Unit I
1
Combustion Basics
• Fuel
• Combustion Stoichiometry
• Air/Fuel Ratio
• Equivalence Ratio
• Air Pollutants from Combustion
2
Fuel
 Gaseous Fuels
• Natural gas
• Refinery gas
 Liquid Fuels
•
•
•
•
Kerosene
Gasoline, diesel
Alcohol (Ethanol)
Oil
 Solid Fuels
• Coal (Anthracite, bituminous, subbituminous, lignite)
• Wood
3
Fuel
 Properties of Selected Fuels
CH4
C2H6
C3H8
Other HCs
H2S
Heating Value
(106 J/m3)
(wt%)
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
H
N
O
(Ultimate analysis)
C
S
Heating value
(106 J kg-1)
(wt%)
Gasoline (No.2)
86.4
(Approximate analysis)
Anthracite
(PA)
Bituminous
(PA)
Subbituminous
Lignite (ND)
(CO)
Carbon
12.7
0.1
Volatile matter
0.1
Moisture
0.4-0.7
Ash
Heating value
(106 J kg-1)
(%)
(%)
(%)
(%)
77.1
3.8
5.4
13.7
27.8
70.0
20.5
3.3
6.2
33.3
45.9
30.5
19.6
4.0
23.6
30.8
28.2
34.8
6.2
16.8
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.
4
Combustion Stoichiometry
 Combustion in Oxygen
Cn H m  O2  CO2  H 2O
1.
2.
Can you balance the above equation?
Write the reactions for combustion of methane and
benzene in oxygen, respectively.
Answer
m
m

Cn H m   n  O2  nCO2  H 2O
4
2

CH4  2O2  CO2  2H 2O
C6 H 6  7.5O2  6CO2  3H 2O
5
Combustion Stoichiometry
 Combustion in Air (O2 = 21%, N2 = 79%)
Cn H m  (O2  3.78N 2 )  CO2  H 2O  N 2
1.
2.
Can you balance the above equation?
Write the reactions for combustion of methane and benzene
in air, respectively.
Answer
m
m
m


Cn H m   n  (O2  3.78 N 2 )  nCO2  H 2O  3.78 n   N 2
4
2
4


CH4  2(O2  3.78N 2 )  CO2  2H 2O  7.56N 2
C6 H 6  7.5(O2  3.78N 2 )  6CO2  3H 2O  28.35N 2
1. What if the fuel contains O, S, Cl or other elements?
2 Is it better to use O2 or air?
6
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?
3/16/2016
Aerosol & Particulate Research Laboratory
7
Air-Fuel Ratio
 Rich mixture
- more fuel than necessary
(AF) mixture < (AF)stoich
 Lean mixture
- more air than necessary
(AF) mixture > (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?
3/16/2016
Aerosol & Particulate Research Laboratory
8
Equivalence Ratio
Equivalence ratio: shows the deviation of an actual
mixture from stoichiometric conditions.
( FA) actual ( AF ) stoich


( FA) stoich ( AF ) actual
The combustion of methane has an equivalence ratio Φ=0.8
in a certain condition. What is the percent of excess air (EA)
used in the combustion?
How does temperature change as Φ increases?
3/16/2016
Aerosol & Particulate Research Laboratory
9
Formation of NOx and CO in Combustion
 Thermal NOx
- Oxidation of atmospheric N2 at high temperatures
N 2  O2  2 NO
NO  12 O2  NO2
- 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
CO2  CO  12 O2
3/16/2016
Aerosol & Particulate Research Laboratory
10
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?
11
Quick Reflections
• Fuel
• Combustion Stoichiometry
• Air/Fuel Ratio
• Equivalence Ratio
• Air Pollutants from Combustion
12
Engine Fuel System (SI Petrol)


Fuel Tank – normally positioned in the rear boot area, either under
the floor pan for estate cars or over the rear axle for saloons, the
latter being a safer position. Should the engine be mounted in the
rear, the fuel tank is normally positioned in the front boot area, either
over the bulkhead or flat across the boot floor pan , the latter
providing more boot space, but is more exposed to danger in a head
on crash. The fuel tank made be made from pressed steel and
coated inside to prevent corrosion, or a synthetic rubber compound
or flame resistant plastic. Inside the fuel tank is normally located the
fuel gauge sender unit and electrically driven fuel pump with a
primary filter in a combined module. Internal fuel tank baffles are
used to prevent fuel surge. The fuel tank is pressurised to about 2
psi to prevent fuel vaporization and pollution. The fuel tank is vented
through its own venting system and the engine managements
emission control systems again to control pollution.
Fuel pipes – These can be made from steel or plastic and are
secured by clips at several points along the underside of the vehicle.
To allow for engine movement and vibration, rubber hoses connect
the pipes to the engine. Later fuel pipes use special connectors
which require special tools to disconnect the pipes.
Engine Fuel System (SI Petrol)




