FKM Combustion Processmohsin/mmj1443/introduction/Mazlan's...Examples of combustion applications: • Gas turbines and jet engines • Rocket propulsion • Piston engines • Guns

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN

Combustion Combustion -- MazlanMazlan 20092009

UTM

FKMFKM

UNIVERSITI TEKNOLOGI MALAYSIAUNIVERSITI TEKNOLOGI MALAYSIA

LECTURER:

DR. MAZLAN ABDUL WAHIDhttp://www.fkm.utm.my/~mazlan

MMJ 1443MMJ 1443

Combustion Process Combustion Process

Semester 2009/2010 - I

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Lecture Hours

Prerequisites Undergraduate Thermodynamics

Grading 20% 1st Test

20% 2nd Test20% Assignments

40% Projects and Presentations

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


References:

1. Stephen R. Turns, An Introduction to Combustion, 2nd Edition,

McGraw-Hill, 2000.

2. Warnatz, Maas, Dibble, Combustion, Springer Verlag.

3. Kenneth K. Kuo, Principles of Combustion, Wiley.

4. C.K. Law, Combustion Fundamentals.

5. Glassman, Combustion, Academic Press.

6. G. L. Borman, and K. W. Ragland, Combustion Engineering,

McGraw-Hill, 1998.

7. A. M. Kanury, Introduction to Combustion Phenomena, Gordon & Breach, 1975.

8. J. M. Beér, and N. A Chigier, Combustion Aerodynamics, Applied Science, 1972.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


1 Introduction 2 Thermodynamics of Combustion Processes3 Fuels4 Chemical Kinetics5 Conservation Equations6 Premixed Combustion 7 Non-premixed Combustion (Diffusion Flames)8 Detonation9 Pollutant Emissions 10 Combustion Applications

Course contentsCourse contents

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


I. Introduction

Introduction to the nature and scope of combustion, definition of combustion, combustion mode and flame type

II. Thermodynamics of Combustion Processes

Treatment of first law of thermodynamics related to combustion process, enthalpies of formation, the em phasis of the importance of chemical equilibrium to combus tion. Use of software to calculate complex equilibrium for co mbustion gases.

III. Fuel

Type and classifications of fuels

Tentative details of course contents:Tentative details of course contents:

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


IV. Chemical Kinetics

Deal with chemical kinetics of combustion by presen ting basic concepts, elementary and global reactions, ch emical mechanism importance to combustion and pollutant formation reactions

V. Premixed Combustion

Describe the essential characteristics of premixed flames and developed simplified analysis of these flames. To investigate factors that influence flame speed, fla me structure and flame stabilization .

VI. Nonpremixed Combustion (Diffusion Flames)

Investigate type of flame that widely used in indus tries, importance of flame geometry in combustor design, parameters that control flame size and shape.

VII. Detonation

The Phenomena of detonation, its mechanism and its characterization

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


VIII. Pollutant Emissions

Introduction to the quantification of emissions as well as discussing the mechanisms of pollutant formation an d their control.

IX. Combustion Applications

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Rapid oxidation of a fuel accompanied by the release of heat and/or light together with the formation of combustion products

Fuel + oxidant heat/light(thermal energy) +combustion products

Definition of combustion as quoted from Webster’s dictionary

“ rapid oxidation generating heat, or both heat and light ; also, slow oxidation accompanied by relatively little heat and no light”

What is Combustion?What is Combustion?

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


• Combustion is a key element of many of modern

society’s critical technologies.

• Combustion accounts for approximately 85 percent

of the world’s energy usage and is vital to our

current way of life.

• Spacecraft and aircraft propulsion, electric power

production, home heating, ground transportation,

and materials processing all use combustion to

convert chemical energy to thermal energy or

propulsive force.

