Turbocharger Operation

Turbocharger Operation

Turbocharger are used to increase engine power by compressing the air that goes into the engine¡¯s combustion chambers. They do not require a mechanical connection between the engine and the pressurizing pump to compress the intake gases. Instead, they rely on the rapid expansion of hot exhaust gases exiting the cylinders. These gases spin the turbine blades (hence the name turbocharger) of the pump. Because exhaust gas is a waste product, the energy developed by the turbine is said to be free since it theoretically does not use any of the engine¡¯s power is helps to produce.

A typical turbocharger, usually called a turbo, consists of the following components:

- turbine or hot wheel

- shaft

- compressor or cold wheel

- waste gate valve

- actuator

- center housing and rotating assembly

This component contains the bearings, shaft, turbine seal assembly, and compressor seal assembly.

The turbocharger is normally located close to the exhaust manifold. An exhaust pipe runs between the exhaust manifold and the turbine housing to carry the exhaust flow to the turbine wheel. Another pipe connects the compressor housing intake to an injector throttle plate assembly or a carburetor.

Inside the turbocharger, the turbine wheel (hot wheel) is attached via a shaft to the intake compressor wheel (cold wheel). Each wheel is encased in its own spiral-shaped housing that serves to control and direct the flow of exhaust and intake gases. The shaft that joins the two wheels rides on bearings.

The air compressing process typically starts when the engine¡¯s speed is above 2000 rpm. The force of the exhaust flow is directed through a nozzle against the side of the turbine wheel. As the hot gases hit the turbine wheel causing it to spin, the specially curved turbine fins direct the air toward the center of the housing where it exits. This action created a flow called a vortex. Once the turbine starts to spin, the compressor wheel (shaped like a turbine wheel in reverse) also starts to spin. This causes air to be drawn into the center where it is caught by the whirling blades of the compressor and thrown outward by centrifugal force. From there, the air exits under pressure through the remainder of the induction system on its way to the cylinder.

Air is typically drawn into the cylinders by the difference in pressure between the atmosphere and engine vacuum. A turbocharger, however, is capable of pressurizing the intake charge above normal atmospheric pressure. Turbo boost is the term used to describe the positive pressure increase created by a turbocharger. For example, 10 psi of boost means the air is being fed into the engine at 24.7 psi (14.7 psi atmospheric plus 10 pounds of boost).

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