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Germany: VW scandal - What′s the dirt on diesel engines?

There are two crucial differences between diesel fuel and gasoline. The former is far less flammable, and as a result it contains more energy. A cubic meter of diesel will yield around 9800 kilowatt-hours of work, and the same amount of gasoline yields just 8760 kWh.

This means, rather obviously, that diesel engines are more efficient, because less fuel is needed to run them. Additionally, diesel is cheaper than gasoline, because there is much more of it at refineries when compared to other natural gas products, for instance, kerosene and benzene.

The low flammability of diesel makes the fuel more secure in car engines; however, it also means that diesel engines must be designed differently. While a gas-powered engine is injected with a mixture of air and gasoline by the carburetor itself, the pistons of a diesel engine are filled at first with air or a combination of air and exhaust. This is compressed to 20 bars of pressure and heated to 900 degrees Celsius, and then the diesel fuel is injected into the combustion chamber. Fine droplets of diesel are evaporated and ignited.

The higher efficiency of a diesel engine is due not only to the fuel's higher energy density; the compression of a diesel engine bay is much higher, which also accounts for its higher degree of efficiency.

Read more: VW scandal - What′s the dirt on diesel engines? | Sci-Tech | DW.COM | 22.09.2015

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