Combustion - 國立中央大學機械工程學系

Course ContentChapter 1 Introduction to CombustionImportance; Applications; Contribution; What is theCombustion Process? Combustion Books & Journals &Proceedings1.1 Preliminary remarks1.2 Some Practical Problems in Combustion1.3 Scientific Disciplines of Combustion1.4 Classification of Fundamental Combustion Phenomena1.5 What is the Combustion Process?1.6 Books, Journals & Proceedings for CombustionChapter 2 Internal Combustion Engine and ItsAlternativesClassification; Premixed Charge Engine; Alternatives to ICEngines;2.1 Internal Combustion Engine2.2 Alternatives to IC EnginesChapter 3 Chemical ThermodynamicsEquilibrium; Chemical Reaction; Heat; Adiabatic FlameTemperature;3.1 Equilibrium3.2 Thermodynamics Laws2

3.3 Chemical Thermodynamics and Flame TemperatureChapter 4 Fuels and Stoichiometry4.1 Fuels4.2 Stoichiometry4.3 Stoichiometry, Equivalence Ratio, and Adiabatic FlameTemperatureChapter 55.1 Motivation5.2 The energy equationThermodynamics Calculations ofCombustion Processes5.3 The second law as applied to a reacting system5.4 Atom conservation5.5 Application of energy, equilibrium, and atom conservation5.6 Condensed phase5.7 Reversible adiabatic compression/expansionChapter 66.1 Types of flames6.2 Chemical reactionsChemical Reactions & Combustion6.3 Application of chemical reaction to combustion processesMore …3

Chapter 1 Introduction to Combustion ME776Section 1Preliminary Remarks1.1.1 CombustionInterrelated processes of Fluid Mechanics, Heat & Mass Transfer, ChemicalKinetics, Thermodynamics, and Turbulence.Understanding of the fundamental concepts of these coupled processes willprovide engineers and scientists with the technical background and training requiredto 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 thelevel 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 alack 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 bysimple, approximate calculations (1-dimensional, ideal gas, constant thermodynamicproperties, 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 studyengineering systems in the future in which the trade off/judgments are required, takinginto account not just our back-of-the-envelope type analyses, but likely direction andmagnitude of the errors which result.4

Ch 1 Introduction to Combustion ME776Sec. 2 Some Practical Problems in Combustion火 文 明 電 、 能 源 etc. etc. 污 染破 壞毀 滅生存5 大 類1.2.1 Energy and Combustion DevicesDevicesFuelsPollution and HealthSafetyDefense and Space• USA Energy Usage at 2004 ( 美 國 能 源 使 用 方 式 ,2004)Source: Annual Energy Review (2004) p. 280; US DOE5

1.2.2 Combustion needs fuele.g. diesel oil gasoline engine• Emphasis on CoalNarrow compositional specifications of gases used in domesticgas rangesEnergy Crisis ≡ Fuel CrisisShortage & reliability of petroleum supplyDirect utilizationFluid bed combustionCoal-derived fuels· Higher boiling pt.· Wider boiling pt. ranges· Higher contents of aromatics andnitrogen containing compounds· more soot & NO 2Advantages:· Direct contact with air· max. burning rates· SO 2 (limestones)· NO 2 (↓; fluidization rate)Coal-water slurries• Finely crushed coal particles40 ~ 70 μm• mixed in water• Sprayed directly → combustion chamber of industrial furnaces• Advantages: less energy expansive than the chemical processes ofcoal liquefaction. easy to transport in pipes min. hardware modification of oil-fired combustor• 70% coal content of slurries have been successfully burned• Alternate & Hybrid Fuelse.g. Methanol & Ethanol & Ethanol with oilNatural 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 engines8

without any engine modification. However, corrosions in engines may be a problem.1.2.3 Pollution and HealthMajor Pollutants from CombustionSoot SO xNO xUHC COCoal-derived fuels Burning coal N 2in atm (unburned (carbonDiesel engine Sulfuric acid N in fuel hydrocarbon) monoxide)Carcinogenic Water in atm Thermal NO x(organic liquid Acid Rain ---High T.combustion products(Qdissociate inert N 2in air)condense on the aquatic life Fuel-bound NO x---less T.surface of the soil erosion sensitive major contributorsoot particles)(burning coal or coal-derived oils)致 癌 物 質 ; 成 癌 質NO x reacts w / UHC & ozoneby sunlight smog (smoke + fog)Detrimental to the respiratory sys.Indoor Pollution (CO, NO x , UHC)• Domestic heating devicesgas rangesfurnacesKerosene heatersIncineration (chemical hazardouswastes)The uncertainty of the toxicity of thecombustion intermediates and productse.g. Halogenated Compounds( 鹵 素 )( 氟 、 氯 、 溴 、 碘 )incineration resistant9

