Delivering fuel to the fire was every early engine designer’s worst headache. In the 1890s, Rudolf Diesel proved the merits of his engine during four years of research. But it was Robert Bosch who made diesels practical by developing the first fuel-injection system, a fifteen-year effort.

On the gasoline side, when Henry Ford was anxious to get an experimental engine running on Christmas Eve in 1893, he assigned his wife carburetion duty. While Henry whirled the flywheel, Clara dripped gas into the intake pipe.

Their collaboration worked: Ford’s single-cylinder engine shot flames from its exhaust and shook the kitchen sink it was clamped to until Henry signaled Clara to cease fuel delivery.

After more than a century of these headaches, an ideal means of getting fuel to the fire is finally gaining production applications. Direct injection-squirting pressurized fuel straight into each cylinder-is the key to keeping internal-combustion engines relevant in the future.

For enabling a major step forward in gas and diesel engine power, efficiency, and cleanliness, direct fuel injection is AUTOMOBILE MAGAZINE’s 2009 Technology of the Year.

During World War II, direct injection enabled German fighters powered by Daimler-Benz V-12s to fly inverted, a maneuver that left their British Spitfire rivals’ carbureted Rolls-Royce engines sputtering. After peace resumed, Mercedes-Benz brought direct injection down to earth, making the 300SL and SLR sports cars the scourge of both street and track.

Gasoline direct injection began trickling into the United States five years ago on BMW V-12s and Isuzu V-6s. While injecting fuel into the combustion chamber requires approximately fifty times the pressure used with port injection and additional electronic control sophistication, significant benefits are delivered. Since no fuel is deposited on intake-port walls, the air/fuel mixture can be more precisely maintained, benefitting both mileage and emissions.

In addition, the cooling effect of gasoline droplets changing to vapor inside the combustion chamber facilitates a higher compression ratio without incurring detonation. Squeezing the mixture harder during compression and allowing it to expand longer on the power stroke wrings additional power out of every ounce of gasoline.

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