Fundamentals of Combustion _NPTEL

NPTEL Online - IIT Kanpur

Course Name Fundamental of Combustion Department

Aerospace Engineering, IIT Kanpur

Instructor

Dr. D.P. Mishra

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture1/main.htm[10/5/2012 11:08:14 AM]

Objectives_template

Question can never be silly, It can be like a beautiful lily, In the garden of knowledge, This is still a truth, age after age. - Dr. D.P. Mishra

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture1/1_1a.htm[10/5/2012 11:08:14 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 1: Introduction The Lecture Contains: Introduction to Combustion What is Combustion? Combustion Triangle Applications of Combustion Contd..

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture1/1_1.htm[10/5/2012 11:08:14 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 1: Introduction

Introduction to Combustion Introduction

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture1/1_2.htm[10/5/2012 11:08:14 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 1: Introduction Combustion Triangle Essential conditions for combustion to occur 1. 2. 3. 4. 5.

Presence of fuel . Presence of oxidizer (Not essentially oxygen). They must be in right proportions. The proportion will be dictated by flammability limit. Ignition energy.

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture1/1_3.htm[10/5/2012 11:08:14 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 1: Introduction Applications of Combustion Power Plants Chemical Industries Domestic Burner Automobiles

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture1/1_4.htm[10/5/2012 11:08:14 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 1: Introduction Contd..

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture1/1_5.htm[10/5/2012 11:08:14 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 2: What is Fuel and Oxidizer? The Lecture Contains: What is Fuel and Oxidizer? Types of Fuels and Oxidizers Contd.. Characterization of a Gaseous Fuel Junker's Calorimeter Liquid Fuels and Oxidizers Refinery End-Products of Typical Crude Oil

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture2/2_1.htm[10/5/2012 11:11:43 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 2: What is Fuel and Oxidizer? What is Fuel and Oxidizer?

Electronegativity The ability of an element to accept or donate electrons. Amount of pull that one atom exerts on the electron that it is sharing with other atom. The term electronegativity was coined by Linus Pauling, a Noble Laureate. Electronegativity

Element

Electronegativity

Element

Electronegativity

F

4

Br

2.8

B

2.0

O

3.5

C,S,I

2.5

Be,Al

1.5

N,Cl

3.0

H,P

2.1

Mg

1.2

Element

Fluorine is having Highest Electronegativity (Most powerful oxidizer). Oxygen has second highest electronegativity. Carbon, Hydrogen, Aluminum and Magnesium have Low Electronegativity (Fuels).

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture2/2_1a.htm[10/5/2012 11:11:43 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 2: What is Fuel and Oxidizer? Types of Fuels and Oxidizers

Gaseous Fuel and Oxidizer

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture2/2_2.htm[10/5/2012 11:11:43 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 2: What is Fuel and Oxidizer? Contd.. Types of Gaseous Fuel and Oxidizer Sl. No.

Fuel

Oxidizer

Application

1

LPG

Air/O2

Domestic Burner, Furnace

2

Natural Gas (NG)

Air/O2

IC Engines, Furnaces

3

Producer Gas

Air/O2

EC/IC Engines

4

CH4 , C 3 H 8 , H 2

Air/O2

EC/IC Engines

5

Biogas

Air/O2

EC/IC Engines, Burners

6

Acetylene

Air/O 2

Gas welding, Gas cutting * EC=External Combustion IC =Internal Combustion

Composition of Some Gaseous Fuels Fuel

CO2

O2

N2

CO

H2

CH4

C 2 H6

C 3 H8

LPG

-

-

-

-

-

-

-

70

30

Natural Gas

-

-

5

-

-

90

5

-

-

Producer Gas

8

0.1

50

23.2

17.7

1

-

-

-

Propane

-

-

-

-

-

-

2.2

97.3

0.5

Biogas

33

-

1

-

1

65

-

-

-

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture2/2_3.htm[10/5/2012 11:11:43 AM]

C 4 H10

Objectives_template

Module 1: Introduction to Combustion Lecture 2: What is Fuel and Oxidizer? Characterization of a Gaseous Fuel Heating Value: Amount of heat released per unit volume when it undergoes oxidation at normal pressure and temperature (0.1 MPa and 298 K). Lower heating value (LHV) – amount of heat released by burning 1 kg of fuel assuming the latent heat of vaporization in the reaction products is not recovered.