1.2.4 SafetyFires 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 accidentspropagation in confined H 2 gasspaces e.g. buildings &a/c cabinsContainmentstructureRadioactivegases1.2.5 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 byProjectiles.• The development of chemical lasers as an intense power source.10

Chapter 1 Introduction to CombustionSection 3Scientific Disciplines of CombustionME776Combustion ⎯ Chemically-reacting flows w/ rapid, highly-exothermic reactionsChemically Reacting FlowsThermodynamics Fluid MechanicsChemical KineticsHeat and Mass TransferMaterial Structure andBehaviourTurbulence1.3.1 ThermodynamicsInitial states Final statesReactants Products (Equilibrium)Heat for utilizationAllows us to do the bookkeeping on how much chemicalenergy can be converted to thermal energy in a combustionprocess.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 10 6 years for completion 當 分 析 cycleperformance of an auto engine.e.g. Calculation amount of NO x11

Finite reaction rates >> Thermodynamic equilibrium• All combustion processes have some finite, characteristic times definingour interest in the phenomena.• Chemical Kinetics is needed to prescribe the paths and rates.• Thermodynamics can be considered to be a special area of chemicalkinetics in that with infinite time a reaction will eventually achieveequilibrium.• A complex subject : a myriad of chemical species exist, each of which hasthe potential of interacting w/ the rest.• Some confidence on fuel oxidation system only for hydrogen, CO, and thelight alkanes.1.3.3 Fluid MechanicsChemical reactions occurring in a flowing medium.Combustion: Knowledge of F.M. is essential for a successfulunderstanding 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.1.3.4 Transport PhenomenaS L ~ 40 cm/s ; D ~ 0.2 cm 2 /sδ ~ 0.2 / 40 = 5×10 -3 cm = 0.05 mm比 一 根 頭 髮 還 細• Transfer of energy & mass from high to low; through the molecular process ofdiffusion.• For heat transfer, radiation is also important.• Diffusive transport is crucial in the sustenance of many types of flames in that itis only through these processes fresh reactants can be continuously supplied tothe flame while the heat generated there is also being continuously used to heatup and thereby cause ignition of these fresh mixture.12

Ch 1 Introduction to Combustion ME776Sec. 4 Classifications of Fundamental Combustion Phenomena1.4.1 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 levelElementsReaction implies that at least one of the reactantsshould be in either the gaseous or theliquid phase so that its mlc. can spreadaround those of the other reactant.• Premixed system : A + B 2B( A : fuel + oxidizer ; B : heat and/or radicals )• Nonpremixed system: Diffusional combustion reactants initiallyseparated, then being brought together, via molecular process ofdiffusion and the bulk convective motion, to a common region wheremixing and subsequently reaction take place.• Diffusion is still essential in transporting the premixture to, and thethermal energy and combustion products away from, the flame regionwhere reactions occur.• Bunsen Flames• As the fuel gas issues from the orifice, air is entrained throughthe adjustable air-intake port and is then mixed with the fuel gasas they travel along the burner tube.• The subsequent reactions between fuel and oxygen in thispremixture forms a premixed flame.• If this premixture is fuel rich (has a high concentration of fuelthan can be consumed by all the oxygen in the entrained air),after passing through the premixed flame, the excess fuel (orrather the fuel-related intermediate species, can further react withthe oxygen in the ambient air.Reactants initially separated need to be transported to acommon region where mixing and reactions occurDiffusion flame.The outwardly-directed excess fuel reacts almost completelyw/ the inwardly-directed oxygen.• It is obvious that one would not find many examples of premixtures innature, because they would have already reacted even if they are onlyslightly reactive.13

