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Combustion Basics


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Title: Combustion Basics

Unit I
  • Combustion Basics
  • Fuel
  • Combustion Stoichiometry
  • Air/Fuel Ratio
  • Equivalence Ratio
  • Air Pollutants from Combustion

  • Fuel
  • Gaseous Fuels
  • Natural gas
  • Refinery gas
  • Liquid Fuels
  • Kerosene
  • Gasoline, diesel
  • Alcohol (Ethanol)
  • Oil
  • Solid Fuels
  • Coal (Anthracite, bituminous, subbituminous,
  • Wood

  • Fuel
  • Properties of Selected Fuels

C2H6 C3H8 Other HCs H2S
Heating Value
(wt) (106
J/m3) Natural gas (No.1) 87.7 5.6
2.4 1.8 2.7
43.2 Natural gas (No.2) 88.8 6.4
2.7 2.0 0.0004
Heating value (wt) (106 J
kg-1) Gasoline (No.2) 86.4 12.7
0.1 0.1 0.4-0.7

(Ultimate analysis)
Volatile matter Moisture Ash Heating
value ()
() () ()
(106 J kg-1) Anthracite (PA) 77.1
3.8 5.4 13.7
27.8 Bituminous (PA) 70.0 20.5
3.3 6.2
33.3 Subbituminous (CO) 45.9 30.5
19.6 4.0 23.6 Lignite
(ND) 30.8 28.2
34.8 6.2 16.8
(Approximate analysis)
Which one has a higher energy density per
mass? Do they burn in the same way?
Data from Flagan and Seinfeld, Fundamentals of
Air Pollution Engineering, 1988, Prentice-Hall.
  • Combustion Stoichiometry
  • Combustion in Oxygen
  1. Can you balance the above equation?
  2. Write the reactions for combustion of methane and
    benzene in oxygen, respectively.

  • Combustion Stoichiometry
  • Combustion in Air (O2 21, N2 79)
  1. Can you balance the above equation?
  2. Write the reactions for combustion of methane and
    benzene in air, respectively.

  • Air-Fuel Ratio
  • Air-Fuel (AF) ratio
  • AF m Air / m Fuel
  • Where m air mass of air in the feed mixture
  • m fuel mass of fuel in the feed mixture
  • Fuel-Air ratio FA m Fuel /m Air 1/AF
  • Air-Fuel molal ratio
  • AFmole nAir / nFuel
  • Where nair moles of air in the feed mixture
  • nfuel moles of fuel in the feed mixture

What is the Air-Fuel ratio for stoichiometric
combustion of methane and benzene, respectively?
  • Air-Fuel Ratio
  • Rich mixture
  • - more fuel than necessary
  • (AF) mixture lt (AF)stoich
  • Lean mixture
  • - more air than necessary
  • (AF) mixture gt (AF)stoich

Most combustion systems operate under lean
conditions. Why is this advantageous?
Consider the combustion of methanol in an engine.
If the Air-Fuel ratio of the actual mixture is
20, is the engine operating under rich or lean
  • Equivalence Ratio

Equivalence ratio shows the deviation of an
actual mixture from stoichiometric conditions.
The combustion of methane has an equivalence
ratio F0.8 in a certain condition. What is the
percent of excess air (EA) used in the
combustion? How does temperature change as F
  • Formation of NOx and CO in Combustion
  • Thermal NOx
  • Oxidation of atmospheric N2 at high temperatures
  • Formation of thermal NOx is favorable at higher
  • Fuel NOx
  • Oxidation of nitrogen compounds contained in the
  • Formation of CO
  • Incomplete Combustion
  • Dissociation of CO2 at high temperature

  • Air Pollutants from Combustion

Source Seinfeld, J. Atmospheric Chemistry and
Physics of Air Pollution.
How do you explain the trends of the exhaust HCs,
CO, and NOx as a function of air-fuel ratio? How
do you minimize NOx and CO emission?
  • Quick Reflections
  • Fuel
  • Combustion Stoichiometry
  • Air/Fuel Ratio
  • Equivalence Ratio
  • Air Pollutants from Combustion

Engine Fuel System (SI Petrol)
  • Fuel Tank normally positioned in the rear boot
    area, either under the floor pan for estate cars
    or over the rear axle for saloons, the latter
    being a safer position. Should the engine be
    mounted in the rear, the fuel tank is normally
    positioned in the front boot area, either over
    the bulkhead or flat across the boot floor pan ,
    the latter providing more boot space, but is more
    exposed to danger in a head on crash. The fuel
    tank made be made from pressed steel and coated
    inside to prevent corrosion, or a synthetic
    rubber compound or flame resistant plastic.
    Inside the fuel tank is normally located the fuel
    gauge sender unit and electrically driven fuel
    pump with a primary filter in a combined module.
    Internal fuel tank baffles are used to prevent
    fuel surge. The fuel tank is pressurised to about
    2 psi to prevent fuel vaporization and pollution.
    The fuel tank is vented through its own venting
    system and the engine managements emission
    control systems again to control pollution.
  • Fuel pipes These can be made from steel or
    plastic and are secured by clips at several
    points along the underside of the vehicle. To
    allow for engine movement and vibration, rubber
    hoses connect the pipes to the engine. Later fuel
    pipes use special connectors which require
    special tools to disconnect the pipes.