Fuel Filters – to prevent dirt and fluff entering the fuel pump a filter is
fitted on the suction side of the pump. On the pressure side of the
pump a secondary filter is used, this is a much finer filter in that it
prevents very small particles of dirt reaching the carburettor or fuel
injection equipment. It should be renewed at the correct service
interval as recommended by the manufacturer. When the filter is
replaced, it must be fitted in the direction of fuel flow.
Air Filters – air cleaners and silencers are fitted to all modern
vehicles. Its most important function is to prevent dust and abrasive
particles from entering the engine and causing rapid wear. Air filters
are designed to give sufficient filtered air, to obtain maximum engine
power. The air filter must be changed at the manufactures
recommended service interval. The air filter/cleaner also acts as a
flame trap and silencer for the air intake system.
Fuel Pump – this supplies fuel under high pressure to the fuel
injection system, or under low pressure to a carburettor.
Carburettor – this is a device which atomizes the fuel and mixes it
which the correct amount of air, this device has now been
superseded by modern electronic fuel injection.
Petrol
Petrol





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.
The Simple
Carburettor
The Float Chamber
Petrol
Operation of the Venturi
Choke
Valve
closed
The Choke Valve is used
to provide a rich air/fuel
ratio for cold starting
The Throttle Valve controls the
amount of air fuel mixture entering
the engine and therefore engine
power
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)
Engine S I Fuel System







ECU – Electronic control unit. This contains a computer which takes
information from sensors and controls the amount of fuel injected by
operating the injectors for just the right amount of time.
Air flow/mass meter – A sensor used to tell the ECU how much air is
being drawn into the engine.
MAP sensor – Manifold absolute pressure sensor. This senses the
pressure in the engines inlet manifold, this gives an indication of the
load the engine is working under.
Speed/crankshaft sensor – This tells the ECU has fast the engine is
rotating and sometimes the position of the crankshaft.
Temperature sensor – Coolant temperature is used determine if
more fuel is needed when the engine is cold or warming up.
Lambda sensor – A sensor located in the exhaust system which tells
the ECU the amount of oxygen in the exhaust gases, form this the
ECU can determine if the air/fuel ratio is correct.
Fuel pump – A pump, normally located in the fuel tank, which
supplies fuel under pressure to the fuel injectors.
Engine S I Fuel System





Fuel filter – keeps the fuel very clean to prevent the injectors
becoming damaged or 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.
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.
25 of 14
Introduction to Electronic Petrol
Throttle/Single Point Fuel Injection Systems
The Carburettor has now been replaced with petrol injection systems.
These systems supply the engine with a highly atomized mixture of air
and fuel in the correct air/fuel ratio. This has the following advantages
over the carburettor systems
Lower exhaust emissions (pollution)
Better fuel consumption
Smoother engine operation and greater power
Automatic adjustment of the air/fuel ratio to keep the vehicles
emissions (pollution) to a minimum.
26 of 14
Throttle Body/Single Point
S.I. Fuel Injection
Air drawn in by the engine
Throttle Body
Fuel Supply
Fuel Injector (one off)
Throttle Valve
Inlet Manifold
The Engine
Single Point Electronic Fuel Injection (EFI)
Systems
EFI systems are classified by using the point of injection.
ECU
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.
Air in
Fuel in
TB injector
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.
Inlet manifold
28 of 14
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
Nozzle/jet
Armature Spring
Fuel filter
Sensor Inputs
Outputs
Single Point Injection
Reference
voltage
+V
V

