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Moses dhilip kumar
Hybrid
technology has blossomed over the last several years to become one of the most
advanced heavy-duty vehicle technologies available today. These vehicles
combine the latest advances in hybrid vehicle technology with the inherent
efficiency and reduced emissions of modern clean technology to produce dramatic
reductions in both emissions and fuel consumption while offering superior
vehicle performance and the benefit of using existing fuelling infrastructures. To investigate and describe human uses of renewable and
nonrenewable resources, describe how alternative fuel technology can contribute
to the solution of a global problem, recognize that issues related to science,
technology, and society often are complex and involve risk/benefit trade-offs,
identify technological advances that are reported in the media, and understand
that engineers and others use scientific knowledge to solve practical problems.
For several reasons,
scientists and engineers are researching and testing alternatives to gasoline
and diesel fuels for use in cars and trucks. Since the United States has
greatly depleted our own supplies of oil, forcing us to import increasing
amounts of oil from overseas, the federal government would like to develop
alternatives that are still available here in the US. The federal government
would also like to develop fuels that produce less air pollution.
As of 2003, the federal government had not yet set a goal of
finding alternative fuels that produce less greenhouse gases. But some of the
locally produced and cleaner fuels that are being tested for other reasons do
just that. Let’s take a look at the type of alternative to gasoline and diesel
that are being looked at and see how it will help to reduce greenhouse gas
emissions.
HYDROGEN AS ALTERNATIVE FUEL
Introduction
Hydrogen
is a simple element - an atom with only one proton and one electron. It is also
the most plentiful element in the universe. Despite its simplicity and
abundance, hydrogen doesn't occur naturally as a gas on the Earth - it is
always combined with other elements.
Water, for example, is a combination
of hydrogen and oxygen. Hydrogen can be separated from hydrocarbons by applying
heat, a process known as "reforming" hydrogen.
Hydrogen is high in energy, yet an
engine that burns pure hydrogen produces almost no pollution. NASA has used
liquid hydrogen since the 1970s to propel the space shuttle into orbit.
Hydrogen fuel cells produce a clean byproduct: pure water. Hydrogen fuel
alternative: nothing can compare.
Fuel Source
Hydrogen does not occur free in
nature; it can be made by "re-forming" natural gas or another fossil
fuel, or by using electricity to split ("electrolyze") water into its
components of oxygen and hydrogen. In this sense, hydrogen is like electricity: the energy to generate it
can be obtained from sources ranging from the burning of high-sulphur coal to
pollution-free photovoltaic cells (solar cells).
Hydrogen
is the ideal alternative fuel for Next platforms. However, while hydrogen offers many
benefits, there are two drawbacks to using it as a fuel with current
technology. Liquid hydrogen, the preferred form of hydrogen, requires four
times the storage space of conventional petroleum-based fuels. The other
problem is that hydrogen production depends on the availability of a non-renewable
resource, petroleum. Currently, hydrogen is produced from raw petroleum for
industrial use, but petroleum supplies may become limited in the near future.
Liquid hydrogen is the best alternative fuel for platforms; however, further research is needed
to move the hydrogen fuel technologies from prototypes to usable hardware and
to optimize power outputs from internal combustion engines (ICE's), gas turbine
engines, and fuel cells.
Petroleum production is expected to decrease
significantly by 2025. Current oil production is 25 billion barrels of oil per
year; by 2025, annual oil production most likely will be between 18 and 19
billion barrels—less than the annual production during the oil shortages of the
1970's. The predicted decrease, as well as possible interruption of imported
oil due to political instability in the Middle East, will result in increased
petroleum prices.
The Attributes of Hydrogen
Hydrogen is considered an alternative fuel for two
reasons: It is renewable, and it is the most abundant element on the earth.
Hydrogen comprises more than 75 percent of the environment; so if it became a
primary fuel, dependence on foreign sources of fuel would be eliminated.
However, hydrogen in nature exists primarily in combination with other
elements. For hydrogen to be useful as a fuel, it must exist as free hydrogen
(H2). One common source of hydrogen is water, which is 11.2 percent
hydrogen by weight. Hydrogen also can be produced from biomass. Biomass is
essentially plant matter, so the vast agricultural resources could be used to
"grow" the fuel required.
Hydrogen's Characteristics
Hydrogen's physical and chemical properties make it
a good candidate for a fuel. At normal atmospheric conditions, hydrogen is a
colourless and odourless gas. It is stable and coexists harmlessly with free
oxygen until an input of energy drives the exothermic (heat releasing) reaction
that forms water. Fuel cells also may use hydrogen as a fuel. A fuel cell is an
electrochemical engine that converts the chemical energy contained in the
hydrogen molecule into electrical energy. Hydrogen can react with oxygen to
produce electricity in a fuel cell.