Some facts about combustionSome facts about combustion

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Examples of combustion applications:Examples of combustion applications:

• Gas turbines and jet engines

• Rocket propulsion

• Piston engines

• Guns and explosives

• Furnaces and boilers

• Flame synthesis of materials (fullerenes, nanomaterials)

• Chemical processing (e.g. carbon black production)

• Forming of materials

• Fire hazards and safety

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Chemical kineticsChemical kinetics

Combustion is a complex interaction ofCombustion is a complex interaction of

ThermodynamicsThermodynamics

Heat and mass transferHeat and mass transfer

Fluid dynamicsFluid dynamics

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


• Physical processes

- fluid dynamics, heat and mass transfer

• Chemical processes

- thermodynamics, and chemical kinetics

Practical applications of the combustion phenomena also involve applied sciences such as aerodynamics, fuel technology, and mechanical engineering.

• Transport of energy, mass, and momentum are the physical processes involved in combustion.

• Conduction of thermal energy, the diffusion of chem ical species, and the flow of gases all follow from the release of chemical energy in the exothermic reaction.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


The complex interaction of various fields in The complex interaction of various fields in combustion processes can be summarized as follows:combustion processes can be summarized as follows:

Thermodynamics:Thermodynamics:

�Stoichiometry

�Properties of gases and gas mixtures

�Heat of formation

�Heat of reaction

�Equilibrium

�Adiabatic flame temperature

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Heat and Mass Transfer:Heat and Mass Transfer:

�Heat transfer by conduction

�Heat transfer by convection

�Heat transfer by radiation

�Mass transfer

Fluid Dynamics:Fluid Dynamics:

�Laminar flows

�Turbulence

�Effects of inertia and viscosity

�Combustion aerodynamics

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Chemical Kinetics:Chemical Kinetics:

�Application of thermodynamics to a reacting system gives us

�equilibrium composition of the combustion products, and

�maximum temperature corresponding to this composition, i.e. the adiabatic flame temperature.

�However, thermodynamics alone is not capable of telling us whether a reactive system will reach equilibrium.

�If the time scalestime scales of chemical reactionschemical reactions involved in a combustion process are larger thanlarger than the time scales of physical processesphysical processes (e.g. diffusion, fluid flow), the system the system may never reach equilibriummay never reach equilibrium .

�Then, we need the rate of chemical reactions involved in combustion.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Fuel

Oxygen Ignition (air) (energy)

Combustion Triangle

Basic Requirements for CombustionBasic Requirements for Combustion

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Combustion modeCombustion mode

FlameFlame

Premixed

Laminar Turbulent

Non-premixed

Laminar Turbulent

NonNon--FlameFlame

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Primary sources of combustion research Primary sources of combustion research literature:literature:

1. Combustion and Flame (journal)

2. Combustion Science and Technology (journal)

3. Computational and Theoretical Combustion (journal )

4. Progress in Energy and Combustion Science (review journal)

5. Proceedings of the Combustion Institute (Biennial Combustion Symposia (International) proceedings).

6. Combustion, Explosions and Shock Waves

7. Shock

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


• Premixed flames– Fuel and air are molecularly

mixed prior to chemical reaction

• Non-premixed (diffusion) flames– Fuel and air are initially

separated, reaction occurs only at the interface between the fuel and the air, where mixing and reaction both take place

Combustion in a spark-ignition engine

Thin zone of intense chemical reaction , known as flame,

propagating through the unburned fuel-air mixture, leaving behind hot

products of combustion

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Combustion of fossil fuelCombustion of fossil fuel

Chemical reaction between hydrogen and carbon atoms (contained in the fuel) with oxygen atoms (usually comes from the air), resulting in the heat release and the formation of combustion products(* )

(*) mainly water vapor and carbon dioxide and a certain amount combustion by-products depending on combustion process

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Simplified Main Processes of CombustionSimplified Main Processes of Combustion

Carbon + Oxygen heat + carbon dioxide

( C + O2 Heat + CO2 )

Hydrogen + Oxygen Heat + Water

( H2 + O Heat + H2O )

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Combustion Diagram

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


•The combining of oxygen in the air and carbon in the fuel to form carbon dioxide and generate heatis a complex process, requiring the right mixing turbulence, sufficient activation temperature and enough time for the reactants to come into contact and combine.

•Unless combustion is properly controlled, high concentrations ofundesirable products can form. Carbon monoxide (CO) and soot, for example, result from poor fuel and air mixing or too little air.

