combustion engineering - ltt -herzlich willkommen … · chemical reaction kinetics 4. ... pure...
TRANSCRIPT
1
COMBUSTION ENGINEERING
Credits to Profs. F. Beyrau (OvGU), F. Dinkelacker (Leibniz Universität Hannover), A.
Leipertz (Erlangen)
2
Combustion Engineering
Benoit Fond, Junior Professor
G10/R119
Website for slides
http://www.ltt.ovgu.de/Lehre.html
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)
4
"Fascination of Fire"
Fire has always been a fascinating phenomenon!
It also provides more then 90% of the worldwide energy support today
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
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.
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 !!!
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)
Diesel truck without particle filter
Source : US Environmental Protection Agency
9
Why Combustion Technology
Pratt & Whitney
PW4000
Turbofan Engine
e.g. Boeing 747-400
Airbus A310-300
10
Why Combustion Technology
• Size of flame and combustion chamber?
• How much fuel and air, respectively?
• Is the fuel consumption reasonable? (efficiency, rate of conversion)
• Safety
• Pollutant- emissions
Heat-
exchanger
Flame
Air
Fuel
Inappropriate
flame sizeBrennkammer
Brenner
Tasks for combustion technology
11
Why Combustion Technology
Traditional
• Experience
• Trial-and-error method
• Design from global computations
Heat-
exchanger
Flame
Air
Fuel
• heat- and mass-transport owing
to convective flows
• diffusion
• vaporization
• reaction
• radiation, etc. ...
increasingly
interdisciplinary
task
Modern approach
• Computation based on local physical and
chemical Processes:
Tasks for combustion technology
12
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 !!
13
Complexity of Combustion
Where flame is bright?
Note: Luminescence of flame is secondary process, not necessary
definition for reaction zone
(also "flameless oxidation" is possible)
Exposure time
1/8 sec 1 sec 8 sec
Where is the reaction zone ?
14
Four Functional Steps
Four functional process steps for combustion (gaseous fuel):
(1) Mixing of fuel and oxidizer
(2) Heat up, that reaction can start (Ignition)
(3) Combustion reaction with heat release
(4) Heat utilization
Feed back
External
Ignition
Combustion is a
self stabilizing
process
Self
Ignition
First characterization
16
Four Functional Steps
Four Processes:
(1) Mixing of fuel and oxidizer
(2) Heating to ignite
(3) Combustion reaction with heat release
(4) Heat utilization
Feed back
How to extinguish a flame ?
Stop fuel supply
(e.g., forest fires,
clear forest aisle)Stop air supply
(Inert extinguisher
e.g. Halon, CO2)
Remove heat
to stop ignition (water;
metal grid)
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: Flowfield independent of time
Turbulent flame: Flowfield depends on time
combustion laminar for 0)(
)()( e.g.
tT
tTTtT
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"
20
Characterizing Concepts
Premixed flame
Fuel
Stoichiome-
tric Surface
Luminous
zone
(yellow)
Air Air
Non-premixed flame
F.+ Air
Flame front
(blue)
Post-
oxidation
(low blue)
Laminar Flame Theory
21
Characterizing Concepts
stoichiometrically
premixed flame
pure
fuel
non-premixed
flame
F OxOx
flame front/
reaction zone
F+ OxF + Ox
(F-rich)
F OxOx
(1.)
partially premixed
flame
Tube Burner / Bunsen Burner
Laminar Flame Theory
22
Flame Types
Premixed Flame Nonpremixed Flame
Partially Premixed
Flame
Photos by Dr. F. Dinkelacker, Erlangen, 2005
Butane/Air
Fuel flow rate is hold constant
24
Characterizing Concepts
laminar
Candle
gas stove
(part. premixed)
Porous burner
turbulent
Fire,
Industrial burner,
Air plane turbine
Modern gas
turbine
Non-
Premixed
(Diffusion-)
flame
Premixed
flame
Important characterization of flames:
25
Examples for Combustion Systems
Fuel
Luminous
zone
(yellow)
Air Air
The candle flame as classical
example of laminar
non-premixed (diffusion) flamme
Wick
Candle Flame
26
Examples for Combustion Systems
Gas stove burner, partly premixed flame with air
intake inside venturi injector
(from Günther)
Bunsen burner, can be modified between
premixed (blue) and non-premixed (yellow) flame
Gas stove burner / bunsen burner
27
Examples for Combustion Systems
Rotary furnace for production of cement (length about 30 m)Turbulent long diffusion flame, radiative heat transfer
(from Görner)
Cement production
28
Examples for Combustion Systems
Pratt & Whitney
F100-PW-229 Engine
Military jet engine with afterburner
CompressorBurning
chamberTurbine
Afterburner with
flame stabilization
Jet engine
29
Examples for Combustion Systems
Modern gas turbine with annular burning chamber for premixed combustion
Siemens V84.3A
Gas turbine
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:
NOx reduction
Soot reduction
But danger of flash back
32
Characterizing Concepts
Further characteristics concerning the temporal behaviour of
combustion
• Stationary CombustionCombustion field remains (on average) stable
• Instationary CombustionLocation of (average) combustion field changes with time
)()(
Combustionent for turbul e.g.
tTTtT f(t)T
T
:ryinstationa
in timeconstant :stationary
33
Characterizing Concepts
laminar
Candle
Lighter
Gas stove
(Part.
Premixed)
turbulent
Woodfire
Jet Engine
Modern gas
turbine
Non-
prem.-
flame
Prem.-
flame
laminar
Droplet
ignition
Ignition
turbulent
Diesel engine
(with direct
injection)
Spark Ignition
engine
Stationary Instationary
Stationary and Instationary Flames
34
Examples for Combustion Systems
Otto engine (SI) with port fuel injection Instationary turbulent premixed combustion
Diesel engine with direct injection Instationary turbulent non-premixed
combustion
Internal combustion engines
35
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
37
Purpose of Combustion
Flares – for the controlled
combustion of excess fuel
(safety reasons)
Sooting (1st Generation)
Quelle: Internet
2nd Generation
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, ...
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, 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 €