Hydrogen is the lightest element occurring in
nature and contains a large amount of energy in its chemical bond. Because of
its low density, liquid hydrogen weighs less than petroleum-based fuels. The
density of gaseous hydrogen is 0.0899 grams per liter (g/l). (Air is 1.4 times
as dense.) Liquid hydrogen boils at -252.77 degrees Celsius, and it has a
density of 70.99 g/l. With these properties, hydrogen has the highest
energy-to-weight ratio of all fuels: 1 kilogram (kg) of hydrogen has the same
amount of energy as 2.1 kg of natural gas or 2.8 kg of gasoline. Hydrogen burns
in air at concentrations in the range of 4 to 75 percent by volume (methane
burns at 5.3 to 15 percent concentrations by volume). The highest burning
temperature of hydrogen is 2,318 degrees Celsius and is reached at 29-percent
concentration by volume in air.
These data give hydrogen both advantages and
disadvantages. The major advantage is that hydrogen stores approximately 2.8
times the energy per unit mass as gasoline. The disadvantage is that it needs
four times the volume for a given amount of energy. For example, a 15-gallon
tank of gasoline contains 90 pounds of gasoline; a 60-gallon tank of gaseous
hydrogen would weigh only 34 pounds. Hydrogen has the potential to reduce the
amount of fuel consumed, but the size of the storage container would increase.
Extraction and Use of Hydrogen Energy
There are two ways to extract the energy contained
in hydrogen: by simple combustion in ICE's or turbine engines or by converting
it to electricity in a fuel cell.
Daimler-Benz AG (now DaimlerChrysler), BMW, and
Mazda have developed and tested ICE's fueled with hydrogen and have concluded
that hydrogen can be used successfully as a vehicle fuel. Hydrogen also can be
used to power aircraft gas turbines. In 1988, a triple-jet-powered, modified
Tupolev-154 airliner was flown in the former Soviet Union using liquid hydrogen
as a fuel. Daimler-Benz Aerospace Airbus (DASA), in cooperation with Russia, is
developing a liquid-hydrogen-powered aircraft. The only drawback is that
adjustments in manufactured parts and components will be necessary to handle
the cryogenic liquid hydrogen. The cryogenic temperature range is from -150
degrees Celsius (-238 degrees Fahrenheit) to -273 degrees Celsius (-460 degrees
Fahrenheit).
Production
Unlike fossil fuels that can be mined or extracted,
hydrogen must be produced. Hydrogen can be produced from a variety of
feedstocks, including oil, coal, natural gas, biomass, and water.
The main feedstock for hydrogen is natural gas,
because the efficiency is high and the production cost is relatively low. Other
feedstocks that are used to produce hydrogen are coal and residual oil from the
treatment of crude oil. However, any process producing hydrogen from
petrochemical-based feedstock does not reduce dependence on foreign oil.
Hydrogen production from biomass, though promising,
is still in the early research and development phase. Basically, biomass
includes all organic substances, such as plants, wood chips, bales of straw,
liquid manure, and organic wastes. Currently, there is no commercially
available process for producing hydrogen from biomass, but the method is to use
a high-temperature process to convert biomass into hydrogen and carbon dioxide.
Electrolysis can be used to separate water into its
basic constituents, hydrogen and oxygen. In electrolysis, a current is passed
through water. Although any power source can be used to produce the electric
current, hydroelectric resources offer the lowest price for hydrogen
production.
Storage
Hydrogen may be stored on platforms using a variety
of technologies. At room temperature, hydrogen is a gas that can be stored in
compressed gas cylinders similar to those used on natural-gas-powered vehicles.
Gaseous fuels contain comparatively little energy per unit volume, so platforms
using gaseous hydrogen may have a somewhat reduced range compared to platforms
using liquid fuels such as gasoline or diesel. Hydrogen also may be stored in
liquid form, but it becomes a liquid only at very low temperatures, so special
fuel tanks are necessary to keep the hydrogen cold and prevent losses.
Compressed-gas cylinders made of stainless steel
are being used for storing fuel aboard natural-gas-powered automobiles. These
cylinders have a pressure level of 20 megapascals (MPa), or 2,900 pounds per
square inch (psi). The pressure levels desired for on-board storage range from
20 to 30 MPa, or 4,350 psi. Under development are high-pressure cylinders made
of plastic composite structural materials with steel or aluminum liners, to be
used for liquid hydrogen.