Engine Fuel System (SI Petrol)
  • Fuel Filters to prevent dirt and fluff entering
    the fuel pump a filter is fitted on the suction
    side of the pump. On the pressure side of the
    pump a secondary filter is used, this is a much
    finer filter in that it prevents very small
    particles of dirt reaching the carburettor or
    fuel injection equipment. It should be renewed at
    the correct service interval as recommended by
    the manufacturer. When the filter is replaced, it
    must be fitted in the direction of fuel flow.
  • Air Filters air cleaners and silencers are
    fitted to all modern vehicles. Its most important
    function is to prevent dust and abrasive
    particles from entering the engine and causing
    rapid wear. Air filters are designed to give
    sufficient filtered air, to obtain maximum engine
    power. The air filter must be changed at the
    manufactures recommended service interval. The
    air filter/cleaner also acts as a flame trap and
    silencer for the air intake system.
  • Fuel Pump this supplies fuel under high
    pressure to the fuel injection system, or under
    low pressure to a carburettor.
  • Carburettor this is a device which atomizes the
    fuel and mixes it which the correct amount of
    air, this device has now been superseded by
    modern electronic fuel injection.

  • Float chamber (function) to set and maintain
    the fuel level within the carburettor, and to
    control the supply fuel to the carburettor
  • Operation when air passes through the venturi
    due to the engines induction strokes, it creates
    a depression (suction), around the fuel spray
    outlet. Atmospheric pressure is acting on the
    fuel in the float chamber, the difference in
    theses pressures causes the fuel to flow from the
    float chamber, through the jet and into the
    stream. This causes the petrol to mix with the
    air rushing in to form a combustible mixture. The
    required air fuel ratio can be obtained by using
    a jet size which allows the correct amount of
    fuel to flow for the amount of air passing
    through the
  • Defects of the simple carburettor.
  • As engine speed increases, air pressure and
    density decreases i.e. the air gets thinner,
    however the quantity of fuel increases i.e.
    greater pressure exerted on the fuel, this causes
    the air/fuel mixture to get progressively richer
    (to much fuel).
  • As the engine speed decreases, the air/fuel
    mixture becomes progressively weaker. Some form
    of compensation is therefore required so that the
    correct amount of air and fuel is supplied to the
    engine under all operating conditions.

The Simple Carburettor
The Float Chamber
Operation of the Venturi
Choke Valve closed
The Throttle Valve controls the amount of air
fuel mixture entering the engine and therefore
engine power
The Choke Valve is used to provide a rich
air/fuel ratio for cold starting
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Air Fuel Ratio
  • Fuel mixture strengths petrol will not burn
    unless it is mixed with air, to obtain the best
    possible combustion of the fuel, which should
    result in good engine power and fuel consumption
    and low emissions (pollution), the air fuel ratio
    must be chemically correct i.e. the right amount
    of air and fuel must be mixed together to give
    an air fuel ratio of 14.7 to 1 by mass. This is
    referred to as the shoitcmetreic air fuel ratio,
    this ratio can also be describe by the term
    Lambda. Lamba is the Greek word meaning air.
    When their is more air present than fuel in the
    air fuel mixture, it is said to be weak or
    lean i.e. not enough fuel e.g. a ratio of 25 to
    1, this results in a Lambda reading of more than
    1.When their is not enough air present, the
    mixture is referred to as rich e.g. a air fuel
    ratio of 8 to 1, in this case Lambda equals less
    than 1.
  • Weak/lean air/fuel mixtures can result in low
    fuel consumption, low emissions (pollution),
    however, weak air fuel mixtures can also result
    in poor engine performance (lack of power) and
    high engine temperatures ( because the fuel burns
    more slowly)
  • Rich air/ fuel mixtures can result in greater
    engine power, however this also results in poorer
    fuel consumption and greatly increased emissions

Engine S I Fuel System
  • ECU Electronic control unit. This contains a
    computer which takes information from sensors and
    controls the amount of fuel injected by operating
    the injectors for just the right amount of time.
  • Air flow/mass meter A sensor used to tell the
    ECU how much air is being drawn into the engine.
  • MAP sensor Manifold absolute pressure sensor.
    This senses the pressure in the engines inlet
    manifold, this gives an indication of the load
    the engine is working under.
  • Speed/crankshaft sensor This tells the ECU has
    fast the engine is rotating and sometimes the
    position of the crankshaft.
  • Temperature sensor Coolant temperature is used
    determine if more fuel is needed when the engine
    is cold or warming up.
  • Lambda sensor A sensor located in the exhaust
    system which tells the ECU the amount of oxygen
    in the exhaust gases, form this the ECU can
    determine if the air/fuel ratio is correct.
  • Fuel pump A pump, normally located in the fuel
    tank, which supplies fuel under pressure to the
    fuel injectors.

