Energy Saving and Conversion
(MSJ0200)
2011. Autumn semester
3. and 4. lectures
Transportation
Transportation
• Energy consumption of transportation
• Emissions from transportations, directives,
regulations.
• Different type of internal combustion engines,
hybrid and hydrogen cars
Introduction
• The private automobile is the primary mode
of transportation for developed countries.
• More than 80 per cent of households have a
personal vehicle (example Canada).
• In total, there are 19.2 million passenger cars,
vans, sport utility vehicles, and pick up trucks
registered in Canada and these are typically
driven more than 332 billion cilometres per
year (16600 km/per car).
• This level of private automobile ownership and use
has had profound impacts on the economy and
people’s lifestyles. But the scale of automobile use
in around the world has also come at a cost.
• Energy is needed to power an automobile, and
most of this energy comes from the burning of fossil
fuels in the vehicle’s engine. This burning or
“combustion” process produces emissions that
pollute the air and contribute to climate change. In
fact, transportation is a major source of these
emissions.
Emissions by Sector (Canada -2006)
Emissions by Sector (Estonia - 2008)
Emissions by Sector (Estonia - 2008)
• To make substantial reductions in emissions,
we need to reduce their overall transportation
energy use.
• One way this can be accomplished is by
minimizing the amount of fuel that an engine
needs to burn while being operated – or, in
other words, increasing vehicle fuel efficiency.
• Transportation alternatives such as public
transit, biking or walking is also an effective
way to reduce one’s transportation energy
use.
• Alternative fuels.
• New construction of car hybrid and electric
car.
Automobile Fuel and Emissions
• The energy to power an automobile comes from its
fuel. The purpose of an automobile’s engine is to
convert the chemical energy of the fuel into kinetic
energy – or motion – that powers the vehicle. In
other words, the engine is simply a mechanical
device that uses the chemical energy of the fuel to
move the vehicle down the road.
• This is done by burning or combusting the fuel
inside the engine, which gives rise to the term
internal combustion engine (ICE).
• If the combustion process followed a perfectly
ideal chemical reaction, then complete
combustion of hydrocarbons in the fuel (HxCy)
with oxygen present in the air (O2) would
produce only carbon dioxide (CO2) and water
(H2O), as shown in the following chemical
reaction equation:
Combustion is neither a complete nor a perfect
process; therefore, the products in the engine
exhaust also contain some unburned fuel.
Emissions of unburned fuel are also classified as
Volatile Organic Compounds (VOCs) – “volatile”
because they easily and quickly evaporate into
the air.1 In addition, there is also a degree of
incomplete or partial combustion of
hydrocarbons, which results in emissions of
carbon monoxide (CO).
The combustion process occurs under
conditions of high heat and pressure, which
causes nitrogen in the air to bond with oxygen
and form Oxides of Nitrogen (NOx).
The sulphur in fuel also bonds with oxygen to
form Oxides of Sulphur (SOx - under some
conditions, the sulphur can also bond with
hydrogen to produce a small amount of
hydrogen sulphide, H2S).
In addition to these chemical compounds,
automobile engines also emit varying amounts
of Particulate Matter (PM), which can include
microscopic liquid droplets and particles of soot
produced during combustion. Thus, the “real”
chemical equation of combustion in the engine
looks more like this:
The characteristics of the major
pollutants associated with
automobile use:
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CARBON DIOXIDE (CO2)
VOLATILE ORGANIC COMPOUNDS (VOCs)
OXIDES OF NITROGEN (NOx)
CARBON MONOXIDE (CO)
PARTICULATE MATTER (PM)
OXIDES OF SULPHUR (SOx)
OTHER ENGINE EMISSIONS
CARBON DIOXIDE (CO2)
CO2 is a greenhouse gas (GHG) that persists
in the atmosphere for about 150 years. Due
to the large amount of CO2 emitted
worldwide from the burning of fossil fuels,
such as gasoline and diesel, it is the main
target of global efforts to reduce
atmospheric concentration levels of GHGs
and lessen the negative impacts of climate
change.
Carbon dioxide is also the most significant
vehicle emission by weight. For each litr of
gasoline burned, approximately 2.3 kg of CO2 is
produced (the exact amount depends on how
much carbon and oxygen end up in other
combustion products for diesel 2,7 kg)).
