Supercharging and Turbocharging System

Construction & Working of Supercharging System and Turbocharging System.


OBJECTIVES:
To get knowledge about the Supercharging its drives, types and their construction and working.and turbo charging system.

Introduction:
A supercharger is an air compressor used for increasing the pressure, temperature, and density of air supplied to an internal combustion engine. This compressed air supplies a greater mass of oxygen per cycle of the engine to support combustion than available to a naturally aspirated engine, enabling for more fuel to be burned and more work to be done per cycle, thus allowing to increase the power produced by the engine.Power for the supercharger can be provided mechanically by means of a belt, gear, shaft, or chain connected to the engine's crankshaft. When power is provided by a turbine powered by exhaust gas, a supercharger is known as a turbo supercharger– typically referred to simply as a turbocharger or just turbo. Common usage restricts the term supercharger to mechanically driven units.

Temperature effect on engine:
One disadvantage of supercharging is that compressing the air increases its temperature. When a supercharger is used on an internal combustion engine, the temperature of the fuel/air charge becomes a major limiting factor in engine performance. Extreme temperatures will cause detonation of the fuel-air mixture (spark ignition engines) and damage to the engine. In cars, this can cause a problem when it is a hot day outside, or when an excessive level of boost is reached.
It is possible to estimate the temperature rise across a supercharger by modeling it as an isentropic.

This temperature is known as the compressor discharge temperature (CDT) and highlights why a method for cooling the air after the compressor is so important.

In addition to causing possible detonation and damage, hot intake air decreases power in at least one way. At a given pressure, the hotter the air the lower its density, so the mass of intake air is decreased, reducing the efficiency and boost level of the supercharger. 

Type of Supercharger:
·         Root super charger
·         Centrifugal supercharger
·         Twin–screw supercharger


ROOTS SUPERCHARGER:



Working of Roots Supercharger:
As the meshing lobes spin, a in trapped in the pockets between the lobes is carried between the fill side and the discharge side & large quantities of air move into the intake manifold and "stack up" to create positive pressure. This pressurizedair is received at the discharge side.
Ø  Roots superchargers are usually large and sit on top of the engine.
Ø  Roots superchargers are the least efficient supercharger for two reasons:-
1.      They had d more weight to the vehicle.
2.      They provide air in discrete bursts instead of providing in a smooth and continuous manner.


CENTRIFUGAL SUPERCHARGER:



Working of Centrifugal Supercharger:
As the air is drawn in the hub of the impeller, centrifugal force causes it to radiate outward.
The air leaves the impeller at high speed, but low pressure. A diffuser converts the high-speed, low-pressure air to low-speed, high-pressure air. Thus pressurized air is achieved.
Impeller speeds can reach µ 50,000 to 60,000 RPM.
Centrifugal superchargers are the most efficient and the most common induction systems.
They are small, light weight and attach able to the front of the engine.
Thus the centrifugal superchargers are the best among the above list.


TWIN-SCREW SUPERCHARGERS
Working of Twin Screw Superchargers:

A twin-screw supercharger operates by pulling air through a pair of meshing lobes that resemble a set of worm gears. The rotors have a conical taper, which means the air pockets decrease in size as air moves from the fillside to the dischargeside.
Thus a twin-screw supercharger compresses the air inside the rotor housing.As theair pockets shrink, the air is squeezed into a smaller space.
Thus twin-screw superchargers are more efficient compared to roots supercharger.
They cost more because the screw-type rotors require more precision in the manufacturing process.


TURBOCHARGING SYSTEM

They are used to increase the volumetric efficiency of the engine by increasing the air-fuel mixture entering the cylinder. This system is located near to the exhaust system and it send the engine exhaust by making it clean and then it pressurized it back to the engine.
The turbocharger housing contains a turbine and centrifugal air compressor on the same shaft
The exhaust leaving cylinder spins turbine
The compressor forces more air into the cylinder
 Compressor typically increases pressure by 6-8 psi, but it can be greaterIncreased air pressure allows more fuel to burnThe compressed air is usually cooled to allow more air in the cylinder and to prevent knocking
The increase of 6-8 psi increases horsepower by 30-40%.

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