Engine S I Fuel System
  • Fuel filter keeps the fuel very clean to
    prevent the injectors becoming damaged or
  • Fuel rail A common connection to multi point
    injectors, acts a reservoir of fuel (small tank
    of fuel).
  • Injector A electrical device which contains a
    winding or solenoid. When turned on by the ECU,
    the injector opens and fuel is sprayed into the
    inlet manifold, or into the combustion chamber
  • Idle actuator A valve controlled by the ECU
    which controls the idle speed of the engine.
  • ECU Electronic Unit. This contains a computer
    which takes information from sensors and controls
    the amount of fuel injected by operating the
    injectors for just the right amount of time. The
    ECU also controls the operation of the ignition
    and the other engine rated systems.

Typical Fuel System
1. Fuel Supply System
Components that supply clean fuel to the fuel
metering system (fuel pump, fuel pipes, fuel
2. Air Supply System
Components that supply controlled clean air to
the engine (air filter, ducting, valves).
3. Fuel Metering System
Components that meter the correct amount of fuel
(and air) entering the engine (injectors,
pressure regulator, throttle valve).
The exact components used will vary with fuel
system type and design.
25 of 14
Introduction to Electronic Petrol Throttle/Single
Point Fuel Injection Systems
The Carburettor has now been replaced with petrol
injection systems. These systems supply the
engine with a highly atomized mixture of air and
fuel in the correct air/fuel ratio. This has the
following advantages over the carburettor
systems Lower exhaust emissions
(pollution) Better fuel consumption Smoother
engine operation and greater power Automatic
adjustment of the air/fuel ratio to keep the
vehicles emissions (pollution) to a minimum.
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Air drawn in by the engine
Throttle Body/Single Point S.I. Fuel Injection
Throttle Body
Fuel Supply
Fuel Injector (one off)
Throttle Valve
Inlet Manifold
The Engine
Single Point Electronic Fuel Injection (EFI)
EFI systems are classified by using the point of
Single Point (Throttle Body) Fuel Injection
A fuel injector (may be 2) is located in a
throttle body assembly that sits on top of the
inlet manifold.
Fuel is sprayed into the inlet manifold from
above the throttle valve, mixing with incoming
Fuel quantity, how much feul is injected is
controlled by an ECU.
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Electronic Fuel Injector Operation
An injector sprays fuel into the inlet manifold
by use of a solenoid coil.
When the coil is switch on by the ECU, it pulls
the armature/needle valve away from the nozzle,
allowing pressurized fuel into the engine.
When the coil is not switched on, the spring
pushes the armature/needle against the nozzle, no
fuel is injected into the inlet manifold
Injectors are more precise and efficient than
Electrical connector
Solenoid coil
Needle valve
Fuel in
Fuel filter
Single Point Injection
The ECU (Brain) receives Information from varies
sensors. From this information it works out how
much fuel the engine needs
Multi Point S.I. Fuel Injection
Air drawn in by the engine
Fuel Injectors
Throttle Valve
Inlet Manifold
Fuel Supply
Typical S.I. Fuel System Layout (Simplified)
Fuel Not used is returned to the fuel tank
Engine Combustion Chamber
Fuel Tank
Fuel Pressure Regulator EFI Only
Inlet Manifold
Fuel Pump
Carburettor Or Single Point Throttle Body Housing
Fuel Filters
Fuel Injector or Carburettor Venturi
Liquid fuel

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What is ethanol?
  • GM Commercial
  • CH3CH2OH
  • Ethanol is a clean-burning, high-octane fuel that
    is produced from renewable sources.
  • At its most basic, ethanol is grain alcohol,
    produced from crops such as corn.
  • Since pure 100 ethanol is not generally used as
    a motor fuel, a percentage of ethanol is combined
    with unleaded gasoline, to form E10 and E85
  • E10 10 ethanol and 90 unleaded gasoline, is
    approved for use in any US vehicle
  • E85 85 ethanol and 15 unleaded gasoline, is an
    alternative fuel for use in flexible fuel
    vehicles (FFVs).

How is it made?
  • Ethanol can be made by fermenting almost any
    material that contains starch.
  • Most of the ethanol in the U.S. is made using a
    dry mill process.
  • In the dry mill process, the starch portion of
    the corn is fermented into sugar then distilled
    into alcohol
  • Prior to fermentation, high-value chemicals are
    removed from the biomass. These include
    fragrances, flavoring agents, food-related
    products, and high value nutraceuticals with
    health and medical benefits.
  • There are two main valuable co-products created
    in the production of ethanol distillers grain
    and carbon dioxide. Distillers grain is used as a
    highly nutritious livestock feed while carbon
    dioxide is collected, compressed, and sold for
    use in other industries.

Energy Balance of Ethanol
Energy Balance
  • Although CO2 is released during ethanol
    production and combustion, it is recaptured as a
    nutrient to the crops that are used in its
  • Unlike fossil fuel combustion, which unlocks
    carbon that has been stored for millions of
    years, use of ethanol results in comparatively
    lower increases to the carbon cycle.
  • Ethanol also degrades quickly in water and,
    therefore, poses a smaller risk to the
    environment than an oil or gasoline spill.
  • Research studies from a variety of sources have
    found ethanol to have a positive net energy
    balance. The most recent, by the U.S. Department
    of Agriculture, shows that ethanol provides an
    average net energy gain of at least 77.
  • It takes less than 35,000 BTUs of energy to turn
    corn into ethanol, while the ethanol offers at
    least 77,000 BTUs of energy. Thus ethanol has a
    positive energy balancemeaning the ethanol
    yields more energy than it takes to produce it.

