What is Supercharger?
A supercharger is an air compressor that increases the pressure or density of air supplied to an internal combustion engine. This gives each intake cycle of the engine more oxygen, letting it burn more fuel and do more work, thus increasing the power output.
Power for the supercharger can be provided mechanically by means of a belt, shaft, or chain connected to the engine’s crankshaft.
Common usage restricts the term supercharger to mechanically driven units; when power is instead provided by a turbine powered by exhaust gas, a supercharger is known as a turbocharger or just a turbo – or in the past a turbosupercharger.
How does a supercharger work?
Superchargers increase intake by compressing air above atmospheric pressure, without creating a vacuum. This forces more air into the engine, providing a “boost.” With the additional air in the boost, more fuel can be added to the charge, and the power of the engine is increased.
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.
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).
Types of Supercharger
There are four main categories of superchargers for automotive use:
- Centrifugal Supercharger
- Root type supercharger
- Twin-screw Superchargers
- Vane type supercharger
1. Centrifugal superchargers
A centrifugal supercharger is a specialized type of supercharger that makes use of centrifugal force in order to increase the manifold air pressure, MAP. An increased MAP allows the engine to burn more fuel, which results in increased power output.
Centrifugal superchargers are generally attached to the front of the engine via a belt-drive or gear-drive from the engine’s crankshaft.
The centrifugal supercharger is used in many applications including, but not limited to, automotive, truck, marine, aircraft, motorcycles, and UTVs.
There are two types of Centrifugal superchargers:
- Automotive superchargers: Centrifugal superchargers have become popular in the aftermarket as a bolt-on addition to improve performance. By design, centrifugal superchargers allow for easy integration of air-to-air or air-to-water intercooling. Several companies build centrifugal superchargers and also offer them as complete systems which can be easily installed by a mechanic or the auto enthusiast at home.
- Aircraft superchargers: Because air pressure decreases with altitude, air compression helps maintain engine power as the aircraft climbs.
2. Root’s type supercharger
Root’s type contains two rotors of epicycloid shape. The rotors are of equal size inter-meshed & are mounted and keyed on 2 different shafts. Anyone shaft is powered by the engine via a V-belt or gear train(depending on the distance). Each rotor can have 2 or more 2 lobes depending upon the requirement. The air enters through the inlet & gets trapped on its way to the outlet. As a result, pressure at the outlet would be greater than the inlet.
3. Twin-screw Superchargers
A twin-screw supercharger operates by pulling air through a pair of meshing lobes that resemble a set of worm gears. Like the Roots supercharger, the air inside a twin-screw supercharger is trapped in pockets created by the rotor lobes.
But a twin-screw supercharger compresses the air inside the rotor housing. That’s because the rotors have a conical taper, which means the air pockets decrease in size as air moves from the fill side to the discharge side. As the air pockets shrink, the air is squeezed into a smaller space.
This makes twin-screw superchargers more efficient, but they cost more because the screw-type rotors require more precision in the manufacturing process. Some types of twin-screw superchargers sit above the engine like the Roots supercharger.
They also make a lot of noise. The compressed air exiting the discharge outlet creates a whine or whistle that must be subdued with noise suppression techniques.
4. Vane type supercharger
A number of vanes are mounted on the drum of the supercharger. These vanes are pushed outwards via pre-compressed springs. This arrangement helps the vane to stay in contact with the inner surface of the body.
Now due to eccentric rotation, the space between two vanes is more at the inlet & less at the oulet. In this way, the quantity of air that enters the inlet decreases its volume on its way to oulet. A decrease in volume results in an increment of the pressure of air. Thus the mixture obtained at the outlet is at a higher pressure than at the inlet.
Advantages of supercharging
- Higher power output
- Greater induction of charge mass
- Better atomization of fuel
- Better mixing of fuel and air
- Better scavenging products
- Better torque characteristics over whole range
- Quick acceleration of vehicle
- Complete and smooth combustion
- Even fuel with poor ignition quality can be used
- Improved cold starting
- Reduced exhaust smoke
- Reduced specific fuel consumption
- Increased mechanical efficiency
- Smooth operation and reduction in diesel knock tendency
Disadvantages of supercharging
- Increased detonation tendency in SI engines
- Increased thermal stress
- Increased heat loss due to increased turbulence
- Increased gas loading
- Increased cooling requirements of the engine