See Inside September 2009

Internal-Combustion Engine

Still powering the world's vehicle fleet 130 years on

Nearly every vehicle on the road today is powered by some version of the four-stroke internal-combustion engine patented by Nikolaus Otto in 1876. Otto exploited the findings of French physicist Sadi Carnot, who in 1824 showed that the efficiency of an engine depends critically on the temperature differential between a hot “source” of energy and a cold “sink.” The four-stroke engine compresses an air-fuel mixture and ignites it with a spark, thus creating a fleeting but intense source of heat. Its portable efficiency has not been matched since.

Yet some consider the internal-combustion engine an anachronism, a dangerously out-of-date vestige of a world that assumed oil was unlimited and the climate stable. The best hope for displacing the engine appears to be an electric motor powered by an energy store such as chemical batteries or a hydrogen-powered fuel cell. What many forget is that electric vehicles had their chance—indeed, they were far more popular than gasoline-powered cars in the late 19th and early 20th century. They could go all day on a single charge and move a driver around a city with ease. They did not require a hand crank to start and did not have gears to shift, both of which made gas-powered vehicles of the day as user-friendly as heavy machinery.

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