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ME776

(Professor Steven Shy)

Office: E2-413 Tel: (03)426-7327 Fax: (03)425-4501 E-mail: sshy@ncu.edu.tw

Combustion

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Course Content Chapter 1 Introduction to Combustion

Importance; Applications; Contribution; What is the Combustion Process? Combustion Books & Journals & Proceedings

1.1 Preliminary remarks

1.2 Some Practical Problems in Combustion

1.3 Scientific Disciplines of Combustion

1.4 Classification of Fundamental Combustion Phenomena

1.5 What is the Combustion Process?

1.6 Books, Journals & Proceedings for Combustion

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Chapter 1 Introduction to Combustion ME776 Section 1 Preliminary Remarks

1.1.1 Combustion

Interrelated processes of Fluid Mechanics, Heat & Mass Transfer, Chemical Kinetics, Thermodynamics, and Turbulence.

Understanding of the fundamental concepts of these coupled processes will provide engineers and scientists with the technical background and training required to solve various combustion problems.

"Everything that happens is due to the flow and transformation of energy ... Control fire and you control everything. The discovery of fire ... lifted man from the level of the beast and gave him dominion over the earth."

Morton Mott-Smith in his book of introduction to Heat and its Workings. D. Appleton & Co. (1933)

Many burning issues in Combustion remain to be solved; there has never been a lack of demand for well-trained, dedicated combustion engineers and scientists.

1.1.2 Some Comments about the Course

* This is a course in fundamental principles

* Not in nuts-and-bolts design

* Throughout the course, emphasis will be on simple physical reasoning backed by simple, approximate calculations (1-dimensional, ideal gas, constant thermodynamic properties, etc). Memorization of empirical results (When A goes up, B decreases, etc.) won't work here. If the reasoning aren't clear------ASK!

* In some sense, this course is really just a vehicle (Basic Concepts) to study engineering systems in the future in which the trade off/judgments are required, taking into account not just our back-of-the-envelope type analyses, but likely direction and magnitude of the errors which result.

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Ch 1 Introduction to Combustion ME776 Sec. 2 Some Practical Problems in Combustion

Devices

Fuels Pollution and Health Safety Defense and Space 1.2.1 Energy and Combustion Devices

USA Energy Usage at 2004 (2004)

Source: Annual Energy Review (2004) p. 280; US DOE

Assignment CH1-1: Find 2014 (or 2013) information to update

etc. etc.

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14%: Nuclear, Solar, Wind, Hydro-electric, Geo. thermal, etc.

85%: Chemical energy derived through combustion of fossil fuels (40% Petroleum, 23% Natural Gas, 22% Coal)

This trend will continue in the foreseeable future. ( convenience, high energy density, and the economics)

1. Domestic Heating

2. Firing of industrial furnaces

3. Operation of automotive engines/gas turbines Design and operation of energy devices

Assignment CH1-2: Find 2014 (or 2013) information to update

Heat and Power

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Taiwan Electric Power Generation [1991 (2006)]

Assignment CH1-3: Find 2014 (or 2013) information to update

! Auto Need more efficient and clean-burning internal combustion engines

e.g. Diesel Engine " Cycle Efficiency < Gasoline Engine @ same compression ratio (C.R.)

" But operates at a higher C.R. (more efficiency overall)

" Not requires highly-refined fuels with narrow specifications " Can use nonconventional or low-grade fuels, e.g. alcohol " Disadvantages: noisy & Heavy soot emitter

e.g. New concept in engine development

ultralean Stratified Charge Combustion :

: Rich

Overall fuel lean mixture easy to ignite

Basic Idea Lean Mixtures Combustion efficiency simultaneously Pollutants formation Hard to ignite

High pressure direct injection gasoline engine

Fire Power 58.1

(73.2%)

18,383 MW (36,122 MW)

Nuclear Electric Power

28 (14.2%)

Hydro Power

13.9 (12.5%)

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1.2.2 Combustion needs fuel e.g. diesel oil gasoline engine

Narrow compositional specifications of gases used in domestic gas ranges Energy Crisis Fuel Crisis Shortage & reliability of petroleum supply

! Emphasis on Coal Direct utilization Coal-derived fuels

Fluid bed combustion Higher boiling pt. Wider boiling pt. ranges Higher contents of aromatics and

nitrogen containing compounds more soot & NO2 Advantages: Direct contact with air max. burning rates SO2 (limestones) NO2 (; fluidization rate)

Coal-water slurries Finely crushed coal particles 40 ~ 70 m

mixed in water Sprayed directly combustion chamber of industrial furnaces

Advantages: # less energy expansive than the chemical processes of coal liquefaction.

