1. travel
2. transports
3. public transport

1
CHAPTER ONE
INTRODUCTION
1.1 Background
Waste of energy and the environmental pollution are among the major global concerns
for all science disciplines including engineering. Also, when designing and applying
specific conditions to fulfill some requirements for certain areas such as vehicle
manufacturing industry, massive energy is wasted on such facilities. The importance of
energy saving exhibits on emission levels and energy cost.
This study focuses on the vehicles aerodynamics, especially drag effects on bus that
influences directly the fuel consumption. The Reynolds number and drag (either friction or
form) will reflect on bus power, which in turn reflects on the fuel consumption.
There are many investigations that tried to study the aerodynamic behavior around
heavy vehicles and tried to find out how to control the air attitude. The studies tried to find
out a better way to improve the vehicle performance throughout modifying the shape and
weight of the vehicle. The present study aims to improve aerodynamic bus performance by
simple and robust means.
1.2 Buses and heavy vehicles
Buses are one type of heavy vehicles that consume much fuel. They are road
vehicles designed to carry passengers. Buses can have a capacity as high as 300
passengers. The most common type of bus is the single-decker rigid bus, with larger loads
carried by double-decker buses and articulated buses, and smaller loads carried by midi
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buses and minibuses. Coaches are used for longer distance services. Bus manufacturing is
increasingly globalized with the same design appearing around the world.
Buses may be used for scheduled bus transport, scheduled coach transport, school transport,
private hire and tourism. Promotional buses may be used for political campaigns and others
are privately operated for a wide range of purposes.
Horse-drawn buses were used from the 1820s, followed by steam buses in the 1830s, and
electric trolleybuses in 1882. The first internal combustion engine buses were used in
1895 [1]. Recently, there has been growing interest in hybrid electric buses, fuel cell
buses, electric buses as well as the one powered by compressed natural gas or bio-diesel.
1.2.1 Models of buses
1.2.1.1. Articulated bus
An articulated bus (either a motor bus or trolleybus) is an articulated vehicle used
in public transportation )Figure 1.1(. It is usually a deck design, and comprises of two rigid
sections linked by a pivoting joint. This arrangement allows a longer legal overall length
than single-decker rigid-bodied buses, and hence a higher passenger capacity, while still
allowing the bus to maneuver adequately on the roads of its service route [2].
Figure 1.1 Articulated bus [2].
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1.2.1.2. Bi-articulated bus
A bi-articulated bus or double-articulated bus is a higher-capacity type of articulated bus
)Figure 1.3(. It is an extension of a conventional or single-articulated bus, in that it has
three passenger compartment sections instead of two. This also involves the addition of an
extra axle and a second articulation joint. One of their main advantages is that they reduce
the number of drivers needed to run a service for a specific number of people, i.e., it is
usually much more cost-efficient to run a bi-articulated bus with one driver, than, for
example, to run two smaller rigid buses providing the same total number of seats.
Figure 1.2 Bi-articulated bus [3].
Disadvantages include some difficulties in traffic, the need to have bus stops catering to the
extended length, and the fact that two buses with the same capacity can be used more
flexibly [3].
1.2.1.3. Coach
A coach (also motor coach, often simply called a bus) is a type of bus used for
conveying passengers on excursions and on longer distance intercity bus service between
cities-or even between countries )Figure 1.3(. Don‟t like transit buses designed for shorter
journeys, coaches often have a luggage hold separate from the passenger cabin and are
normally equipped with facilities required for longer trips including comfortable seats and
sometimes a toilet [4].
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Figure 1.3 Coachbuses [4].
1.2.1.4. Combination bus
A combination bus, also called a truck bus or shift bus (Figure 1.4), is a purposebuilt truck with a "passenger container" fulfilling the role of a bus. Such vehicles used to be
common
in Communist
Bloc countries
and
in developing
countries.
Alternative
combination buses can be a passenger/cargo module/container mounted on a truck chassis
or a bus with a large open or closed in cargo area. Truck buses were mainly used by
the military, the police anti-riot units, as school buses, and by state owned companies on
short routes for employees [5].
Figure 1.4 Combination buses [5].
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1.2.1.5. Double-decker bus
A double-decker bus is a bus that has two stories or decks (Figure 1.5). Red doubledecker buses are used for mass transit in London. Double-decker buses are also used in
other cities in Europe, Asia and former British colonies and protectorates such as Hong
Kong, Singapore and Canada. Almost all double-deckers have a single, rigid chassis.