Higher heating value (HHV) – heating value of the fuel when water is condensed. is the Latent heat of vaporization of water at 298.15 K

Junker's Calorimeter

(Figure 2.1)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture2/2_4.htm[10/5/2012 11:11:43 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 2: What is Fuel and Oxidizer? Determines the heating value of the gaseous fuel. Fuel and air are burnt in a burner. Cooling water in the water jacket-absorbs the heat released during combustion. Heating value- calculated from the water flow rate and rise in temperature.

Liquid Fuels and Oxidizers Liquid fuel is one of the major energy sources in the transport sector. Crude oil is formed from organic sources, animals, vegetables – which are entrapped in rocks under high pressure and temperature for million years.

Fuel

Oxidizer

Application

1

Gasoline

Air

S.I. Engine, Aircraft Piston Engine

2

HSD

Air

C.I. Engine

3

Furnace Oil

Air

Furnaces

4

Kerosene

Air

Aircraft, Gas Turbine, Engines Ramjet, Domestic Burner

5

Alcohols

Air

I.C. Engine

6

Hydrazine, UDMH, MMH, Liquid Hydrogen, Triethyl Amine

7

Hydrogen, Kerocene

Liquid O 2 , RFNA (Red Fuming Nitric Acid) N2 O 4

Liquid propellant rocket Engines

Air

Ramjet/Scramjet

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture2/2_5.htm[10/5/2012 11:11:43 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 2: What is Fuel and Oxidizer? Refinery End-Products of Typical Crude Oil Crude oil undergoes several process in the refinery. Generally separation of petroleum constituents occur in the distillation column. Constituents of typical crude oil is shown below.

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture2/2_6.htm[10/5/2012 11:11:43 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 3: Fuels The Lecture Contains: Bomb Calorimeter Properties of Liquid Fuels Properties of Common Liquid Fuels Solid Fuels and Oxidizers Contd..

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture3/3_1.htm[10/5/2012 11:12:20 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 3: Fuels Bomb Calorimeter Used to determine the calorific value of the liquid fuel. Liquid is burnt in the bomb in the presence of oxygen at about 2.5 MPa . The change in temperature in the water bath provides the calorific value of the fuel.

(Figure 3.2)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture3/3_2.htm[10/5/2012 11:12:20 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 3: Fuels Properties of Liquid Fuels Specific Gravity

: Ratio of mass density of fuel to mass density of water at the same temperature

Reference temperature for fuel and water: 288.8 K American Petroleum Institute (API) Scale:

Relation between APISG and HHV: For Gasoline

:

For Kerosene

:

Auto Ignition : The lowest temperature required to make the combustion self sustained without Temperature any external aid

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture3/3_3.htm[10/5/2012 11:12:20 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 3: Fuels Properties of Liquid Fuels Flash : Minimum temperature at which liquid fuel will produce sufficient vapors to form a Point flammable mixture with air. Indicates maximum temperature at which liquid fuel can be stored without any fire hazard. Fire : Minimum temperature at which liquid fuel produces sufficient vapors to form a flammable Point mixture with air that continuously supports combustion establishing flame instead of just flashing. Smoke : Measure of the tendency of a liquid fuel to produce soot. Point

Properties of Common Liquid Fuels Automotive Gasoline

Diesel Fuel

0.72 - 0.78

0.85

0.796

0.8 X 10 -6

2.5 X 10 -6

0.75 X 10 -6

303 - 576

483 - 508

338

423-473

442

Flash point (K)

230

325

284

311

325

Auto ignition temperature (K)

643

527

737

483

--

Stoichiometric air/fuel by weight

14.7

14.7

6.45

15

15.1

Heat of Vaporization (kJ/kg)

380

375

1185

298.5

--

Lower heating value (MJ/kg)

43.5

45

20.1

45.2

43.3

Fuel Type Specific gravity Kinematics viscosity @ 293 K (m 2 /s) Boiling point range (K) @ STP

Methanol Kerosene 0.82 3.626 X 10 -6

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture3/3_4.htm[10/5/2012 11:12:21 AM]

ATF (JP8) 0.71 --

Objectives_template

Module 1: Introduction to Combustion Lecture 3: Fuels Solid Fuels and Oxidizers Solid Fuels:

(Figure 3.2) Constituents of Solid Fuel:

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture3/3_5.htm[10/5/2012 11:12:21 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 3: Fuels Contd.. Types of Solid Fuels and Oxidizers: S. No.