$ easy to transport in pipes % min. hardware modification of oil-fired combustor 70% coal content of slurries have been successfully burned

! Alternate & Hybrid Fuels e.g. Methanol & Ethanol & Ethanol with oil

Natural gas & coal biomass Ethanol: smaller heats of combustion ( extra oxygen atom in the mlc.)

Blends of 10% ethanol and 90% gasoline have been successfully burned in IC engines

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without any engine modification. However, corrosions in engines may be a problem. 1.2.3 Pollution and Health

Major Pollutants from Combustion Soot SO x NO x UHC CO Coal-derived fuels Burning coal N 2 in atm (unburned (carbon Diesel engine Sulfuric acid N in fuel hydrocarbon) monoxide)

Carcinogenic Water in atm Thermal NO x (organic liquid Acid Rain ---High T.

combustion products (dissociate inert N 2 in air) condense on the aquatic life Fuel-bound NO x ---less T. surface of the soil erosion sensitive major contributor soot particles) (burning coal or coal-derived oils) ; NOx reacts w / UHC & ozone by sunlight smog (smoke + fog) Detrimental to the respiratory sys. Indoor Pollution (CO, NOx, UHC) Domestic heating devices gas ranges furnaces Kerosene heaters Incineration (chemical hazardous wastes) The uncertainty of the toxicity of the combustion intermediates and products e.g. Halogenated Compounds() incineration resistant

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1.2.4 Safety

Fires Explosions Materials Structural & wild land Mine galleries Inhalation of smoke & life & financial loss Grain elevators toxic products Research improving Liquefied natural gases Choice of structure & fire detection tech. spills decoration Fire control Understanding the fire Nuclear reactor accidents propagation in confined H2 gas spaces e.g. buildings & a/c cabins Containment structure Radioactive gases

1.2.5 Defense and Space

! High-energy propellants.

! The suppression of combustion instability within jets and rockets.

! Signature and detection vulnerability from exhausts.

! Measures at preventing explosion of fuel tank when being penetrated by Projectiles.

! The development of chemical lasers as an intense power source.

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Chapter 1 Introduction to Combustion ME776 Section 3 Scientific Disciplines of Combustion

Combustion Chemically-reacting flows w/ rapid, highly-exothermic reactions

Chemically Reacting Flows

Thermodynamics Fluid Mechanics Chemical Kinetics

Heat and Mass Transfer Material Structure and Behaviour

Turbulence

1.3.1 Thermodynamics Initial states Final states

Reactants Products (Equilibrium)

Heat for utilization Allows us to do the bookkeeping on how much chemical

energy can be converted to thermal energy in a combustion process.

Determines the properties of the products ( T ; composition ) when equilibrium is reached.

! Mature science & its laws have been firmly established.

1.3.2 Chemical Kinetics ! What path and how long of such a process.

! Conclusions based on equilibrium calculations could be quite erroneous. e.g. A particular reaction needs 106 years for completion cycle

performance of an auto engine. e.g. Calculation amount of NOx

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Finite reaction rates >> Thermodynamic equilibrium

! All combustion processes have some finite, characteristic times defining our interest in the phenomena.

! Chemical Kinetics is needed to prescribe the paths and rates. ! Thermodynamics can be considered to be a special area of chemical

kinetics in that with infinite time a reaction will eventually achieve equilibrium.

! A complex subject : a myriad of chemical species exist, each of which has the potential of interacting w/ the rest.

! Some confidence on fuel oxidation system only for hydrogen, CO, and the light alkanes.

1.3.3 Fluid Mechanics Chemical reactions occurring in a flowing medium.

Combustion: Knowledge of F.M. is essential for a successful understanding of many combustion phenomena.

Highly-localized and exothermic nature of chemical reactions significant temperature, and therefore density variations in a flow, implying that fluid incompressibility can be a rather poor assumption.

