What Are the Functions of a Turbo Charger?

A turbo charger is a device that uses the energy of exhaust gases coming out from an engine to compress the air going into the engine. It must have at least 4 openings: 1 for the engine exhaust gas to enter; a 2nd for the exhaust gas to exit; a 3rd opening for intake air to enter the turbocharger; and a 4th for the intake air to exit the turbo charger on its way to the engine intake. A turbo charger will also have 1 additional opening to vent excess air pressure. Increasing the intake air pressure going into an engine can increase the engine's power, but too much air pressure can damage the engine. Increasing the pressure increases the power of the engine because of the increased density of the air. Increased air density means more oxygen molecules, which means the engine can respond by increasing the amount of fuel it mixes with that oxygen. When the fuel and oxygen are burned, the result is a more powerful explosion with each piston stroke, and thus more power coming out of the engine.

The function of a turbo charger is to increase the power output of an engine without adjusting the engine itself. Typically, an engine would have to be made larger and consequently heavier to gain power; on the other hand, a turbo charger is much smaller and lighter. Additionally, a turbo charger is powered by the exhaust gases of the engine, which would normally just leave the engine and vehicle unused.

The function of a turbo charger can be thought of as beginning at the exhaust opening. Exhaust gases from the engine go through the turbo charger before exiting through the exhaust system of the vehicle. The flow of these gases causes a turbine wheel inside the turbo charger to spin. On the other side of this turbine, on the same axis, is a different wheel at the intake opening of the turbo charger.

At the intake opening of the turbo charger is a 2nd wheel that spins whenever with the exhaust-side turbine wheel spins, since they are connected by the same shaft. This 2nd wheel is called the "compressor" or "impeller wheel" because its spinning compresses the air coming into the turbo on the intake side. This compressed air is fed into the engine intake and, because of the higher density of oxygen molecules in compressed air as opposed to uncompressed, the engine throws in more fuel for each piston stroke, resulting in increased power.

The compressed air coming in the intake of the engine is burned off inside and becomes exhaust gas. This exhaust gas has more energy than it would had the intake air not been compressed and burned with more fuel, and thus spins the exhaust-end turbine of the turbo charger faster than before. In turn, this spins the compressor wheel faster than before, which compresses the intake air more than before. The increase in compression of the air results in even more oxygen molecules and even more fuel for each piston stroke. As this cycle continues, the turbo charger can easily continue to further increase the compression of the intake air. However, at some point, too much air compression combined with too much fuel can result in too much power that can damage the engine.

To limit the amount of air pressure a turbocharger generates by compressing the intake air, a control system must be used. Typically, this happens through a mechanism called a "waste gate" that, when open, allows some exhaust gas to bypass the exhaust-side turbine wheel, which limits how fast the wheel can spin. Limiting the speed of the turbine wheel limits the speed of the intake-side compressor wheel, which limits the amount of air compression.