•Other undesirable products, such as nitrogen oxides (NO, NO2), form in excessive amounts when the burner flame temperature is too high.

•If a fuel contains sulfur, sulfur dioxide (SO2) gas is formed. For solid fuels such as coal and wood, ash forms from incombustible materials in the fuel.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Combustion ByCombustion By--ProductsProducts

Carbon monoxide (CO)Aldehydes mainly due to incomplete Unburned Fuel combustionRadicals

Oxides of nitrogen (NOx) – reaction between O2 (in air) and nitrogen (present in air or fuel)

Oxides of sulphur (SOx) – only for Sulphur-containing fuel

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Requirements for Successful CombustionRequirements for Successful Combustion

FuelAir

Ignition

Correct Amount of

Fuel and Air

MolecularlyMixed

Fuel andAir

MinimumIgnitionEnergy

(Temperature)

Residence time

LaminarTurbulent

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Categories of Combustion Process

• Stoichiometric Combustion

• Excess Air or Oxygen Combustion

(Fuel Lean Combustion)

• Excess Fuel Combustion

(Fuel Rich Combustion)

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Stoichiometric Combustion

Relative (chemically-correct) proportion of fuel and air quantities that are the theoretical minimum needed to give complete/perfect combustion (i.e., no unburned fuel and residual oxygen present in combustion products)

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Stoichiometric Combustion of Methane

CH4 + 202 (+ ignition) = C02 + 2H20 (+ heat)

means that

1 mole of methane to be proportionately (and molecularly) mixed with 2 moles of oxygen to produce 1 mole of

carbon dioxide and 2 moles of water vapor

or1 cubic metre (m3) of methane requires 2 cubic metre (m3)

of oxygen for complete combustion and will produce 1 cubic metre (m3) of carbon dioxide and 2 cubic metre

(m3) of water vapor

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Excess Air or Oxygen Combustion

Combustion of fuel-lean mixture

When oxygen or air is supplied more than the stoichiometric proportion

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Excess Air Combustion of Methane

CH4 + 302 (+ ignition) = C02 + 2H20 + 02 (+ heat)means that

1 mole of methane to be molecularly mixed with 3 moles of oxygen to produce 1 mole of carbon dioxide, 2 moles of

water vapor and 1 mole of un-reacted oxygen

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Excess Fuel Combustion

Combustion of fuel-rich mixture

When fuel is supplied more than the stoichiometric proportion

Insufficient amount of oxygen or air available to burn in the fuel-rich mixture caused incomplete combustion

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Excess Fuel Combustion of Methane

CH4 + 02 (+ ignition) = C0 + 2H20 (+ heat) + (other products of incomplete combustion )

means thatmeans that1 mole of methane to be molecularly mixed with 1 mole of

oxygen to produce 1 mole of carbon monoxide, 2 moles of water vapor and other products of incomplete combustion

such as unburned fuel, aldehydes etc.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Combustion Air Requirement

Theoretical Oxygen (air)

(Chemically-corrected amount of oxygen (air) required for complete combustion for a given quantity of a

specific fuel)Excess Air

(Sum of all primary and secondary air needed for perfectly complete the combustion of a specific fuel)

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Fossil Fuel Combustion

Gas CombustionLiquid CombustionSolid Combustion

• Successful combustion of fossil fuels requires all criteria as previously discussed

• Methods of combustible mixture preparation are of great importance not only for successful combustion but also to industrial applications

• Solid, liquid and gaseous fuels have different combustible mixture preparation mechanisms and hence combustion characteristics

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Gaseous fuel burner

• Unlike liquid burners, as the fuels are already in thegaseous form, gas burners require only good air/fuel mixing (either in a premixer or in the combustion chamber), before they can be burned

• The characteristics of the flames produced are largely dependent on both the fuel and the rate at which mixing can be achieved

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Liquid fuel burner combustible mixture preparation

atomization process

large drops of oil are broken up or atomized into small

droplets

vaporisation process

small fuel droplets are then vaporized to be in gaseous state vaporized/atomized

mixing process

Vaporized / unvaporized fuel droplets are then mixed with

combustion air to form combustible mixture

The above processes take place at very short time (order of millisecond) and may be simultaneous

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Solid fuel burner

Pulverized fuel particles(pulverization is analogous to atomization process)

Devolatilization(analogous to the vaporization process for the liquid fuel)

Gas phases fuels(CO, O2, CO2 etc.)

