Fuel 101: Know what you put in your car

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Each gallon of gas represents about 124,000 British thermal units, which is roughly equal to the amount of electrical energy the average U.S. family consumes in a day. Only an average of 15 percent of that energy is actually used to move your car -- engine and drivetrain inefficiencies eat up the rest.


  • Midgrade is rated 88 to 90
  • Ethanol

    Praised and vilified in equal measure, ethanol (and, to a lesser extent, methanol) is a biofuel additive that stretches supplies of gasoline. It's an alcohol derived from corn primarily as well as sugar cane and other plant materials, and it was first popularized by an oil-starved Nazi Germany. Today, ethanol comprises only about 3 percent of the total gasoline stores in the United States.



    Of course, ethanol is a renewable energy source, which wins over many environmentalists as well as people who don't want to import oil. The downside is that redirecting edible biomass -- particularly corn -- toward fuel production can inadvertently jack up the cost of food.



    Diesel doesn't need a spark to explode in an engine's cylinders the way gas does. Compressing diesel and air alone is enough to ignite the mixture and power the engine. With more potential energy (139,000 Btu per gallon), diesel pushes a vehicle 20 percent to 40 percent farther than gas. Diesel creates more greenhouse gases than gasoline, but its greater efficiency means it produces 10 percent to 20 percent less of the pollutants per gallon than gas.


    Governments in North America and Europe have been restricting the amount of sulfur in diesel for about 20 years. Ceilings in the United States fell from 5,000 parts per million to 500 ppm (low-sulfur diesel) in 1993. All retail pumps in the country are required to dispense ultra-low-sulfur diesel, spewing just 15 ppm, by Dec. 1. Some engine modifications are needed in order to run on ultra-low-sulfur diesel.

    As a pollutant, sulfur does double duty. Some antipollution devices capable of curbing other noxious fumes and soot can't be used with low-sulfur diesel engines because the dirtier fuel gums up the works. Ultra-low-sulfur diesel is, in a sense, clean enough to be cleaned.

    In another interesting twist, U.S. buyers of diesel European vehicles -- which come standard with ultra-low-sulfur diesel-compliant engines -- have had to pay for engine modifications so that the cars will run on the low-sulfur diesel common here. In a sense, they pay to make their cars more polluting.

    Efforts to reduce sulfur in diesel have added to pump prices, but so has increasing demand in the United States, Europe, India and China. In fact, according to the Department of Energy, diesel in the United States has topped regular gas prices for a few years because of its popularity and environmental regulations.















  • The gas engine is small -- three or four cylinders -- and sized to deliver enough power for the average demand.
  • Most models capture and store the energy released while braking.
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