Fuel

Oxidizer

Applications

1

Biomass (Wood, Saw Dust, Rice Husk, Rice Straw, Wheat Straw, etc)

Air/O2

Domestic Burner, Engine With Producer Gas

2

Coal, Coke, Charcoal

do

do

3

Special Fuels Nitrocellulose (NC), HTPB, CTPB

Nitroglycerine, Ammonium Perchlorate , Ammonium Nitrate, Nitrogen Tetraoxide

Solid Propellant Rocket, Hybrid Rocket

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture3/3_6.htm[10/5/2012 11:12:21 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 4: Characterization of Solid Fuels The Lecture Contains: Oxygen, Water and Ash Content of Certain Solid Fuels Characterization of Solid Fuels Various Combustion Modes

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture4/4_1.htm[10/5/2012 11:13:04 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 4: Characterization of Solid Fuels Oxygen, Water and Ash Content of Certain Solid Fuels Moisture in Solid Fuel: 1. Free 2. Bound water Fuel moisture content will affect rate of combustion and overall efficiency. Ash: The inorganic materials, which remain as residue even after complete combustion. Ash content affects the performance of the combustion system. Ash content causes fouling of the boilers. Fuel

Oxygen (Dry, Ash-free) Moisture (Ash-free)

Ash (Dry)

Wood

40-45%

15-70%

0.1-1.0%

Peat

30-35%

70-90%

0.1-20%

Lignite coal

20-25%

20-30%

>5%

Bituminous coal

3-5%

10-5%

>5%

Anthracite coal

1-2%

2-4%

>5%

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture4/4_2.htm[10/5/2012 11:13:05 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 4: Characterization of Solid Fuels Characterization of Solid Fuels: Proximate Analysis: Used to determine the moisture content, volatile matter, fixed carbon and ash content in the solid fuel. To determine water content, few grams of fuel is heated around 378 K till it attains constant weight. Volatile matter is determined by heating the sample at 1173 K. Ultimate Analysis: Used to determine the major elemental composition of the solid fuel. Nitrogen content is determined by chemical method. Sulphur content is evaluated by burning the fuel to convert it into SO4 followed by precipitation method. Calorific value can be determined by bomb calorimeter.

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture4/4_3.htm[10/5/2012 11:13:05 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 4: Characterization of Solid Fuels Various Combustion Modes

Premixed Flame

: Fuel and oxidizer are mixed before actual combustion. Examples: Bunsen burner, LPG Stove

Diffusion Flame

: Fuel and oxidizer are mixed in the region where chemical reaction takes place.

Laminar and Turbulent : Based on the flow characteristics; Turbulent flow occurs in practical Flames combustion devices.

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture4/4_4.htm[10/5/2012 11:13:05 AM]

Objectives_template

Module 1: Introduction to Combustion Lecture 5: Scope of Combustion The Lecture Contains:

Scope of Combustion Image Sources

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture5/5_1.htm[10/9/2012 4:09:29 PM]

Objectives_template

Module 1: Introduction to Combustion Lecture 5: Scope of Combustion Scope of Combustion Industrial Process Thermal energy for process chemical plants, sugar industries, food processing industries are obtained through combustion. Iron, steel and other metals are produced from raw materials through combustion. Heat treatment and annealing of metals. Rotary kilns are used to produce Portlant cement.

Sugar Industry

Food Processing

Process Chemical Plant

Steel Plant (Figure 5.1)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture5/5_1a.htm[10/9/2012 4:09:30 PM]

Objectives_template

Module 1: Introduction to Combustion Lecture 5: Scope of Combustion Transportation Surface transport vehicles are operated by reciprocating IC Engines Gas turbine combustors are used widely in air and marine transportation sectors.

(Figure 5.2)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture5/5_1b.htm[10/9/2012 4:09:30 PM]

Objectives_template

Module 1: Introduction to Combustion Lecture 5: Scope of Combustion

Power Generation Most of the thermal power plants are operated by burning coal. Recently gas turbine power plants are coming up.

Fluidized Bed Power Plant

Coal Power Plant

Biomass Based Power Plant

Gas Turbine Power Plant (Figure 5.3)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture5/5_2.htm[10/9/2012 4:09:30 PM]

Objectives_template

Module 1: Introduction to Combustion Lecture 5: Scope of Combustion Waste Disposal Combustion finds application in disposing waste materials. Incinerators are used to dispose domestic and industrial wastes. In modern hospitals, incinerators are used to dispose hospital wastes safely.