Impact on air quality
  • Using ethanol-blended fuel has a positive impact
    on air quality. By adding oxygen to the
    combustion process which reduces exhaust
    emissionsresulting in a cleaner fuel for cleaner
  • Ethanol reduces the emissions of carbon monoxide,
    VOX, and toxic air emissions
  • Since ethanol is an alcohol based product, it
    does not produce hydrocarbons when being burned
    or during evaporation thus decreasing the rate of
    ground level ozone formation.
  • Ethanol reduces pollution through the volumetric
    displacement of gasoline. The use of ethanol
    results in reductions in every pollutant
    regulated by the EPA, including ozone, air
    toxins, carbon monoxide, particulate matter, and

Impact on energy independence
  • Since it is domestically produced, ethanol helps
    reduce America's dependence upon foreign sources
    of energy. U.S. ethanol production provides more
    than 4 billion gallons of renewable fuel for our
  • Current U.S. ethanol production capacity can
    reduce gasoline imports by more than one-third
    and effectively extend gasoline supplies at a
    time when refining capacity is at its maximum.
  • According to the Energy Information
    Administration, the 7.5 billion gallon ethanol
    production level in the recently enacted
    Renewable Fuels Standard could reduce oil
    consumption by 80,000 barrels per day.

Impact on economy
  • In a 1997 study The Economic Impact of the Demand
    for Ethanol, Northwestern Universitys Kellogg
    School of Management found that
  • During ethanol plant construction, approximately
    370 local jobs are created.
  • During ethanol plant operation, up to 4,000 local
    jobs are created.
  • Ethanol plant construction creates 60 million to
    130 million in additional income.
  • Ethanol plant operation creates 47 million to
    100 million in additional income.
  • American-made, renewable ethanol directly
    displaces crude oil we would need to import,
    offering our country critically needed
    independence and security from foreign sources of
  • The U.S. Department of Agriculture has concluded
    that a 100 million gallon ethanol facility could
    create 2,250 local jobs for a single community.
    Ethanol production creates domestic markets for
    corn and adds 4-6 cents a bushel for each 100
    million bushels used. Better prices mean less
    reliance on government subsidy programs not to
    mention higher income and greater independence
    for farmers.

Impact on auto industry
  • Ethanol could be the alternative fuel source that
    catapults sales of American auto manufacturers.
  • GM and Ford are looking for environmental fixes
    that are quicker and cheaper than the more costly
    hybrids and futuristic fuel cells. Both companies
    started promoting flexible-fuel vehicles (FFVs)
    aggressively this year.
  • General Motors tied their new campaign "Live
    Green, Go Yellow.'' to not only Super Bowl Sunday
    but the opening of the Winter Olympics as well.
  • Since only about 600 of the nation's 170,000
    filling stations sell E85, both companies
  • have begun programs to install
  • E85 pumps at more stations.

Impact on politics
  • President Bush gave ethanol a big plug in his
    State of the Union address, by stating that
  • The United States must move beyond a
    petroleum-based economy and develop new ways to
    power automobiles. The Administration will
    accelerate research in cutting-edge methods of
    producing "cellulosic ethanol" with the goal of
    making the use of such ethanol practical and
    competitive within 6 years.
  • The Biorefinery Initiative. To achieve greater
    use of "homegrown" renewable fuels in the United
    States, advanced technologies need to be
    perfected to make fuel ethanol from cellulosic
    (plant fiber) biomass, which is now discarded as
    waste. The President's 2007 Budget will include
    150 million a 59 million increase over FY06
    to help develop bio-based transportation fuels
    from agricultural waste products, such as wood
    chips, stalks, or switch grass. Research
    scientists say that accelerating research into
    "cellulosic ethanol" can make it cost-competitive
    by 2012, offering the potential to displace up to
    30 of the Nation's current fuel use.
  • Associated Press, March 2, 2006 To increase the
    production of alternative fuel sources, the Bush
    administration has proposed allowing ethanol
    plants to emit more air pollutants. The EPA
    announced that it would propose a rule to raise
    the emissions threshold for corn milling plants
    that produce ethanol fuel, allowing them to emit
    up to 250 tons a year of air pollutants before
    setting off tougher restrictions on production.
    Corn milling plants can now emit 100 tons a year.

Problems with Ethanol
  • Odors as a public nuisance, ex New Energy
    Ethanol Plant here in South Bend
  • Green house gas emissions have sometimes shown to
    be equivalent to those of gasoline (data is often
  • Environmental performance of ethanol varies
    greatly depending on the production process
  • Costs involved with building new facilities for
    ethanol production
  • New ways to maximize crop production are
  • Research is needed to refine the chemical
    processes to separate, purify and transform
    biomass into usable fuel

Gaseous Fuels

1. Introduction
  • There are numerous factors which need to be taken
    into account when selecting a fuel for any give
  • Economics is the overriding consideration-the
    capital cost of the combustion equipment together
    with the running costs, which are fuel purchasing
    and maintenance.

