Function of a turbocharger
A turbocharger is for achieving high torques and therefore higher motor
performance. This is doable by compressing the induction air. Because of
the increased density of the oxygen, more oxygen can get into the
internal engine. With the increased oxygen supply a better combustion is
possible - the motor performance goes up. The heat and motion energy of
the exhaust fumes are used to power the exhaust-gas turbine of the
turbocharger. The exhaust-gas turbine drives the compressor. The
compressor compresses the induction air which causes a warming up of the
compressed air. In the air-cooler the hot compressed air is cooled down.
Problem areas of the turbocharger:
In the upper motor speed range a higher speed range of the
exhaust-gas turbine is reached which causes a higher compression of the
induction air as necessary. In the lower motor speed range the
exhaust-gas turbine is not reaching the required speed range. This is
causing that the induction air is not enough compressed. Therefor the
motor is not reaching the wanted performance (turbogap).
The “adjustable” VNT/VTG turbocharger
In comparison to the regular turbocharger the VNT/VTG model is
reaching the necessary compression of the induction air through the
entire speed range of the motor. This is possible because of adjustable
guide-blades which guide the exhaust-fume-flow over the
turbine-impeller.
If your motor speed range is low and you wish to have high boost
pressure:
The cross-section of the exhaust-gas-flow is reduced before the
turbine-impeller by means of guide-blades. Because the exhaust fumes
have to flow faster through the reduced cross-section, the
turbine-impeller speed range is increased. This way you will always get
the required boost pressure, also in the lower motor speed range.
High motor speed range:
The cross-section of the turbocharger fits to the exhaust-gas-flow.
To make sure that the required boost-pressure is not exceeded, the
guide-blades are giving a big enough cross-section for the
exhaust-fume-flow.
What developments are expected in the future?
Here opinions are divided. What is research recommending?
What type of turbocharger is required in the future?
The automotive industry is more and more looking into new developments
to stay below the maximum emission values according to the law. The
automotive industry also requires cost effective solutions.
What effect does that have regarding the turbocharger? Well,
turbocharger have to become more simple and much more efficient. Many of
the new turbochargers are based on new technologies which allow less and
smaller spare parts. New procedures which allow to balance smallest
parts of the turbocharger at operation speed range are becoming more and
more complex and require increased precision. Operation speed range up
to 300.000 RPM is not going to be a rare thing in the future. New
materials like ceramics are going to be used more often in the future.
The common slide bearing will replaced by new technologies like ball
bearings and air bearings.
There will also be new operational areas for the turbocharger. Leading
car manufacturer are already testing turbochargers in combination with
fuel-cells.
Sincerely,
STK Turbo Technik Team
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