7.4 1.3.4 Transport Phenomena

SL ~ 40 cm/s ; D ~ 0.2 cm2/s ~ 0.2 / 40 = 510-3 cm = 0.05 mm

! Transfer of energy & mass from high to low; through the molecular process of diffusion.

! For heat transfer, radiation is also important. ! Diffusive transport is crucial in the sustenance of many types of flames in that it

is only through these processes fresh reactants can be continuously supplied to the flame while the heat generated there is also being continuously used to heat up and thereby cause ignition of these fresh mixture.

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Ch 1 Introduction to Combustion ME776 Sec. 4 Classifications of Fundamental Combustion Phenomena

1.4.1 Premixed and Nonpremixed Combustion ! Most important classification of combustion phenomena.

! Reactions generally involve two or more reactants. Frequently a fuel & an oxidizer ( molecular mixedness ) Essential mixed at mlc level Elements

Reaction implies that at least one of the reactants should be in either the gaseous or the liquid phase so that its mlc. can spread around those of the other reactant.

! Premixed system : A + B 2B ( A : fuel + oxidizer ; B : heat and/or radicals )

! Nonpremixed system: Diffusional combustion reactants initially separated, then being brought together, via molecular process of diffusion and the bulk convective motion, to a common region where mixing and subsequently reaction take place.

! Diffusion is still essential in transporting the premixture to, and the thermal energy and combustion products away from, the flame region where reactions occur.

! Bunsen Flames As the fuel gas issues from the orifice, air is entrained through

the adjustable air-intake port and is then mixed with the fuel gas as they travel along the burner tube.

The subsequent reactions between fuel and oxygen in this premixture forms a premixed flame.

If this premixture is fuel rich (has a high concentration of fuel than can be consumed by all the oxygen in the entrained air), after passing through the premixed flame, the excess fuel (or rather the fuel-related intermediate species, can further react with the oxygen in the ambient air.

Reactants initially separated need to be transported to a

common region where mixing and reactions occur Diffusion flame.

The outwardly-directed excess fuel reacts almost completely w/ the inwardly-directed oxygen.

! It is obvious that one would not find many examples of premixtures in nature, because they would have already reacted even if they are only slightly reactive.

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! Nonpremixed system abound.

Indeed w/ oxygen in the air as the oxidizer, then all the materials which would burn in air are fuels. e.g. fossil deposits: petroleum & coal cellulosic material: paper & cloth metallic substances: aluminum & magnesium

1.4.2 Laminar and Turbulent Combustion ! Distinct streamlines exist for the bulk, convective motion Laminar ! Streamlines do not exist such that at any point in space the flow quantities

randomly fluctuate in time Turbulent ! Turbulent facilitates the coarse mixing process, and therefore has a

particularly strong influence on nonpremixed systems in which reactant mixing is essential.

! The final mixing before reactions can take place, however, must still occur through the molecular diffusion process whether the flow is laminar or turbulent.

1.4.3 Subsonic and Supersonic Combustion ! The velocity of flow

Subsonic flow combustion: The molecular collision processes of diffusion are predominant while reactions also have more time to complete.

Most frequently in our daily lives, such as the candle flame and the pilot flame.

Supersonic flow combustion: The high flow velocity usually renders convective transport to dominate over diffusive transport.

Reactions also have less time to proceed.

Wave motions involving shocks and rarefactions abound.

Explosions and supersonic flights.

1.4.4 Homogeneous and Heterogeneous Combustion ! Most confusing terminology in combustion literature ! Homogeneous: If both reactants initially exist in the same fluid phase, either

gas or liquid (e.g. Bunsen flame). Heterogeneous: If two reactants initially exist in different phases, whether gas

/liquid, liquid/solid, or solid/liquid, then the combustion is heterogeneous (e.g. coal particle burning in air).

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! Chemists define a heterogeneous reaction as one in which the reactants actually exist in different phases at the location where reaction takes place.

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! Traditional combustion definition : Both modes of burning are called heterogeneous combustion.

! To designate the uniformity of the mixture. ! Homogeneous no temperature or concentration gradients in the mixture. ! Heterogeneous a gaseous mixture containing fuel vapor pockets produced,

say, through vaporization of fuel droplets.

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Chapter 1 Introduction to Combustion ME776 Section 5 What is The Combustion Process?