Transport
Both compressed gaseous hydrogen and liquid
hydrogen can be transported by trucks or rail. Liquid hydrogen can be
transported in pressurized tanks by truck, rail, barge, or ship. Insulation of
the storage tanks is of utmost importance. Due to the very low boiling point of
hydrogen, losses resulting from boil-off can be considerable.
Safety
Hydrogen's explosive range is a 13- to 79-percent
concentration in air. It is colourless and odourless and burns with a nearly
invisible flame. Hydrogen's wide explosive range, coupled with its very low
ignition energy, give it a potential disadvantage since an accumulation of
hydrogen in a poorly ventilated vehicle interior may explode easily.
The minimum ignition energy required to ignite a
hydrogen mixture is 0.02 millijoules, which is equal to the energy of a static
electric discharge from the arcing of a spark. However, the vapours of
petroleum-based fuels ignite just as easily.
The diffusion coefficient for hydrogen is 0.61
cubic centimeters per second (cm3/sec), which means that hydrogen mixes with air faster than does
gasoline vapour. Hydrogen's low vapour density and high diffusion coefficient
cause it to rise quickly, so that in the open, hydrogen mixes with air and
disperses rapidly with no pooling on the ground—unlike petroleum-based fuels.
Since there is a possibility that hydrogen might
leak into the crew compartment, hydrogen detectors must be used aboard
platforms to detect explosive concentrations of hydrogen. A ventilation system
could be used to exhaust the explosive mixture to the atmosphere. Also, since
hydrogen's ignition energy is extremely low, a sparkless environment must be
provided. The sparkless environment should include an extremely well-insulated
electrical system and some form of grounding for the crew so they do not build
up a static charge during platform operation.
Environmental Considerations
Hydrogen is the cleanest fuel available.
Hydrogen-fueled ICE's and gas turbine engines have negligible emissions of air
pollutants. Hydrogen-powered-fuel-cell vehicles have zero emissions. On the
other hand, platforms powered by petroleum-based fuels emit significant amounts
of air pollutants (hydrocarbons, carbon monoxide, nitrogen oxides, sulphur
oxides, and particulate matter), air toxics (either confirmed or suspected
human carcinogens, including benzene, formaldehyde, 1,3-butadiene, and
acetaldehyde), and carbon dioxide. The health effects of these pollutants range
from headaches to serious respiratory damage such as lung cancer.
Burning hydrogen with air under appropriate
conditions in ICE's or gas turbines results in very low emissions. Trace
hydrocarbon and carbon monoxide emissions, if generated at all, can result only
from the combustion of motor oil in the combustion chamber of ICE's. Nitrogen
oxides (NOx) emissions increase exponentially with the combustion
temperature. Therefore, these can be influenced through appropriate process
control. Particulate and sulphur emissions are limited to small quantities of
lubricant remnants. Aircraft gas turbine engines fueled with hydrogen produce
no carbon dioxide emissions and cut nitrogen emissions up to 80 percent.
Using hydrogen in fuel cell propulsion systems with
low temperature fuel cells completely eliminates all polluting emissions. The
only byproduct resulting from the generation of electricity from hydrogen and
atmospheric oxygen is water.
Hydrogen as a motor fuel
Hydrogen
can be used as a motor fuel, whereas neither nuclear nor solar energy can be
used directly.
Nuclear power requires heavy shielding
to keep the neutrons away from people - too heavy for cars. It can be used in
ships, and is used in American, British and Russian warships, especially
submarines and aircraft carriers. The U.S. and Japan built commercial nuclear
powered ships, one each (Savannah and Mutsu). (There were even proposals to use
it in locomotives.)
Solar energy can't be used directly in
cars except as a stunt. The current solar-powered cars are just religious exercises
in the solar religion. The problem is that a solar array of a size that can be
mounted on a car produces too little energy to give useful performance, and
even that little isn't available at night or when it is very cloudy.
Hydrogen can be used as a fuel
directly in an internal combustion engine not much different from the engines
used with gasoline. The problem is that while hydrogen supplies three times the
energy per pound of gasoline it has only one tenth the density when the
hydrogen is in a liquid form and very much less when it is stored as a
compressed gas. This means that hydrogen fuel tanks must be large.
Demonstrations of hydrogen powered
vehicles have usually used compressed hydrogen gas. However, because of the low
density, compressed hydrogen will not give a car as useful a range as gasoline.
It may be even worse than using lead-acid batteries. Hydrogen can achieve a
reasonable density adsorbed in metal hydrides, but then the weight of the
metals makes the system very heavy.
Comparison
The Comparison between
current costs of gasoline and hydrogen power for cars seems to be somewhat
biased in favour of hydrogen. Taxes seem to be included in gasoline cost and
not in hydrogen estimates, but roads will still have to be maintained when hydrogen
is used as a fuel. However, I suspect the Worldwide estimate of the "real
cost" of burning a litre of gasoline is exaggerated.