2. Natural Gas
  • Natural gas is obtained from deposits in
    sedimentary rock formations which are also
    sources of oil.
  • It is extracted from production fields and piped
    (at approximately 90 bar) to a processing plant
    where condensable hydrocarbons are extracted from
    the raw product.

  • It is then distributed in a high-pressure mains
  • Pressure losses are made up by intermediate
    booster stations and the pressure is dropped to
    around 2500 Pa in governor installations where
    gas is taken from the mains and enters local
    distribution networks.

  • The initial processing, compression and heating
    at governor installations uses the gas as an
    energy source.
  • The energy overhead of the winning and
    distribution of a natural gas is about 6 of the
    extracted calorific value.

  • The composition of a natural gas will vary
    according to where it was extracted from, but the
    principal constituent is always methane.
  • There are generally small quantities of higher
    hydrocarbons together with around 1 by volume of
    inert gas (mostly nitrogen).

  • The characteristics of a typical natural gas
    areComposition ( vol) CH4 92 other
    HC 5 inert gases 3Density (kg/m3) 0.7Gross
    calorific value (MJ/m3) 41

3. Town gas (Coal Gas)
  • The original source of the gas which was
    distributed to towns and cities by supply
    utilities was from the gasification of coal.
  • The process consisted of burning a suitable grade
    of coal in a bed with a carefully controlled air
    supply (and steam injection) to produce gas and
    also coke.

  • This is still the gas supplied by utility
    companies in many parts of the world (e.g. Hong
    Kong) and there is continuing longer-term
    development of coal gasification, since it is one
    of the most likely ways of exploiting the
    substantial world reserves of solid fuel.
  • It was first introduced into the UK and the USA
    at the beginning of the 19th century.

  • The gas was produced by heating the raw coal in
    the absence of air to drive off the volatile
  • This was essentially a two-stage process, with
    the carbon in the coal being initially oxidized
    to carbon dioxide, followed by a reduction to
    carbon monoxide C O2 ? CO2 CO2 C ? 2CO

  • The volatile constituents from the coal were also
    present, hence the gas contained some methane and
    hydrogen from this source.
  • An improved product was obtained if water was
    admitted to the reacting mixture, the water being
    reduced in the so-called water gas shift
    reaction C H2O ? CO H2

  • This gas was produced by a cyclic process where
    the reacting bed was alternately blown with air
    and steam- the former exhibiting an exothermic,
    and the latter an endothermic, reaction.
  • A typical town gas produced by this process has
    the following propertiesComposition (
    vol) H2 48 CO 5 CH4 34 CO2 13Density
    (kg/m3) 0.6Gross calorific value (MJ/m3) 20.2

  • A more recent gasification process, developed
    since 1936, is the Lurgi gasifier.
  • In this process the reaction vessel is
    pressurized, and oxygen (as opposed to air) as
    well as steam is injected into the hot bed.
  • The products of this stage of the reaction are
    principally carbon monoxide and hydrogen.

  • Further reaction to methane is promoted by a
    nickel catalyst at temperatures of about
    250-350? CO 3H2 ? CH4 H2O
  • The sulfur present in the coal can be removed by
    the presence of limestone as follows H2 S ?
    H2S H2S CaCO3 ? CaS H2O CO2

4. Liquefied Petroleum Gas (LPG)
  • LPG is a petroleum-derived product distributed
    and stored as a liquid in pressurized containers.
  • LPG fuels have slightly variable properties, but
    they are generally based on propane (C3H8) or the
    less volatile butane (C4H10).

  • Compared to the gaseous fuel described above,
    commercial propane and butane have higher
    calorific values (on a volumetric basis) and
    higher densities.
  • Both these fuels are heavier than air, which can
    have a bearing on safety precautions in some

  • Typical properties of industrial LPG are given
    below Gas Propane Butane Density
    (kg/m3) 1.7-1.9 2.3-2.5 Gross calorific value
    (MJ/m3) 96 122 Boiling point (? at 1
    bar) -45 0

5. Combustion of Gaseous Fuels
  • 5.1 Flammability Limits
  • Gaseous fuels are capable of being fully mixed
    (i.e. at a molecular level) with the combustion
  • However, not all mixtures of fuel and air are
    capable of supporting, or propagating, a flame.

  • Imagine that a region of space containing a
    fuel/air mixture consists of many small discrete
    (control) volumes.
  • If an ignition source is applied to one of these
    small volumes, then a flame will propagate
    throughout the mixture if the energy transfer out
    of the control volume is sufficient to cause
    ignition in the adjacent regions.

  • Clearly the temperature generated in the control
    volume will be greatest if the mixture is
    stoichiometric, where as if the mixture goes
    progressively either fuel-rich or fuel-lean, the
    temperature will decrease.
  • When the energy transfer from the initial control
    volume is insufficient to propagate a flame, the
    mixture will be nonflammable.

  • This simplified picture indicates that there will
    be upper and lower flammability limits for any
    gaseous fuel, and that they will be approximately
    symmetrically distributed about the
    stoichiometric fuel/air ratio.

  • Flammability limits can be experimentally
    determined to a high degree of repeatability in
    an apparatus developed by the US Bureau of
  • The apparatus consists of a flame tube with
    ignition electrodes near to its lower end (Fig.
    7.1, next slide).

