COMBUSTION ENGINEERING. Credits to Profs. F. Beyrau (OvGU), F. Dinkelacker (Leibniz Universität Hannover), A. Leipertz (Erlangen)

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1 COMBUSTION ENGINEERING Credits to Profs. F. Beyrau (OvGU), F. Dinkelacker (Leibniz Universität Hannover), A. Leipertz (Erlangen) 1

2 Combustion Engineering Benoit Fond, Junior Professor G10/R119 Website for slides 2

3 Content of Lecture 1. Phenomenology of Combustion 2. Thermodynamic Fundamentals 3. Chemical Reaction Kinetics 4. Ignition and Ignition Limits 5. Laminar Flame Theory 6. Turbulent Combustion 7. Pollutants of Combustion 8. Combustion of Liquid and Solid Fuels 9. Numerical Simulation 10. Measurement Techniques of Combustion Processes 11. Applied Aspects of Turbulent Combustion 12. Technical Burner Systems 13. (Internal Combustion Engines) 3

4 "Fascination of Fire" Fire has always been a fascinating phenomenon! It also provides more then 90% of the worldwide energy support today 4

5 Content 1. Phenomenology of Combustion Combustion Technology - Why? Complexity of Combustion Characterising Concepts Four Functional Process Steps of Combustion - Excursion: How to extinguish a fire? Laminar Flames - Turbulent Flames Premixed Flames Non-Premixed (Diffusion) Flames First Comparison Examples of Flames and Combustion Systems Purpose of Combustion Summary 5

6 Why Combustion Technology Combustion is one of the oldest technologies of mankind Fire for heating, to protect from animals Clearing of forest Food preparation Metal processing Weapon technology : Incendiary devices Combustion has two sides: Technology to use Destruction by Fire Greek Mythology: Prometheus brought fire to mankind. But his "boss" (the highest god Zeus) feared the increase of human power. Therefore he punished Prometheus, chained him to a rock, where an eagle picks his liver. 6

7 Why Combustion Technology Development of Industry: Significant Progress from Energy- and Combustion Technology: Steam engine Power plant Process engineering Internal engines Gas turbines Jet propulsion Transportation systems (Steam engine, Railway, Road traffic, Aviation, Space?) Note: More than 90% of worldwide use of energy is connected with combustion!!! 7

8 Why Combustion Technology Modern Combustion Technology for : Increase of Efficiency (natural resources are limited) Reduction of pollutants (poisonous,carcinogen, change of climate etc.) Noise abatement Reduction of size of burning chamber (e.g. airplane + automobile engines) Keywords are for example: "Drei-Liter-Auto" - Three liter per 100 km "ULEV" - Ultra Low Emission Vehicle "ZEV" - Zero Emission Vehicle "Single-Digit NOx" - (< 10 ppm NOx) 8 Diesel truck without particle filter Source : US Environmental Protection Agency

9 Why Combustion Technology Pratt & Whitney PW4000 Turbofan Engine e.g. Boeing Airbus A

10 Why Combustion Technology Tasks for combustion technology Heatexchanger Flame Air Fuel Brennkammer Brenner Inappropriate flame size Size of flame and combustion chamber? How much fuel and air, respectively? Is the fuel consumption reasonable? (efficiency, rate of conversion) Safety Pollutant- emissions 10

11 Why Combustion Technology Tasks for combustion technology Traditional Experience Trial-and-error method Design from global computations Modern approach Computation based on local physical and chemical Processes: Heatexchanger Flame Air Fuel heat- and mass-transport owing to convective flows diffusion vaporization reaction radiation, etc.... increasingly interdisciplinary task 11

12 Complexity of Combustion Combustion: "Transformation of chemical bound energy into heat" Typical Fuel and oxidizer react together Oxidizer O 2 (Air). Explosives and solid rocket propellant contains O 2 in chemical bound form (Monergole). Energy release (exothermic reaction) Reaction often is very "fast" Many reaction steps. e.g. CH 4 + 2O 2 -> CO 2 + 2H 2 O is an oversimplification Heat and mass transport is significantly involved. Combustion is complex, still not fully understood!! 12

13 Complexity of Combustion Where is the reaction zone? Where flame is bright? Exposure time 1/8 sec 1 sec 8 sec Note: Luminescence of flame is secondary process, not necessary definition for reaction zone (also "flameless oxidation" is possible) 13

14 Four Functional Steps First characterization Four functional process steps for combustion (gaseous fuel): (1) Mixing of fuel and oxidizer (2) Heat up, that reaction can start (Ignition) External Ignition Self Ignition Feed back (3) Combustion reaction with heat release (4) Heat utilization Combustion is a self stabilizing process 14

15 Four Functional Steps How to extinguish a flame? 15

16 Four Functional Steps How to extinguish a flame? Stop fuel supply (e.g., forest fires, clear forest aisle) Stop air supply (Inert extinguisher e.g. Halon, CO 2 ) Remove heat to stop ignition (water; metal grid) Four Processes: (1) Mixing of fuel and oxidizer (2) Heating to ignite (3) Combustion reaction with heat release (4) Heat utilization Feed back 16

17 Characterizing Concepts Typical times: Mixing 0,1-10 sec Reaction 10-3 sec Often mixing dominates combustion Often mixing supported by convective flow: either laminar or turbulent flow Laminar flame: Turbulent flame: Flowfield independent of time Flowfield depends on time e.g. T( t) T T ( t) T ( t) 0 for laminar 17 combustion

18 Characterizing Concepts Essential characterization: laminar and turbulent flame 18

19 Characterizing Concepts 2 fundamental types of flames Non-premixed flame: Fuel + Ox. come together in reaction zone Premixed flame: Fuel + Ox. mixed before reaction Note 1: Detailed analysis shows that even in premixed flames diffusion is an essential phenomenon. Thus name "diffusion flame" is too simplified; better is "non premixed flame"). Note 2: Intermediate types possible "partially premixed flames" 19