Less than ideal combustion produces less CO2
but more air pollutants, whereas the use of
“cleaner” fuels better controlled combustion
and exhaust after-treatment technology reduces
air pollution emissions and leads to a minor
increase in emission of CO2 (since more of the
carbon in the fuel ends up bonded with oxygen).
For each litr of diesel burned, approximately 2.7
kg of CO2 is produced. The average car produces
about two to three times its weight in CO2 every
year.
VOLATILE ORGANIC COMPOUNDS
(VOCs)
VOCs are defined as “volatile” because they
easily and quickly evaporate into the air.
There are many thousands of different types
of VOCs emitted into the atmosphere from a
range of natural and manmade sources,
including those that are harmful and those
that are not.
VOCs also react with nitric oxide (NO) and
nitrogen dioxide (NO2) (which are also engine
combustion products, see following page) in the
presence of sunlight and heat to form groundlevel ozone (O3). O3 is considered a by-product
of automobile emissions (and many other nonautomobile sources of emissions) and is both
toxic and a major component of smog.
VOCs emitted from automobile engines are also
referred to as hydrocarbons (HC) because they
are primarily uncombusted hydrocarbon fuels.
Gasoline and diesel are complex mixtures of
different types of hydrocarbon molecules,
some of which are harmful and can end up in
tailpipe emissions, including benzene (H6C6)
and formaldehyde (HCHO). VOCs such as these
can be toxic (even in small doses), impair brain
function or cause cancer.
Another hydrocarbon emitted from automobile
engines is methane (CH4), which is not very
reactive and hence does not contribute to smog
formation as other types of VOCs do. However,
it is a very potent GHG, with more than 20 times
the global warming potential of CO2 and persists
in the atmosphere for approximately 12 years.
OXIDES OF NITROGEN (NOx)
Under the high pressure and temperature
conditions of a typical engine, nitrogen and
oxygen in the air (that is drawn into the
engine) combine to form NOx. Fuel is not
directly the cause of NOx formation, but
rather it is the heat produced by the
combustion of the fuel that leads nitrogen
and oxygen to bond.
Thus, NOx emissions are likely to be a problem
regardless of the type of fuel burned, although
the amount of NOx formed may vary among fuel
types. The chemical arrangements of NOx
include nitric oxide (NO), nitrogen dioxide (NO2)
and nitrous oxide (N2O). NO and NO2 are air
pollutants while N2O is a potent greenhouse
gas.
NO and NO2 react with VOCs in the presence of
sunlight and heat to form ground-level ozone
(O3) and play a part in the formation of fine
particulate matter, or PM (discussed on
following page). They can also combine with
water vapour to form nitric acid, which
contributes to acid rain.
NO2 irritates the lungs, impairs lung function
(even with short term exposure) and lowers
resistance to respiratory infection. In children
and adults with respiratory disease, NO2 can
cause symptoms including coughing, wheezing
and shortness of breath. In itself, N2O does not
contribute to poor air quality, but it is a potent
GHG. With roughly 300 times the global
warming potential of CO2, N2O persists in the
atmosphere for about 100 years.
CARBON MONOXIDE (CO)
CO is a colourless, odourless gas that is
poisonous, and forms in the engine as a result of
incomplete combustion. This phenomenon is
worsened when the fuel-to-air mixture is too
rich (perhaps due to a poorly tuned engine or
faulty engine control systems). In the human
body, CO reduces the ability of the blood to
carry oxygen from the lungs.
Everyone’s health is threatened by this
potentially lethal emission, but people with
heart disease are most vulnerable to its effects.
Other high risk groups include pregnant women
(and their fetuses), infants, children, the elderly
and people with anemia and respiratory or lung
disease. As it decays, CO also contributes to the
formation of ozone (O3).
PARTICULATE MATTER (PM)
PM is emitted directly from automobile tailpipes
as microscopic carbon residues (a product of
fuel combustion) and as liquid droplets. Particles
are measured by their diameter and range in
size from 0.005 to 100 microns (one micron
equals one thousandth of a millimetre or 1/50
of the width of an average human hair).
Some PM is visible, such as the black smoke
often seen in diesel truck exhaust. These
particles can be large enough to become
trapped in the body’s filters that are the nose
and throat, limiting the potential health threat.
Smaller particulates, measuring less than 10
microns (PM10), are invisible and can be
breathed into the lungs.