This type of bus is often used for touring rather than for mass transit [6].
Figure 1.5 Double-decker bus [6].
1.2.1.6. High-floor
High-floor is an expression used to distinguish tram (Figure 1.6) light rail and
other rail vehicles, along with buses and trolleybuses, built to formerly conventional design,
from their counterparts of low-floor design [7].
Figure 1.6 High-floor [7].
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1.2.1.7. Low bridge double-deck bus
A low bridge double-deck bus is a double-decker bus which has an asymmetric interior
layout (Figure 1.7), enabling the overall height of the vehicle to be reduced compared to
that of a conventional double-decker bus. The upper deck gangway is offset to one side of
the vehicle, normally the offside (or driver's side), and is sunken into the lower deck
passenger saloon. Low railway bridges and overpasses were the main reason that a reduced
height was desired [8].
Figure 1.7 Lowbridge double-deck bus [8].
1.2.1.8. Low-floor bus
A low-floor bus is a bus that has no steps between one or more entrances and part or the
entire passenger cabin (Figure 1.8). Being low floor improves the accessibility of the bus
for the public, particularly the elderly or infirm, or those with push chairs, and increasingly,
those in wheel chairs.
In the modern context, "low floor bus" refers to a bus that is accessible from a certain
minimum height of step from ground level, to distinguish it from some historical bus
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designs that did feature a level interior floor throughout but with a relatively highfloor height [9].
Figure 1.8 Low-floor bus [9].
1.2.1.9. Midi buses
A midi bus is a classification of single-decker minibuses which are generally larger than
a traditional minibus but smaller than a full-size single decker and can be anywhere
between 8 meters (26 ft 3 in) and 11 meters (36 ft 1 in) long (Figure 1.9). Midibuses are
often designed to be light weight to save on diesel fuel (e.g. smaller wheels than on larger
buses), making them not as durable as heavier 'full size' buses. Some midibuses, such as
the Scania Omni Town, are heavier and therefore more durable [10].
Figure 1.9 Midibus [10].
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1.2.1.10. Mini bus
A mini bus or mini coach is a passenger carrying motor vehicle that is designed to carry
more people than a multi-purpose vehicle or minivan, but fewer people than a full-size bus
(Figure 1.10). In the United Kingdom, the word "minibus" is used to describe any full-sized
passenger carrying van. Minibuses have a seating capacity of between 8 and 30 seats.
Larger minibuses may be called midi buses. Minibuses are typically front-engine stepentrance vehicles, although low floor minibuses do exist [11].
Figure 1.10 General View of Minibus [11].
1.2.1.11. Multi-axle bus
A multi-axle bus is a bus or coach that has more than the conventional two axles
(Figure 1.11), usually three (known as a tri-axle bus) or more rarely, four (known as
a quad-axle bus). Extra axles are usually added for legal weight restriction reasons, or to
accommodate different vehicle designs such as articulation, or rarely, to implement trailer
buses [12].
Figure 1.11 General View of Multi-axle bus [12].
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1.2.1.12. Open-top bus
An open top bus is a bus, usually but not exclusively a double-decker bus, where all or
part of the roof has been removed to provide fresh air and uninterrupted views from a high
viewpoint [13].
Figure 1.12 General View of Open-top [13].
1.2.1.13. Rigid bus
A rigid
bus (either
a motor
bus or trolleybus)
is
a vehicle used
in public
transportation with a single, rigid chassis (Figure 1.13). A bus of this type is to be
contrasted with an articulated or bi-articulated bus, which will have two or more rigid
sections linked by a pivoting joint, and also with a trailer bus, which is formed
bodied semi-trailer pulled by a conventional tractor unit.
The expression "rigid bus" is seldom used to describe a double-decker bus, because very
few double-decker buses have anything other than a rigid chassis [14].
Figure 1.13 Rigid bus [14].
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1.2.1.14. Single-decker bus
A single-decker bus or single-decker is a bus that has a single deck for passengers
(Figure 1.14). Normally the use of the term single-decker refers to a standard twoaxled rigid bus, in direct contrast to the use of the term double-decker bus, which is
essentially a bus with two passengers‟ decks and a staircase. These types of single-deckers
may feature one or more doors, and varying internal combustion engine positions [15].
Figure 1.14 General View of Single-decker bus [15].