(Figure 5.4)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture5/5_3.htm[10/9/2012 4:09:30 PM]

Objectives_template

Module 1: Introduction to Combustion Lecture 5: Scope of Combustion Fire Sometimes fire causes damage to life and property. Forest Fire: Damages natural resources and lives. Structural Fire: Damages property and human lives. Effective fire breakers should be designed and implemented to avoid fire hazard. By using proper construction materials, Fire hazard can be minimized. Marine life is very much affected by oil spill fire.

(Figure 5.5)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture5/5_4.htm[10/9/2012 4:09:30 PM]

Objectives_template

Module 1: Introduction to Combustion Lecture 5: Scope of Combustion Environmental pollution Combustion of any fuel produces certain amount of emissions such as smoke, ash, soot, and other harmful gases. Major pollution generated in combustion system are CO, CO 2 , NO, NO 2 , SO2 , ash, etc. These are due to incomplete combustion and can be minimized by increasing the residence time of fuel-oxidizer mixture in the combustor. Sources

Particulates

Carbon Monoxide

Unburnt Hydrocarbon

Nitrogen Sulfur oxides dioxides

Transportation

7

79

60

15

6

Stationary Combustion Systems/Electricity

8

speed of sound at isochoric condition detonation attains infinite velocity Region III: In this region Hence

Therfore

in this region is imaginary and physically impossible

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture22/22_5.htm[10/5/2012 4:06:06 PM]

weak

Objectives_template

Module 5: Premixed Flame Lecture 22: Introduction Laminar Premixed Flame

(Figure 22.6) (Figure 22.7) First laboratory premixed Glame burner : Invented by Robert Bunsen in 1855

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture22/22_6.htm[10/5/2012 4:06:07 PM]

Objectives_template

Module 5: Premixed Flame Lecture 22: Introduction

Luminous Zone

Flame radiation: 3300 to 4400 A°

(Figure 22.8)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture22/22_7.htm[10/5/2012 4:06:07 PM]

Objectives_template

Module 5: Premixed Flame Lecture 23: Structure of 1D Premixed Flame

The Lecture Contains: Structure of 1D Premixed Flame Laminar Flame Theory Flame Thickness Burning Velocity Measurement Methods

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture23/23_1.htm[10/5/2012 4:07:22 PM]

Objectives_template

Module 5: Premixed Flame Lecture 23: Structure of 1D Premixed Flame Structure of 1D Premixed Flame

Preheat zone: Negligibly small heat release Certain chemical reactions take place in this zone Reaction zone: most of the chemical energy is released in the form of heat Decomposition of fuel takes place, leading to intermediate radical formation Reaction zone is very thin as compared to the preheat zone. Temperature gradient and concentration gradient are high .

(Figure 23.1)

Recombination zone: CO 2 and H 2 O are formed; No heat release in this zone

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture23/23_2.htm[10/5/2012 4:07:22 PM]

Objectives_template

Module 5: Premixed Flame Lecture 23: Structure of 1D Premixed Flame Laminar Flame Theory Assumptions: 1D, steady, inviscid flow. Flame is quite thin. Ignition temperature is very close to flame temperature. No heat loss including radiation; Adiabatic flame. Pressure difference across the flame is negligibly small. Binary diffusion, Fourier and Fick's law are valid. Unity Lewis number. Constant transport properties

(1)

Mass conservation: Species conservation:

Energy equation:

Fuel:

(2)

Oxidizer:

(3)

Product:

(4)

(5) Global reaction mechanism:

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture23/23_3.htm[10/5/2012 4:07:22 PM]

(6)

Objectives_template

Module 5: Premixed Flame Lecture 23: Structure of 1D Premixed Flame Laminar Flame Theory (Contd.) Heat release due to chemical reaction: (7) Now energy equation becomes

In the reaction zone, (8)

Boundary conditions (For preheat zone) (10) (11) Recasted energy preheat zone,

equation

for

Rewriting, E.g. (11). (9)

(12)

Heat transfer due to conduction is balanced by convective heat transfer.