0V
Engine coolant
temperature sensor
+5V
TPS
0V
ECU
Wires
to ECU
Heating
element
Sensor
element
Protective
cap with gas
intake slots
The ECU (Brain) receives
Information from varies sensors.
From this information it works out
how much fuel the engine needs
IAC valve
Solenoid coil
Air in
Throttle valve
Multi – Point S.I. Fuel Injection
Air drawn in by the engine
Fuel Injectors
Throttle Valve
Inlet Manifold
Fuel
Supply
Injectors
Engine
Typical S.I. Fuel System Layout (Simplified)
Fuel Tank
Fuel Pump
Fuel
Filters
Fuel Not
used is
returned to
the fuel tank
Engine Combustion
Chamber
Fuel Pressure
Regulator
EFI Only
Inlet Manifold
Carburettor
Or Single
Point Throttle
Body Housing
Fuel Injector or
Carburettor
Venturi
Liquid fuel
UNIT II
What is ethanol?
– GM Commercial
– CH3CH2OH
– Ethanol is a clean-burning, high-octane fuel that is
produced from renewable sources.
– At its most basic, ethanol is grain alcohol, produced
from crops such as corn.
– Since pure 100% ethanol is not generally used as a
motor fuel, a percentage of ethanol is combined with
unleaded gasoline, to form E10 and E85
• E10: 10% ethanol and 90% unleaded gasoline, is
approved for use in any US vehicle
• E85: 85% ethanol and 15% unleaded gasoline, is an
alternative fuel for use in flexible fuel vehicles (FFVs).
How is it made?
– Ethanol can be made by fermenting almost any material that
contains starch.
– Most of the ethanol in the U.S. is made using a dry mill
process.
– In the dry mill process, the starch portion of the corn is
fermented into sugar then distilled into alcohol
– Prior to fermentation, high-value chemicals are removed from
the biomass. These include fragrances, flavoring agents,
food-related products, and high value nutraceuticals with
health and medical benefits.
– There are two main valuable co-products created in the
production of ethanol: distillers grain and carbon dioxide.
Distillers grain is used as a highly nutritious livestock feed
while carbon dioxide is collected, compressed, and sold for
use in other industries.
Energy Balance of Ethanol
Energy Balance
– Although CO2 is released during ethanol production and combustion,
it is recaptured as a nutrient to the crops that are used in its
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 balance—meaning the ethanol yields
more energy than it takes to produce it.
Impact on air quality
• Using ethanol-blended fuel has a positive impact on air
quality. By adding oxygen to the combustion process
which reduces exhaust emissions—resulting 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.
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.
Impact on economy
• In a 1997 study The Economic Impact of the Demand for Ethanol,
Northwestern University’s 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.
Impact on auto industry
• Ethanol could be the alternative fuel source that
catapults sales of American auto manufacturers.
• GM and Ford are looking for environmental fixes that are
quicker and cheaper than the more costly hybrids and
futuristic fuel cells. Both companies started promoting
flexible-fuel vehicles (FFVs) aggressively this year.
• General Motors tied their new campaign "Live Green, Go
Yellow.'' to not only Super Bowl Sunday but the opening
of the Winter Olympics as well.
• Since only about 600 of the nation's 170,000 filling
stations sell E85, both companies
have begun programs to install
E85 pumps at more stations.
Impact on politics
•
President Bush gave ethanol a big plug in his State of the Union address, by
stating that:
– The United States must move beyond a petroleum-based economy and develop
new ways to power automobiles. The Administration will accelerate research in
cutting-edge methods of producing "cellulosic ethanol" with the goal of making the
use of such ethanol practical and competitive within 6 years.
– The Biorefinery Initiative. To achieve greater use of "homegrown" renewable
fuels in the United States, advanced technologies need to be perfected to make
fuel ethanol from cellulosic (plant fiber) biomass, which is now discarded as waste.
The President's 2007 Budget will include $150 million – a $59 million increase over
FY06 – to help develop bio-based transportation fuels from agricultural waste
products, such as wood chips, stalks, or switch grass. Research scientists say that
accelerating research into "cellulosic ethanol" can make it cost-competitive by
2012, offering the potential to displace up to 30% of the Nation's current fuel use.
•
Associated Press, March 2, 2006: To increase the production of alternative
fuel sources, the Bush administration has proposed allowing ethanol plants to
emit more air pollutants. The EPA announced that it would propose a rule to
raise the emissions threshold for corn milling plants that produce ethanol fuel,
allowing them to emit up to 250 tons a year of air pollutants before setting off
tougher restrictions on production. Corn milling plants can now emit 100 tons
a year.
Problems with Ethanol
•
•
•
•
•
•
Odors as a public nuisance, ex: New Energy Ethanol
Plant here in South Bend
Green house gas emissions have sometimes shown to
be equivalent to those of gasoline (data is often
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
Gaseous Fuels
UNIT III
46
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 considerationthe capital cost of the combustion
equipment together with the running costs,
which are fuel purchasing and
maintenance.
47
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.
48
• 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.
49
• 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.
50
• 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).
51
• The characteristics of a typical natural gas are:
Composition (% vol)
CH4
92
other HC
5
inert gases
3
Density (kg/m3)
0.7
Gross calorific value (MJ/m3)
41
52
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.
53
• 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.
54
• 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
55
• 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
56
• 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 properties:
Composition (% vol)
H2
48
CO
5
CH4
34
CO2
13
Density (kg/m3)
0.6
Gross calorific value (MJ/m3)
20.2
57
• 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.
58
• 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
59
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).
60
• 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.
61
• Typical properties of industrial LPG are given below:
Gas
Propane
Butane
Density (kg/m3)
Gross calorific value (MJ/m3)
Boiling point (℃ at 1 bar)
1.7-1.9
96
-45
2.3-2.5
122
0
62
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.
63
• 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.
64
• 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.
65
• 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.
66
• 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).
67
• 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.
69
• 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 are:
Fuel
Lower Explosion Limit (LEL) %
Methane
Propane
Hydrogen
Carbon monoxide
5
2
4
13
Upper Explosion Limit (UEL) %
15
10
74
74
70
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.
71
• 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).
72
• If U represents the mean velocity of the gas-air
mixture at the end of the tube and α 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 (α)
• 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.
74
• 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
Propane
Town gas
Hydrogen
Carbon monoxide
0.34
0.40
1.0
2.52
0.43
75
• 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.
76
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.
77
• 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 78
• If we consider the restriction to
behave like a sharp-edged
orifice plate, and if the crosssectional area of the orifice (A0)
is much less than the crosssectional area of the supply
pipe then the mass flow rate of
fuel is given by:
m = C A (2ρ△p)0.5
d 0
or in terms of volume flow rate:
 2p 
V  Cd A0 