1.2.1.15. Trailer bus
A trailer bus or articulated trailer bus is a bus formed out of a bus bodied semitrailer pulled
by
a
conventional tractor
unit in
the
same
way
as
a
conventional articulated semi-trailer truck (Figure 1.15). Trailer buses are usually pulled by
a conventional truck from various truck manufacturers, while others have larger space cabs.
Trailer bus bodies are built by various local builders [16].
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Figure 1.15 General View of Trailer bus [16].
Some of these buses used in Saudi Arabia in Hajj and general massive transportation.
1.3 Bus Companies in Saudi Arabia
Many companies work in Saudi Arabia but the following two are the most famous:
1.3.1. Saudi Public Transport Co. (SAPTCO)
Saudi Public Transport Co. (SAPTCO) was established in 1399 H (1979 G) with a fully
paid up capital of SR 1000 million to provide public bus transport services. SAPTCO
operates around the clock with terminals in the Kingdom's major cities and through an
extensive network of local and international agents. SAPTCO operates a fleet around 3000
buses of various capacities and sizes according to the latest production of the global up to
date carrying out 579 daily scheduled trips, connecting 600 cities, towns and villages
Kingdom wide. Daily international trips are scheduled to Kuwait, Bahrain, Qatar, U.A.E.,
Yemen, Egypt, Jordan, Syria, Sudan and Lebanon.
SAPTCO's inter city services cover 10 major cities which include: (Makkah, Madinah,
Riyadh, Jeddah, Taif, Dammam, Abha, Gaseem, Tabuk, Hael), and special transportation to
the Holy Shrines during Hajj and Ramadan. SAPTCO also provides a distinguished VIP
service, offers Charter bus service and operates school/college transportation services.
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The number of passengers transported by SAPTCO has reaches more than 2,005 Billion
passengers.
The number of local and international agents of the company reached 161 Agents. The
distinguished VIP services are between Riyadh - Al Khobar, Makkah - Madinah and to
Bahrain. These trips are direct and non-stop. Passengers are provided meals, hot and cold
drinks, newspapers and the outlet to use mobile phones and laptop. The company is
planning to expand its VIP services to include new routes [17].
There is a team of skilled and well trained bus drivers, comes in compliance and
adherence with safety and security precautions for the customers. All fleet drivers and
passengers are fully insured. SAPTCO, as future plans, is looking forward to cope with the
developments that transport sector witness. It continues to update its fleet with most recent
technologies in bus's manufacturing in addition to its efforts to introduce "Integral Umrah
and Tourist" service [18].
1.3.2. DaIIah Hajj Transport Co.
The company went under the umbrella of the General Automobile Association in 1386
H the Number of Company's fleet at Launch was 336 buses and the number of the
company's fleet currently features 748 buses. It owns a modern fleet of luxury buses to
transport pilgrims and visitors [19].
1.4 Bus Fuel Economy
Factors below be implemented if considered “ordinary” (non hybrid) natural gas or
diesel bus and want to maximize its miles per gallon (MPG) potential Ideas of buses [20].
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1.4.1 Slow Down
Potential benefit of slow down buses were 2.2% mpg loss for every mph over 55
otherwise the problem will be Transit and school buses don‟t often go that fast [20].
1.4.2 Lower HP Engine and BSFC Engine Curve
In case of the buses have Lower HP Engine and BSFC Engine Curve, the potential
benefits were better fuel economy and lower vehicle cost but on other side the Potential
problems were driver complaints and longer route times. BSFC Engine Curve of the Diesel
engine Brake Specific Fuel Consumption Curve from Heywood, “Internal Combustion
Engine Fundamentals” [20].
Lower RPM = better fuel economy100 N-m = 74 lb-ft HP= (Torque X RPM) / 5252. 1 hp =
0.75 KW.
Figure 1.16: BSFC Engine Curve [20].
BSFC engine curve (Moral) the Lower RPM = better fuel economy (FE).
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1.4.3 Better transmission/drivetrain match
Better transmission/drivetrain match will give a potential benefit were better FE that
transmission should allow operation of the vehicle near “low-RPM, high MPG, sweet spot
and lower noise level but the potential problems were driver complaints [20].
1.4.4 Lower Rolling Resistance Tires
The Lower Rolling Resistance Tires that will give a potential benefit around 2-3% Better
FE and benefits at all speeds but the potential problems are available for transit buses and
Initial cost [20].
1.4.5 Wide-Base Singles in place of Duals
In case of Wide-Base Singles in place of Duals the potential benefit 2% Better FE, lower
initial cost and lower weight but the potential problems were the availabilities of transit
buses and there was no reserve if tire fails [20].