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  • Intimate mixing of the gas/air mixture is
    obtained by recirculating the mixture with a
  • Once this has been achieved, the cover plate is
    removed and a spark is activated.
  • The mixture is considered flammable if a flame
    propagates upwards a minimum distance of 750 mm.

  • The limits are affected by temperature and
    pressure but the values are usually quoted as
    volume percentages at atmospheric pressure and
  • Typical values for some gaseous fuels
    areFuel Lower Explosion Limit (LEL) Upper
    Explosion Limit (UEL) Methane 5 15Propane 2
    10Hydrogen 4 74Carbon monoxide 13 74

5.2 Burning Velocity
  • The burning velocity of a gas-air mixture is the
    rate at which a flat flame front is propagated
    through its static medium, and it is an important
    parameter in the design of premixed burners.
  • A simple method of measuring the burning velocity
    is to establish a flame on the end of a tube
    similar to that of a laboratory Bunsen burner.

  • When burning is aerated mode, the flame has a
    distinctive bright blue cone sitting on the end
    of the tube.
  • The flame front on the gas mixture is travelling
    inwards normally to the surface of this cone
    (Fig. 7.2, next slide).

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  • If U represents the mean velocity of the gas-air
    mixture at the end of the tube and a is the
    half-angle of the cone at the top of the tube,
    then the burning velocity S can be obtained
    simply from S U sin (a)
  • This method underestimates the value of S for a
    number of reasons, including the velocity
    distribution across the end of the tube and heat
    losses from the flame to the rim of the tube.

  • More accurate measurements are made with a burner
    design which produces a flat, laminar flame.
  • Some typical burning velocities
    are Fuel Burning velocity (m/s) Methane 0.34
    Propane 0.40 Town gas 1.0 Hydrogen 2.52 Car
    bon monoxide 0.43

  • Burning velocity should not be confused with the
    speed of propagation of the flame front relative
    to a fixed point, which is generally referred to
    as flame speed.
  • In this case, the speed of the flame front is
    accelerated by the expansion of the hot gas
    behind the flame.

5.3 Wobbe Number
  • This characteristic concerns the
    interchangeability of one gaseous fuel with
    another in the same equipment.
  • In very basic terms, a burner can be viewed in
    terms of the gas being supplied through a
    restricted orifice into a zone where ignition and
    combustion take place.

  • The three important variables affecting the
    performance of this system are the size of the
    orifice, the pressure across it (or the supply
    pressure if the combustion zone is at ambient
    pressure) and the calorific value of the fuel,
    which determines the heat release rate.
  • If two gaseous fuels are to be interchangeable,
    the same supply pressure should produce the same
    heat release rate.

  • If we consider the restriction to behave like a
    sharp-edged orifice plate, and if the
    cross-sectional area of the orifice (A0) is much
    less than the cross-sectional area of the supply
    pipe then the mass flow rate of fuel is given
    by CdA0 (2??p)0.5or in terms of volume
    flow ratewhere Cd is a discharge coefficient
    ? is the density of fuel

  • The heat release rate, Q, will be obtained by
    multiplying the volume flow rate by the
    volumetric calorific value of the fuel
  • If we have two fuels denoted as 1 and 2, we would
    expect the same heat release from the same
    orifice and the same pressure drop ?p, if

  • This ratio is known as the Wobbe number of a
    gaseous fuel and is defined as
  • Some typical Wobbe numbers are Fuel Wobbe
    number (MJ/m3) Methane 55 Propane 78 Natura
    l gas 50 Town gas 27

  • The significant difference between the values for
    natural gas and town gas illustrates why
    appliance conversions were necessary when the UK
    changed its mains-distributed fuel in 1966.
  • Example 1Calculate the Wobbe number for a
    by-product gas from an industrial process which
    has the following composition by
    volume H2 12 CO 29 CH4 3 N2 52 CO2 4

  • SolutionThe gross calorific values
    are CO 11.85 MJ/m3 CH4 37.07 MJ/m3 H2 11.92
  • The calorific value of the mixture CV(0.1211.9
    2)(0.2911.85)(0.0337.07)5.98 MJ/m3

  • The relative density of the mixture is calculated
    by dividing the mean molecular weight of the gas
    by the corresponding value for air (28.84).
  • The mean molecular weight of this mixture

  • The relative density is thus 25.1628.840.872.
  • The Wobbe number is then 5.98/(0.872)0.56.36
  • The Wobbe number of a fuel is not the only factor
    in determining the suitability of a fuel for a
    particular burner.
  • The burning velocity of a fuel is also important.

  • In general, any device will operate within a
    triangular performance map, such as that sketched
    in Fig. 7.3 (next slide).
  • Outside the enclosed region, combustion
    characteristics will be unsatisfactory in the way
    indicated on the diagram.

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6. Gas Burners
  • 6.1 Diffusion Burners
  • The fuel issues from a jet into the surrounding
    air and the flame burns by diffusion of this air
    into the gas envelope (Fig. 7.4, next slide).

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  • A diffusion flame from a hydrocarbon fuel has a
    yellow color as a result of radiation from the
    carbon particles which are formed within the
  • The flame can have laminar characteristics or it
    may be turbulent if the Reynolds number at the
    nozzle of the burner is greater than 2,000.