20 Characterizing Concepts Laminar Flame Theory Postoxidation (low blue) Luminous zone (yellow) Stoichiometric Surface Flame front (blue) Air Air F.+ Air Premixed flame Fuel Non-premixed flame 20

21 Characterizing Concepts Laminar Flame Theory Tube Burner / Bunsen Burner flame front/ reaction zone Ox F Ox Ox F Ox (1.) F+ Ox stoichiometrically premixed flame F + Ox (F-rich) partially premixed flame 21 pure fuel non-premixed flame

22 Flame Types Partially Premixed Flame Premixed Flame Photos by Dr. F. Dinkelacker, Erlangen, Butane/Air Fuel flow rate is hold constant Nonpremixed Flame

23 Non- Premixed (Diffusion-) flame laminar turbulent Premixed flame 23

24 Characterizing Concepts Important characterization of flames: Non- Premixed (Diffusion-) flame Premixed flame laminar Candle gas stove (part. premixed) Porous burner turbulent Fire, Industrial burner, Air plane turbine Modern gas turbine 24

25 Examples for Combustion Systems Candle Flame Luminous zone (yellow) Wick Fuel Air Air The candle flame as classical example of laminar non-premixed (diffusion) flamme 25

26 Examples for Combustion Systems Gas stove burner / bunsen burner Gas stove burner, partly premixed flame with air intake inside venturi injector Bunsen burner, can be modified between premixed (blue) and non-premixed (yellow) flame (from Günther) 26

27 Examples for Combustion Systems Cement production Rotary furnace for production of cement (length about 30 m) Turbulent long diffusion flame, radiative heat transfer (from Görner) 27

28 Examples for Combustion Systems Jet engine Compressor Burning chamber Turbine Afterburner with flame stabilization Pratt & Whitney F100-PW-229 Engine Military jet engine with afterburner 28

29 Examples for Combustion Systems Gas turbine Siemens V84.3A Modern gas turbine with annular burning chamber for premixed combustion 29

30 Examples for Combustion Systems Oil heating furnace Biomass Heater (Guntamatic Powerchip) 30

31 Characterizing Concepts First comparitive discussion: Laminar -->Turbulent Flames: Mixing increases Combustion faster, concentrated Nonpremixed Flame: Quite stable combustion, "secure" Premixed Flame: Controlled reaction possible: NO x reduction Soot reduction But danger of flash back 31

32 Characterizing Concepts Further characteristics concerning the temporal behaviour of combustion Stationary Combustion Combustion field remains (on average) stable Instationary Combustion Location of (average) combustion field changes with time e.g. for turbulent Combustion stationary: T constant in time T ( t) T T ( t) instationary: T f(t) 32

33 Characterizing Concepts Stationary and Instationary Flames Stationary Instationary laminar turbulent laminar turbulent Non- prem.- flame Candle Lighter Woodfire Jet Engine Droplet ignition Diesel engine (with direct injection) Prem.- flame Gas stove (Part. Premixed) Modern gas turbine Ignition Spark Ignition engine 33

34 Examples for Combustion Systems Internal combustion engines Otto engine (SI) with port fuel injection Instationary turbulent premixed combustion Diesel engine with direct injection Instationary turbulent non-premixed combustion 34

35 Purpose of Combustion Primarily chemical energy is transformed to heat. This can be used for different purposes Purpose Heat for heating system Heat for high temperature processing Electricity Mech. power, e.g. for traffic Chemical decomposition Light, "Comfort" Examples Heating burner (Oil, Gas, Solids) Cement furnace Melting furnace Boiler (Coal, Oil, Gas) - Rankine Stationary gas turbine - Brayton Internal combustion engine Jet engine Waste incineration Candle 35

36 Purpose of Combustion Example: waste incineration Quelle: Martin GmbH 36

37 Purpose of Combustion Flares for the controlled combustion of excess fuel (safety reasons) Sooting (1st Generation) 2nd Generation Quelle: Internet 37

38 Summary Summary: Combustion technology - one of the most important technologies Most important tasks for combustion technology today are pollutant reduction and an increasing efficiency Characterizing Concepts 4 functional process steps of combustion Characteristics: Laminar - Turbulent Flames Diffusion Flame - Premixed Flame Stationary - Instationary Combustion Purpose of Combustion Heat, Power, Light, Chemical processing and decomposition,... 38

39 Combustion Literature English: Turns, S. R. "An Introduction to Combustion: Concepts and Application", McGraw-Hills 2011 (quite new, relatively good, ca. 60E) Warnatz, J., Maas, U., Dibble, R. "Combustion", Springer, 2006 (Basic Processes, Kinetics, Modelling, ca. 80E) Kuo, K. "Principles of Combustion", J. Wiley 1986 (Detailed Theory) Lewis, v. Elbe "Combustion, Flames and Explosions of Gases", 3. Auflage 1986, Academic Press (a "classical" book) Peters, N. : "15 Lectures on laminar and turbulent combustion", Aachen, (theoretical orientation) German: Warnatz, J., Maas, U., Dibble, R. "Verbrennung", 3. Auflage, Springer 2001, 40 Günther, R. "Verbrennung und Feuerungen", Springer 1974 (Technische Aspekte, Viele Brennerformen, Theorie tw. veraltet, ca. 40 ) Görner, K. "Technische Verbrennungssysteme", Springer 1991 (Grundlagen, Simulation, Kohleverbrennung, ca. 65 ) Merker, Schwarz, Stiesch, Otto "Verbrennungsmotoren - Simulation der Verbrennung und Schadstoffbildung", 2. Auflage, Teubner 2004, 40 39