What Are Superchargers ? | Working, Types, Advantages, Limitations

Superchargers

In simple words, Superchargers are pressure boosting devices(compressors) which increase the pressure of the air before letting it get into the cylinder of the internal combustion engine! And the process of increasing the pressure OR forcing more air to get into the engine is called supercharging.

supercharger

Why do we need superchargers?

Let’s keep this simple by not diving into those big lengthy formulas, alright.

The power generated by the engine is a function of the mean effective pressure aka. the average pressure in the cylinder. Power is directly proportional to the average pressure.

Power  ∝  Mean effective pressure (MEP)

Pressure goes on increasing during compression stroke & goes on decreasing during the exhaust stroke. So average pressure is calculated with the help of these data. More the MEP, the more the efficiency of the engine!

So if more air is forced & compressed into the cylinder, there will be an increase in the mean pressure & hence will produce more power! This is why we need them – to force the air into the engine!

Working of Superchargers

Superchargers are basically compressors/blowers which take air at normal ambient pressure & compress it and forcefully push it into the engine ! Power to the compressor/blower is transmitted from the engine via the belt drive.

The addition of an extra amount of air-fuel mixture into the cylinder increases the mean effective pressure of the engine. An increment in MEP makes the engine produce more power. In this way, adding a compressor to the engine makes it more efficient.

Types of superchargers

Centrifugal superchargers

These are commonly used in the vehicles & are powered by the engine via a belt-pulley system. The air-fuel mixture enters the impeller at the center. The air is then passed through a diffuser, which increases the pressure. Finally, the air makes its way through the volute casing to the engine.

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. Any one shaft is powered by the engine via a V-belt or gear train(depending on the distance). Each rotor can have 2 or more than 2 lobes depending upon the requirement. The air enters through the inlet & gets trapped on its way to the outlet. As a result, the pressure at the outlet would be greater than the inlet.

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 outlet. In this way, the quantity of air that enters the inlet decreases its volume on its way to the outlet. 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. This was the whole point of studying & installing superchargers.
• Reduced smoke from exhaust gases. The extra air pushed into the cylinder, helps the air to complete combust leading to lesser smoke generation.
• Quicker acceleration of the vehicle. The supercharger starts working as soon as the engine starts running. This way the engine gets a boost even at the beginning leading to quicker acceleration.
• Cheaper than a turbocharger.

Limitations:-

• Draws power from the engine. Though the overall mechanical efficiency is increased it consumes power from the engine. The same job is done by a turbocharger without consuming extra power!
• Increased heat generation. The engine should have proper heat dissipation systems as well as it should be able to withstand thermal stresses!
• Induces stress. The engine must hold up against the high pressure & bigger explosions generated in the cylinder. If the engine is not designed considering these stresses, it may damage the piston head.