A Beginner's Guide to Alternative-Fuel Vehicles

Hybrids often use other technologies, such as stop/start systems that turn off the internal-combustion at idle to save gas and regenerative braking.

W

ith gas prices continuing to hover at stratospheric levels, interest in alternative-fuel vehicles has never been higher. For consumers who don't know much about alternative powertrains, the various green options can be confusing. Here, then, is a quick rundown on the other choices out there.

Diesel: A diesel engine is similar to a gasoline engine in some ways, but different in others. Diesels are generally more fuel-efficient than gasoline engines. Furthermore, today's diesel engines have overcome some of the problems of the past, such as poor starting performance in cold weather. Current diesels are much quieter and smoother than in years past.

2012 Toyota Prius

Simply put, a diesel engine uses heat from air compression as a source of ignition, as opposed to using a spark, which is how a gasoline engine operates. Because of the high compression needed for ignition, diesels are the most efficient internal combustion engine.

One drawback of diesels is the production of high quantities of nitrous oxides, although the introduction of technologies such as ultra-low-sulfur diesel fuel and urea injection has helped diesels meet emissions standards. Another drawback is that diesels tend to command a sticker-price premium.

Diesel fuel is generally easily available, although not all gas stations sell it. Diesel is usually, though not always, slightly more expensive per gallon than gas, but diesel-powered cars tend to offer much higher mile-per-gallon ratings and a longer range (amount of miles between fill-ups, or recharge in an electric car) than gas cars, necessitating fewer fill-ups.

Current examples of vehicles that offer diesel engines include the Mercedes-Benz GL-Class, the Volkswagen Jetta, and the Volkswagen Passat. As an example, the Jetta promises 30 mpg city and 42 mpg highway.

Electric: An electric car is one that relies solely on an electric motor for power. The electricity needed to operate the motor is supplied by a battery pack.

Electric cars are virtually emissions free and operate nearly silently, and they also offer lots of torque at even the lowest of RPMs, but they are limited in range, and recharge times are generally inconvenient. For this reason, most electric cars are currently used as short-distance urban commuters.

Current examples include the Nissan Leaf and Ford Focus Electric. For one example, the EPA rates the Leaf at 106 miles per gallon equivalent (mpge) city and 92 mpge highway.

Hybrids: A hybrid uses a combination of a gas engine and an electric motor to provide propulsion. In some cases, the gas engine drives the wheels and the electric motor merely provides an assist, while in other cases, the gas engine and electric motor can drive the wheels together or independently, as conditions warrant.

Hybrids often use other technologies, such as stop/start systems that turn off the internal-combustion at idle to save gas and regenerative braking, which turns the heat generated under braking into energy that can be stored.

Plug-in hybrids can be plugged into the electrical grid in order to recharge the batteries, whereas non-plug-in hybrids use the internal combustion engine (and, perhaps, regenerative braking) to recharge the batteries.

2011 Honda FCX Clarity

Hybrids offer greater mpgs than gasoline-powered cars, and they don't give owners the same range anxiety that can be found with electric cars, since their range is similar to or greater than a gasoline-powered car and they can be refueled at conventional gas stations. Hybrids generally do cost more up front, mainly due to the cost of the battery pack and the powertrain.

Current examples include the Toyota Prius and Ford Fusion Hybrid, among many others. As an example, the Prius offers 51 mpg city and 48 mpg highway.

Extended-Range Electric: This is essentially another term for certain plug-in hybrids that use their gasoline engines as generators that rarely drive the wheels, instead pumping juice to the batteries. These cars are similar to hybrids in most other respects.

As with hybrids, the key advantage here is avoiding range anxiety, since these cars can switch to gasoline once the batteries are depleted. Extended-range electrics are considered to be different from standard hybrids, because the gasoline engine does little or no driving of the wheels.

Current examples include the Chevrolet Volt and Fisker Karma. The EPA rates the Volt at 94 mpge and 35 mpg city/40 mpg highway. The Karma is rated at 54 mpge and 20 mpg city/21 mpg highway.

Compressed Natural Gas: Compressed natural gas (natural gas differs from gasoline in that it's naturally occurring, as opposed to extracted from crude oil) can be used in place of gasoline, but it comes with a big drawback. It takes a lot of space to store, making it somewhat impractical for most passenger-car use, although designers probably could work around this by designing a CNG car from scratch. Currently most CNG cars are gasoline-powered cars modified to run on CNG.

The only production compressed-natural gas car on sale is the Honda Civic Natural Gas. The Civic Natural Gas is rated at 27 mpg city and 38 mpg highway.

Fuel-cells, biofuels, and beyond: Fuel-cells use a chemical reaction (generally a reaction between hydrogen and oxygen) to create electricity, but none are currently on sale in the U.S. This is mainly because they are costly, so they're hard to market, despite not suffering from the same range and refueling limitations as an electric car. The closest thing to an on-sale production fuel-cell car in the U.S. is the Honda FCX Clarity, which can only be leased by customers in Southern California, where "fast-fill" hydrogen stations are located.

Biofuel vehicles generally use bioethanol derived from corn or sugarcane crops or biodiesel derived from vegetable oils or animal fat. Cellulosic alcohol, which comes from tress or grasses, is also being developed. Currently, there aren't any biofuel cars available for sale in the U.S., but plenty of people perform their own conversions, and there are biofuel-powered buses on some city streets. Not to mention that ethanol is often added to certain gasoline blends, such as E85. Similarly, biodiesel is available, often in rural areas.