Solid phase fuel(char particle –

carbon)

Oxygen (Air)

Mixing / diffusion

Homogeneous reaction Heterogeneous reactionGas-gas reaction gas-solid / gas-liquid reaction

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Excess Air Requirement

Solid fuelSolid fuel highhigh

Liquid fuelLiquid fuel moderatemoderate

Gas fuelGas fuel lowlow

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Combustion calculations

Fuel properties

Mass balanceEnergy balance

Combustion productsCombustion efficiency

Thermal efficiencyExcess air requirement

Air-fuel ratioFlame temperature

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


•What is flame?

•Laminar premixed flames•Laminar diffusion flames

•Turbulent premixed flames

•Turbulent nonpremixed flames•Wild forest fires

•Flame stability

•Flame instabilities•Spray combustion

•Droplet combustion

•Solid propellant combustion•Detonation and deflagration

•External effects on flames

•Buoyancy effect on flames•Pollutant emissions

•Soot formation

•Combustion laser diagnostics

Combustion flames visualization, emissions and diagnosticsCombustion flames visualization, emissions and diagnostics

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


What is Flame?What is Flame?

A self-sustaining propagation of a localizedlocalized (* )

combustion zone at subsonicsubsonic(#) velocities

(*) Flame occupies only a small portion of the combustible Flame occupies only a small portion of the combustible mixture at any one timemixture at any one time

(#) Combustion wave that travels subCombustion wave that travels sub--sonically relative to the sonically relative to the speed of sound in the unburned combustible mixture is speed of sound in the unburned combustible mixture is known as deflagrationknown as deflagration

Combustion wave that travels super-sonically relative to the speed of sound in the unburned combustible mixture is known as detonation

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Flame stability

•Flame shape: combined effects of•Velocity profile•Heat losses to the tube wall

•For the flame to remain stationary:Flame speed must equal the speed of normal component of unburned gas at each location

FLAME SPEED = SPEED OF NORMAL COMPONENT OF GAS FLOW

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Flame stabilityFlame stabilityA free burning flame is said to be stable if there is no flash back or blow off , i.e.

the normal velocity of he mixture (Vu,n) is vectorically equal and opposite to the velocity of fuel-air mixture at the flame front (V u)

•The normal velocity of flame propagation , Vu,n ,depends upon the–type of fuel–composition and temperature of fuel-air mixture–burner tube diameter

•The temperature of fuel-air mixture at the burner tip depends on the heat transfer from the reaction zone, heat loss to the surrounding and size, shape and material of construction of burner wall.

•The average gas velocity, Vu, depend upon–desired flow rate–burner nozzle diameter

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Laminar premixed Laminar premixed flamesflames

�Reactants are completely mixed on a molecular level prior to ignition and combustion. �Kinetically controlled and the rate of flame propag ation, called the burning velocity.�Dependent upon chemical composition and rates of ch emical reaction. �Safety reasons: Less applied (i.e.flashback and blow -off) and stability

Lean Premixed flame

Open TipLean Premixed flame

Closed Tip

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Schematic diagram of Bunsen burner showing the typical flame configuration (left) and the photograph of Bunsen flame (right).

The typical Bunsen-burner flame is a dual flame: a fuel rich premixed inner flame surrounded by a diffusion flame. The dark zone is consists of unburned premixed gases before they enter the area of the luminous zone where reaction and heat release takes place. The secondary diffusion flame results when the carbon monoxide product from the rich inner flame encounters the ambient air. Luminous zone is that portion where most of the reaction takes place and therefore it’s the hottest. The temperature at the tip of the primary flame can reach about 1,500º C (2,700º F) [ ].

