Top 10 Alternative Fuels on the Road Right Now

Using hydrogen to fuel your car may conjure up "Oh the humanity!" images of the Hindenburg, but it's actually quite safe. Hydrogen can actually fuel two different types of cars: fuel cell vehicles and vehicles that have an internal combustion engine that's been engineered to use hydrogen instead of gasoline.

In a fuel-cell vehicle, the hydrogen is used to generate electricity that's then used to power electric motors. So, rather than running strictly off of battery power alone, a hydrogen-powered car uses a fuel cell to generate its own electricity. In a chemical process within the fuel cell, hydrogen and oxygen are combined to create electricity, and the only byproduct of this process is water vapor. The Honda FCX Clarity uses this technology and is currently being leased to drivers in southern California.

In a hydrogen combustion engine, the car uses an internal combustion engine just like a gasoline-powered car, but instead of gasoline, hydrogen is the fuel source. Instead of harmful CO2 emissions, like gasoline cars produce, again, hydrogen cars produce only water vapor. Lots of automakers are currently testing hydrogen vehicles. Currently, the BMW Hydrogen 7 is perhaps the most famous; the company has leased several to high-profile individuals in Germany and the United States, and some tests have even shown that the car actually cleans the air around it [source: U.S. News Rankings and Reviews].

Hydrogen cars aren't widespread largely because there isn't the necessary infrastructure of hydrogen fueling stations. But our next alternative fuel is somewhat easier to find -- in fact, you're using some right now.

It may seem like electric cars have been a long time coming, but the fact is, some of the earliest automobiles used electric motors. However, it's only due to recent developments that electric cars have become a more viable method for everyday travel.

So, what's been the hold up? Battery technology. Moving a car takes a lot of power, and having to do it at high speeds and over long distances can significantly drain an electric car's batteries. In the past, electric cars couldn't go very far, and once their batteries were dead, they could take hours and hours to recharge.

However, with new battery technology, some automakers are overcoming these limitations. The new batteries (lithium-ion batteries, to be exact) are the same kind that power your cell phone or laptop. They charge quickly and the charges last longer, too. Cars like the Tesla Roadster use them to get supercar performance from their electric motors. Other cars that are soon to be on the market, like the Chevy Volt, for example, use these types of batteries in combination with an internal combustion engine to create a new class of automobile called an extended-range electric vehicle. The batteries can be charged by plugging the car into a regular wall outlet; however, when the battery power begins to fade, an onboard gasoline generator switches on to recharge the batteries and keep the car going.

We hope you've gotten the message that a low-fat diet with limited quantities of fried foods is good for your health. However, the same doesn't necessarily hold true for your car.

Biodiesel is a type of fuel made from cooking oil and grease. Any car with a diesel engine can run on it -- but don't start wringing the napkins from your last McDonald's run into your fuel tank. In order to power the car, the oil and grease need to be converted into biodiesel through a chemical process.

The process itself can actually be done at home. In fact, a lot of biodiesel enthusiasts make their own fuel using cooking oil from local restaurants. However, there is a little risk involved with the process. If you get it wrong, you could do a lot of damage to your vehicle (not to mention your house and yourself). Before trying to make biodiesel on your own, it's a good idea to train for a while with someone who's successfully done it before.

Biodiesel enthusiasts swear by the stuff. Not only is it much cheaper and cleaner than fossil diesel, but it'll make your car smell like french fries, too. No kidding! Just make sure you and your car can handle it before you brew up a batch.

So now you know that you can run a car on fry grease, but what if you're a little more heath conscious and don't necessarily want to drive around town smelling of fries? What are your other options? Well, how about making sure your car gets its fresh vegetables, too?

Ethanol is an increasingly common alternative fuel. In fact, it's often added to gasoline in the summertime to help cut emissions. Ethanol is a type of alcohol (but don't even think about drinking it) that's made from plant matter. In the United States it's commonly made from corn, while in other countries, like Brazil, it's made from sugar cane.

Lots of automakers offer their cars with flex-fuel engines. These engines can run on either standard gasoline from the pump or E85 ethanol, a fuel blend that's 15 percent gasoline and 85 percent ethanol. Ethanol has been widely hailed as a good way to end America's addition to foreign oil. After all, we can grow this fuel domestically, and it's not a finite resource like oil is. Still, it takes a lot of energy to create ethanol. Also, some people say that since farmers can make more money growing crops for ethanol, they'll stop growing crops for food, which could drive food prices up.

Despite these concerns, ethanol offers a lot of benefits as an alternative fuel, and the network of ethanol fueling stations continues to increase.

Not to push the cooking theme too hard, but the next alternative fuel that's already on the road is similar to stuff you may have in your kitchen as well. Unlike ethanol or biodiesel, it's not created using something you could eat or drink, but it is something that top chefs insist on cooking with: natural gas.

Natural gas is a fossil fuel that's found between layers of underground rock. It's drilled for, like oil, but there's a lot more of it available here in the United States and it burns cleaner than oil or gasoline. The natural gas that you may use to cook your food and heat your bathwater is natural gas in a very low-pressure form. That keeps this particular fuel in a gaseous state and means that it releases a relatively small amount of energy when it's burned.

