Turbodiesel colloquially a diesel engine, wherein the combustion air supplied to the engine is precompressed by means of one or more turbochargers, and thus more air can be directed into the combustion chamber. So with the same capacity allows more oxygen, and consequently more diesel fuel are fed and burned. This measure is a significant increase of the possible power of the diesel engine.
Meanwhile turbo diesel with direct injection are produced almost exclusively. In order not to limit the speed range up turbo engines are designed short stroke.
Daimler -Benz introduced in 1978 in the experimental vehicles C 111 tests with turbocharged diesel engines by. With the engine OM 617 was in the same year for the first time in series production passenger car, a turbocharged diesel engine (still without direct injection) in the export model 300 SD of the W 116 series are used. The engine was used from 1979 TD in the model 300 turbo diesel in the W 123 series.
As a turbo lag effect is called, which occurs exclusively in turbocharged engines. In the lower load region, the engine operates only as a suction motor when the amount of exhaust gas is not sufficient to keep the turbine at high speed. Because of the low rotational speed of the compressor can not compress the air strong enough; it reaches its control charge pressure only above a certain speed.
The driver noticed the turbo lag by a first moderate acceleration of the car, even if it fully operates the accelerator pedal, because a dependent of the boost pressure control system ensures that the maximum injection quantity is (despite "full throttle" ) increased only by the degree to the boost pressure increases. During the initial viscous acceleration, the rotational speed of the turbocharger increases only slowly and thus the boost pressure from a critical engine speed ( depending on the engine from 1600 to 2500 rpm ), it, however, relatively quickly reaches its maximum, as the shaft of the turbocharger due to the now sufficient exhaust flow to rotate fast enough and therefore can build the control boost pressure. It is learned that the increase in the torque based on the square of the speed of effect by a slightly delayed, but then disproportionate power delivery of the engine, and a corresponding acceleration of the car. The delay before the optimum flow of the exhaust turbine is perceived and referred to as a "hole ".
In modern turbo charged diesel engines, the variable turbine geometry is used, thereby the airflow to the turbine impeller is optimized even at a lower exhaust gas volume, the supercharger speed and the charger power increases and therefore the supercharging pressure of the compressor. However, the turbo lag can be completely prevented only by a compressed air reservoir with the corresponding control.
After high load ( high average power output ) the engine should not be turned off immediately after stopping, but should one be left to two minutes at idle (typical example: stopping on a highway rest area ): This is due to the high exhaust gas temperatures under load that heat and the turbine impeller strong. If the motor is hot in this state immediately turned off, crawling the heat to the turbine-side bearing of the loader, which is no longer cooled by fresh oil with the engine off. Coked The residual oil in the bearing, sits firmly in the camp and an ever smaller the bearing clearance. Power is often the immediate shutdown, the game is sometime too small or uneven, at full load then fails the camp completely, oil enters the exhaust with dangerous consequences for the subsequent transport (smoke and oil on the road ). By leave overrun the exhaust temperature drops rapidly, the effect does not occur or is not as strong on.
In turbo petrol engines ( " petrol " ) this is particularly important, since the exhaust gas temperatures are a bit higher.
Due to the inertial of the motor can be avoided so that the life of the turbocharger reduces unnecessary. In addition to aging effects, such as worn injection pump and nozzles, incorrect adjustment of the pump parameters and the principle handicaps older carburetion systems ( swirl chamber ) it is this effect which is consistent with the old turbo diesel engines to the famous blue smoke and increased oil consumption.