Fuel Cell Vehicles - the ZEVs of the future?
Another type of
Zero-Emission Vehicle is the fuel cell
powered vehicle. When the fuel cells are fueled with pure
hydrogen, they are considered to be zero emission vehicles.
Fuel cells have been used on spacecraft for many years to
power electric equipment. These are fueled with liquid
hydrogen from the spacecraft's rocket fuel tanks.
Fuel cell vehicles turn hydrogen fuel and oxygen into
electricity. The electricity then powers an electric motor,
just like electricity from batteries powers the motor of an
electric vehicle. Fuel cells combine oxygen from the air with
hydrogen from the vehicle's fuel tank to produce electricity.
When oxygen and hydrogen are combined they give off energy and
water (H2O). In fuel cells this is done without any
burning (combustion). A graphic showing how a typical fuel
cell works is shown below.
When we think of vehicles that are fueled with hydrogen, we
may think of rocket-powered spacecraft, like the space
shuttle. The space shuttle is fueled with liquid oxygen and
liquid hydrogen. To fly, the oxygen and hydrogen are mixed
together and ignited to make a very hot fire. The expanding
gases from that fire are what propel the spacecraft. The
exhaust from spacecraft rocket motors (and hydrogen-fueled
fuel cells) is mostly water. That is why hydrogen-fueled fuel
cell vehicles are also ZEVs. Very little is in the exhaust
except water. Fuel cells do get hot though, so the water comes
out of the fuel cells as water vapor, or steam.
There are a number of ways that hydrogen can be provided to
the fuel cell. One way is simply to put hydrogen gas into the
fuel cell, along with air. Hydrogen gas can come from gaseous
or liquid hydrogen stored on the vehicle.
To carry gaseous hydrogen on a vehicle, it must be
compressed. When compressed (usually to a pressure of about
3000 pounds per square inch), it must be stored in special
high-pressure containers. This is similar to the way
compressed natural gas is stored on natural gas-fueled
The other way to provide hydrogen gas to the fuel cell is
to store it on the vehicle in liquid form. To make hydrogen
liquid, it is chilled and compressed. Liquid hydrogen is very,
very cold--more than 423.2 degrees Fairenheit below
zero! This super-cold liquid hydrogen is the kind used in
space rockets. The containers are able to hold pressure, but
they are also insulated to keep the liquid hydrogen from
warming up. Warming the liquid, or lowering the pressure,
releases gas (like boiling water), and the gas can go to the
Another way to get hydrogen to the fuel cell is to use a
"reformer". A reformer is a device that removes the hydrogen
from hydrocarbon fuels, like methanol or gasoline. When a fuel
other than hydrogen is used, the fuel cell is no longer
zero-emission, but it still may be very low emitting.
There is also a type of fuel cell that can be fueled with
methanol directly. This is called a direct-methanol fuel cell.
This type of fuel cell does not need a reformer to separate
the hydrogen from the methanol. The fuel cell removes the
hydrogen from the liquid methanol inside the fuel cell.
Many people in the vehicle manufacturing business think
that fuel cell vehicles may be the technology of the future.
However, a lot of work will have to be done to make fuel cell
vehicles perform well enough to replace the internal
combustion engine in the vehicles we use today. They also will
need to be made much less expensive.
At present, fuel cell vehicles have only been developed to
what might be called the pre-prototype stage. That means there
are very few fuel cell vehicles in existence, and all of them
are actually used for testing. Most car manufacturers have or
are working on demonstration models, some of which can reach a
speed of 90 mph and can travel up to about 280 miles before
they need refueling. DaimlerChrysler has developed the NECAR 4 (pictured above) and Ford
calls its demonstration model the P2000 Sedan. Some
manufacturers claim they will have fuel cell cars available
for the public in the next ten years. Find out more about
fuel cell vehicles by going to the California Fuel Cell
Partnership web site called Driving the Future.
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