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A Student's Guide to Alternative Fuel Vehicles

Fuel Cell Vehicles - the ZEVs of the future?

NECAR 4 fuel cell car
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.

Animated GIF on How a Fuel Cell Works

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 vehicles.

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 fuel cell.

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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