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Alternative Fuel Vehicles

Virtually all cars, trucks, and buses on the road today are designed to operate using gasoline or diesel fuel. These are nonrenewable fossil fuels that won't last forever. Finding alternatives is a sensible way to plan for future transportation needs.

Alternative fuel vehicles are designed to run on fuels other than gasoline or diesel fuel. Some of these vehicles are already on the road. Others are still in the research and development stage.

Hybrid Electric Vehicles

A hybrid vehicle is any vehicle that uses two or more power sources. The most common hybrids on the road today are gasoline-electric hybrids, also called hybrid electric vehicles, or hybrid EVs. A gasoline engine and an electric motor power these vehicles.

Since 1999, more than 575,000 hybrid EVs have been sold in the United States. The popularity of hybrid EVs is on the increase, and automakers are busy designing and building new models. Approximately 250,000 were sold during 2006 alone, indicating a sharp upturn in popularity.

The major components of a hybrid EV include a gasoline engine, an electric motor, a transmission, and, in some models, a generator. A fuel tank stores gasoline for the engine, and a battery pack stores electricity for the motor. The transmission moves, or transmits, mechanical energy from the engine or motor to the vehicle's wheels.

Hybrid EVs use smaller, more efficient gasoline engines than conventional gasoline or diesel vehicles. They also produce less tailpipe emissions and provide much better gas mileage—today's models get up to 55 mpg. Burning less fuel means producing fewer pollutants. Hybrid EVs also release less carbon dioxide into the air. Carbon dioxide is a greenhouse gas that contributes to global warming.

Current hybrid EV models are similar in size and comfort level to the most popular gasoline-powered automobiles. Unlike battery EVs, hybrids don't have to be plugged in. Their batteries are charged by the gasoline engine and by the electric motor or generator during normal operation. Regenerative braking also charges the batteries slightly when the car stops, slows, or goes downhill, recovering some of the energy that's usually lost when brakes are applied.

Battery Electric Vehicles

Battery-powered EVs run on electrical energy instead of gasoline or diesel fuel. Instead of a fuel tank, batteries store the electricity that is used to operate an EV. These batteries can be charged by plugging the vehicle into a charging station or a 220-volt outlet at a home or office. The batteries store the electricity until the vehicle is driven.

Many different types of EVs have been introduced in recent years. New battery technology gives EVs the capacity to reach highway speeds and travel 20 to 120 miles per charge, depending on the type and size of the vehicle and its battery.

Under the hood, an EV consists of an electric motor, one or more controllers, and batteries. The controller governs the amount of electricity that flows from the batteries to the motor when the driver steps on the accelerator. The motor changes electrical energy from the batteries to mechanical energy, which makes the vehicle move.

Driving a battery-powered EV down the road produces no pollution at all. Even when pollution related to power plant electricity production is factored in, battery EVs produce less pollution than gasoline or diesel vehicles. Battery EVs are also twice as efficient as gasoline or diesel vehicles, if you compare the energy used in creating gasoline at a refinery or producing electricity in a power plant.

When a battery EV is stopped in traffic, it doesn't have to use fuel to keep the motor running like a gasoline engine does. Added efficiency is created by regenerative braking.

Natural Gas Vehicles

Vehicles that run on natural gas instead of gasoline are called natural gas vehicles (NGVs). Natural gas that has been compressed into special high-pressure cylinders to get more volume into a smaller amount of space is called compressed natural gas, or CNG. Some NGVs run on CNG only, and others can run on either CNG or gasoline. Some long-haul trucks and transit buses run on liquefied natural gas, or LNG, which is made by refrigerating natural gas to condense it into a liquid.

When the engine of an NGV is started, natural gas flows into a fuel line, and then enters a regulator where the gas pressure is reduced. A fuel injection system mixes the gas with air and feeds the mixture into the engine. The fuel/air mixture is adjusted to burn efficiently and with the least possible emissions. Natural gas burns in the engine just like gasoline.

NGVs produce fewer pollutants than gasoline or diesel vehicles and cost less to maintain. The tanks used to store natural gas can withstand crashes and heat far better than most gasoline tanks can. In the event of a crash, natural gas disperses into the air, whereas gasoline pools on the ground, creating a fire hazard.

Fuel-Cell Vehicles

Fuel-cell vehicles (FCVs), currently in development, are powered by hydrogen fuel cells. Fuel cells produce electricity by combining oxygen with hydrogen. A fuel-cell car would operate much like an EV, except that it would depend on a supply of hydrogen, rather than a battery pack, for power.

The components of one prototype FCV include three stacks of fuel cells, a tank of hydrogen, an electric motor, and an inverter. The fuel cells operate something like batteries in reverse. Inside each fuel cell, hydrogen and oxygen from the air are combined in a reaction that splits the molecules into protons and electrons and produces electric current. The inverter changes the direct current produced by the fuel cell into alternating current that powers the electric motor, which turns the vehicle's wheels. The electric current also charges a conventional car battery that powers the car's lights, radio, air conditioning, and so on.

FCVs are twice as efficient as gasoline or diesel engines, and they produce no pollutants or carbon dioxide. The only tailpipe emission is water vapor. The biggest challenge now facing the developers of FCVs is where to get the hydrogen.

Hydrogen is plentiful in fossil fuels such as methane and natural gas. At the present time, fossil fuels are the most convenient source of hydrogen. But using fossil fuels to produce hydrogen creates pollution and adds to the consumption of nonrenewable resources.

Alternative sources of hydrogen include plant crops, agricultural waste, and wastewater from food processing plants. But, at least so far, so much energy is required to extract hydrogen from these sources that it becomes too expensive to use as a vehicle fuel. FCVs that arrive on the market in the next few years probably will use hydrogen-rich fuels such as methanol, natural gas, or even gasoline, but these fuels must first be converted into pure hydrogen gas by an onboard device called a reformer. The long-term goal is to find more effective and efficient ways to produce and store hydrogen.

Biodiesel Vehicles

Biodiesel is a fuel that can be made from vegetable oils, recycled cooking oils from fast food restaurants, and certain animal fats, such as fish oil or beef tallow. Biodiesel can be used in any diesel engine in place of diesel fuel. No engine modification is necessary, because diesel engines were originally designed to run on a variety of fuels, including vegetable oils.

Biodiesel is easy to make and store, and is safer to transport than diesel fuel. It helps increase engine life. Using it reduces the consumption of fossil fuels. Compared to diesel fuel, biodiesel produces almost no pollutants and significantly reduces carbon dioxide emissions. It's also more pleasant to use—the exhaust from a biodiesel vehicle often smells like popcorn or French fries! In some regions of the United States, biodiesel is becoming popular as a fuel for agricultural equipment, such as tractors and trucks, as well as for passenger vehicles.

People-Powered Vehicles

Some vehicles run solely on people power. Wheelbarrows, rickshaws, and bicycles are just a few examples of transportation devices powered by people. In many parts of the world, especially in places where vehicles and fuel are expensive and difficult to obtain, people depend on their own two feet for transportation.

Using people power whenever possible makes a lot of sense. Walking and bicycling produce no pollutants and help keep the environment healthy. They also contribute to personal health—getting plenty of exercise can lengthen a person's life span and help avoid health problems like obesity and heart disease. And people are easy to fuel—all it takes is food!