With an excess of air, the reaction zone appears blue. This blue radiation results from excited CH radicals in the high-temperature zone. When the air is decreased to less than stoichiometric proportions, the flame zones appears blue-green, now as a result of radiation from excited C2. OH radicals also contribute to the visible radiation, and to a lesser degree, chemiluminescence from the reaction CO + O →→→→ CO2 + hv. If the flame is made richer still, soot will form. The flame can be seen as bright yellow to dull orange emission, depending on the flame temperature [1].

The Bunsen flame is a common example of premixed flames. The mixed gas burns with a pale blue flame, the primary flame, seen as a small inner cone, and a secondary, almost colorless flame, seen as a larger, outer cone, which results when the remaining gas is completely oxidized by the surrounding air.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Nonpremixedflames•Reactants mix by diffusion into a thin flame zone, and reaction rates are diffusion controlled. •They are preferred in industrial practice, gas turbines, internal combustion engines. Safer since the fuel and oxidant are kept separate and flexibility in controlling flame size and shape and combustion intensity

Laminar Laminar nonpremixednonpremixed (diffusion) flames(diffusion) flames

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


NonpremixedNonpremixed (diffusion) flame (diffusion) flame -- Candle flameCandle flame

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM



•Diffusion flames (either laminar or turbulent) are characterized as combustion state controlled by mixing phenomena, i.e. molecular or turbulent diffusion of fuel into oxidizer (i.e. air) or vice versa until some flammable mixture ratio is reached

•Mixing is slow compared with reaction rates…so mixing controls the burning rate

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


•Shape of laminar jet flame depends on the mixture strength, i.e. quantity of air supplied

•If fuel is admitted into a large volume of quiescent air, over-ventilated type of diffusion flame is formed

•If excess fuel or air supply is reduced below an initial mixture strength of stoichiometric, a bell or fan shaped under-ventilated flame is formed.


IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Almost all Almost all flamesflames used in used in practical combustionpractical combustion devices are devices are turbulentturbulent because because turbulent mixing increases burning ratesturbulent mixing increases burning rates , , allowing more power/volumeallowing more power/volume

Even with forced turbulence, if the Even with forced turbulence, if the GrashofGrashof number gdnumber gd 33//νννννννν22 is is larger than about 10larger than about 10 66 (g = 10(g = 1033 cm/scm/s 22, , νννννννν ≈≈ 1 cm1 cm 22/s /s ⇒⇒⇒⇒⇒⇒⇒⇒ d > 10 cm), d > 10 cm), turbulent flow will exist due to buoyancyturbulent flow will exist due to buoyancy

Examples

��Premixed turbulent flamesPremixed turbulent flames

»»GasolineGasoline --type (spark ignition, premixedtype (spark ignition, premixed --charge) internal charge) internal combustion enginescombustion engines

»»Stationary gas turbines (used for power generation, not Stationary gas turbines (used for power generation, not propulsion)propulsion)

��NonpremixedNonpremixed turbulent flamesturbulent flames

»»DieselDiesel --type (compression ignition, type (compression ignition, nonpremixednonpremixed --charge) charge) internal combustion enginesinternal combustion engines

»»Gas turbinesGas turbines

»»Most industrial boilers and furnacesMost industrial boilers and furnaces

Turbulent Combustion

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Turbulent premixed flamesTurbulent premixed flames

(b) Schlieren image of (a) reveling its turbulent nature

(a) Premixed flames

Stiochiometric mixture of natural gas and air , Re = 3000

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Premixed conical flame


IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM



An experimental setup of fan stirred bomb facility at Leeds University to study the premixed turbulent flame of various mixtures

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Glassman (1996)

Turbulent Turbulent nonpremixednonpremixedflamesflames

The transition from laminar to turbulent diffusion (nonpremixed) flames

Laminar diffusion flame is converted into the turbulent type by increasing the gas velocity beyond a critical value of cold Reynolds number depending on fuel and quantity of primary air.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Turbulent Turbulent nonpremixednonpremixedflamesflames

