Turbocharger: Description and Operation

Fig. 3 Section view of Garret-AiResearch T3 type turbocharger:

The turbocharger is comprised of 2 impellers (compressor and turbine) connected by a single shaft, bearings, seals, and the housing that contains these components. The turbine impeller is driven by, and located in the exhaust stream. The compressor impeller is driven by the turbine impeller and located in the intake air stream. The compressor impeller compresses the intake air before it enters the intake manifold.

When the compressor impeller rotates, it creates and forces a highly compressed amount of air into the combustion chamber. As more air (and fuel) is forced into the combustion chamber, more horsepower is developed due to higher density and compression of the incoming air. The amount of air that enters the combustion chamber is dependant upon the rpm of the turbocharger. As the rpm of the turbocharger increases so does the amount of air that is forced into the combustion chamber (the horsepower increases as the rpm of the turbocharger increases).

Because the turbocharger is controlled by the pressure of the exhaust gases, when the vehicle is accelerating from idle there is a period of time before it will accelerate with full power. This time is called "turbo lag". "Turbo lag" is evident in virtually all single turbo applications, because the exhaust pressure is very low at idle and the exhaust pressure has to increase to get the turbine impeller rotating (the turbine impeller has to be rotating in order for air to be forced into the combustion chamber).

The seals inside the turbocharger are of a very special design to withstand the extreme temperatures under which the turbocharger operates.
CAUTION: The turbocharger housing can reach temperatures exceeding 1500 ~F (815 ~C), and can glow red. Do not touch the turbocharger housing unless the vehicle has been OFF for an extended period of time.

The bearings are also of a special design, they are designed to handle extreme revolutions per minute. A turbocharger can turn from 20,000 to 140,000 revolutions per minute depending upon the engine application and load.