1.4.6 Low HP Engine Accessories
The potential benefit of Low HP Engine Accessories is improved FE but the potential
problems were how well they worked, the cost and engine warranty [20].
1.4.7 Effect of Aerodynamics
The potential benefits of aerodynamics effect were better FE and better image but the
potential problems were real benefit at higher speeds [20].
1.4.8 Less Idling
The potential benefits of Less Idling were infinite MPG, Zero emissions and better
Image but potential problems were driver complaints, engine restarts and there is always an
idled bus [20].
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1.5 Drag
1.5.1 Aerodynamic Drag
Aerodynamic drag is the force that resists the movement of a body through a fluid
medium. Aerodynamic drag varies with the square of the vehicle speed
. When a vehicle
travels through still air, doubling the vehicle speed approximately quadruples the
aerodynamic drag. In the presence of terrestrial winds that are not in-line with the vehicle
motion, cross winds generate a non-zero yaw angle of the wind relative to the vehicle travel
direction. For heavy-duty vehicles, such as tractor-trailer combinations, the drag coefficient
increases significantly with yaw angle [21].
To account for typical cross winds, a wind-average-drag coefficient can be defined that
represents an average drag coefficient based on the predominant winds for a given region
(typically an 11 km/hr (7 mph) wind speed in North America). The non-linearity of drag
with wind-speed is what accounts for the disparity in the aerodynamic contributions to
power consumption between urban and highway environments. In general, the mechanical
losses in the system vary linearly with vehicle speed. At 53 km/h the power required to
overcome mechanical resistance is approximately double that required to overcome
aerodynamic drag. At 80 km/h, the power necessary to overcome aerodynamic drag is
roughly equal to the mechanical losses, and for higher vehicle speeds the aerodynamic
losses dominate [21].
Friction drag is the component of drag that acts parallel to a surface as a result of shear and
viscous effects in the flow adjacent to the body surface.
For heavy vehicles such as tractor-trailer combinations and buses, pressure drag is the
dominant component due to the large surfaces perpendicular to the main flow direction and
due to the large wake resulting from the bluntness of the back end of such vehicles. The
pressure forces acting on the front and back face of the vehicle, as well as in the gap region
between a tractor and trailer, are dominant. The large empty spaces in underbody regions of
tractor-trailer combinations also contribute to the pressure drag. The cooling flows through
a vehicle engine compartment are also dominated by pressure-drag effects [21].
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Although friction drag occurs along the external surfaces of heavy vehicles, particularly
along the sides and top of buses and trailers, its contribution to overall drag is small (10%
or less) and is not a strong candidate for drag-reduction technologies. Unlike flight vehicles
that have streamlined bodies for which friction drag is the dominant contribution, roadvehicle aerodynamics is predominantly concerned with pressure drag and therefore the
large body of knowledge concerning drag-reduction for flight vehicles is not strictly
applicable to the road-vehicle and ground-transportation industries [21].
All combination vehicles are different, but in general terms, at zero yaw, the drag on the
tractor accounts for approximately 70% of the total drag and the trailer accounts for the
remaining 30% of the drag. However, at yaw angles in excess of 5 deg the tractor drag
component increases very little but the trailer drag increases substantially such that it can
exceed that of the tractor .Aside from saving fuel, there are other potential benefits to
reducing drag such as improved aerodynamic stability and reduced splash and spray [21].
1.5.2 Effect of density
Air density is another factor that can affect drag. As temperature drops, the density of
the air increases which increases the drag on a vehicle. This can cause significant changes
of drag on a vehicle in climates such as Canada where temperature differences of
60 degrees Celsius can occur in the same location when comparing July conditions to say,
February conditions [21].
Table 1.1 Effect of the temperature on drag with reference temperature of +15 °C [21].
Present increase in drag at various
% increase in drag
Temperature (°C)
+15
0
-15
-30
0
5.5
11.6
18.5
1.5.3 Assessment criteria for drag-reduction technologies
In general, the implementation of any drag-reduction technology must be tempered with
the need to maintain the practicality, legality and usability of the vehicle. In order for an
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aerodynamic technology to gain acceptance in the industry, it must meet the following
criteria [21]:
1. Reduce fuel consumption by a measurable amount.
2. Be cost effective and have a reasonable return on investment (the definition of
“reasonable” varies from operator to operator).