Particulates that measure less than 2.5 microns
(PM2.5) are able to penetrate deep into the
lungs. The smaller the particle, the deeper it
may enter the lungs and theoretically, the
greater the damage it can cause. The toxicity
and carcinogenic effect of PM can vary according
to its source and composition. Other toxic
chemicals can adhere to fine PM, compounding
the threat as they are carried deep into the
lungs where they can pass into the bloodstream.
PM is also a component of smog and is
suspected to have a secondary impact on global
warming trends as it reflects, absorbs and
scatters solar radiation.
OXIDES OF SULPHUR (SOx)
Under the high pressure and temperature
conditions of a typical automobile engine,
sulphur in the fuel and oxygen from the air
combine to form SOx. The chemical
arrangement of primary concern is sulphur
dioxide (SO2). SO2 contributes to the formation
of fine PM and therefore is a smog pollutant.
Exposure to SO2 leads to eye irritations,
shortness of breath, and impaired lung function.
Combining with water molecules to form
sulphuric acid, SO2 is one of the more persistent
pollutants and is a major source of acid rain,
acid snow, and acid fog that impact ecosystems
and urban environments. SOx can also interfere
with the proper functioning of a vehicle’s
emissions after-treatment system (i.e., catalytic
converter) and, as a result, reduce its ability to
decrease other harmful emissions such as HC,
CO and NOx.
OTHER ENGINE EMISSIONS
In addition to the above list, there are various
other possible emissions to consider. Over the
years, various chemical compounds have been
added to gasoline by oil refiners to enhance
combustion properties and comply with
emissions standards.
Examples include tetraethyl lead, which when
added to gasoline increases its octane number
(i.e., leaded gasoline), and methyl tertiary butyl
ether (MTBE) and methylcyclopentadienyl
manganese tricarbonyl (MMT), which reduces
incomplete combustion by adding oxygen to the
fuel formulation. Additives such as these can
end up in the combustion products in one form
or another and emitted to the atmosphere.
These substances can be toxic to human health
or otherwise harmful to the environment.
Particle Number
Emissions. Under
the draft
implementing
legislation, a
particle number
emission limit of
5 × 1011 km-1
(PMP method,
NEDC test)
becomes
effective at the
Euro 5/6 stage
for all categories
of diesel vehicles
(M, N1, N2). The
particle number
limit must be
met in addition
to the PM mass
emission limits
listed in the
above tables.
Emission Durability. Effective October 2005 for new type
approvals and October 2006 for all type approvals,
manufacturers should demonstrate that engines comply with the
emission limit values for useful life periods which depend on the
vehicle category, as shown in the following table.
Comparing with US Conclusion:
Testing
Emission Testing
Emissions are tested over the NEDC (ECE 15 + EUDC)
chassis dynamometer procedure. Effective year 2000
(Euro 3), that test procedure was modified to
eliminate the 40 s engine warm-up period before the
beginning of emission sampling. This modified cold
start test is referred to as the New European Driving
Cycle (NEDC) or as the MVEG-B test. All emissions are
expressed in g/km.
The draft Euro 5/6 implementing legislation adopts a new PM
mass emission measurement method (similar to the US 2007
procedure) developed by the UN/ECE Particulate
Measurement Programme (PMP) and adjusts the PM mass
emission limit to account for differences in results using the
old and the new method.
The legislation also introduces a particle number emission
limit at the Euro 5/6 stage (PMP method), in addition to the
mass-based limits. At the time of adoption of the Euro 5/6
regulation, its mass-based PM emission limits could only be
met by closed particulate filters. Number-based PM limits
would prevent the possibility that in the future open filters
are developed that meet the PM mass limit but enable a high
number of ultra fine particles to pass.
How do increase fuel consuption
Shape drag
The forward motion of the vehicle pushes the
air in front of it. However, the air cannot
instantaneously move out of the way and its
pressure is thus increased, resulting in high air
pressure. In addition, the air behind the vehicle
cannot instantaneously fill the space left by the
forward motion of the vehicle. This creates a
zone of low air pressure.
The motion of the vehicle, therefore, creates
two zones of pressure that oppose the motion
by pushing (high pressure in front) and pulling it
backwards (low pressure at the back) as shown
in Figure 2.5. The resulting force on the vehicle
is the shape drag. The name “shape drag”
comes from the fact that this drag is completely
determined by the shape of the vehicle body.
