Tech Through Time: How a Supercharged Engine Works

The heart of most vehicles today, the internal combustion engine has advanced significantly over its century long history.

This series outlines some of the key innovations in engine technology before taking a look at alternatives to the combustion engine. This week, how a supercharger works.

Check out other parts in this series

Tech through time: Fuel injection
Tech through time: Turbocharging
Tech through time: Variable Valve Timing
Tech through time: Hydrogen Fuel Cells

The need for power

The 1923 Mercedes 6/25/40 HP was the world's first mass-produced car with a supercharger.

There are many ways to get more power out of an engine. The most obvious method is to simply increase displacement, by increasing the combustible surface area through the addition of more cylinders. However, this comes with its own disadvantages in terms of increased fuel consumption, weight, and a larger engine, which can adversely affect ride and handling. Another option is to increase the amount of fuel that enters the combustion chamber. Adding more fuel results in a larger explosion and thus the production of more power. 

To burn the fuel completely and prevent waste, an engine requires a set amount of air. This is known as the air to fuel ratio, or stoichiometric ratio, and varies depending on the type of fuel used. For example, petrol requires between 13-15 parts of air per part of petrol, depending on its octane rating. Thus, adding more fuel into the combustion chamber alone will not increase engine power, but rather make the air to fuel ratio ‘rich.’ The amount of air entering the chamber must also be proportionally increased so that the ideal air/fuel ratio is maintained.

Superchargers are one way to increase the flow of air into the combustion chamber.

How do they work?

Fundamentally, superchargers work as air compressors. A belt or chain connects the engine’s crankshaft to the supercharger rotor, providing the power necessary for the compressor to run.

Today, there are three main types of supercharger that utilise this fundamental principle, namely Roots, twin screw and centrifugal.

Roots type supercharger

Roots-type superchargers are rudimentary, but get the job done.

The Roots type supercharger is the oldest application of this technology, invented by Philander and Francis Roots in 1860, originally to blow air into blast furnaces that melted iron. The Roots supercharger works through a pair of rotors that blow air at a high speed into the intake port. As the port then contains a greater quantity of air, it becomes compressed. In turn, this enables a higher quantity of fuel to be injected into the combustion chamber (and thus greater power to be generated).

Roots-type superchargers are commonly associated with 'hot-rod' vehicles.

Roots superchargers are often mounted on top of the engine, thus giving the characteristic protruding air intake that ‘hot-rod’ vehicles are known for.

Twin-screw supercharger

Image credit: HowStuffWorks.

The main difference with twin-screw superchargers is how and where the air is compressed. Instead of air being compressed in the intake port (as with a Roots supercharger) a twin screw supercharger compresses air within the supercharger housing itself.

A twin-screw supercharger sits in the bay of a Camaro SS. (image credit: Camaro5.com)

Two screw type rotors draw in and squeeze the air before sending it to the engine.

Centrifugal supercharger

Centrifugal Superchargers can offer advantageous packaging.

Centrifugal superchargers are perhaps the most unique supercharger design. Instead of a pair of rotors, an impeller fan draws air in.

A centrifugal supercharger sits in the bay of a Nissan 350Z. (image credit: ProCharger)

This is similar in principle to how a common household exhaust fan draws in steam or smoke. In a supercharged car, this impeller rotates at a very high RPM, often in excess of 50,000 RPM. Whilst this causes air to be drawn in at a high speed, centrifugal forces compress and slow down the air as it leaves the housing.

Superchargers today

Jaguar's performance vehicles such as the new XE Project 8 SV still use superchargers to draw more power.

Today, most affordable, mainstream vehicles incorporate turbochargers rather than superchargers as a means to generate additional power, in part due to the greater fuel economy that turbocharging provides. However, certain automakers continue to use the supercharger for their performance vehicles. Jaguar, for example, uses the supercharger high-performance variants of the F-Type and XE, whilst Volvo has incorporated both turbocharging and supercharging for its new Drive-E engines in models such as the S90 and new XC60.

Volvo's new Drive-E engines incorporate both turbocharging and supercharging to extract high power from small displacements.

Do you think superchargers should go extinct, or do they have more to offer? Tell us what you think in the comments below.