1.5.1 Chemical Reaction e.g. Methane burning in air

(1) The global reaction of methane and oxygen CH4 + 2O2 CO2 + 2H2O (2) The elementary reaction mechanism

( by T. P. Coffee,1984 ) Reaction Ab B C 1. OH + H2 H2O + H 1.17E9 1.3 1825 2. H + O2 OH + O 1.42E14 0.0 8250 3. O + H2 OH + H 1.80E10 1.0 4480 4. H + O2 +M H2O +M 1.03E18 - 0.72 0 5. H + HO2 OH + OH 1.40E14 0.0 540 6. H + HO2 O + H2O 1.00E13 0.0 540 7. H + HO2 H2 + O2 1.25E13 0.0 0 8. OH + HO2 H2O + O2 7.50E12 0.0 0 9. O + HO2 OH + O2 1.40E13 0.0 540 10. O + HO2 OH + O2 1.25E12 0.0 0 11. H + H + H2 H2 + H2 9.20E16 - 0.6 0 12. H + H + N2 H2 + N2 1.00E18 - 1.0 0 13. H + H + O2 H2 + N2 1.00E18 - 1.0 0 14. H + H + HO2 H2 + O2 6.00E19 - 1.25 0 15. H + H + CO H2 + CO 1.00E18 - 1.0 0 16. H + H + CO2 H2 + CO2 5.49E20 - 2.0 0 17. H + H + CH4 H2 + CH4 5.49E20 - 2.0 0 18. H + OH + M H2O +M 1.60E22 - 2.0 0 19. H + O + M OH +M 6.20E16 - 0.6 0 20. OH + OH O + H2O 5.75E12 0.0 390 21. OH + CO CO2 + H 1.50E7 1.3 -385 22. O + CO + M CO2 + M 5.40E15 0.0 2300 23. H + CO + M CHO + M 5.00E14 0.0 755 24. CH4 + O2 CH3 + OH 4.07E14 0.0 7040 25. CH4 + H CH3 + H2 7.24E14 0.0 7590 26. CH4 + OH CH3 + H2O 1.55E6 2.13 1230 27. CH4 + M CH3 + H + M 4.68E17 0.0 46910 28. CH3 + O CH2O + H 6.02E13 0.0 0 29. CH2O + O CHO + OH 1.82E13 0.0 1550 30. CH2O + H CHO + H2 3.31E14 0.0 5290 31. CH2O + OH CHO + H2O 7.58E12E 0.0 72 32. CHO + O2 CO + H2O 3.00E12 0.0 0 33. CHO + H CO + H2 4.00E13 0.0 0

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34. CHO + OH CO + H2O 5.00E12 0.0 0 35. CHO + O CO + OH 1.00E13 0.0 0 36. CH2O + CH3 CHO + CH4 2.23E13 0.0 2590 37. CH3 + OH CH2O + H2 3.98E12 0.0 0 38. CH3 + H2O CH4 + O2 1.02E12 0.0 200 39. CO + H2O CO2 + OH 1.50E14 0.0 11900 40. CH3 + CH3 C2 H6 4.56E37 - 7.65 4250 41. C2 H6 + O C2 H5 + OH 2.51E13 0.0 3200 42. C2 H6 ++ H C2 H5 + H2 5.00E2 3.5 2620 43. C2 H6 + OH C2 H5 + H2O 6.63E13 0.0 675 44. C2 H5 + H C2 H6 7.23E13 0.0 0 45. C2 H5 + H CH3 + CH3 3.73E13 0.0 0 46. C2 H5 C2 H4 + H 2.29E11 0.0 19120 47. C2 H5 + O2 C2 H4 + H2O 1.53E12 0.0 2446 48. C2 H4 + O CH2 + CH2O 2.53E13 0.0 2516 49. C2 H4 + OH CH2O + CH3 5.00E13 0.0 3020 50. C2 H4 + O C2 H3 + OH 2.53E13 0.0 2516 51. C2 H4 + O2 C2 H3 + HO2 1.33E15 0.0 27680 52. C2 H4 + H C2 H3 + H2 2.00E15 0.0 10000 53. C2 H4 + OH C2 H3 + H2O 4.40E14 0.0 3270 54. C2 H3 + M C2 H2 + H + M 3.01E16 0.0 20380 55. C2 H3 + O2 C2 H2 + HO2 1.57E13 0.0 5030 56. C2 H3 + H C2 H2 + H2 7.53E13 0.0 0 57. C2 H3 + OH C2 H 2 + H2O 1.00E13 0.0 0 58. C2 H2 + OH CH3 + CO 5.48E13 0.0 6890 59. CH3 + H CH 2 + H2 2.00E11 0.7 -1500 60. CH3 + OH CH 2 + H2O 6.00E10 0.7 1010 61. CH2 + O2 CHO + OH 1.00E14 0.0 1860 62. CH2 + O2 CH2O + O 1.00E14 0.0 1860 63. CH2 + O2 CO 2 + H2 1.00E14 0.0 1860 a [M] = total concentration; [M] = [H2] + 0.74[CO] + 1.47[CO2] + 0.35[O2] +