• Nonpremixed system abound.Indeed w/ oxygen in the air as the oxidizer, then all the materials whichwould burn in air are fuels.e.g. fossil deposits: petroleum & coalcellulosic material: paper & clothmetallic substances: aluminum & magnesium1.4.2 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 quantitiesrandomly fluctuate in time ─ Turbulent• Turbulent facilitates the coarse mixing process, and therefore has aparticularly strong influence on nonpremixed systems in which reactantmixing is essential.• The final mixing before reactions can take place, however, must stilloccur through the molecular diffusion process whether the flow islaminar or turbulent.1.4.3 Subsonic and Supersonic Combustion• The velocity of flow• Subsonic flow combustion: The molecular collision processes ofdiffusion are predominant whilereactions also have more time tocomplete.Most frequently in our daily lives,such as the candle flame and the pilotflame. 瓦 斯 爐 標 示 燈 等 的 火 燄• Supersonic flow combustion: The high flow velocity usuallyrenders convective transport todominate over diffusive transport.Reactions also have less time toproceed.Wave motions involving shocks andrarefactions 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, eithergas or liquid (e.g. Bunsen flame).Heterogeneous: If two reactants initially exist in different phases, whether gas14

liquid, liquid/solid, or solid/liquid, then the combustion isheterogeneous (e.g. coal particle burning in air).• Chemists define a heterogeneous reaction as one in which the reactantsactually exist in different phases at the location where reaction takes place.•• Traditional combustion definition : Both modes of burning are calledheterogeneous 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.15

Chapter 1 Introduction to CombustionSection 5 What is The Combustion Process?ME7761.5.1 Chemical Reactione.g. Methane burning in air(1) The global reaction of methane and oxygenCH 4 + 2O 2 CO 2 + 2H 2 O(2) The elementary reaction mechanism( by T. P. Coffee,1984 )Reaction A b B C1. OH + H 2 ↔ H 2 O + H 1.17E9 1.3 18252. H + O 2 ↔ OH + O 1.42E14 0.0 82503. O + H 2 ↔ OH + H 1.80E10 1.0 44804. H + O 2 +M’ ↔ H 2 O +M’ 1.03E18 - 0.72 05. H + HO 2 ↔ OH + OH 1.40E14 0.0 5406. H + HO 2 ↔ O + H 2 O 1.00E13 0.0 5407. H + HO 2 ↔ H 2 + O 2 1.25E13 0.0 08. OH + HO 2 ↔ H 2 O + O 2 7.50E12 0.0 09. O + HO 2 ↔ OH + O 2 1.40E13 0.0 54010. O + HO 2 ↔ OH + O 2 1.25E12 0.0 011. H + H + H 2 ↔ H 2 + H 2 9.20E16 - 0.6 012. H + H + N 2 ↔ H 2 + N 2 1.00E18 - 1.0 013. H + H + O 2 ↔ H 2 + N 2 1.00E18 - 1.0 014. H + H + HO 2 ↔ H 2 + O 2 6.00E19 - 1.25 015. H + H + CO ↔ H 2 + CO 1.00E18 - 1.0 016. H + H + CO 2 ↔ H 2 + CO 2 5.49E20 - 2.0 017. H + H + CH 4 ↔ H 2 + CH 4 5.49E20 - 2.0 018. H + OH + M” ↔ H 2 O +M” 1.60E22 - 2.0 019. H + O + M” ↔ OH +M” 6.20E16 - 0.6 020. OH + OH ↔ O + H 2 O 5.75E12 0.0 39021. OH + CO ↔ CO 2 + H 1.50E7 1.3 -38522. O + CO + M’ ↔ CO 2 + M’ 5.40E15 0.0 230023. H + CO + M’ ↔ CHO + M’ 5.00E14 0.0 75524. CH 4 + O 2 ↔ CH 3 + OH 4.07E14 0.0 704025. CH 4 + H ↔ CH 3 + H 2 7.24E14 0.0 759026. CH 4 + OH ↔ CH 3 + H 2 O 1.55E6 2.13 123027. CH 4 + M ↔ CH 3 + H + M 4.68E17 0.0 4691028. CH 3 + O ↔ CH 2 O + H 6.02E13 0.0 029. CH 2 O + O ↔ CHO + OH 1.82E13 0.0 155030. CH 2 O + H ↔ CHO + H 2 3.31E14 0.0 529031. CH 2 O + OH ↔ CHO + H 2 O 7.58E12E 0.0 7232. CHO + O 2 ↔ CO + H 2 O 3.00E12 0.0 033. CHO + H ↔ CO + H 2 4.00E13 0.0 016

