Diesel

Diesel are thriftier than similar gasoline-powered cars. And as result of the ultra-low-sulfur diesel fuel phased in during 2006, we’re beginning to see a new wave of “clean diesel” cars and SUVs with emission levels similar to those of gas-powered vehicles.

Advantages:

• About 30 percent better fuel economy than similar gasoline-powered vehicles.

• Strong torque, or pulling power, for their size.

• Emission are similar to that of gasoline engines.

• Diesel engines can run on some bio-diesel blends without modification.

Disadvantages:

• Typically cost about $1,000 to $3,000 more than similar gas cars.

• Diesel fuel currently costs more than gasoline.

• Fuel available at only about 40 percent of U.S. filling stations.

• More engine noise and vibration in some vehicles.

• Extra maintenance for some emissions systems.

Bottom line:
Modern diesel cars much better than those of yesteryear. But the price of diesel can be high. If it’s no more than about 30 percent higher than regular gasoline, you could still come out ahead, thanks to the better fuel economy.

Ethanol

Most ethanol is being blended into gasoline as E10, a 10 percent ethanol/90 percent gasoline mix that reduces smog-causing emissions. E85, which is 85 percent ethanol can be used only in flex-fuel vehicles. Almost all U.S. ethanol is made from corn. Coming is cellulosic ethanol, made from nonfood vegetation.

Advantages:

• A renewable fuel that’s domestically produced.

• Reduces petroleum consumption.

• Burns cleaner than gasoline, which lowers pollutants.

• More than 5 million flex-fuel vehicles can run on E85.

Disadvantages:

• Fewer than 1 percent of U.S. filling station have it.

• In a test, a Chevrolet Tahoe FFV got 27 percent fewer miles per gallon on E85 than on gasoline.

• Most current FFVs are large vehicles that get poor fuel economy.

• Increased production has contributed to higher prices for related food products.

Bottom line:
There are no inherent disadvantages in buying a flex-fuel vehicle. But unless E85 is readily available in your area, you will need to run it on gasoline. Even on E85, the fewer miles per gallon can mean it will cost you more than gasoline overall, depending on the fuel’s price. For now, blending ethanol as E10 seems to provide the most overall benefit.

Biodiesel

Biodiesel is made from vegetable oils or animal fats. Pure biodiesel is labeled B100, but it’s typically blended with diesel fuel as B2 (2 percent biodiesel), B5, or B20. Most diesel engines can run on up to B5 without warranty issues or modifications.

Advantages:

• Renewal and domestically produced.

• Reduces petroleum consumption.

• Nontoxic and biodegradable.

• Burns cleaner than petroleum diesel.

• Slightly better city fuel economy and acceleration than diesel in our tests or B5 and B100 (no notable difference with waste vegetable oil).

Disadvantages:

• Difficult to find; available only at about 1 percent of U.S. filling stations.

• Blends higher than B5 can void an automaker warranty.

• Slightly more oxides of nitrogen emissions.

• Pure biodiesel thickens at lower temperatures, making it less suitable for cold climates.

Bottom line:
If you have a diesel-powered vehicle and access to the fuel, biodiesel provides a way to cut your use of petroleum. Cars can also be run on waste vegetable oil, such as recycled restaurant grease, but doing so requires extensive modifications and the oil must be filtered prior to use.

Natural Gas

The Honda Civic GX NGV is the only production car in the U.S. designed to run on natural gas, although conventional vehicles can be modified to do so. The fuel can be much cheaper than gasoline, and fuel economy is good.

Advantages:

• Burns cleaner than gasoline; emits 60 to 90 percent less pollutants, 30 to 40 percent less greenhouse gases.

• Costs about $1 per gallon equivalent with a home-fueling system.

• Abundant in the U.S. and Canada.

• Very good fuel economy; the Civic GX got the equivalent of about 32 mpg overall in our tests.

Disadvantages:

• Few retail stations in most states and prices vary widely.

• Fuel tanks reduce cargo space and carry relatively little fuel, limiting driving range.

• A limited, nonrenewable resource.

• Fueling can be slow; home refueling systems cost thousands.

• Limited dealer support for Civic GX outside California and New York.

Bottom line:
The Civic GX can be a reasonable commuter or around-town car, but it costs about $7,000 more than a similar gasoline-powered Civic before tax credits. Countries such as Argentina, Brazil, and Italy have developed relatively good infrastructures for NGVs. With plenty of domestic supply, a similar effort in the U.S. could make this an appealing petroleum alternative.