(13)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture23/23_4.htm[10/5/2012 4:07:23 PM]

Objectives_template

Module 5: Premixed Flame Lecture 23: Structure of 1D Premixed Flame Laminar Flame Theory (Contd.) Combining equations (10) and (13), (14)

(15) Mean fuel burning rate can also be expressed as,

Also, (16)

(19) Expression becomes,

Combining equations (15) and (16),

for

burning

(17) Mean fuel burning rate per unit volume, (18)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture23/23_5.htm[10/5/2012 4:07:23 PM]

velocity

Objectives_template

Module 5: Premixed Flame Lecture 23: Structure of 1D Premixed Flame Flame Thickness

Ignition temperature can be approximated as

The temperature gradient at the flame surface is

Flame thickness: (Figure 23.2) Where,

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture23/23_6.htm[10/5/2012 4:07:23 PM]

Objectives_template

Module 5: Premixed Flame Lecture 23: Structure of 1D Premixed Flame Burning Velocity Measurement Methods

(Figure 23.3) Flame front visualization Luminous photography Shadowgraph photography Schlieren Photography

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture23/23_7.htm[10/5/2012 4:07:23 PM]

Objectives_template

Module 5: Premixed Flame Lecture 24: Tube Method

The Lecture Contains: Tube Method Combustion Bomb Method Soap Bubble Method Stationary Flame Method (Bunsen Burner) Flat Flame Burner Effect of Equivalence Ratio on S L

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture24/24_1.htm[10/5/2012 4:08:31 PM]

Objectives_template

Module 5: Premixed Flame Lecture 24: Tube Method Tube Method

(Figure 24.1) Procedure:

Combustible mixture is filled in the tube On ignition at one end, the flame propagates through the tube

Features:

Inner dia of tube should be greater than the quenching diameter The flame is planar in the beginning and curved towards downstream, due to buoyancy Natural convection distorts the planar flame front due to difference in densities Friction at the tube wall is also a reason for parabolic shape of the flame

The burning velocity is given by

: Flame front velocity : Unburnt gas velocity

: Cross-sectional area of tube

: Flame surface area

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture24/24_2.htm[10/5/2012 4:08:31 PM]

Objectives_template

Module 5: Premixed Flame Lecture 24: Tube Method Combustion Bomb Method

(Figure 24.2)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture24/24_3.htm[10/5/2012 4:08:32 PM]

Objectives_template

Module 5: Premixed Flame Lecture 24: Tube Method Soap Bubble Method

(Figure 24.3)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture24/24_4.htm[10/5/2012 4:08:32 PM]

Objectives_template

Module 5: Premixed Flame Lecture 24: Tube Method Stationary Flame Method (Bunsen Burner)

(Figure 24.4)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture24/24_5.htm[10/5/2012 4:08:32 PM]

Objectives_template

Module 5: Premixed Flame Lecture 24: Tube Method Flat Flame Burner

(Figure 24.5)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture24/24_6.htm[10/5/2012 4:08:32 PM]

Objectives_template

Module 5: Premixed Flame Lecture 24: Tube Method Effect of Equivalence Ratio on S L

(Figure 24.6)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture24/24_7.htm[10/5/2012 4:08:32 PM]

Objectives_template

Module 5: Premixed Flame Lecture 25: Effect of Oxygen Concentration on S L

The Lecture Contains: Effect of Oxygen Concentration on S L Effect of Initial Pressure and Temperature on S L Effect of Inert Additives Flame Extinction Flame Quenching Simplified Analysis for Quenching Diameter

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture25/25_1.htm[10/5/2012 4:09:09 PM]

Objectives_template

Module 5: Premixed Flame Lecture 25: Effect of Oxygen Concentration on S L Effect of Oxygen Concentration on S L

(Figure 25.1)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture25/25_2.htm[10/5/2012 4:09:09 PM]

Objectives_template

Module 5: Premixed Flame Lecture 25: Effect of Oxygen Concentration on S L Effect of Initial Pressure and Temperature on S L

This relation is supported by experimental data n: Overall order of global chemical reaction for HC flames with for HC flames with for HC flames with

Pressure index, For

,

m

is

negative,

indicating burning velocity with decreasing pressure

increases

For

,

m

(Figure 25.2)

is

constant, indicating burning velocity is constant

For

,

m

is positive,

indicating burning velocity decreases with decrease in initial pressure

(Figure 25.3)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture25/25_3.htm[10/5/2012 4:09:09 PM]

Objectives_template

Module 5: Premixed Flame Lecture 25: Effect of Oxygen Concentration on S L Effect of Inert Additives

(Figure 25.4)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture25/25_4.htm[10/5/2012 4:09:09 PM]