3. Be relatively easy to install and maintain.
4. Have little to no detrimental effects on operations on the road and around loading
docks.
5. Not contravene existing provincial or local regulations.
The relative advantages and drawbacks of each technology are presented as well as their
relevance to the Canadian trucking industry. Where possible, the reduction in drag
coefficient has been quantitatively stated as well as any factors that must be maintained in
order to achieve those stated or tested results [21].
1.5.4 Factors affecting drag
When a solid body is moved through a fluid (gas or liquid), the fluid resists the motion.
The object is subjected to an aerodynamic force in a direction opposed to the motion which
is called drag [22]. The effect of drag is substance of the current study.
1.5.4.1 The Object
Geometry has a large effect on the amount of drag generated by an object. As with lift,
the drag depends linearly on the size of the object moving through the air. The crosssectional shape of an object determines the form drag created by the pressure variation
around the object. The three dimensional platform shapes affects the induced drag of a
lifting object. If aerodynamic friction drag considered the amount of drag depends on the
surface roughness of the object; a smooth, waxed surface produces less drag than a
roughened surface. This effect is called skin friction and is usually included in the
measured drag coefficient of the object [22].
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1.5.4.2 Motion of the Air
Drag is associated with the movement of the object through the air, so drag depends on
the velocity of the air. Like lift, drag actually varies with the square of the relative velocity
between the object and the air. The inclination of the object to the flow also affects the
amount of drag generated by a given shaped object. If the object moves through the air at
speeds near the speed of sound, shock waves are formed on the object which create an
additional drag component called wave drag. The motion of the object through the air also
causes boundary layers to form on the object. A boundary layer is a region of very low
speed flow near the surface which contributes to the skin friction [22].
1.5.4.3 Properties of the Air
Drag depends directly on the mass of the flow going past the aircraft. The drag also
depends in a complex way on two other properties of the air, its viscosity and its
compressibility. These factors affect the wave drag and skin friction which hare described
above. The Drag Equation is a gathering all of information on the factors that affect drags
into a single mathematical equation. With the drag equation there is an ability to predict
how much drag force is generated by a given body moving at a given speed through a given
fluid [22].
1.5.5 Shape effect on drag
The drag coefficient is a number which aerodynamicists use to model all of the
complex dependencies of drag on shape, inclination and some flow conditions. The drag
coefficient
is equal to the drag D divided by the quantity: density r times reference area
a time one half of the velocity V squared.
= D / (.5 * r * V^2 * A)
The values shown here were determined experimentally by placing models in a wind
tunnel and measuring the amount of drag, the tunnel conditions of velocity and density, and
the reference area of the model. The drag equation given above was then used to calculate
the drag coefficient. The projected frontal area of each object was used as the reference
area. A flat plate has
has
= 1.28, awedge shaped prism with the wedge facing downstream
= 1.14, a sphere has a
that varies from .07 to .5, abullet
= .295, and a typical
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airfoil
= .045. Studding the effect of shape on drag by comparing the values of drag
coefficient for any two objects as long as the same reference area is used and the Mach
number and Reynolds number are matched. All of the drag coefficients were produced in
low speed (subsonic) wind tunnels and at similar Reynolds number, except for the sphere.
A quick comparison shows that a flat plate gives the highest drag and a streamlined
symmetric airfoil gives the lowest drag by a factor of almost 30 shapes have a very large
effect on the amount of drag produced. Comparing the flat plate, the prism, the sphere and
the bullet that the downstream shape can be modified to reduce drag. The drag coefficient
for a sphere is given with a range of values because the drag on a sphere is highly
dependent on Reynolds number [23].
1.5.6 Size effect on drag
The amount of drag generated by an object depends on the size of the object. Drag is an
aerodynamic force and therefore depends on the pressure variation of the air around the
body as it moves through the air. The total aerodynamic force is equal to the pressure times
the surface area around the body. Drag is the component of this force along the movement
direction. Like the other aerodynamic force lift, the drag is directly proportional to the area
of the object. Doubling the area doubles the drag. There are several different areas from
which to choose when developing the reference area used in the drag equation. If the
thinking of drag as being caused by friction between the air and the body, a logical choice
would be the total surface area (
) of the body. If the thinking of drag as being a resistance
to the flow, a more logical choice would be the frontal area (
) of the body which is
perpendicular to the flow direction. Finally, if comparing wanted with the lift coefficient,
should use the same area used to derive the lift coefficient, the wing area, (
). Each of the
various areas is proportional to the other areas. Since the drag coefficient is determined
experimentally, by measuring the drag, measuring the area and performing the necessary
math to produce the coefficient, there are free area to use any area which can be easily
measured. If the wing area were choose, the computed coefficient has a different value than
if the cross-sectional area choose, but the drag is the same, and the coefficients are related
by the ratio of the areas. In practice, drag coefficients are reported based on a wide variety
of object areas [24].
