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How Natural-gas Vehicles Work

Advantages and Disadvantages

The biggest advantage of NGVs is that they reduce environmentally harmful emissions. natural-gas vehicles can achieve up to a 93 percent reduction in carbon monoxide emissions, 33 percent reduction in emissions of various oxides of nitrogen and a 50 percent reduction in reactive hydrocarbons when compared to gasoline vehicles. NGVs also rate higher in particulate matter 10 (PM10) emissions. PM10 particles transport and deposit toxic materials through the air. NGVs that operate in diesel applications can reduce PM10 emissions by a factor of 10.

Natural-gas vehicles also offer these benefits:

Build vs. Buy
NGVs can be built from scratch to include the design enhancements described above. A brand-new natural-gas vehicle costs $4,000 to $8,000 more than a comparable gasoline vehicle. It's also possible to modify conventional gasoline vehicles to run on natural gas. This, too, can be expensive, with the modifications typically costing $3,000 to $5,000. Vehicles that run solely on natural gas are known as "dedicated" NGVs. Vehicles that can operate on both natural gas and gasoline are known as "bi-fuel" vehicles. In bi-fuel vehicles, the driver can safely switch from one fuel to another while driving.

  • NGVs are safer. The fuel storage tanks on an NGV are thicker and stronger than gasoline or diesel tanks. There has not been an NGV fuel-tank rupture in more than two years in the United States.

  • Natural gas costs are lower than gasoline. On average, natural gas costs one-third less than gasoline at the pump.

  • Natural gas is convenient and abundant. A well-established pipeline infrastructure exists in the United States to deliver natural gas to almost every urban area and most suburban areas. There are more than 1,300 NGV fueling stations in the United States, and more are being added every day.

  • Natural gas prices have exhibited significant stability compared to oil prices. Historically, natural gas prices have exhibited significant price stability compared to the prices of petroleum-based fuels. This stability makes it easier to plan accurately for long-term costs.

  • NGVs have lower maintenance costs. Because natural gas burns so cleanly, it results in less wear and tear on the engine and extends the time between tune-ups and oil changes.

One of the biggest complaints about NGVs is that they aren't as roomy as gasoline cars. This is because NGVs have to give up precious cargo and trunk space to accommodate the fuel storage cylinders. Not only that, these cylinders can be expensive to design and build -- a contributing factor to the higher overall costs of a natural-gas vehicle compared to a gasoline-powered car.

Photo courtesy Johns Hopkins University Applied Physics Laboratory
Rear undercarriage showing fuel cylinders

Another drawback is the limited driving range of NGVs, which is typically about half that of a gasoline-powered vehicle. For example, Honda's natural gas Civic, the Civic GX, can go up to 220 miles without refueling. A typical gasoline-powered Civic can go approximately 350 miles without refueling. If a dedicated NGV ran out of fuel on the road, it would have to be towed to the owner's home or to a local natural gas refueling station, which might be harder to find than a "regular" gas station.

Finally, it should be noted that natural gas, like gasoline, is a fossil fuel and cannot be considered a renewable resource. While natural gas reserves in the United States are still considerable, they are not inexhaustible. Some predict that there are enough natural gas reserves remaining to last another 67.1 years, assuming that the 2003 level of production continues.

Despite some of the advantages offered by NGVs, they are still relatively uncommon. According to the Natural Gas Coalition, there are currently 130,000 NGVs on the road in the United States today and more than 2.5 million worldwide. To put this into perspective, consider that there were 142.5 million registered vehicles in 2001 -- which means gas-powered vehicles outnumber NGVs almost 1,100 to one in the United States. And yet more than 40 different manufacturers, including Ford, General Motors, Toyota and Volvo, currently produce NGVs.

Photo courtesy Honda
The Phill Home Refueling Appliance
Two car companies leading the way in NGV design and engineering are Honda and DaimlerChrysler. Honda is the first manufacturer to offer a retail NGV -- the Honda Civic GX sedan, which also comes with a home refueling station the company has dubbed "Phill." The Civic GX is a dedicated NGV, which means it can only run on natural gas. DaimlerChrysler is manufacturing an E-class Mercedes that runs on both gasoline and natural gas. It is given a classification of "NGT," which stands for "Natural Gas Technology," and can travel 621 miles on a single fueling -- 186 miles using natural gas and 435 miles using gasoline.

While vehicles such as the Civic GX and the E 200 NGT are only available in very limited markets (the former in certain western states, the latter in Europe), NGVs are expected to become more widely available to consumers in the next two decades, especially as the price of oil continues to rise. When that happens, being green will be a little bit easier.

For more information on natural-gas vehicles and related topics, check out the links on the next page.

NGV Fleets
Fuel-intensive fleets that travel many miles each day have been using natural gas for years. This would include fleets of taxicabs, transit and school buses, airport shuttles, construction vehicles, garbage trucks, delivery trucks and public works vehicles. Why are fleets especially suited to natural gas? First, the larger volume of vehicles makes it more economical to convert vehicles or to purchase them outright. But more importantly, fleet vehicles are centrally maintained, making the refueling process convenient and reliable.

Many long-haul trucks and buses run on a different form of natural gas called liquefied natural gas, or LNG. LNG is made by refrigerating natural gas to -260°F, condensing it into a liquid. The liquid form is much more dense and thus has more potential energy for the amount of space it takes up. That means more energy can be stored in the same amount of space on a car or truck.



Thank You
Thank you to Jeff Beckman for his assistance with this article.

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More Great Links


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