Reaction zone

TemperatureFuel

concentrationProduct

concentration

2000K

300K

Distance from reaction zone Convection-diffusion zone

Oxygen concentration

300K

Nonpremixed flames establish themselves at the interface between fuel and oxidizer; the flame is sustained by diffusion on each side. The flame does not propagate and moves only as fuel and air are convected by, sometimes turbulent, fluid motion.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Pool FiresPool Fires

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Wild forest firesWild forest fires

Alaska forest fires Canada forest fires

US wild forest fire

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Pyrolysis Flaming fire

Yellowstone Park forest fire (USA)

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Solid combustionSolid combustion

Paper combustion

Flame of burning tree bark

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Solid coal particles on flameSolid coal particles on flame

Flat flame burner – propane gas with coal particles

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Flame instabilityFlame instability

Cellular flame

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Spray combustionSpray combustion

Schematic of diesel simulation facility, DSF,

Diesel spray ignition in the DSF.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Flame of liquid heptanes spray NASA spray jet

NASA spray flames – luminous top NASA spray flames – highly turbulent

Spray flamesSpray flames

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Spray combustion main terminologySpray combustion main terminologyPrimary atomization/break-up - Break-up of the liquid core into liquid ligaments.

Secondary atomization/break-up- Break-up of liquid droplets into smaller droplets.

Droplet evaporation - Evolutions of droplet diameters and temperatures due to due to mass- and heat exchange in the course of phase transition.

Turbulent diffusion/dispersion - Random motion of droplets.

Turbulent modulation - Generation and change, modulation, of turbulent properties due to liquid/air interaction.

Turbulent combustion – Heat release due to chemical reactions complicated by smallscale flow-field fluctuations.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Spray AtomizationSpray Atomization

Normal air at 25 C Pre-heated air at 185 C Steam at 195 C

Observed Features of Spray with Three Different Atomization Gases

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


DROP COLLISION/COALESCENCEDROP COLLISION/COALESCENCEBinary Collision of Droplets

Drop collision and coalescence phenomena become important in dense sprays. In the event of particle collision, the time for a particle to respond to the local aerodynamic field is important.

Stretching separation collision of two unequalStretching separation collision of two unequal--size droplets at size droplets at WeWe = 52= 52..

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Possible outcomes of a binary collision as We number is increased:

a) coalescence,

b) collision followed by break-up,

c) shattering,

Droplet collisions may result in a) droplet coalescence, b) grazing, and c) shattering, depending on the relative velocity of the colliding droplets. In grazing collisions, a droplet formed immediately breaks up into two big droplets and many small ones.

Possible outcomes of a binary droplets collisionPossible outcomes of a binary droplets collision

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Droplet combustionDroplet combustion

Spray combustion lead to the study of individual droplet, or called – droplet combustion

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


�In combustion systems swirling flows help to increase burning intensity through enhance mixing and higher residence time.�With strong swirl, the centrifugal forces and induced pressure gradients generate a toroidal vortex type of recirculation zone help in stabilizing the high intensity combustion process

��In reacting (combustion system): ExamplesIn reacting (combustion system): ExamplesInternal combustion engines, gas turbines and industrial furnaInternal combustion engines, gas turbines and industrial furna cesces

Swirl combustionSwirl combustion

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Rotating FlamesPremixed flames: φφφφ = 0.59, V = 43 cm/s, ωωωω = 3240 rpm

LOW VELOCITY JET FLAME

(b) Rotating with the speed of 3240 rpmFlame buckles – forming Cusp Flame Shape

(a) StationaryOpen tip flame

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Rotating flameRotating flame

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Swirling flameSwirling flame

Injector burner with a swirling

propane flame

Swirling (lifted) flame

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Detonation and deflagrationDetonation and deflagration

A detonation is defined as a combustion wavepropagating at supersonic velocity relative to the unburned gas immediately ahead of the flame, i.e., the detonation velocity, D, is larger than the speed of sound, C, in the unburned gas.

In simple terms, a detonation wave can be described as a shock wave immediately followed by a flame(ZND theory). The shock compression heats the gas and triggers the combustion. However, an actual detonation wave is a three-dimensional shock wave followed by the reaction zone.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Summary of High Explosives

• Condensed (or high) explosives generate very high pressures, ~106 psi

• Extremely high pressures generate extremely destructive shock waves

• Detonation velocities ~8,000 to 9,000 m/sec - that’s 20,000 mph!