Aerodynamic drag
is a function of vehicle speed V, vehicle frontal
area, Af , shape of the vehicle body, and air
density, ρ:
where CD is the aerodynamic drag coefficient
that characterizes the shape of the vehicle body
and Vw is component of the wind speed on the
vehicle moving direction, which has a positive
sign when this component is in the same
direction of the moving vehicle and a negative
sign when it is opposite to the vehicle speed.
The aerodynamic drag coefficients for typical
vehicle body shapes are shown in Figure 2.6.
Ar engine (IC) (as well named
Power Plant) Characteristics
The ideal performance characteristic of a power plant is
a constant power output over the full speed range.
Consequently, the torque varies with speed
hyperbolically as shown in Figure 2.12.
Characteristics of a gasoline engine in wide open
throttle are shown in Figure 2.13
Characteristics far from the ideal performance
characteristic required by traction.
The IC engine has a relatively flat torque–speed profile
(as compared with an ideal power plant), as shown in
Figure 2.13. Consequently, a multigear transmission is
usually employed to modify it, as shown in Figure 2.14
The electric motor is another candidate as a
vehicle power plant, and becoming more and
more important with the rapid development of
electric, hybrid electric, and fuel cell vehicles.
Electric motors with good speed adjustment
control usually have a speed–torque
characteristic that is much closer to the ideal, as
shown in Figure 2.15.
Fuel Economy Characteristics of IC
Engines
The fuel economy characteristic of an IC engine is evaluated
by the amount of fuel per kWh energy output, which is
referred to as the specific fuel consumption (g/kWh). The
typical fuel economy characteristic of a gasoline engine is
shown in Figure 2.30.
The fuel consumption is quite different from one operating
point to another. The optimum operating points are close to
the points of full load (wide open throttle). The speed of the
engine also has a significant influence on the fuel economy.
With a given power output, the fuel consumption is usually
lower at low speed than at high speed.
Basic Techniques to Improve
Vehicle Fuel Economy
The effort to improve the fuel economy of
vehicles has always been an ongoing process in
the automobile industry. Fundamentally, the
techniques used mainly include the following
aspects:
1. Reducing vehicle resistance:
Using light materials and advanced
manufacturing technologies can reduce the
weight of vehicles, in turn reducing the rolling
resistance and inertial resistance in acceleration,
and therefore reducing the demanded power on
the engine. The use of advanced technologies in
tire production is another important method in
reducing the rolling resistance of vehicles.
For instance, steel wire plied radial tires have a
much lower rolling resistance coefficient than
conventional bias ply tires. Reducing
aerodynamic resistance is also quite important
at high speeds. This can be achieved by using a
flow-shaped body style, a smooth body surface,
and other techniques. Furthermore, improving
transmission efficiency can reduce energy losses
in the transmission. Proper transmission
construction, good lubrication, proper
adjustment and tightening of moving parts in
the transmission, and so on will achieve this
purpose.
2. Improving engine operation
efficiency:
Improving engine operation efficiency has great
potential to contribute to the improvement of
vehicle fuel economy. There are many effective
advanced techniques, such as accurate air/fuel ratio
control with computer-controlled fuel injection,
high thermal isolated materials for reducing thermal
loss, varying ignition-timing techniques, active
controlled valve and port, and so on.
Example, impact of out-of-time of exhaust valve for
burning rate
3. Properly matched transmission:
Parameters of the transmission, especially gear
number and gear ratios, have much influence on
operating fuel economy as described previously.
In the design of the transmission, the
parameters should be constructed so that the
engine will operate close to its fuel optimum
region.
4. Advanced drive trains:
Advanced drive trains developed in recent years,
such as new power plants, various hybrid drive
trains, etc., can greatly improve the fuel
economy of vehicles. Fuel cells have higher
efficiency and lower emissions than
conventional IC engines. Hybridization of a
conventional combustion engine with an
advanced electric motor drive may greatly
enhance the overall efficiency of vehicles.
Example
How an Internal Combustion
Engine Works
The torque performance of the 4S SI engine is determined by
the pressure within the cylinder, as shown in Figure 3.3. In the
induction stroke (g–h–a), the pressure in the cylinder is
usually lower than the atmospheric pressure because of the
resistance of the airflow into the cylinder. In the compression
stroke (a–b–c), the pressure increases with the upward
movement of the piston.
