What is the function of turbo?

Answer 1

The function of a turbo is to provide more air (a greater volume of air often under pressure) through the intake and into the cylinder. The added air allows for a more efficient use of the atomized fuel. A more efficent combustion provides more power. The turbo compresses air on the intake-side (compressor) of the system by using expended gases on the exhaust side (impeller) of the the system.

Answer 2

Design and Function of a Turbocharger: CompressorThe turbocharger's basic functions have not fundamentally changed since the times of Alfred Büchi. A turbocharger consists of a compressor and a turbine connected by a common shaft. The exhaust-gas-driven turbine supplies the drive energy for the compressor.

• Compressor
• Turbine
• Control system
• Bearing system

Design and functionTurbocharger compressors are generally centrifugal compressors consisting of three essential components: compressor wheel, diffuser, and housing. With the rotational speed of the wheel, air is drawn in axially, accelerated to high velocity and then expelled in a radial direction.

The diffuser slows down the high-velocity air, largely without losses, so that both pressure and temperature rise. The diffuser is formed by the compressor backplate and a part of the volute housing, which in its turn collects the air and slows it down further before it reaches the compressor exit.

Operating characteristicsThe compressor operating behaviour is generally defined by maps showing the relationship between pressure ratio and volume or mass flow rate. The useable section of the map relating to centrifugal compressors is limited by the surge and choke lines and the maximum permissible compressor speed. Surge lineThe map width is limited on the left by the surge line. This is basically "stalling" of the air flow at the compressor inlet. With too small a volume flow and too high a pressure ratio, the flow can no longer adhere to the suction side of the blades, with the result that the discharge process is interrupted. The air flow through the compressor is reversed until a stable pressure ratio with positive volume flow rate is reached, the pressure builds up again and the cycle repeats. This flow instability continues at a fixed frequency and the resultant noise is known as "surging".

Compressor map of a turbocharger for passenger car applications

Enlarge picture

Choke lineThe maximum centrifugal compressor volume flow rate is normally limited by the cross-section at the compressor inlet. When the flow at the wheel inlet reaches sonic velocity, no further flow rate increase is possible. The choke line can be recognised by the steeply descending speed lines at the right on the compressor map.