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1.6 Gasoline Engine Emissions and Health Cars and Pollution
Emissions from an individual car are generally low, relative to the smokestack image
many people associate with air pollution. But in numerous cities across the country, the
personal automobile is the single greatest polluter, as emissions from millions of vehicles
on the road add up. Driving a private car is probably a typical citizen‟s most “polluting”
daily activity [25].
1.6.1 Sources of Auto Emissions
The power to move a car comes from burning fuel in an engine. Pollution from cars
comes from by-products of this combustion process (exhaust) and from evaporation of the
fuel itself [25].
1.6.2 Exhaust Pollutants
Hydrocarbons: Hydrocarbon emissions result when fuel molecules in the engine do not
burn or burn only partially. Hydrocarbons react in the presence of nitrogen oxides and
sunlight to form ground-level ozone, a major component of smog. Ozone irritates the eyes,
damages the lungs, and aggravates respiratory problems. It is our most widespread and
intractable urban air pollution problem. A number of exhaust hydrocarbons are also toxic,
with the potential to cause cancer.
Nitrogen Oxides (NOx): Under the high pressure and temperature conditions in an engine,
nitrogen and oxygen atoms in the air react to form various nitrogen oxides, collectively
known as NOx. Nitrogen oxides, like hydrocarbons, are precursors to the formation of
ozone. They also contribute to the formation of acid rain.
Carbon Monoxide: Carbon monoxide (CO) is a product of incomplete combustion and
occurs when carbon in the fuel is partially oxidized rather than fully oxidized to carbon
dioxide (CO). Carbon monoxide reduces the flow of oxygen in the bloodstream and is
particularly dangerous to persons with heart disease.
Carbon Dioxide: Carbon dioxide (CO2) does not directly impair human health, but it is a
greenhouse gas that traps the earth‟s heat and contributes to the potential for global
warming.
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Benzene: A carcinogen that is added to gasoline to decrease the frequency of improper
combustion, which can lead to engine malfunction. Long-term exposure to even lower
concentrations of the chemical has also been shown to cause reduced red blood cell counts
and anemia.
1.6.3 Evaporative Emissions
Hydrocarbon pollutants also escape into the air through fuel evaporation. With today‟s
efficient exhaust emission controls and today‟s gasoline formulations, evaporative losses
can account for a majority of the total hydrocarbon pollution from current model cars on
hot days when ozone levels are highest [25].
1.6.4 IN VERMONT: Motor vehicles (all types) contribute to air pollution
• Motor vehicles are the largest source of carbon monoxide (61%). More than 120,000
tons of carbon monoxide is emitted annually from motor vehicles in Vermont.
• Motor vehicles are the largest source of hydrocarbons (48%). More than 10,000 tons of
hydrocarbons are emitted annually from motor vehicles in Vermont.
• Motor vehicles are the largest source of nitrogen oxides (79%). More than 15,000 tons
of NOx are emitted annually from motor vehicles in Vermont [25].
1.6.5 IN VERMONT: Health and Environmental Concerns
Toxic and carcinogenic air pollutants threaten human health even at very low
concentrations.
• Pollution from motor vehicles contributes to formation of ground-level ozone.
• Breathing ozone may lead to serious harm to health, including premature death,
shortness of breath, inflammation of the lining of the lungs, increased risk of asthma
attacks4.
• Children, people with lung disease and the elderly are especially vulnerable to ground
level ozone.
• Ground-level ozone from vehicles inhibits plant growth and can cause widespread
damage to crops and forests.
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• Air pollution from motor vehicles contributes to the formation of acid rain and global
climate change [25].
1.7 Present Study
In the present study, a computational study on the bus was carried out for different shape
of drag reduction devices. The aerodynamic performance of the bus was evaluated by
numerical modelling using the commercial software-package ANSYS-FLUENT. The drag
reduction device was modified to reduce the aerodynamic drag. The computational were
carried out at different values of Reynolds number and the optimum shape design of the
drags reduction device is recommended.