34. CHO + OH ↔ CO + H 2 O 5.00E12 0.0 035. CHO + O ↔ CO + OH 1.00E13 0.0 036. CH 2 O + CH 3 ↔ CHO + CH 4 2.23E13 0.0 259037. CH 3 + OH ↔ CH 2 O + H 2 3.98E12 0.0 038. CH 3 + H 2 O ↔ CH 4 + O 2 1.02E12 0.0 20039. CO + H 2 O ↔ CO 2 + OH 1.50E14 0.0 1190040. CH 3 + CH 3 ↔ C 2 H 6 4.56E37 - 7.65 425041. C 2 H 6 + O ↔ C 2 H 5 + OH 2.51E13 0.0 320042. C 2 H 6 + + H ↔ C 2 H 5 + H 2 5.00E2 3.5 262043. C 2 H 6 + OH ↔ C 2 H 5 + H 2 O 6.63E13 0.0 67544. C 2 H 5 + H ↔ C 2 H 6 7.23E13 0.0 045. C 2 H 5 + H ↔ CH 3 + CH 3 3.73E13 0.0 046. C 2 H 5 ↔ C 2 H 4 + H 2.29E11 0.0 1912047. C 2 H 5 + O 2 ↔ C 2 H 4 + H 2 O 1.53E12 0.0 244648. C 2 H 4 + O ↔ CH 2 + CH 2 O 2.53E13 0.0 251649. C 2 H 4 + OH ↔ CH 2 O + CH 3 5.00E13 0.0 302050. C 2 H 4 + O ↔ C 2 H 3 + OH 2.53E13 0.0 251651. C 2 H 4 + O 2 ↔ C 2 H 3 + HO 2 1.33E15 0.0 2768052. C 2 H 4 + H ↔ C 2 H 3 + H 2 2.00E15 0.0 1000053. C 2 H 4 + OH ↔ C 2 H 3 + H 2 O 4.40E14 0.0 327054. C 2 H 3 + M ↔ C 2 H 2 + H + M 3.01E16 0.0 2038055. C 2 H 3 + O 2 ↔ C 2 H 2 + HO 2 1.57E13 0.0 503056. C 2 H 3 + H ↔ C 2 H 2 + H 2 7.53E13 0.0 057. C 2 H 3 + OH ↔ C 2 H 2 + H 2 O 1.00E13 0.0 058. C 2 H 2 + OH ↔ CH 3 + CO 5.48E13 0.0 689059. CH 3 + H ↔ CH 2 + H 2 2.00E11 0.7 -150060. CH 3 + OH ↔ CH 2 + H 2 O 6.00E10 0.7 101061. CH 2 + O 2 ↔ CHO + OH 1.00E14 0.0 186062. CH 2 + O 2 ↔ CH 2 O + O 1.00E14 0.0 186063. CH 2 + O 2 ↔ CO 2 + H 2 1.00E14 0.0 1860a[M] = total concentration; [M’] = [H 2 ] + 0.74[CO] + 1.47[CO 2 ] + 0.35[O 2 ] +6.5[H 2 O] + 0.44[N 2 ] ; [M”] = [H 2 ] + [CO] + [CO 2 ] + [O 2 ] +5.0[H 2 O] + [N 2 ]bA is in units of cm 3 /mole s or cm 6 /mole 2 s, k = AT B exp(-C/T)c 1.17E9 = 1.17 × 10 9Westbrook and Dryer (1984)Frenklach and Bornside (1984)150 forward reactions∼ Recently proposed chemical reaction mechanisms for soot formationconsist of as many as 2000 reactions.17

Ch 1 Introduction to Combustion ME776Sec. 6 Books, Journals & Proceedings for CombustionBOOKS1. 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”, Qcademic, 1977.8. D. B. Spalding, “ Combustion and Mass Transfer”, Pergamon, 1979.9. J. D. Buckmaster and G. S. S. Ludford, “Theory of Laminar Flame”, CambridgeUniversity 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”, 2 nd 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 andExplosion”, 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 Modelingof Combustion”, Springer-Verlag, 1987.21. A. C. Eckbreth, “Laser Diagnostics for Combustion Temperature and Species”,Abacus, 1988.22. C. K. Law 1996 ? Combustion ? (Notes; Draft; 1989 → 2005 → ?)18

JOURNALS and PROCEEDINGS (for COMBUSTION)1. Proceedings of The Combustion Institute2. Combustion and Flame3. Combustion Science and Technology4. Progress in Energy and Combustion Science5. Combustion, Explosion, and Shock Waves6. Journal of Chemical Physics7. Journal of Fluid Mechanics8. Acta Astronautica9. AIAA Journal10. ASME Transaction: Journal of Heat Transfer and Journal of Engineering forPower11. International Journal of Heat and Mass Transfer12. Physics of Fluids …19