials Tested Polypropylene Wood (Fir) Rigid foam Polycarbonate Liquid fuels 4cm 14.7cm 8cm 18.5cm 13cm 28.9cm

Width Effects : 

Width Effects Z Y X W Xp X Z Y Excess Pyrolyzate A. Rangwala, S. Buckley and J. Torero, “Upward Flame Spread on a Vertically-Oriented Fuel Surface: The Effect of Finite Width,” Proc. Comb. Instit, (accepted, 2006)

Applying the new B-number obtained to predict flame propagation : 

Applying the new B-number obtained to predict flame propagation

Slide 39: 

B Time (s) Trailing Edge Leading edge Emmons B-Number (Adiabatic) Bcritical and Bmax for Laminar Flame Propagation

Slide 40: 

t (s) XP (cm) Pello Orloff Current work *Theory B = 0.9 B = 0.37e0.15t Free Convective Burning of PMMA(Theory vs. Experiment) * Annamalai and Sibulkin (1979)

Slide 41: 

XF /XP Bmin_leading edge YO2 = 0.233 Bmax_leading edge Theory (Pagni) (mm/s) Experimental Data (Torero et al., 2002) Burning of PMMA in Microgravity(Forced Convection)

Future Work : 

Future Work X Y Applying the theory to model flame spread in numerical solvers such as FDS* * Fire Dynamic Simulator – A numerical solver developed by National Institute of Standards and Technology to solve fire problems

Future Work (contd.) : 

Future Work (contd.) Flow Separation The boundary layer approximation breaks down at injection velocities higher than 0.01 m/s Chemical kinetics Radiation feedback Test new materials

Acknowledgements : 

Acknowledgements NASA Fire Safety Program of the Bioastronautics Initiative, Grant #NAG-32568 Dr. Gary Ruff and Dr. Fletcher Miller Undergraduate Students: Vanty Do, David Hoffman, Tyler Mayer, Annie Monkowski, Anthony Nguyen, Freddy Plascensia, Rick Sozzi, Nick Statom, Jeff Yin, and Conan Z.

Acknowledgements : 

Prof. Steven Buckley Center for Energy Research UC San Diego Prof. Jose Torero Chair, BRE Centre for Fire Safety Engineering University of Edinburgh, UK Acknowledgements

Thank You! : 

Thank You!

Questions : 

Questions

Triple flame at the leading edge : 

Triple flame at the leading edge

Validity of Emmons Assumption : 

Validity of Emmons Assumption

CONSERVATION EQUATIONSFree convection : 

CONSERVATION EQUATIONSFree convection

Classical solutionFree convection : 

Classical solutionFree convection

BOUNDARY CONDITIONS : 

Species and Energy coupled via Shvab-Zeldovich Boundary Conditions Momentum B-number BOUNDARY CONDITIONS

ANNAMALAI AND SIBULKIN : 

ANNAMALAI AND SIBULKIN