  
0.5
where Cd is a discharge
coefficient
ρ is the density of fuel
79
• The heat release rate, Q, will be obtained by
multiplying the volume flow rate by the volumetric
calorific value of the fuel:
 2P 
Q  CVCd A0 

  
0.5
• 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
0.5
 2p 
 2p 
CV1Cd A0 
  CV2Cd A0 

 1 
 2 
CV1 CV2
i.e.
 0.5
0.5
1
0.5
2
80
• This ratio is known as the Wobbe number of a
gaseous fuel and is defined as:
Gross calorific value (MJ/m3 )
 Relative density (air=1)
0.5
• Some typical Wobbe numbers are:
Fuel
Wobbe number (MJ/m3)
Methane
Propane
Natural gas
Town gas
55
78
50
27
81
• 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 1:
Calculate the Wobbe number for a by-product gas from an
industrial process which has the following composition by volume:
H2
CO
CH4
N2
CO2
12%
29%
3%
52%
4%
82
• Solution:
The 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=(0.12×11.92)+(0.29×11.85)+(0.03×37.07)=5.98 MJ/m3
83
• 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:
(0.12×2)+(0.29×28)+(0.03×16)+(0.52×28)+(0.04×44)=25.16
84
• The relative density is thus
25.16÷28.84=0.872.
• The Wobbe number is then:
5.98/(0.872)0.5=6.36
• 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.
85
• 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.
86
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).
88
• 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.
90
• 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.
91
• 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
92
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.
93
• 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.
94
• 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.
96
• 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.
97
Engine Modification
UNIT IV
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.
•
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 1970’s, when vehicles were operating on ethanol blends of
between 14 and 24% ethanol:
Changes to cylinder walls, cylinder heads, valves and valve seats
Changes to pistons, piston rings, intake manifolds and carburettors
Nickel plating of steel fuel lines and fuel tanks to prevent ethanol E20
corrosion
Higher fuel flowrate injectors to compensate for oxygenate qualities of ethanol
Biodiesel Modification
Almost all modern diesel engines will run biodiesel quite happily provided that the
biodiesel is of high enough quality. Generally speaking biodiesel requires much less
engine modification than bioethanol.
Rubber Seals
With some older vehicles rubber seals used in the fuel lines may require replacing
with non-rubber products such as VITONTM. This is due to the way biodiesel
reacts with rubber. If a low blend is used (5% biodiesel for example) then the
concentration of biodiesel isn't high enough to cause this problem.
Cold Starting
Cold starting can sometimes be a problem when using higher blends. This is due to
biodiesel thickening more during cold weather than fossil diesel. Arrangements
would have to be made for this, either by having a fuel heating system or using
biodegradable additives which reduce the viscosity. This effect is only a problem
with higher blends.
•
•
•
Oil Changing
It was noticed that during many field trials that engines running on biodiesel
tended to require more frequent oil changes. This was generally the case with
blends above 20%. During an ALTENER project where two Mercedes Benz
buses were run on diesel and biodiesel it was found that the bus running on
biodiesel required an oil change after 12,000 km compaired to 21,000 km for
the bus running fossil diesel. It is worth noting however that the engine had not
been significantly effected in any adverse manner.
Engine Timing
For higher blends engine performance will be improved with a slight change to
engine timing, 2 or 3 degrees for a 100% blend. The use of advanced injection
timing and increased injection pressure has been known to reduce NOx
emissions. It is worth noting that catalytic converters are just as effctive on
biodiesel emissions as on fossil diesel.
ELECTRIC VEHICLE
UNIT V
Electric Vehicle – Mission Statement:
• In an effort to save the environment and reduce our dependence on
foreign oil, we wanted to convert a gasoline powered car into an
electric 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.
Overview On The Importance of Electric Vehicles:
