How does a turbocharger work in a car?

Question

Also, how is it different from a supercharger?

In: Engineering

Answer 1

A “charge” in an internal combustion engine is the mix of air and fuel that’s placed into the cylinder. The more charge you have, the more energy you can produce.

If the engine is “naturally aspirated” the only thing drawing in air is the movement of the cylinder downward. The “charge” is whatever air flows into the cylinder due to the slightly lower pressure of the cylinder with respect to the atmosphere. For such engines, the “charge” can be around 0.6-0.7 atmospheres at idle, and >0.9 atmospheres when running at full power. But it’s never going to be greater than (or even equal to) the pressure of the air outside the car.

Supercharging is the act of putting more charge than that into an engine. This is done by using an air compressor to suck up and squeeze air into the engine, making the pressure in the cylinders much more than the pressure outside. More pressure means more mass of air, and if you add more fuel to that mass, you get more power per stroke.

In the first superchargers, the energy to run that air compressor was originally from a belt that ran off the engine crankshaft. This causes the engine to work harder, but the extra power it can produce from having more air and fuel in the cylinder more than makes up for it. Superchargers using belts were invented really early into the development of the automobile, so they were around for a long time, and it became common vernacular that a “supercharger” was specifically a supercharger that got power via a belt on the crankshaft, because that was the only type of supercharger there was.

Starting in the 1960s, a completely new type of automotive supercharger became popular. Instead of using a belt, the power for the compressor comes from a turbine that the exhaust gas blows over. This turbo-supercharger had some benefits and drawbacks. It was generally more efficient and had fewer moving parts, but it was also subject to extreme temperatures and chemicals from the exhaust.

After a while, the turbo-supercharger was just called a turbocharger. Meanwhile, the belt-driven supercharger was never called a “belt-supercharger.” So belt-driven superchargers are called “superchargers” and exhaust-driven superchargers called “turbochargers.”

There are benefits and drawbacks to both types. Generally, turbochargers get less practical the larger the engine, so you’ll usually see turbochargers in passenger cars and superchargers in heavy duty trucks.