Combustion Basics

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Unit I
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• Combustion Basics

• Fuel
• Combustion Stoichiometry
• Air/Fuel Ratio
• Equivalence Ratio
• Air Pollutants from Combustion

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• Fuel

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

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• 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.
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• 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.

Answer
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• 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.

Answer
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?
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• 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
conditions?
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• 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?
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• 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

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• 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?
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• Quick Reflections

• Fuel
• Combustion Stoichiometry
• Air/Fuel Ratio
• Equivalence Ratio
• Air Pollutants from Combustion

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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.

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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.

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Petrol
Petrol
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• 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.

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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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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)

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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.

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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.

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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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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
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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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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
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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
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Multi Point S.I. Fuel Injection
Air drawn in by the engine
Fuel Injectors
Throttle Valve
Inlet Manifold
Fuel Supply
Injectors
Engine
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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
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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).

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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.

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Energy Balance of Ethanol
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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.

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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.

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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.

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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
  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.

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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.

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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.

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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

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Gaseous Fuels

• UNIT III

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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.

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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.

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• 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.

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• 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.

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• 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).

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• 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

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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.

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• 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.

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• 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

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• 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

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• 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

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• 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.

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• 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

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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).

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• 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.

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• 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

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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.

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• 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.

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• 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.

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• 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.

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• 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.

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• 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

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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.

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• 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.

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• 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

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• 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
  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

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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
  system or using biodegradable additives which
  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
• 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
  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
generator, powered by an internal combustion
engine, could be installed and used for longer
trips.
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HEVs Advantages

• 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