You
are now entering into one of the most interesting and controversial areas in
the field of alternative energy:
Just as solar, hydro and biomass
energy has been utilized for thousands of years, hydrogen technology as a fuel
source has also been known for over 150 years. What's more interesting, anybody
can produce hydrogen gas as a fuel source to be used in their vehicle or small
engine by converting water (H2O) to HHO, or Brown's Gas or oxyhydrogen.
There is much debate about the economics of producing hydrogen as a fuel, but either way, it sure makes a great alternative to do further research on in the future.
As of now, hydrogen cars that run on
pure hydrogen (not as a supplement) cost around $3,000,000. Not in the ballpark
of the common man. But to at least supplement your gas or alcohol engine with
hydrogen and oxygen produced from water really makes your head spin.
Advantages
Hydrogen has been called the
"most alternative" of the alternative fuels: if it is made by
electrolysis of water using electricity from a non-polluting source like wind
or solar power, then no pollutants of any kind are generated by burning it in
an internal combustion engine except for trace amounts of nitrogen oxides, and
if it is used in a fuel cell then even these disappear.
Furthermore, no greenhouse gases are generated because there's no carbon in the fuel. All that
comes out the vehicle's exhaust is drinkable water! Using hydrogen as the
"battery" to store energy from a non-polluting, renewable source
would result in a truly unlimited supply of clean fuel. The advantage of using
hydrogen to store energy rather than a battery pack is that a hydrogen tank can
be refilled in minutes rather than recharged in hours, and it takes less space
and weight to store enough hydrogen to drive a given distance on a single refuelling
than it does to carry enough battery capacity to go the same distance on a
single recharging. The battery-electric drive train uses energy more
efficiently, and can handle the vast majority of daily commute-and-errands
driving that people do, but for long trips hydrogen could prove to be a lot
more convenient.
Disadvantages
Hydrogen is currently very expensive,
not because it is rare (it's the most common element in the universe!) but
because it's difficult to generate, handle, and store, requiring bulky and
heavy tanks like those for compressed natural gas (CNG) or complex insulating
bottles if stored as a cryogenic (super-cold) liquid like liquefied natural gas (LNG). It can also be
stored at moderate temperatures and pressures in a tank containing a
metal-hydride absorber or carbon absorber, though these are currently very
expensive. It is possible to store a hydrogen-bearing fuel like natural gas,
methanol, or even gasoline aboard the vehicle and re-form it to get hydrogen as
needed; this simplifies storage and refuelling, but adds cost and complexity to
the drive train (and reduces efficiency). It is not a very good fuel for an
internal combustion engine, being prone to preignition, though BMW, Mazda, and
Ford have done some tests; the most efficient way to use it is in fuel cell vehicles, but these are
still in the demonstration stage.
Under "Advantages" above, I
discussed the benefits of using hydrogen generated from renewable, non-polluting
power like solar electricity. However, as
hydrogen fuel has gained political momentum, concern is growing that the
inefficiencies of generating, transporting, and storing hydrogen may make it a
poor choice if the energy used to generate the hydrogen comes from fossil fuels
(whether via re-forming those fuels directly, or by burning them to generate
electricity for electrolysis of water). It is definitely more efficient to
generate electricity from a fossil fuel, transport it via wires, and use it to
charge up a battery-electric vehicle than it is to burn the same fossil fuel in
an internal-combustion engine aboard a conventional vehicle; however, it is
uncertain whether it is more or less efficient to use that fossil fuel to
generate hydrogen for use in a vehicle. If the hydrogen is produced at a
central plant, there are inefficiencies associated with generating it,
transporting it via truck or pipeline, and storing it aboard the vehicle as a
compressed gas or cryogenic liquid; if it is generated at the point of sale by
electrolysis, you can replace the inefficiency of trucking or piping the
hydrogen with the efficient utility-line transportation of electricity, but you
still have the other losses, and you add the fact that a smaller-scale hydrogen
generator will be less efficient than a large-scale one. The jury is still out
on whether it is more energy-efficient to use fossil fuels to make hydrogen
than it is to burn them in a hybrid-electric vehicle, though on balance
it looks likely that use of hydrogen will cut down on ordinary
combustion-engine pollutants like carbon monoxide, soot, and oxides of
nitrogen.
Conclusion
To
maintain economic property and quality of life, we require a sustainable energy
system that meets the conflicting demands for increased supply and increased
energy security, whilst maintaining cost-competitiveness, reducing climate
change, and improving air quality. Therefore if we adapt hydrogen as an
alternative fuel we can prevent our environment from pollution.
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