• Detonation velocity and pressure maintained in the HE only

• Shock velocity degrades after leaving HE

Detonation initiation Expanding fireball Dissipating shock wave

Condensed Phase or “High Explosives”

“High Explosives” normally refer to condensed phase materials (solids, liquids and mixtures)

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Buoyancy effect on flames

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


External effects on flamesExternal effects on flames

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Pollutant emissionsPollutant emissions��Description of pollutantsDescription of pollutants

��NONOxx

��SootSoot

��COCO

��Unburned hydrocarbons (UHC)Unburned hydrocarbons (UHC)

��Emissions are a Emissions are a NONNON--EQUILIBRIUM PROCESSEQUILIBRIUM PROCESS ””

��If we follow two simple rules:If we follow two simple rules:

��Use lean or Use lean or stoichiometricstoichiometric mixturesmixtures

��Allow enough time for chemical equilibrium to occurAllow enough time for chemical equilibrium to occur as the as the products cool downproducts cool down

��…… then NO, CO, UHC and then NO, CO, UHC and C(sC(s) (soot) are ) (soot) are practically zeropractically zero

��So the problem is that we are So the problem is that we are not patient enoughnot patient enough (or unable to (or unable to allow the products to cool down slowly enough)!allow the products to cool down slowly enough)!

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Soot formation Soot formation -- what is soot?what is soot?•Soot is good and bad news

–Good: increases radiation in furnaces

–Bad: radiation & abrasion in gas turbines, particles in atmosphere

•Typically C8H1 (mostly C)

•Structure mostly independent of fuel & environment

–Quasi-spherical particles, 105 - 106 atoms (100 - 500 Å), strung together like a “fractal pearl necklace”

–Each quasi-spherical particle composed of many (~104) slabs of graphite (chicken wire) carbon sheets, randomly oriented

•Quantity of soot produced highly dependent on fuel & environment

•Formation dependent on

–Pyrolysis vs. oxidation of fuel

–Formation of gas-phase soot precursors

–Nucleation of particles

–Growth of particles

–Agglomeration of particles

–Oxidation of final particles

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Soot photographsSoot photographs

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Combustion DiagnosticsCombustion Diagnostics

Spectroscopic methods in combustion researchSpectroscopic methods in combustion research

1. LIF: Laser induced fluorescence

2. Raman spectroscopy

3. CARS: Coherent anti-Stokes Raman spectroscopy

4. Quantitative aspects of LIF

5. Observation of sound generating flames in a gas turbine burner

6. Fuel oil concentration measurements in gas turbine burners

High temperatures and pressures in the combustion chamber make it a

most hostile environment.

Laser diagnostics have been used in a number of measurements, such as:

- air/fuel flows and velocities

- pollutant formation

- combustion processes; - droplet and particle sizes

- identification of molecular components, etc.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


First, why at all are optical and spectroscopic methods used in combustion research?

The methods have a couple of striking advantages ov er conventional techniques

Overview of methods most commonly used for spectros copicOverview of methods most commonly used for spectros copiccombustion diagnosticscombustion diagnostics

The advantages:The advantages:+ The methods are nonnon --intrusiveintrusive , nonnon --contactcontact measuring methods.

+ In general, optical methods allow for fast observationfast observation .

+ Often a 22--dimensional informationdimensional information (an image) is intrinsically available

+ The methods can be applied to situations inaccessible by conven tional methodcan be applied to situations inaccessible by conven tional method ss, e.g. Harsh and hostile environments.

+ Minority or trace species as pollutants are detectabletrace species as pollutants are detectable .

+ In situ measurementsIn situ measurements are possible.

The drawbacks:The drawbacks:- Optical methods need, of course, optical accessoptical access . The implementation of windows

may be difficultdifficult , especially at IC engines and alike.

- The high laser intensitieslaser intensities used do change the mediumdo change the medium

- Quantitative measurements are more difficult as gen erally believQuantitative measurements are more difficult as gen erally believ eded.