The Importance of Electric Vehicles:
• Gas is a scarce, natural resource.
• Electricity is cheaper than gas. Electricity can come from renewable
resources such as solar and wind power.
• Electric cars pollute less than gas-powered cars.
• Electric cars are much more reliable and require less maintenance
than gas-powered cars. You don't even need to get your oil changed
every 3,000 miles!
• By using domestically-generated electricity rather than relying on
foreign oil, the USA can become more independent.
The Problems With Gasoline Powered Vehicles:
1. Gasoline Is A Scarce Resource:
–
Production Shortages
•
•
–
–
2. Heavy Reliance On Imports:
Alaskan oil has reduced.
US Coastal oil impacted
by hurricanes.
Oil Spills can occur
Gasoline Is Expensive
3. Creates Smog & Ozone in Big Cities:
–
–
–
–
–
–
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.
4. Creates Greenhouse Gases:
Nitrogen oxides, the main source of urban smog
Unburned hydrocarbons, the main source of urban
-
ozone
–
Carbon monoxide, a poisonous gas is
one of the major “Greenhouse
Gases”.
Greenhouse effects the planet, rising
sea levels, flooding, etc.
The main source (95%) of carbon
monoxide in our air is from vehicle
emissions. (Per EPA studies)
Electric Vehicles Have A Few Downsides:
• Batteries need to be charged.
• Car can not be used when batteries are being charged.
• Car can only go 40 Miles between charges.
• Battery disposal needs to be carefully managed.
Electric Vehicle-Decision Making:
• The car ran great!
• The body of the car was in
good condition.
• It was under 3,000 lbs gross
body weight.
• It had a standard transmission.
• It fit the criteria for an eligible
car to convert to an Electric
Vehicle.
HEVs combine the internal
combustion engine of a
conventional vehicle with the
battery and electric motor of
an electric vehicle.
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.
High fuel efficiency.
Decreased emissions.
No need of fossil fuels.
Less overall vehicle weight.
Regenerative braking can
used.
be
Toyota Prius
Honda Insight
Honda Civic(hybrid)
1.. INTERNAL COMBUSTION
ENGINE
2..WHEEL
3.. ELECTRIC MOTOR
4..INTELLIGENT POWER
ELECTRONICS
5.. BRAKE
6.. BATTERIES
Fuel tank
Body chassis
Energy management
& system control
Accessories
Energy
Storage
unit
Hybrid
Power
unit
Traction
motor
Thermal
Management
system
HEVs will contain a mix of
aluminum, steel, plastic,
magnesium, and composites
(typically a strong, lightweight
material composed of fibers in a
binding matrix, such as fiberglass).
Ultra capacitors are higher
specific energy and power
versions of electrolytic
capacitors devices that
store energy as an
electrostatic charge.
Lead acid batteries, used
currently in many electric
vehicles, are potentially usable in
hybrid applications. Lead acid
batteries can be designed to be
high power and are inexpensive,
safe, and reliable.
Flywheels store kinetic energy within a
rapidly spinning wheel-like rotor or disk.
Ultimately, flywheels could store amounts of
energy comparable to batteries. They contain
no acids or other potentially hazardous
materials. Flywheels are not affected by
temperature extremes, as most batteries are.
Fuel cells offer highly efficient and fuelflexible power systems with low to zero
emissions for future HEV designs. There
are a variety of thermal issues to be
addressed in the development and
application of fuel cells for hybrid vehicles.
Spark ignition engine mixes fuel
and air in a pre-chamber. Throttle
and heat losses, which occur as
the fuel mixture travels from prechamber into the combustion
chamber.
A Compression Ignition engine achieves
combustion through compression without use
of sparkplug. It becomes CIDI engine when it is
enhanced with direct injection.
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.
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.
60% to 80% of amiss ions in an autos
typical driving cycle comes from cold
start emissions, that is, pollutants that
are emitted before the catalytic
converter is hot enough to begin
catalyzing combustion products.
Heat recovered from any of the above
sources can be used in a variety of ways.
For winter driving, heat recovery from
HEV sources such as the power unit
exhaust, propulsion motors, batteries,
and power inverter can significantly
improve cabin warm-up.
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.