When the piston approaches the TDC, the spark plug
produces a spark to ignite the air/fuel mixture trapped in the
cylinder, and the pressure increases quickly. In the expansion
stroke (c–d–e), the high-pressure gases in the cylinder push
the piston downward, producing torque on the crankshaft. In
the exhaust stroke (e–f–g), the gases in the cylinder are
propelled out of the cylinder with a higher pressure than in
the induction stroke.
The torque performance is usually evaluated by
the gross work done in one cycle, usually called
gross indicated work, Wc,in. The gross indicated
work can be calculated by
where p is the pressure in the cylinder and V is
the volume.
The work done in area B is negative, because the
pressure in the induction stroke is lower than
that in the exhaust stroke. In order to achieve
much work in one cycle, area A should be made
as large as possible by increasing the pressure in
the expansion stroke, and area B should be
made as small as possible by increasing the
pressure in the induction stroke and decreasing
it in the exhaust stroke.
The torque of an engine depends on engine size
[engine displacement, which is defined as the
volume that the piston sweeps from TDC to
bottom dead center (BDC)]. A more useful
relative performance measure is the mean
effective pressure (mep), which is defined as the
work per cycle per displacement:
Mechanical Efficiency
Not all the power produced in the cylinder
(indicated power) is available on the crankshaft.
Part of it is used to drive engine accessories and
overcome the frictions inside the engine. All of
these power requirements are grouped together
and called friction power Pf ; thus
where Pb is brake power (useful power on the
crankshaft). It is quite difficult to determine the
friction accurately. In practice, one common
approach for automotive engines is to drive or
motor the engine on a dynamometer (operate
the engine without firing it) and measure the
power supplied by the dynamometer.
The ratio of brake power (useful power on the
crankshaft) to indicated power is called
mechanical efficiency, ηm:
Specific Fuel Consumption and
Efficiency
In engine tests, fuel consumption is measured as
a flow rate—mass flow per unit time, ˙ mf . A
more useful parameter is the specific fuel
consumption (sfc)— the fuel flow rate per useful
power output. It measures how efficiently an
engine is using the fuel supplied to produce
work:
where ˙ mf is fuel flow rate and P is engine
power. If the engine power P is measured as the
net power from the crankshaft, the specific fuel
consumption is called brake specific fuel
consumption (bsfc). The sfc or bsfc is usually
measured in SI units by the gram numbers of
fuel consumed per kW power output per hour
(g/kWh). Low values of sfc (bsfc) are obviously
desirable. For SI engines, typical best values of
bsfc are about 250–270 g/kWh.
Specific Emissions
• The level of emission of oxides of nitrogen
[nitric oxide (NO) and nitrogen dioxide (NO2)
usually grouped together as NOx], carbon
monoxide (CO), unburned HCs, and
particulates are important engine operating
characteristics.
• The concentrations of gaseous emissions in
engine exhaust are usually measured in parts
per million or percent by volume (mole
fraction).
Specific emissions are the flow rate of pollutant
per power output:
Fuel/Air Equivalent Ratio
Proper fuel/air (or air/fuel) ratio in the fuel/air
mixture is a crucial factor that affects the
performance, efficiency, and emission
characteristics of an engine, as shown in Figure
3.8.
Basic Techniques for Improving
Engine Performance,
Efficiency, and Emissions
Forced Induction
The amount of torque produced in an IC engine
depends on the amount of air induced into its
cylinders. An easy way of increasing the amount of
air induced is to increase the pressure in the intake
manifold. This can be done by three means:
variable intake manifold, supercharging, or
turbocharging.
The intake manifold is like a wind instrument: it
has resonant frequencies. A variable intake
manifold tunes itself according to engine speed
in order to exploit those resonant frequencies. If
the tuning is proper, the amount of air induced
into the cylinders can be optimized because the
pressure in the intake manifold is increased. This
technique improves the “breathing” of the
engine but does not result in a very large
increase of torque output.
A supercharger is an air compressor turned by
the engine crankshaft. The air thus compressed
is fed to the intake manifold. The advantage of a
supercharger is that it can significantly increase
the pressure in the intake manifold, even at low
speed. The most significant disadvantage is that
the supercharging power is taken from the
engine crankshaft. This reduces the engine
output and harms fuel consumption.