However, if you cool natural gas, it becomes liquefied. And when it's liquefied, it becomes much more energy dense. When liquefied natural gas (LNG) is burned, it releases much more energy. So, for example, instead of simply heating up some soup, like low-pressure natural gas is capable of doing quite well, liquefied natural gas can power large equipment, like a truck. And that's just what it's used for -- powering heavy-duty trucks over long distances.

If you've been to a cookout recently, you're probably familiar with our next alternative fuel: liquefied petroleum gas, or LP gas. Still not sure if you've seen it? Well, do you ever grill with propane?

Propane is the common name for liquefied petroleum gas, although that's not exactly right. LP gas is a hydrocarbon gas under low pressure. It's made up mainly of propane, but it also includes other hydrocarbon gases. LP gas is kept pressurized in order to keep it in liquid form. Similar to liquefied natural gas, keeping LP gas liquefied makes it more energy dense, and thus more useful for powering cars and trucks.

LP gas powers a car through an internal combustion engine that's been engineered for that type of fuel. While this type of fuel isn't widely used for cars in the United States, LP gas accounts for 10 percent of automotive fuel in the Netherlands, and lots of other counties have experimented with it, too [source: California Energy Commission].

What if, instead of heading to the gas station when you needed to fuel up your car, you had a fuel line running to your house, ready whenever you needed it?

With a compressed natural gas (CNG) car, you already do (well, probably). Compressed natural gas is the same fuel you might use in your home for cooking and heating, and it runs to your home in a line supplied by the gas company. For a CNG vehicle, the gas is stored in high-pressure cylinders. When you have a compressed natural gas vehicle, there's actually a little more to the process than just hooking up to the nearest stove fitting. You'll also need a fueling station in your house that's capable of compressing the gas. The compressed gas is then stored in the car's fuel tank (or tanks), as CNG takes up a greater amount of space than gasoline does.

Honda introduced the Honda Civic GX in 1998. The Civic GX is a regular Honda Civic that runs on compressed natural gas. As CNG is cheaper and burns cleaner than gasoline, these types of cars may gain popularity -- especially if the initial expense of installing a fuel station in a home is offset by savings on fuel. One downside, however, is that there isn't yet a nationwide network of fuel stations offering compressed natural gas -- which means that if you run out of fuel when you're far from home, you're simply out of luck.

Air is everywhere, so why not use it to fuel cars? Well, compressed air cars can do just that.

In this type of vehicle, air is compressed in high-pressure tubes. While a typical engine uses air mixed with gasoline (or diesel fuel) which is then ignited with a spark (or high-pressure) to generate power, a compressed-air vehicle's engine makes use of the expansion of the compressed air as it's released from the high-pressure tubes to drive the engine's pistons.

But compressed-air cars don't run entirely on air. Electric motors are also on-board to compress the air into the car's high-pressure tubes. However, these cars can't be considered fully electric cars either, mainly because the motors don't directly power the wheels. The electric motors are much smaller than the electric motors used in other electric cars where the primary function of the motor is to power the wheels. Compressed-air cars do have to be charged, similar to an electric car, but because the motors use much less energy, the charge time tends to be much less, too.

Liquid nitrogen is another alternative fuel. Like hydrogen, nitrogen is abundant in our atmosphere. Also like hydrogen, nitrogen-powered cars make fewer harmful emissions than gasoline or diesel. But while hydrogen is used in fuel cell cars as well as hydrogen-combustion engines, liquid nitrogen cars use a different type of engine altogether.

In fact, a liquid nitrogen car uses an engine similar to the engine used in a compressed-air car. In a liquid nitrogen car, the nitrogen is kept cold, keeping it in a liquid form. To power the car, the nitrogen is released into the engine where it is heated and it expands to create energy. While a typical gasoline- or diesel-powered engine uses combustion to move pistons, a liquid nitrogen engine uses the expanding nitrogen to power turbines.

While it's a clean an efficient way to power a vehicle, liquid nitrogen faces the same hurdles as many other alternative fuels: At this time, there's no nationwide network of fueling stations to deliver it to consumers.

The final alternative fuel on our list is probably a surprise. So, how can coal fuel cars?

Technically, coal is a relatively new alternative fuel for cars -- indirectly, anyway. As electric cars, plug-in hybrids and extended-range electric vehicles become more common, coal will be fueling more and more cars. How exactly? Well, owners aren't going to have to shovel buckets of the stuff into incinerators, if that's what you're wondering.

Electric vehicles (for the most part), don't make their own electricity. They carry the energy in their charged batteries. And the batteries get their charge from a standard wall outlet, which gets its power from an electricity plant, which, in turn, gets its power from burning coal. In fact, 50 percent of all of the electricity in the United States comes from coal-fired plants [source: PBS.org]. That means that, when you go all the way down the energy chain, a lot of electric cars are actually coal-powered cars.

While coal has similar drawbacks to gasoline, it also has some benefits. On a per-mile basis, electricity from coal is a cheaper way to power a car than gasoline. Also, there's plenty of coal in the United States, so international relations shouldn't disrupt the supply too much. Also, people who get their electricity from other sources, such as hydro-electric power plants or nuclear power plants, can charge their electric cars without creating more coal emissions.

Still, the fact that some of the most anticipated clean cars heading to your local dealership will likely get their energy from a less-than-clean source just goes to show you that in the world of energy, there's no such thing as a free lunch.

For more information about alternative fuels, hybrid cars and other related topics, follow the links on the next page.