COMBUSTION ENGINEERING
Credits to Profs. F. Beyrau (OvGU), F. Dinkelacker (Leibniz Universität Hannover), A.
Leipertz (Erlangen)
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Combustion Engineering
Benoit Fond, Junior Professor
benoit.fond@ovgu.de
G10/R119
Website for slides
http://www.ltt.ovgu.de/Lehre.html
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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)
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"Fascination of Fire"
Fire has always been a fascinating phenomenon!
It also provides more then 90% of the worldwide energy support today
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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
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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.
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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 !!!
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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)
Diesel truck without particle filter
8 Source : US Environmental Protection Agency
Why Combustion Technology
Pratt & Whitney
PW4000
Turbofan Engine
e.g. Boeing 747-400
Airbus A310-300
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Why Combustion Technology
Tasks for combustion technology
Heat-
exchanger
Brennkammer Inappropriate
flame size
Flame
Brenner
Air
Fuel
• Size of flame and combustion chamber?
• How much fuel and air, respectively?
• Is the fuel consumption reasonable? (efficiency, rate of conversion)
• Safety
• Pollutant- emissions
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Why Combustion Technology
Tasks for combustion technology
Traditional
• Experience Heat-
exchanger
• Trial-and-error method
• Design from global computations
Flame
Modern approach
• Computation based on local physical and Air
chemical Processes: Fuel
• heat- and mass-transport owing
to convective flows
• diffusion
increasingly
• vaporization
interdisciplinary
• reaction task
• radiation, etc. ...
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Complexity of Combustion
Combustion:
"Transformation of chemical bound energy into heat"
Typical
• Fuel and oxidizer react together
• Oxidizer O2 (Air).
• Explosives and solid rocket propellant contains O2 in chemical bound
form (Monergole).
• Energy release (exothermic reaction)
• Reaction often is very "fast"
• Many reaction steps.
e.g. CH4 + 2O2 -> CO2 + 2H2O is an oversimplification
• Heat and mass transport is significantly involved.
Combustion is complex, still not fully understood !!
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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)
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Four Functional Steps
First characterization
Four functional process steps for combustion (gaseous fuel):
External
(1) Mixing of fuel and oxidizer Ignition
Self
Ignition
(2) Heat up, that reaction can start (Ignition)
Feed back
(3) Combustion reaction with heat release
Combustion is a
(4) Heat utilization self stabilizing
process
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Four Functional Steps
How to extinguish a flame ?
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Four Functional Steps
How to extinguish a flame ?
Stop fuel supply
(e.g., forest fires, Stop air supply
clear forest aisle) (Inert extinguisher
e.g. Halon, CO2)
Remove heat
to stop ignition (water;
metal grid)
Four Processes:
(1) Mixing of fuel and oxidizer
(2) Heating to ignite
Feed back
(3) Combustion reaction with heat release
(4) Heat utilization
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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: Flowfield independent of time
Turbulent flame: Flowfield depends on time
e.g. T (t ) T T (t )
T (t ) 0 for laminar combustion
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Characterizing Concepts
Essential characterization:
laminar
and
turbulent flame
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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"
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Characterizing Concepts
Laminar Flame Theory
Post- Luminous
oxidation zone Stoichiome-
(low blue) (yellow) tric Surface
Flame front
(blue)
Air Air
F.+ Air Fuel
Premixed flame Non-premixed flame
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Characterizing Concepts
Laminar Flame Theory
Tube Burner / Bunsen Burner
flame front/
reaction zone Ox F Ox Ox F Ox
(1.)
F + Ox pure
F+ Ox (F-rich) fuel
stoichiometrically partially premixed non-premixed
premixed flame flame flame
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Flame Types
Partially Premixed
Flame
Premixed Flame Nonpremixed Flame
Butane/Air
Photos by Dr. F. Dinkelacker, Erlangen, 2005 Fuel flow rate is hold constant
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laminar turbulent
Non-
Premixed
(Diffusion-)
flame
Premixed
flame
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Characterizing Concepts
Important characterization of flames:
laminar turbulent
Non-
Candle Fire,
Premixed
Industrial burner,
(Diffusion-)
Air plane turbine
flame
gas stove
(part. premixed)
Premixed
Modern gas
flame
Porous burner turbine
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Examples for Combustion Systems
Candle Flame
Luminous
zone
(yellow)
Fuel
Wick
Air Air
The candle flame as classical
example of laminar
non-premixed (diffusion) flamme
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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)
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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)
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Examples for Combustion Systems
Jet engine
Burning Afterburner with
Compressor Turbine
chamber flame stabilization
Pratt & Whitney
F100-PW-229 Engine
Military jet engine with afterburner
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Examples for Combustion Systems
Gas turbine
Siemens V84.3A
Modern gas turbine with annular burning chamber for premixed combustion
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Examples for Combustion Systems
Oil heating furnace
Biomass Heater
(Guntamatic Powerchip)
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Characterizing Concepts
First comparitive discussion:
Laminar -->Turbulent Flames: Mixing increases
Combustion faster, concentrated
Nonpremixed Flame: Quite stable combustion, "secure"
Premixed Flame: Controlled reaction possible:
NOx reduction
Soot reduction
But danger of flash back
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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)
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Characterizing Concepts
Stationary and Instationary Flames
Stationary Instationary
laminar turbulent laminar turbulent
Candle Woodfire Droplet Diesel engine
Non-
Lighter Jet Engine ignition (with direct
prem.-
injection)
flame
Gas stove
Modern gas
(Part. Ignition Spark Ignition
Prem.- turbine
Premixed) engine
flame
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Examples for Combustion Systems
Internal combustion engines
Otto engine (SI) with port fuel injection Diesel engine with direct injection
Instationary turbulent premixed combustion Instationary turbulent non-premixed
combustion
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Purpose of Combustion
Primarily chemical energy is transformed to heat. This can be used for different
purposes
Purpose Examples
Heat for heating system Heating burner (Oil, Gas, Solids)
Heat for high temperature processing Cement furnace
Melting furnace
Electricity Boiler (Coal, Oil, Gas) - Rankine
Stationary gas turbine - Brayton
Mech. power, e.g. for traffic Internal combustion engine
Jet engine
Chemical decomposition Waste incineration
Light, "Comfort" Candle
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Purpose of Combustion
Example: waste incineration
Quelle: Martin GmbH
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Purpose of Combustion
Flares – for the controlled
combustion of excess fuel 2nd Generation
(safety reasons)
Sooting (1st Generation)
Quelle: Internet
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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, ...
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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, 1992
http://www.itm.rwth-aachen.de (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 €
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