A turbocharger consists of a turbine driven by
exhaust gases and of a compressor turned by
the turbine. A turbocharger has the great
advantage of taking its energy from the exhaust
gases, which are normally wasted. Therefore,
the efficiency of the engine does not suffer from
the addition of the turbocharger. Turbocharging
can tremendously increase the power output of
the engine, especially if coupled to a charge
cooling system Supercharging and turbocharging
both suffer from two disadvantages: knock and
emissions.
Compressing the intake air also increases its
temperature. An increased temperature means a greater
risk of auto-ignition and knocks for the mixture, and
increased nitric oxide emissions. The solution to this
problem consists in cooling down the intake air after
compression by means of an intercooler or heat
exchanger. The compressed air is passed through a
radiator, while the ambient air or water is passed on the
exterior of the radiator, removing the heat from the
charge. The temperature of induced air can be reduced
sufficiently to avoid auto-ignition and knock. Nitric oxide
emissions are also reduced. It should be noted that an
engine designed for forced induction has a lower
compression ratio than an engine that is designed for
normal induction.
Exhaust Gas Recirculation
In internal combustion engines, exhaust gas recirculation (EGR)
is a nitrogen oxide (NOx) emissions reduction technique used
in most petrol/gasoline and diesel engines.
EGR works by recirculating a portion of an engine's
exhaust gas back to the engine cylinders. In a gasoline
engine, this inert exhaust increases the amount of
matter in the cylinder, which means the energy of
combustion raises the temperature of the matter less,
and the combustion generates the same pressure
against the piston at a lower temperature. In a diesel
engine, the exhaust gas replaces some of the excess
oxygen in the pre-combustion mixture. Because NOx
formation progresses much faster at high
temperatures, EGR reduces the amount of NOx the
combustion generates. NOx forms primarily when a
mixture of nitrogen and oxygen is subjected to high
temperature.
Catalyst converter
Eugene Houdry patent:
Hybrid Electric Vehicles
Today, there are hybrid electric vehicles
composed of an internal combustion engine, a
large battery pack, and one (or more) electric
motors to deliver power to the driveshaft. As
described above, this can help reduce fuel
consumption by shutting off the engine when it
is running inefficiently (e.g., driving at low
speeds or idling), and by making use of
regenerative braking.
However, if a larger or more advanced battery
system is added that can store more energy and
produce more power when needed, then the
electric motor can play a much larger role in
moving the vehicle, by providing significant
power to the driveshaft and wheels. Since extra
power is available to the wheels from the
electric motor, there is less demand on the
internal combustion engine to produce power
across all operating conditions.
Therefore, the engine can operate at its peak
efficiency more often, while the electric motor
helps manage the load under conditions where
the engine is less efficient, saving fuel. The extra
power provided by the electric motor also
allows the automobile manufacturer to
downsize the combustion engine to reduce fuel
consumption, while maintaining an acceptable
level of acceleration performance. Some
companies are adding extra battery capacity to
enable their hybrids to run on all-electric drive
at higher speeds and for extended periods of
time.
With this extra energy storage capacity onboard, there is an opportunity to “top up” the
charge with an external supply of electricity (say,
from a household outlet) when the automobile
is parked. Such vehicles are called plug-in
hybrids. While the term “hybrid” generally refers
to the combination of an internal combustion
engine with an electric motor in a vehicle, there
are a variety of ways that these two sources of
power can be integrated.
As the electric architecture becomes more
robust, the motor can displace the engine as the
primary power source. Figure 3-1 conceptually
describes a spectrum of electrification for
automobiles, from minor to major roles for
electrical power. Different configurations for
hybrid systems are possible along a wide
spectrum.
Parallel Architecture (opposite, top)
In a parallel hybrid system, power to the wheels can
be delivered by the engine and the electric motor
simultaneously. The motor and engine drive shafts are
coupled together, either before or after the vehicle’s
transmission. The electric motor receives its power
from the battery and, conversely, the motor running
in reverse can also charge the battery via regenerative
braking. Examples of this architecture can be found in
Honda’s Integrated Motor Assist IMA® System used in
the Civic Hybrid, and the Belt-Alternator-Starter (BAS)
system used in GM’s Saturn Vue and Aura Green Line
models.
Series Architecture
(opposite, middle)
The series hybrid architecture is unique in that
the engine does not directly power the wheels;
instead, the wheels are powered entirely by the
electric motor. The engine drives a generator,
which produces electricity that can be stored in
the battery for use by the electric motor later
on, or delivered immediately to the motor to
drive the wheels.