Objectives_template

Module 5: Premixed Flame Lecture 25: Effect of Oxygen Concentration on S L Flame Extinction

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture25/25_5.htm[10/5/2012 4:09:09 PM]

Objectives_template

Module 5: Premixed Flame Lecture 25: Effect of Oxygen Concentration on S L Flame Quenching Fuel

Oxidizer

SL (cm/s)

dq (mm)

CH4

Air

40

2.5

CH4

O2

C3 H8

Air

C3 H8

O2

C2 H2

Air

C2 H2

O2

0.2

CO

Air

2.8

H2

Air

H2

O2

0.3 45

2.0 0.25

140

210

0.8

0.5 0.2

Quenching diameter for various stoichiometric fuel-oxidizer ratio.

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture25/25_6.htm[10/5/2012 4:09:09 PM]

Objectives_template

Module 5: Premixed Flame Lecture 25: Effect of Oxygen Concentration on S L Simplified Analysis for Quenching Diameter

Rate of heat generated per unit volume

Heat generated in flame volume

Heat loss rate due to wall conduction

(Figure 25.5) Assuming linear temperature distribution in flame,

Quenching diameter

After simplification,

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture25/25_7.htm[10/5/2012 4:09:09 PM]

Objectives_template

Module 5: Premixed Flame Lecture 26: Flammability Limits

The Lecture Contains: Flammability Limits Effect of Pressure on Limit Mixture Ignition Flame Stabilization Flame Stabilization by Burner Rim Turbulent Premixed Flame

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture26/26_1.htm[10/5/2012 4:09:50 PM]

Objectives_template

Module 5: Premixed Flame Lecture 26: Flammability Limits Flammability Limits

Instrument to determine flammability limit

Vertical glass tube of 1.2 m length and 50 mm ID

(Figure 26.1)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture26/26_2.htm[10/5/2012 4:09:50 PM]

Objectives_template

Module 5: Premixed Flame Lecture 26: Flammability Limits Effect of Pressure on Limit Mixture

(Figure 26.2)

Fuel

Oxidizer

Stoichiometry (% Fuel)

LFL (%)

UFL (%)

Methane

Air

9.5

5

15

Ethane

Air

5.6

2.8

12.4

Propane

Air

5.6

2.1

9.1

CO

Air

29.5

12

74.2

Hydrogen

Air

29.2

4

74.2

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture26/26_3.htm[10/5/2012 4:09:50 PM]

Objectives_template

Module 5: Premixed Flame Lecture 26: Flammability Limits Ignition

Energy generated in flame = Ensible enthalpy Mass

Substituting quenching diameter

Substituting flame thickness

Dependence on pressure

(Figure 26.3)

Fuel-Air

MIE (mJ)

Methane-air

0.47

Ethane-air

0.4

Butane-air

0.34

Acetylene-air

0.03

CO-air

0.05

Hydrogen-air

0.02

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture26/26_4.htm[10/5/2012 4:09:51 PM]

Objectives_template

Module 5: Premixed Flame Lecture 26: Flammability Limits Flame Stabilization Local gas flow velocity = Local burning velocity

(Figure 26.4)

(Figure 26.5)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture26/26_5.htm[10/5/2012 4:09:51 PM]

Objectives_template

Module 5: Premixed Flame Lecture 26: Flammability Limits Flame Stabilization by Burner Rim

(Figure 26.6) Stability of flame front near the rim of Bunsen burner

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture26/26_6.htm[10/5/2012 4:09:51 PM]

Objectives_template

Module 5: Premixed Flame Lecture 26: Flammability Limits Turbulent Premixed Flame

(Figure 26.7)

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture26/26_7.htm[10/5/2012 4:09:51 PM]

Objectives_template

Module 5: Premixed Flame Lecture 27: Flame Stabilization

The Lecture Contains: Turbulent Flame Regimes The Borghi Diagram Turbulent Burning Velocity Wrinkled Laminar Flame Distributed Reaction Flamelet in Eddies

file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture27/27_1.htm[10/5/2012 4:10:34 PM]

Objectives_template

Module 5: Premixed Flame Lecture 27: Flame Stabilization Turbulent Flame Regimes Turbulent Flame Regimes

Reynolds number for turbulent flame:

Chemical reaction time:

Chemical reaction time:

Damkohler number

If Da >> 1, fast chemistry regime If Da