6.5[H2O] + 0.44[N2] ; [M] = [H2] + [CO] + [CO2] + [O2] +5.0[H2O] + [N2] b A is in units of cm3/mole s or cm6/mole2 s, k = ATB exp(-C/T) c 1.17E9 = 1.17 109

Westbrook and Dryer (1984) 150 forward reactions Frenklach and Bornside (1984)

Recently proposed chemical reaction mechanisms for soot formation consist of as many as 2000 reactions.

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Ch 1 Introduction to Combustion ME776 Sec. 6 Books, Journals & Proceedings for Combustion

BOOKS

1. S. S. Penner, Chemistry Problems in Jet Propulsion, Pergamon, 1957.

2. B. Lewis and G. von Elbe, Combustion, Flames and Explosions of Gases, Academic Press, 1961.

3. C. P. Fenimore, Chemistry in Premixed Flames, Pergamon, 1964.

4. R. M. Fristrom and A. A. Westenberg, Flame Structure, McGraw-Hill, 1965.

5. A. G. Gaydon and H. G. Wolfhard, Flames, Chapman and Hall, 1970.

6. A. M. Kanury, Introduction to Combustion Phenomena, Gordon and Breach, 1975.

7. I. Glassman, Combustion, Academic Press, London, 1977; Irvin Glassman & Richard A. Yetter, Combustion (fourth edition), Academic Press, London, 2007.

8. D. B. Spalding, Combustion and Mass Transfer, Pergamon, 1979.

9. J. D. Buckmaster and G. S. S. Ludford, Theory of Laminar Flame, Cambridge University Press, 1982.

10. T. Y. Toony, Combustion Dynamics, McGraw-Hill, 1983.

11. R. A. Strehlow, Combustion Fundamentals, McGraw-Hill, 1984.

12. F. A. Wiliams, Combustion Theory, 2nd ed., Addison-Wesley Publishing Co., Redwood City, 1985.

13. N. Chigier, Energy, Combustion and Environment, McGraw-Hill, 1981.

14. A. W. Leferbore, Gas Turbine Combustion, McGraw-Hill, 1983.

15. Ya. B. Eeldovich, et. Al., The mathematical Theory of Combustion and Explosion, translated by D. H. McNeil, Consultants Bureau, 1985.

16. K. K. Kuo, Principles of Combustion, John Wiley and Sons, 1986.

17. D. E. Rosner, Transport Processes in Chemically Reacting Flow Systems, Butterworth, 1986.

18. E. S. Oran and J. P. Boris, Numerical Simulation of Reactive Flow, Elsevier, 1987.

19. D. Merrick, Coal Combustion and Conversion Technology, Elsevier, 1984.

20. K. Iinuma, T. Asanuma, T. Ohsawa and J. Doi, Laser Diagnostics and Modeling of Combustion, Springer-Verlag, 1987.

21. A. C. Eckbreth, Laser Diagnostics for Combustion Temperature and Species, Abacus, 1988.

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22. C. K. Law, Combustion Physics, Cambridge University Press, New York, 2006 JOURNALS and PROCEEDINGS (for COMBUSTION)

1. Proceedings of The Combustion Institute

2. Combustion and Flame

3. Combustion Science and Technology

4. Progress in Energy and Combustion Science

5. Combustion, Explosion, and Shock Waves

6. Journal of Chemical Physics

7. Journal of Fluid Mechanics

8. Acta Astronautica

9. AIAA Journal

10. ASME Transaction: Journal of Heat Transfer and Journal of Engineering for Power

11. International Journal of Heat and Mass Transfer

12. Physics of Fluids