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Combustion Basics

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Title: Combustion Basics

1
Unit I
2
• Combustion Basics
• Fuel
• Combustion Stoichiometry
• Air/Fuel Ratio
• Equivalence Ratio
• Air Pollutants from Combustion

3
• Fuel
• Gaseous Fuels
• Natural gas
• Refinery gas
• Liquid Fuels
• Kerosene
• Gasoline, diesel
• Alcohol (Ethanol)
• Oil
• Solid Fuels
• Coal (Anthracite, bituminous, subbituminous,
lignite)
• Wood

4
• Fuel
• Properties of Selected Fuels

CH4
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
41.9
C
H N O S
Heating value (wt) (106 J
kg-1) Gasoline (No.2) 86.4 12.7
0.1 0.1 0.4-0.7

(Ultimate analysis)
Carbon
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.
5
• 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.

6
• 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.

7
• 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?
8
• 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
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
conditions?
9
• 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
increases?
10
• Formation of NOx and CO in Combustion
• Thermal NOx
• Oxidation of atmospheric N2 at high temperatures
• Formation of thermal NOx is favorable at higher
temperature
• Fuel NOx
• Oxidation of nitrogen compounds contained in the
fuel
• Formation of CO
• Incomplete Combustion
• Dissociation of CO2 at high temperature

11
• 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?
12
• Quick Reflections
• Fuel
• Combustion Stoichiometry
• Air/Fuel Ratio
• Equivalence Ratio
• Air Pollutants from Combustion

13
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
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.

14
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.

15
Petrol
Petrol
16
• Float chamber (function) to set and maintain
the fuel level within the carburettor, and to
control the supply fuel to the carburettor
venturi.
• 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.

17
The Simple Carburettor
The Float Chamber
Petrol
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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22
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
(pollution)

23
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.

24
Engine S I Fuel System
• Fuel filter keeps the fuel very clean to
prevent the injectors becoming damaged or
blocked.
• 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
itself.
• 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.

25
Typical Fuel System
1. Fuel Supply System
Components that supply clean fuel to the fuel
metering system (fuel pump, fuel pipes, fuel
filters).
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.
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26
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
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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27
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
28
Single Point Electronic Fuel Injection (EFI)
Systems
EFI systems are classified by using the point of
injection.
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
air.
Fuel quantity, how much feul is injected is
controlled by an ECU.
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29
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
carburettors.
Electrical connector
Solenoid coil
Needle valve
Fuel in
Fuel filter
Spring
Armature
Nozzle/jet
30
Outputs
Inputs
Single Point Injection
Sensor
The ECU (Brain) receives Information from varies
sensors. From this information it works out how
much fuel the engine needs
31
Multi Point S.I. Fuel Injection
Air drawn in by the engine
Fuel Injectors
Throttle Valve
Inlet Manifold
Fuel Supply
Injectors
Engine
32
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
33
Liquid fuel
• UNIT II

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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).

37
• 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.

38
Energy Balance of Ethanol
39
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
production.
• 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.

40
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
air.
• 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
NOX.

41
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
country.
• 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.

42
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
• Ethanol plant operation creates 47 million to
displaces crude oil we would need to import,
offering our country critically needed
independence and security from foreign sources of
energy.
• 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.

43
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.

44
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
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
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.

45
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
inconclusive)
• 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
necessary
• Research is needed to refine the chemical
processes to separate, purify and transform
biomass into usable fuel

46
Gaseous Fuels
• UNIT III

47
1. Introduction
• There are numerous factors which need to be taken
into account when selecting a fuel for any give
application.
• Economics is the overriding consideration-the
capital cost of the combustion equipment together
with the running costs, which are fuel purchasing
and maintenance.

48
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.

49
• It is then distributed in a high-pressure mains
system.
• 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.

50
• 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.

51
• 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).

52
• 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

53
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.

54
• 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.

55
• The gas was produced by heating the raw coal in
the absence of air to drive off the volatile
products.
• 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

56
• 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

57
• 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

58
• 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.

59
• 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

60
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).

61
• 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
circumstances.

62
• 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

63
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
air.
• However, not all mixtures of fuel and air are
capable of supporting, or propagating, a flame.

64
• 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

65
• 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.

66
• This simplified picture indicates that there will
be upper and lower flammability limits for any
gaseous fuel, and that they will be approximately
stoichiometric fuel/air ratio.

67
• Flammability limits can be experimentally
determined to a high degree of repeatability in
an apparatus developed by the US Bureau of
Mines.
• 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
pump.
• 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.

70
• The limits are affected by temperature and
pressure but the values are usually quoted as
volume percentages at atmospheric pressure and
25?.
• 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

71
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.

72
• 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.

75
• 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

76
• 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.

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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.

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• 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.

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• 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

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• 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

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• 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

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• 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

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

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• 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
is(0.122)(0.2928)(0.0316)(0.5228)(0.044
4)25.16

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• 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.

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• 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
flame.
• 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.

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• 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.

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

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• 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
fan.

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• 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.

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• 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.

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Engine Modification
• UNIT IV

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• 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
engines.
• 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

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• 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
reduce the viscosity. This effect is only a
problem with higher blends.

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• 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.

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ELECTRIC VEHICLE
• UNIT V

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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
vehicle.
• 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.

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Overview On The Importance of Electric Vehicles
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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
miles!
• By using domestically-generated electricity
rather than relying on foreign oil, the USA can
become more independent.

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The Problems With Gasoline Powered Vehicles
• Gasoline Is A Scarce Resource
• Production Shortages
• 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
US.
• 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
ozone
• 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)

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

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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.

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hev
HYBRID ELECTRIC VEHICLES
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What Are HEVs?
HEVs combine the internal combustion engine of a
conventional vehicle with the battery and
electric motor of an electric vehicle.
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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
engine, could be installed and used for longer
trips.
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• High fuel efficiency.
• Decreased emissions.
• No need of fossil fuels.
• Less overall vehicle weight.
• Regenerative braking can be used.

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

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HOW HEV WORKS
1.. INTERNAL COMBUSTION ENGINE 2..WHEEL 3..
ELECTRIC MOTOR 4..INTELLIGENT POWER
ELECTRONICS 5.. BRAKE 6.. BATTERIES
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baseline hev design
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HEV Components
Fuel tank
Body chassis
Energy management system control
Accessories
Energy Storage unit
Thermal Management system
Hybrid Power unit
Traction motor
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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).
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HEVs
combines
ULTRA CAPACITORS
SPARK IGNITION ENGINE
ELECTRIC MOTOR
BATTERIES
CIDI ENGINE
FUEL CELL
FLY WHEEL
GAS TURBINE
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ULTRA CAPACITORS
Ultra capacitors are higher specific energy and
power versions of electrolytic capacitors devices
that store energy as an electrostatic charge.
ENERGY STORAGE UNIT
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BATTERIES
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.
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FLY WHEEL
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.
ENERGY STORAGE UNIT
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FUEL CELLS
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.
HYBRID POWER UNIT
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SPARK IGNITION ENGINE
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.
HYBRID POWER UNIT
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CIDI ENGINE
COMPRESSION IGNITION DIRECT INJECTION
A Compression Ignition engine achieves combustion
through compression without use of sparkplug. It
becomes CIDI engine when it is enhanced with
direct injection.
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vehicle propulsion system
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vehicle propulsion system
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ELECTRIC MOTOR
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.
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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.
THERMAL MANAGEMENT
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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.
THERMAL MANAGEMENT
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WASTE HEAT UTILISATION
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
warm-up.
THERMAL MANAGEMENT
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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.
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thank you