The Diesel Engine

By Jonathan Spira on 5 December 2009
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Invented by Rudolf Diesel in the 1890s, the diesel engine is a type of internal combustion engine that uses the heat of highly compressed air to ignite a spray of fuel introduced after the start of the compression stroke.

The engine of a 2009 BMW 335d

The engine of a 2009 BMW 335d

It is highly efficient in converting heat energy into work.

A diesel engine differs from its gasoline counterpart in that the ignition of fuel is caused by compression of air in its cylinders instead of by an ignition spark: the high compression ratio causes the air in the cylinder to become hot enough to ignite the fuel. This is referred to as compression ignition as opposed to spark ignition.

Diesel engines burn fuel oil, which requires less refining and is cheaper than higher-grade fuel such as gasoline. During the combustion process, the stored chemical energy in the fuel is converted to thermal, or heat, energy. The temperature in each cylinder rises as high as 2,480 °C, thus creating pressures of about 100 kilograms per square centimeter. The pressure pushes against the tops of the pistons, forcing them to the other end of their cylinders. The pistons are connected by a rod to a crankshaft which they turn, thus supplying power to a vehicles or machinery.

Diesel engines were first used in automobiles in the 1930s. The first manufacturer to produce a diesel-powered car was Mercedes-Benz in 1936.

In Europe, ca. 50% of all new car sales are diesel. In the U.S. that figure is closer to 3%.