To extract more power out of an engine something is for certain: you need more air.
The larger the quantity of air that enters the engine, the more fuel can be burnt. Consequently, the engine will develop a deeper and more powerful explosion inside the cylinder, translating into more power at the crank. Following, there aren’t many ways to compress extra air inside an engine, although one alternative is a supercharger (a turbocharger is another). A supercharger is a fan variant that manages to suck air, maybe compress it, and feed it into the engine by using the engine’s power.
4 Types of Superchargers
Let’s examine the four types of superchargers.
1. Roots Superchargers
In the mid-1850s, the Roots brothers needed an efficient way of inserting pressurized air into blast furnaces, hence they developed a basic design for an air pump with a type of lobed rotors. In 1900, Gottlieb Daimler, whose company merged with Karl Benz’s into Daimler-Benz AG, patented an engine design that used a Roots-style blower. Therefore, the Roots-type supercharger was born.
Their working principle is rather simple but clever, notwithstanding the early time of adoption. By meshing two-lobed rotors in an 8-shaped chamber, the rotors will catch a bit of air at an inlet, trap it thanks to their shape, and transport it to the outlet. The air isn’t compressed at all, just transported like a pump. Hence, this supercharger focuses on airflow and how it moves more air than a naturally aspirated engine can (1).
A low-pressure area will form at the inlet, much more significant than the one created by the engine alone, and the outside air will quickly fill that up. Accordingly, the Roots-type supercharger can create a significant low-pressure area at the inlet, so high that the outside air doesn’t have enough time to refill that spot, resulting in lower performance. Following suit, the Roots-type supercharger is fantastic for low RPM applications.
As such, diesel engines enjoyed great success by using them. On top of that, they are frequently used in dragster applications, thanks to their impressive response. Contemporary models that use a Roots-type supercharger are the 2003 Terminator Cobra SVT or the renowned 2020 Shelby GT500.
2. Twin-Screw Superchargers
The rotary-screw supercharger was developed in Sweden, thanks to an engineer, Alf Lysholm. He needed a way to overcome a stalling issue with gas turbines, found the Roots-type blower but deemed it as ineffective. As such, he tried to figure out a way to improve the previous variant by employing a screw-like design, hence the name.
They are quite similar to the Roots-type blower as in the basic mode of operation, in the way that they also work as a pump. However, they also compress the air by quite a decent amount. When viewed from above, the screws meshing with each other produce multiple V-type chambers. By spinning, these chambers shrink progressively, hence compressing the air until it’s fed into the engine. This process is continuous.
Compared to the Roots-type blower, the twin-screw supercharger is vastly more efficient since not only does it move a greater quantity of air inside the engine, but the air is also denser. Denser air has more mass, so, even more, the air is pushed into the combustion chamber. Denser air is also cooler, and the engine suffers fewer power losses in the process and suffers less mechanical strain (2).
There are significantly more automotive applications done here, with bolt-on kits being readily available for a myriad of cars. Notwithstanding this, a few models that successfully employed twin-screw superchargers are the Chevrolet Corvette ZR1 on its LS9 engine or the Dodge Challenger SRT Demon.
3. Centrifugal Supercharger
Before talking about these superchargers, we first need to talk about impellers. An impeller is a sort of fan that siphons fluid in around its center and throws it outside. No one knows precisely when an impeller was first developed. A few people consider that Leonardo Da Vinci designed the first impeller, while they were also wildly used in the 17th and 18th centuries to ventilate mines.
The working principle of a centrifugal supercharger is, consequently, simple. An impeller sits in a round housing with an outlet. The impeller siphons air via the fan side and throws it within the housing. When that air is expelled from the impeller, it greatly slows down. However, in turn, the compressor can gather vast amounts of air increasing its pressure drastically (3).
These types of superchargers are turbocharger compressors, but instead of being turned around by exhaust gases, they are spun by the engine itself. To work well, centrifugal superchargers must spin at tens of thousands of RPMs and even hundreds of thousands. To achieve that, the impeller uses a high ratio reduction gear. Nevertheless, these superchargers still only work well at high RPMs.
Centrifugal superchargers are wildly available aftermarket, being easy to mount on any car while also maintaining a manageable package. OEM variants aren’t particularly common, one of which is the Koenigsegg CCR.
4. Electric Superchargers
Electric superchargers are significantly more recent than any other technology discussed so far. BorgWarner had a go with this concept in the 1990s. Unfortunately, they couldn’t develop it due to high power consumption that couldn’t have been managed at the time. However, thanks to the improvements in hybrid technology, a myriad of cars employ a 48-volt electrical system at the very least, which is adequate for an electric supercharger.
How do they work? Well, as you expect them to work. Instead of having the engines run the superchargers, they use an electric motor. These motors are controlled electronically based on multiple factors, such as load and RPM. Producers can use any kind of supercharger mentioned, but more commonly centrifugal superchargers are used. Seeing how electric motors already reach high speeds, using a reduction gear is just enough to reach into the tens of thousands of RPMs described above, so their downside is nullified (4).
They can be used for any vehicle as long as it has a way to power the electric motor efficiently. That means that the power output is enough to provide a meaningful performance increase despite the charging efficiency. Hence, they are used on hybrid powertrains that certainly do, translating into free performance across the board. By linking such a supercharger to a turbocharger, we can also eliminate turbo-lag and improve city driving by optimizing stop-and-go traffic. Not a few people think that they are the missing link to the new Euro norms.
Given that it’s a new technology, cars with such a system are rare, but their number is surely rising. Audi employed such a system on the Audi SQ7, Volvo started implementing it in 2010, and Mercedes-AMG signed a deal with Garret to implement them in the future.
Superchargers seem to have an exciting future, notwithstanding the aftermarket culture that already exists around them. Plenty of enthusiasts still purchase a variety of supercharger kits to bolt onto their vehicles, be it just for fun or for actual motorsport usage. There’s also the question of whether they’re better than turbochargers, and the answer is that it depends on what you’re looking after and that the answer is completely subjective.
(1) Tec-Science. What is a roots-type blower and how does it work? [Online].
(2) Kenne Bell. Twin Screw vs. Roots. [Online].
(3) Rotrex. Centrifugal Superchargers. [Online].
(4) Garret Motion. Electric Turbo Innovation. [Online].
2020 Ford Shelby GT 500 photo copyright the Ford Motor Company.
Twin-screw supercharger in a Chevrolet LS9 crate engine per GM.
Electric supercharger by Aeristech.