A
new concept for automobiles
By G V
Joshi
Until only
a few years ago, when environmentalists
and automobile manufacturers spoke about
low-emission vehicles, they were almost
thinking about electric vehicles (EV)
cars, trucks, and buses powered by
batteries of one kind or another. The
electricity from the battery turned the
motors connected to wheels.
However,
the scientists have so far failed in the
development of a battery that could make
EVs practical. Today, car-makers are
looking once again at hybrid electric
vehicles (HEV), which they had earlier
rejected, even as an interim solution.
Batteries
are not actually foreign, but even after
more than 100 years of research and
development, there is no battery, which
is ideally suited for a car, leave apart
a bus or truck.
They
either weigh too much, or cost to much,
or take too long to charge. However, HEVs
based on a combination of electric motors
and internal combustion engines (ICE) are
attractive for two main reasons.
First,
they do not require any new technology or
new infrastructure. Secondly, they work
with existing lead-acid, nickel-cadmium
metal hydride batteries because they do
not depend upon them as a primary source
of power. They can obtain fuel-petrol or
diesel at any petrol or diesel pump.
The
battery in a modern HEV provides bursts
of power for acceleration, overtaking and
hill climbing. That allows the internal
combustion engine (ICE) to drive a car on
highway, where its efficiency is high and
emissions low.
The first
major HEV was 'Prius' made by Toyota
Motor Corporation of Japan, which went on
sale in 1999 in Japan. Although the Prius
uses its ICE most of the time, it
operated as an EV at very low speeds when
crawling along in stop-and-go traffic of
cities.
Honda
Motors of Japan developed a HEV, in which
all power came from the motor. The ICE
never drives the wheels directly, but
instead operates a dynamo that keeps the
batteries charged.
The
advantages of HEV over pure EVs are
clear. They can be filled up with fuel
like any other car, and need no special
charging infrastructure since they keep
their batteries charged from the
engine/dynamo and via regenerative
braking.
Pressing
the brake pedal reverses the action of
vehicle's electric motor, so that it acts
as a dynamo, converting the kinetic
energy of the vehicle's motion into
reusable electricity, instead of wasting
its as heat. For emergency stops, HEVs
also have normal brakes, activated when
the driver really presses hard on the
brake pedal.
However,
even here there are drawbacks. Like
conventional vehicles, HEVs are not
zero-emission vehicles, worse, as they
get old or if their maintenance were
neglected, they become serious polluters.
They are
more complex to maintain than
conventional vehicles and may be expected
to have many of the same reliability and
maintenance problems. And, of course,
their use of traditional fuels is
strength as well as a weakness.
It is here
that cells enter the field. An
alternative technology-the fuel cell-has
made a quantum jump from laboratory
phenomenon to commercial highway product.
The basic
principle of the fuel cell has been know
for over 100 years. However, a variety of
technical and economic problems has kept
the devices away from the automobile
industry.
They were
used in the spacecraft like Apollo and
Space Shuttles, where they provided
reliable power but were too bulky and
expensive for use in automobiles.
Fuel cells
convert the chemical energy in a fuel
directly into electricity through an
electrochemical reaction. A hydrogen fuel
cell will supply electric power so long
as it is provided with hydrogen and
oxygen.
However,
storing the hydrogen at very low
temperature and high pressure and
carrying it in a vehicle is a serious
problem.
Several
avenues are being explored for dealing
with that problem, Ovonic Battery Co, the
Troy, Mich, company behind the
nickel/metal-hydride battery, has applied
its metal-hydride expertise and developed
metal alloys that can store about seven
per cent of their weight in hydrogen at a
fairly low pressure.
According
to the company, with that technology, 6
kg of hydrogen can be stored in a system
occupying 120 litres, or about twice the
size of the fuel tank on a mid-sized
automobile.
But there
are still other alternatives. One such
fuel is an aqueous solution of sodium
borohydride (NaBH4), which yields
hydrogen gas and a sodium borate (NaBO2)
solution on exposure to a catalyst. A
Company in the US has developed a
suitable catalyst, based on rhodium, and
has demonstrated the technical viability
of the concept.
The fact
that the starting point for making sodium
borohydride is an irreplaceable
mineral-borax is no drawback, for unlike
traditional fossil fuels, it is
recyclable. In the scheme, the boron
compounds serve more as a mechanism for
transporting energy than as a fuel.
Even
metals like zinc and aluminium also lend
themselves to similar uses. Metallic
Power, a fuel cell developer in the US,
has tested the world's first on road
refuelable zinc air fuel cell (ZAFC)
powered car successfully.
In
addition to demonstrating the viability
of the concept, the company showed that
the robust simplicity of its proprietary
regenerative ZAFCs could lead to more
rapid development of products based on
their technology.
The
demonstration included more than 160 km
of test-driving on highways and streets
over various terrains in humid as well as
dry, hot areas.
For the
demonstration, four ZAFC systems were
fitted into an electric car. The test
crew drove the vehicle at speeds reaching
more than 80 km/hour and then quickly
refueled it in approximately 30 minutes
using simple fuel hoses that can make the
process as simple as filling petrol or
diesel.
A set of
small lead-acid batteries connected in
parallel with the fuel cells provided
extra power for short bursts of
acceleration and hill climbing, while the
fuel cells supplied the bulk of the
energy or long-range driving.
Another
American company has devised a completely
solid-state aluminum-air fuel cell (AAFC)
based on a proprietary membrane
electrolyte. The device uses no liquids,
just a rolled up three-layer sandwich
aluminum anode, membrane electrolyte, and
air cathode.
As a
sealed unit, it becomes a rechargable
battery in which aluminium is oxidized on
discharge and the resulting oxide is
reduced during recharge. Or, as a fuel
cell, it has a mechanism for replacing
spent rolls of aluminum oxide with fresh
rolls of aluminum. Since the device is
both a battery and a fuel cell, the
company calls it revolutionary power
cell.
Research
on zinc-air and aluminum- air fuel cells
should be taken up in India, to develop
small power packs for automobiles or
large ones for small communities to
reduce their dependence on national grid.
PTI
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