  • Pratical burner operate in the turbulent regime
    since more efficient combustion is obtained in
    this case because the turbulence improves the
    mixing of the fuel with air.
  • Industrial diffusion burners will have typical
    supply gas pressures of 110 Pa.

  • Diffusion burners have the following positive
    characteristics(a) Quiet operation(b) High
    radiation heat transfer (about 20 of the
    total)(c) Will burn a wide range of gases (they
    cannot light back)(d) Useful for low calorific
    value fuels

  • 6.2 Premixed Burners
  • The vast majority of practical gaseous burners
    mix the air and fuel before they pass through a
    jet into the combustion zone.
  • In the simplest burners, such as those that are
    used in domestic cookers and boilers, the
    buoyancy force generated by the hot gases is used
    to overcome the resistance of the equipment.
  • However, in larger installations the gas supply
    pressure is boosted and the air is supplied by a

  • The principle is illustrated by the flame from a
    Bunsen burner with the air hole open, and is
    shown diagrammatically in Fig. 7.5 (next
    slide).The gas and air are mixed between the
    fuel jet and the burner jet, usually with all the
    air required for complete combustion.

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  • The velocity of the mixture through the burner
    jet is important.
  • If the velocity is too low (below the burning
    velocity of the mixture) the flame can light back
    into the mixing region.

  • If the velocity is too high the flame can lift
    off from the burner to the extent where it can be
    extinguished by, for instance, entrainment of
    additional (secondary) air around the burner.
  • The flame from a premixed burner will emit very
    little heat by radiation but, because of its
    turbulent nature, forced convection in a heat
    exchanger is very effective.

Engine Modification

  • Engine Modification The aim of this section of
    Biofuels for Transport is to discuss the engine
    modifications that may be required to run
    biofuels in conventional internal combustion
  • The fuels being looked at specifically are
    biodiesel, used in a compression ignition engine,
    and bioethanol, used in a spark ignition engine.

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  • Fuel Filters It maybe necessary to change the
    vehicles fuel filter more often as ethanol blends
    can loosen solid deposits that are present in
    vehicle fuel tanks and fuel lines.
  • Cold Starting Ethanol blends have a higher
    latent heat of evaporation than 100 petrol and
    thus ethanol blends have a poorer cold start
    ability in Winter. Therefore some vehicles have a
    small petrol tank fitted containing 100 petrol
    for starting the vehicle in cold weather.
  • Engine Modifications for Ethanol blends of 14 to
    24 The following engine modifications were
    carried out by car companies in Brazil, in the
    1970s, when vehicles were operating on ethanol
    blends of between 14 and 24 ethanol
  • Changes to cylinder walls, cylinder heads, valves
    and valve seats
  • Changes to pistons, piston rings, intake
    manifolds and carburettors
  • Nickel plating of steel fuel lines and fuel tanks
    to prevent ethanol E20 corrosion
  • Higher fuel flowrate injectors to compensate for
    oxygenate qualities of ethanol

  • Biodiesel Modification 
  • Almost all modern diesel engines will run
    biodiesel quite happily provided that the
    biodiesel is of high enough quality. Generally
    speaking biodiesel requires much less engine
    modification than bioethanol.
  • Rubber Seals With some older vehicles rubber
    seals used in the fuel lines may require
    replacing with non-rubber products such as
    VITONTM. This is due to the way biodiesel reacts
    with rubber. If a low blend is used (5 biodiesel
    for example) then the concentration of biodiesel
    isn't high enough to cause this problem.
  • Cold Starting Cold starting can sometimes be a
    problem when using higher blends. This is due to
    biodiesel thickening more during cold weather
    than fossil diesel. Arrangements would have to be
    made for this, either by having a fuel heating
    system or using biodegradable additives which
    reduce the viscosity. This effect is only a
    problem with higher blends.

  • Oil Changing It was noticed that during many
    field trials that engines running on biodiesel
    tended to require more frequent oil changes. This
    was generally the case with blends above 20.
    During an ALTENER project where two Mercedes Benz
    buses were run on diesel and biodiesel it was
    found that the bus running on biodiesel required
    an oil change after 12,000 km compaired to 21,000
    km for the bus running fossil diesel. It is worth
    noting however that the engine had not been
    significantly effected in any adverse manner.
  • Engine Timing For higher blends engine
    performance will be improved with a slight change
    to engine timing, 2 or 3 degrees for a 100
    blend. The use of advanced injection timing and
    increased injection pressure has been known to
    reduce NOx emissions. It is worth noting that
    catalytic converters are just as effctive on
    biodiesel emissions as on fossil diesel.

  • UNIT V

Electric Vehicle Mission Statement
  • In an effort to save the environment and reduce
    our dependence on foreign oil, we wanted to
    convert a gasoline powered car into an electric
  • With the support of Mr. Mongillio, the Macari
    fund and Jim Lynch (mechanic for Lorusso
    Construction) as well as Bob and Bryan from
    Electric Vehicle of America (EVA), we converted
    a 1998 Saturn gas powered vehicle into an
    electric vehicle.

