Turbo diesel

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Turbodiesel lettering of a diesel engine from the 1980s ( BMW M21 )

Turbodiesel is the colloquial term for a supercharged diesel engine , in which the combustion air supplied to the engine is pre-compressed by one or more turbochargers , so that more air can be directed into the combustion chamber. This means that more oxygen, and consequently more diesel fuel, can be supplied and burned with the same displacement . This measure means a significant increase in the possible output of the diesel engine.

By reducing the cubic capacity, the fuel consumption can also be reduced while maintaining the same power through turbocharging. In combination with a charge air cooler , the turbodiesel engine can also improve the thermal efficiency, which also reduces fuel consumption.


In 1978 Daimler-Benz carried out tests with supercharged diesel engines in the C 111 experimental vehicles. In the same year, with the OM 617 engine , a turbocharged diesel engine (still without direct injection) was used for the first time in series production of passenger cars in the export model 300 SD of the W 116 series . The engine was also used in the 300 TD turbodiesel model of the W 123 series from 1979 . In Europe, it was the French car manufacturer Peugeot who, with the 604, offered a turbocharged diesel engine in a passenger car for the first time.


In the meantime almost only turbo diesels with direct injection are produced. A design with a short stroke and a large piston diameter allows high speeds and thus a high power density with a compact design.

Turbo lag

Turbo lag is an effect that only occurs in supercharged engines : In the lower load range, the amount of exhaust gas is not sufficient to keep the exhaust gas turbine at high speed, so that the compressor cannot compress the air strongly enough to deliver the standard boost pressure : the The engine works more or less as a naturally aspirated engine and only achieves weak torque, which the driver perceives as too weak, "tough" acceleration, even though he fully depresses the accelerator pedal, because a control system that is dependent on the boost pressure ensures that the maximum possible injection quantity (despite "full throttle") ) is only increased by the degree by which the boost pressure increases. Only from a characteristic engine speed between 1600 and 2500 min −1 does the turbocharger reach the standard boost pressure and the engine develops its full power with rapidly increasing torque and noticeable acceleration, roughly square with the speed.

Modern turbochargers (VTG chargers) use adjustable guide vanes in the turbine inlet to optimize the supercharger speed and thus the boost pressure of the compressor by means of the inflow with a lower amount of exhaust gas.

The turbo lag can also be bridged by a compressed air reservoir with a corresponding control or by driving the compressor with an electric motor so that its speed is independent of the exhaust gas mass flow.


Individual evidence

  1. Konrad Reif (ed.): Diesel engine management at a glance . 2nd Edition. Springer Fachmedien, Wiesbaden 2014, ISBN 978-3-658-06554-6 . P. 41
  2. ^ Roger Barlow: The Diesel Car Book , Grove Press 1981, p. 189