- The problem of reasonable temperature field measurements is still not solvedreasonable temperature field measurements is still not solved in a satisfactory way.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


The underlying process is almost the same for all methods discussed. Electromagnetic radiation infrared, visible, or ultraviolet light - impinges on the molecule under investigation and is scattered. The methods differ in scattering angle, in the energetics of the scattering process, the polarization of the scattered light, the temporal evolution of the signal, and the efficiency ("cross section") of the process.

Optical versus spectroscopic methodsOptical versus spectroscopic methods

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Optical versus spectroscopic methodsOptical versus spectroscopic methods

In the optical methodsoptical methods the exact value of the wavelength of the light used is of minorimportance.

The spectroscopic methodsspectroscopic methods on the other hand use specific wavelengths for the light source or they analyze the emerging signal with res pect to its spectral composition, or both. These wavelengths closely relate to the mo lecules under investigation .

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Combustion Diagnostics Combustion Diagnostics -- LIFLIF

Laser induced fluorescence (LIF)Of the spectroscopic techniques applied to combustion processes, LIF is

among the most often used. Mostly LIF of the OH radical is used, for flame for m/position analysis.

Experimental setup for 2Experimental setup for 2--D LIFD LIF

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Example of the results of using LIFExample of the results of using LIF

Summary:Summary:

LIF is well suited for combustion diagnostics. A co mparatively simple and straightforward experimental setup readily yields 2 -D images. However, the fun ends with trials to extract quantitative concentration data o r to map species with really low concentration (CH, CN, C2, ...). So LIF is mostly used to visualize OH radicals indi cating flame positions and flame forms. The equipment is n ot cheap and the lasers use are a source of many frustrations.

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


A short look back at laser induced fluorescence

Which kind of species can be observed by the LIF te chnique? Comparing the species leads to a more general answer:

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


•Because of its insensitivity to quenching (the lifetime of the virtual state is ~10-14s), Raman spectroscopy is of considerable interest for quantitative measurements on combustion processes.

•Further, important flame species such as O2, N2 and H2 that do not exhibit IR transitions can be readily studied with the Raman technique.

•However, because of the inherent weakness of the Raman scattering process only non-luminous (non-soothing) flames can be studied.

Raman SpectroscopyRaman Spectroscopy

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Coherent antiCoherent anti--stokes Raman scattering stokes Raman scattering

(CARS)(CARS)

•CARS spectroscopy is of particular interest for combustion diagnostics because of the strong signal availablestrong signal available as a new laser beam emerging from the irradiated gas sample.

•Thus CARS is largely insensitive to the strong background light that

characterizes practical combustion systemscharacterizes practical combustion systems such as industrial flame and internal combustion engines.

Coherent anti-Stokes Raman scattering is a nonlinea r four wave mixing process. A general

formulation of the reaction of matter on electric f ields has been proposed by Bloembergen in 1965:

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


Magnetic support flames

IIIIIIII

NNNNNNNN

TTTTTTTT

RRRRRRRR

OOOOOOOO

DDDDDDDD

UUUUUUUU

CCCCCCCC

TTTTTTTT

IIIIIIII

OOOOOOOO

NNNNNNNN


UTM

FKMFKM


The above picture shows image of a two-dimensional Bunsen flame using methane at equivalence ratio of ϖϖϖϖ = 1.2. Blue flame luminosity due to emission from CH and C2 radicals, green particle tracks due to scattering from MgO particles under 6kHz excitation of a Cu-Vp laser. FUJI 1600 ASA film (Echekki and Mungal, 1990).

Reference: Tarek Echekki & M. G. Mungal (1990), "Flame Speed Measurements at the Tip of a Slot Burner: Effects of Flame Curvature and Hydrodynamic Stretch," Twenty-Third Symposium (Int.) on Combustion, The Combustion Institute, 455-461.

Documents

FKM Combustion Processmohsin/mmj1443/introduction/Mazlan's...Examples of combustion applications: • Gas turbines and jet engines • Rocket propulsion • Piston engines • Guns