Cars 101: How Does a Supercharger Work?
One day, you may find yourself at a traffic light alongside a Ford Mustang Shelby GT500. Along with its beautiful paint job and classic pony car styling, you'll notice some distinct sounds if you listen closely.
The first will be the rumble of the American-made V8 engine as the cylinders turn over underneath the hood. Next will be the deep exhaust note that burbles and pops as the revs rise and fall. Lastly, as the GT500 accelerates away, you'll notice an unusual whine rising in pitch as speed increases.
That whining sound is a supercharger, a unique way of increasing horsepower by forcing more air into an engine's cylinders, allowing it to combust greater amounts of fuel.
As today's automakers search for ways to increase horsepower without simply increasing engine displacement, superchargers are a trusted solution.
But what is a supercharger? And what are some different types of superchargers? Let's explore the subject of superchargers in more detail.
What is a supercharger?
An internal combustion engine works by drawing air into a cylinder, compressing it, igniting a mixture of fuel and air, then sending the exhaust gases through the muffler. When the fuel and air ignite, it creates a power stroke of the piston, which is the force that eventually travels through the driveline to the wheels.
An engine's ability to produce horsepower depends on how much air and fuel it can combust.
So it would seem that just building larger and larger engines would be the only way to gain extra power. Or one might think you could inject additional fuel into the cylinder for a more powerful explosion and obtain additional ponies.
However, a corresponding amount of air needs to be present for fuel to ignite correctly.
The answer is a forced induction system, where pressurized air is fed into the cylinder to accompany increased amounts of fuel. The resulting mixture creates a more substantial explosion and, in turn, pavement-rippling power that goes through the transmission, wheels, and tires.
A supercharger is a type of forced induction that sends compressed air through the engine's intake manifold and then into its cylinders. Usually, an accessory belt connected to a car's crankshaft powers a supercharger, so they offer an instantaneous response. Other forced induction methods, such as turbocharging, can take a while to get going as they build pressure, also known as turbo lag.
When air is compressed, its temperature increases, making it less dense and explosive. For this reason, an intercooler is placed between the supercharger and manifold to cool the air and optimize ignition.
How much horsepower does a supercharger add? Amazingly, supercharging an engine can result in an average of 46 percent more horsepower and 31 percent more torque. And the added weight of a supercharger pales in comparison to the heft of a larger engine.
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Types of superchargers
When was the supercharger invented? Interestingly enough, inventors Philander and Francis Roots drew up the first design in 1860 for mine shaft ventilation. It was Gottlieb Daimler who brought the Roots supercharger to automobiles in 1900.
The Roots supercharger is the oldest design and uses two spinning rotors that mesh together to create pressure. Air pockets between lobes on the rotors compress, sending pressurized air through the intake manifold and into the cylinders.
Roots superchargers sit on top of the engine and sometimes protrude through the hood. For this reason, they're popular on muscle cars and other souped-up vehicles. However, Roots superchargers are the least efficient type of this technology because they're heavier and produce bursts of pressurized air rather than a stable flow.
A twin-screw supercharger works similarly to the Roots design but is more efficient. While a twin-screw also uses rotors, compressing the air inside the rotor housing goes a step further. Also different from the Roots design, a twin-screw uses tapered rotors to increase pressure from the fill side to the discharge side of the housing. While a twin-screw is more efficient than a Roots, its tighter manufacturing tolerances can drive up costs.
Louis Renault designed the centrifugal supercharger in 1902, which is a noticeable departure from either a Roots or twin-screw. First, an impeller is powered to 50,000-60,000 rpm to draw air into the housing, where centrifugal forces cause it to radiate from the center. Then the air is passed through a diffuser – a series of vanes on the perimeter of the impeller – to pressurize it before it reaches the intake manifold. The advantages of a centrifugal supercharger are its compact size, low weight, and convenient positioning on the front of the engine.
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Turbocharger or supercharger?
While both superchargers and turbochargers increase engine power, each has pluses and minuses.
Superchargers offer a robust initial response because they're connected directly to the engine's crankshaft. The direct connection causes them to wind up faster and feed pressurized air into the intake instantaneously. But because of their direct link to the engine, they create parasitic loss and are less efficient than turbochargers.
Today's advanced turbocharged engines approach supercharged engines in their low-RPM response but benefit from being more efficient. Because exhaust gases power a turbocharger, it doesn't sap power from the motor while building boost. The drawback of a turbocharger is delayed power off the line while the turbine spools up.
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Supercharged Engines: Power and sound
A supercharged engine has several benefits when compared to a naturally aspirated version. Increased horsepower and torque are the most obvious. Extra oomph off the line is a nice feature to have whether you're driving through the city or traveling through the countryside.
In the case of a centrifugal supercharger, you're getting a smaller engine to produce power similar to a larger one while still achieving good fuel economy. A centrifugal supercharger's clean design and placement mean your car has the same flat hood and open engine bay as any other.
Then there's the sound. You have to hear it to understand it. The same way a high-performance engine sings all the right notes, a supercharger spinning at 50,000 rpm lets out a noise that's racy and innovative all at once.
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October 4, 2021
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