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From Atomic to Cosmic: A Panoramic View of Combustion
• What is combustion?- as a driver of technology- as a scientific discipline
• Examples of new challenges and frontiers
PrincetonPrinceton UniversityUniversityC. K. Law
Hong Kong Polytechnic University
April 13, 2007
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What is Combustion?
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The Dawn of Civilization
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Companion in Learning and Love
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Provider of Warmth and Joy
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Furnace for Industry and Pleasure
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Power for Mobility
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Agent of Destruction, and…
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…of Catastrophe
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Combustion as A Major Driver of Technology
• Energy & power
• Environment, climate & health
• Fuels
• Fire & explosion hazards
• Aerospace & defense
• New technologies
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Combustion as A Major Scientific Discipline
• Study of flows with highly exothermic, temperature-sensitive reactions
• Interdisciplinary:– Fluid mechanics– Chemical kinetics
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Reaction Kinetics at Atomic Scale• Characteristic time needed to resolve reaction
dynamics at the atomic scale:
Kinetic energy of colliding atoms
~ vibration energy of activated complex
• Use femto-second pump-probe laser pulses to study detailed reaction dynamics (Zewail, Nobel prize in chemistry, 1999)
300Kat 160 ~
motion atomicoftimesticCharacteri
1- fsTk
ho ≈=
⇒
ν
Tk o
21 Tk o
21
hν
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New Challenges & Frontiers in Combustion
• Energy sustainability & climate change
• Hydrogen economy
• Micro-engines & -burners
• Combustion synthesis of materials
• Bio-inspired interests
• Combustion in space exploration
• Cosmic combustion
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Energy Sustainability &
Climate Change
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Energy & Fuels
– Dwindling petroleum reserve (50 – 75 years)
– Geopolitical uncertainty in supply stresses global economy & harmony
– Increasing prosperity of developing, populous countries aggravates demand & competition
• Fossil fuels supply 85%of the US energy needs; petroleum: 40%
• Energy crisis = Fuel crisis
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Pollution & Climate• Pollution continues to be a
major concern; however, it is regional and mostly reversible on short time scales
• Global warming is reversible only on geological time scales, hence considerably more worrisome
Glacier National Park, Montana
1911
2000
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Effects of Global Warming• Sea level rise due to
- glacier melting- thermal expansion of ocean water
• Change in climate• Change in ecology; desertization• Spread of disease vectors
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Urgency of Global Warming• Global temperature will rise about 2-3 °C by
doubling the pre-industrial CO2 concentration in the atmosphere:
Pre-industrial 280 ppmPresent 370 ppmDoubling 560 ppm
• Doubling will occur within roughly 50-75 years if business as usual
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Climate-Energy Coupling:The Feedback Loop
Fossil fuel burning aggravates
global warming
Deteriorating climate requires
more energy expenditure to sustain
living environment
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Climate-Energy Coupling:The 50-75 Year Window
Period of petroleum depletion
20502000
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7
Bill
ions
of T
ons
of C
arbo
n Em
itted
per
Yea
r
1850
Projected
carbon path
1950 2075
Perio
d of
pet
role
umde
plet
ion
Era
of c
oal,
tar s
and,
an
d oi
l sha
le
(280 ppmv)( ΔT = 0 °C)
(370 ppmv)( ΔT = 0.8 °C)
(560 ppmv)( ΔT = 3 °C)
Historicalemissions
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Some Roles of Combustion
• Combustion characteristics of fuels that are hydrogen-enriched, carbon-neutral in production, or coal-derived
• System studies of combustor, sensors, fuels, & processes as an integral unit (e.g. design engine based on fuel)
• Apply combustion knowledge to alternate energy/fuel productions: fuel cells, nuclear, & biological
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Hydrogen Economy
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Case for Developing Hydrogen Economy
• Potential benefits of hydrogen as energy carrier:- Zero GHG emission at point of use- Derivable from widely available primary
sources (fossil, renewable, nuclear)- Rapid progress in hydrogen and fuel cell
technologies
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Relevant Combustion Issues (1/3)
• Hydrogen-based powerplants- Fuel cells (long term)- Engines & burners (short to long term)
• Problem areas in internal combustion engines- Low power density ⇒ needs supercharging and
near-stoichiometric burning- High flame temperature ⇒ high NOx emissions- High initial pressure and reactivity ⇒ pre-ignition
and knock
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Relevant Combustion Issues (2/3)
• High reactivity permits ultra-lean operations ⇒Enhanced engine efficiency - Reduced NOx emission- Requires novel engine and combustion
process designs
• No soot formation and emission- Environmentally beneficial- Impedes radiation transfer in stationary
powerplants
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Relevant Combustion Issues (3/3)
• Explosion hazards- Highly explosive- Nonluminous flame- The Hindenburg syndrome
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Micro-Engines & -Burners
