The Physics of Turbocharging

As automakers are looking for ways to squeeze more power out of smaller engines, allowing for more fuel-efficient cars that pollute less, many of them are turning to a fairly old technology, the turbocharger. The turbocharger was patented in 1905and was in widespread use on some applications, like large diesel engines in steamships and locomotives, by the 1930’s.

But, how does the turbocharger, or turbo, work?

A turbocharger uses energy from the exhaust flowing out of the engine to compress the air flowing into the engine. The energy of the hot flowing exhaust is usually wasted. In a turbo the exhaust is used to spin blades on a shaft. The exhaust exits the turbocharger cooler than it goes in because of the energy that is transferred to the shaft in the turbocharger.

On the other end of the shaft, in a separate chamber, another set of blades compress the air flowing into the engine. When the exhaust spins the blades as it exits the engine, the shaft those blades are on connect to this other side. This side is the compressor.

When the compressed air flows into the engine it is capable of burning more fuel. For ideal performance the mixture of fuel and air is perfectly balanced such that all of the fuel is burned efficiently. If you increase the quantity of air, you can increase the quantity of fuel burned in the engine. That increased fuel means more power to the cylinders and, ultimately, to the wheels to make the car go.

Since a turbocharger operates using energy that would otherwise be wasted from the exhaust, a turbo can make an engine more efficient, even though the increased airflow means it uses more fuel per engine cycle. While the physics of heat energy can get complicated, to simplify the idea you can think of it as taking some of the extra energy from the exhaust and dumping it back inside the engine to drive the car.

But, where turbos really make things better is in decreasing the size of the engine needed to make the car go. Since a turbocharger can make a smaller engine create more power automotive engineers can design a lighter, smaller car with the same power of a heavier and larger vehicle. This weight savings can contribute significantly to fuel economy and drivability.

There are disadvantages to installing turbochargers on vehicles. Increased cost and complexity are just a couple of those. But, many automotive engineers and manufacturers are finding that these disadvantages are significantly outweighed by the increased performance and operating economy of these systems.