Overview On The Importance of Electric Vehicles
The Importance of Electric Vehicles
  • Gas is a scarce, natural resource.
  • Electricity is cheaper than gas. Electricity can
    come from renewable resources such as solar and
    wind power.
  • Electric cars pollute less than gas-powered cars.
  • Electric cars are much more reliable and require
    less maintenance than gas-powered cars. You don't
    even need to get your oil changed every 3,000
  • By using domestically-generated electricity
    rather than relying on foreign oil, the USA can
    become more independent.

The Problems With Gasoline Powered Vehicles
  • Gasoline Is A Scarce Resource
  • Production Shortages
  • Alaskan oil has reduced.
  • US Coastal oil impacted by hurricanes.
  • Oil Spills can occur
  • Gasoline Is Expensive
  • 2. Heavy Reliance On Imports
  • US only manufactures 34 of gasoline needed in
  • Heavy reliance on foreign countries.
  • Pricing is uncontrollable
  • Future availability may be limited especially
    with 3rd world country expansion.
  • 3. Creates Smog Ozone in Big Cities
  • Nitrogen oxides, the main source of urban smog
  • Unburned hydrocarbons, the main source of urban
  • 4. Creates Greenhouse Gases
  • Carbon monoxide, a poisonous gas is one of the
    major Greenhouse Gases.
  • Greenhouse effects the planet, rising sea levels,
    flooding, etc.
  • The main source (95) of carbon monoxide in our
    air is from vehicle emissions. (Per EPA studies)

Electric Vehicles Have A Few Downsides
  • Batteries need to be charged.
  • Car can not be used when batteries are being
  • Car can only go 40 Miles between charges.
  • Battery disposal needs to be carefully managed.

Electric Vehicle-Decision Making
  • The car ran great!
  • The body of the car was in good condition.
  • It was under 3,000 lbs gross body weight.
  • It had a standard transmission.
  • It fit the criteria for an eligible car to
    convert to an Electric Vehicle.

What Are HEVs?
HEVs combine the internal combustion engine of a
conventional vehicle with the battery and
electric motor of an electric vehicle.
Why HEVs?
Hybrid power systems were conceived as a way to
compensate for the shortfall in battery
technology. Because batteries could supply only
enough energy for short trips, an onboard
generator, powered by an internal combustion
engine, could be installed and used for longer
HEVs Advantages
  • High fuel efficiency.
  • Decreased emissions.
  • No need of fossil fuels.
  • Less overall vehicle weight.
  • Regenerative braking can be used.

Available HEVs
  • Toyota Prius
  • Honda Insight
  • Honda Civic(hybrid)

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baseline hev design
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HEV Components
Fuel tank
Body chassis
Energy management system control
Energy Storage unit
Thermal Management system
Hybrid Power unit
Traction motor
Body Chassis
HEVs will contain a mix of aluminum, steel,
plastic, magnesium, and composites (typically a
strong, lightweight material composed of fibers
in a binding matrix, such as fiberglass).
Ultra capacitors are higher specific energy and
power versions of electrolytic capacitors devices
that store energy as an electrostatic charge.
Lead acid batteries, used currently in many
electric vehicles, are potentially usable in
hybrid applications. Lead acid batteries can be
designed to be high power and are inexpensive,
safe, and reliable.
Flywheels store kinetic energy within a rapidly
spinning wheel-like rotor or disk. Ultimately,
flywheels could store amounts of energy
comparable to batteries. They contain no acids or
other potentially hazardous materials. Flywheels
are not affected by temperature extremes, as most
batteries are.
Fuel cells offer highly efficient and
fuel-flexible power systems with low to zero
emissions for future HEV designs. There are a
variety of thermal issues to be addressed in the
development and application of fuel cells for
hybrid vehicles.
Spark ignition engine mixes fuel and air in a
pre-chamber. Throttle and heat losses, which
occur as the fuel mixture travels from
pre-chamber into the combustion chamber.
A Compression Ignition engine achieves combustion
through compression without use of sparkplug. It
becomes CIDI engine when it is enhanced with
direct injection.
vehicle propulsion system
vehicle propulsion system
Motors are the "work horses" of HEV drive
systems. In an HEV, an electric traction motor
converts electrical energy from the energy
storage unit to mechanical energy that drives the
wheels of the vehicle. Unlike a traditional
vehicle, where the engine must "ramp up" before
full torque can be provided, an electric motor
provides full torque at low speeds. This
characteristic gives the vehicle excellent "off
the line" acceleration.
Fuel System
As emissions standards tighten and exhaust
control technologies improve, the issue of
evaporative emissions becomes increasingly
important. Thermal management of fuel tanks is
one approach to reducing these emissions.
Exhaust Systems
60 to 80 of amiss ions in an autos typical
driving cycle comes from cold start emissions,
that is, pollutants that are emitted before the
catalytic converter is hot enough to begin
catalyzing combustion products.
Heat recovered from any of the above sources can
be used in a variety of ways. For winter driving,
heat recovery from HEV sources such as the power
unit exhaust, propulsion motors, batteries, and
power inverter can significantly improve cabin
What's Next for HEVs?
HEVs are now at the forefront of transportation
technology development. Hybrids have the
potential to allow continued growth in the
automotive sector, while also reducing critical
resource consumption, dependence on foreign oil,
air pollution, and traffic congestion.
thank you
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