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Technological Interests• Micro-scale thrust for fine locomotion
and steering of satellites
• High energy density (100×) mobile power sources to replace conventional battery– Inexpensive– Nearly infinite shelf life– More constant voltage, no memory
effect, instant recharge– Environmentally superior to
disposable batteries– Applications: foot soldiers; portable
electronics (laptops, cell phones, …)
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Technological Challenges
• Large surface-to-volume ratio• Increased heat loss• Flame quenching• Laminar flows: hard to mix• Increased friction• Fabrication
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Possible Remedies
• Reduce heat loss at wall
• Preheat mixture
• Implement surface catalytic reaction
• Reduce moving parts
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Micro-Engines:Miniaturized version of conventional
engines (Berkeley)
12.5 mm
3.6 mm9.5 mm
12.5 mm
3.6 mm
12.5 mm
3.6 mm9.5 mm
Abo
ut 1
mm
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• “Swiss roll” heat recirculating burner - minimizes heat losses
• Toroidal 3-D geometry - further reduces losses - minimizes external temperature on all surfaces
Micro-Engines:Swiss Roll Design (USC)
One-dimensional counterflowcombustor / heat exchanger
Two-dimensional “Swiss-roll” burner
Products
Reactants
Combustionvolume
1600 1200 400 300 K500
1400 600 5007001600
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Combustion Synthesis of
Materials
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Gaseous Flame Synthesis of Nano-Particle Materials
• High production rate & purity• Nano-sized particles; increased catalyticity• Metal & metal oxide particles: Al, SiO2, TiO2, Al2O3,
YBa2Cu3O7-x
– Lower sintering temperature– Higher theoretical density– Higher fracture toughness and ductility
• Carbonaceous particles: C, fullerenes, carbon nano-tubes Hi-Mag
Low-Mag
Hi-Mag
Low-Mag
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Solid Flame Synthesis: Process
Undesirablelaminated product
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• Extreme high temperature process (~3000 to 4000 ºC)
• No heating source• Rapid process• Self-purifying• Preform• Vast variety of products
Solid Flame Synthesis: Advantages
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Solid Flame Synthesis: Applications• Carbides: Abrassives, cutting tools, ceramic
reinforcements
• Borides: Abrasives, cutting tools, cathodes• Silicides: Heating elements, electrical connectors• Aluminides & Titanites: Aerospace materials, shape
memory alloys• Nitrides: Ceramic engine parts, ball bearings, nuclear
safety shields• Hydrides: Hydrogen storage, catalytic materials• Oxides: High-temperature superconductors, gas sensors
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Bio-Inspired Combustion
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Some Practical Interests• Obvious interests
- Bio-fuels from biomass- Health effects of inhaling
combustion-generated aerosols
• Bacteria in the service of mankind- Waste scavenging- Fuels production- Microbial fuel cells
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Origin of Life
• Previous theory: Formation of amino acids through lightning in atmosphere containing methane, ammonia, hydrogen, and water
• New hypothesis: Formation of organic compounds in geothermal vents on ocean floor
• Role of combustion: Biological reactions in turbulent, buoyant jets
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Relevance in Molecular & Cellular Biology
• Diffusive transport and reaction of ions and enzymes• Example: pattern formation in aggregating slime molds,
developing oocytes, cardiac muscles, spreading depression in chicken retina, and over flame surfaces!
c
slime mold flame surface
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Movie on Spiral Development over Surface of Expanding Flame
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Combustion in Space
Exploration
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Candle in Microgravity
• Microgravity produces a round, cooler candle flame with no soot
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Microgravity CombustionBuoyancy-affected phenomena suitable for microgravity investigation:
• Distortion from symmetry (e.g. spherical and cylindrical flames)
• Large flame dimensions• Slow burning flames (e.g. near-limit flames,
smoldering)• High pressure flames• Suspensions• Fire safety in space
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NASA’s 3M Mission: Mars Exploration & Colonization
• 3M: Man, Moon & Mars
• Fire hazard and detection
• CO2-breathing propulsion
• In-situ heat/power generation on Mars:
Thermite-class reactions
Fe2O3 + 2Al → Al2O3 + 2Fe + heat
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Cosmic Combustion:
Supernovae
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Phenomenon
• Exploding stars of few seconds duration; light emission ~ entire galaxy
• Fundamental phenomenon:- Accretion of white dwarf in binary star system to Chandrasekhar mass (~ 1.4 solar mass) - Violent explosion after ~102
years of thermonuclear “cooking”
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Possible Mechanism• Theory has to fit light curve:
composition, temperature & velocity
• Combustion characteristics:- Buoyantly unstable (106g)
- Highly turbulent (Re~1014)
- Highly temperature sensitive (T12 at 1010 K) and complex nuclear reactions
- Transition from subsonic to supersonic combustion
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Summary• Combustion intimately affects almost every aspect of
our daily life• Combustion is at the center of studies on reacting flows
– physical, chemical, biological; traditional & new frontiers
• Combustion is:- Rich in phenomena- Technologically relevant - Intellectually stimulating
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Thanks for Coming!
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