As in parallel architecture, the electric motor can
also function as a generator, slowing the wheels
and converting some of this energy into
electricity to charge the battery. A computer
continuously manages the direction of energy
flow. An example of this type of vehicle is the
Chevrolet Volt, which is under development by
GM.
Series-Parallel Architecture
(opposite, bottom)
The most complicated design is a combination
of the series and the parallel systems. In this
architecture, the engine can deliver direct power
to the wheels and it can power a generator that
supplies electricity to the battery. The battery
supplies electricity to the motor that, in turn,
delivers direct power to the wheels. As with the
parallel and series architectures, the electric
motor can deliver regenerative braking energy
to the battery for later use.
This architecture allows greater flexibility and
control over the engine, while minimizing the
total mass and size of the accompanying
electrical motors. Here the engine and two
motors are all connected to a planetary gear
system. Unlike a conventional transmission,
which has discrete gears (4, 5 or 6, typically), a
planetary gear system configured with two
electrical motors can operate at any gear ratio
that is deemed best by independently varying
the speeds of the motors.
This allows the engine to run at the most
efficient speed and results in excellent fuel
efficiency performance. Examples of this type of
system are Toyota’s Hybrid Synergy Drive® (used
in the Prius, Camry hybrid and others), Ford’s
Escape/Mariner Hybrid system, and the GM
Two-Mode hybrid system (used in the Chevrolet
Tahoe and GM Sierra).
Hydrogen vehicle
Sequel, a fuel cell-powered vehicle from General
Motors
A hydrogen vehicle is a vehicle, such as an
automobile, aircraft, or any other kind of vehicle that
uses hydrogen as its primary source of power for
locomotion. These vehicles generally use the
hydrogen in one of two methods: electrochemical
conversion in a fuel-cell or combustion :
• In combustion, the hydrogen is burned in engines in
fundamentally the same method as traditional
gasoline cars.
• In fuel-cell conversion, the hydrogen is reacted with
oxygen to produce water and electricity, the latter
of which is used to power electric motors.
The molecular hydrogen needed as an on-board
fuel for hydrogen vehicles can be obtained
through various thermochemical methods
utilizing natural gas, coal (by a process known as
coal gasification), liquefied petroleum gas,
biomass (biomass gasification), by a process
called thermolysis, or as a microbial waste
product called biohydrogen or Biological
hydrogen production. Hydrogen can also be
produced from water by electrolysis. If the
electricity used for the electrolysis is produced
using renewable energy or nuclear power, the
production of the hydrogen would (in principle)
result in no net carbon dioxide emissions.
Hydrogen is an energy carrier, not an energy
source, so the energy the car uses would
ultimately need to be provided by a
conventional power plant. A suggested benefit
of large-scale deployment of hydrogen vehicles
is that it could lead to decreased emissions of
greenhouse gases and ozone precursors. The
pollution generated at the point of use in the
vehicle would be greatly reduced compared to
conventional automobile engines.
Further, the conversion of fossil fuels would be
moved from the vehicle, as in today's
automobiles, to centralized power plants in
which the byproducts of combustion or
gasification can be better controlled than at the
tailpipe. However, there are both technical and
economic challenges to implementing widescale use of hydrogen vehicles. The timeframe in
which such challenges may be overcome is likely
to be at least several decades, as is the case with
other advanced vehicles, such as gasoline
electric hybrids, that are proposed to replace
conventional gasoline and diesel vehicles.
Biofuels
• A biodiesel fuel vehicle is a vehicle that uses
renewable fuel sources, such as vegetable oil
and animal fats, to power and run a diesel
engine.
• Biodiesel fuel, which is a type of biofuel, can
be created from animal fats, restaurant grease
from cooking food, oil from vegetables such as
soybeans and corn, and even algae.
A biodiesel fuel car can use 100% biodiesel
sources to power a car engine, or it can combine
natural oils and fats with regular petroleum
diesel to create a biodiesel blend. But you can’t
just use straight animal fats or vegetable oils as
fuel. They have to undergo a chemical reaction,
known as transesterification, in which the fat or
oil is purified and reacted with alcohol to form
esters and glycerol. The end product can be
used alone or mixed with regular petroleum
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