Carbon Hooch; How Things Work; Exclusive Online Issues; by Mark Fischetti; 2 Page(s)

Heating oil, gasoline, jet fuel, kerosene and plastics. These products and more are derived from crude oil in one big fuming silo, siphoned off and fine-tuned through a bewildering maze of pipes.

Crude oil contains hundreds of different hydrocarbons. Yet U.S. refineries convert half of all crude into gasoline--a blend of fuel stocks, particularly 2,2,4-trimethylpentane (eight carbon atoms chained together) and heptane (seven carbon atoms). The more complex the chain, the more the molecule can be compressed before it ignites spontaneously, allowing an engine to operate at a higher compression ratio--greater power output. The test mixture by which a gasoline's octane rating is judged combines 2,2,4-trimethylpentane and heptane (87 to 13 percent for "87 octane").