20 December 2016

Supercharger System

Introduction of supercharging :

The supercharging principal aim is to achieve the twin goals given below :

  1. Improved power output
  2. Minimum exhaust emission
The power output of a natural engine ( without supercharger engine ) mainly depends on the following factors :
  1.  Amount of air inducted into the cylinder
  2. Speed of the engine
  3. Quantity of fuel entered
  4. Combustion characteristics
  5. The thermal efficiency of the engine
  6. Utilization of inducted air
The most preferred method of increasing the power output is by means of increasing the mean effective pressure. this can be achieved by supplying air or air-fuel mixture at a pressure which is higher than the atmospheric pressure because this will increase density. this will increase the power output of the engine.

This method of supplying air or air-fuel mixture higher than the pressure at which the natural engine did by means of a boosting device is called the supercharging.

The device which boosts the pressure is called supercharger.

The points to be noted in supercharging engine are given below :
  • Supercharging increases power output it does not increase the fuel consumption 
  • A certain percentage of power is consumed in compressing the air. this power has to be taken from the engine itself. this will lead to some power loss. however, it is seen that the net power output will be more than the power output of and engine of the same capacity, without supercharging
  • Supercharging may lead to detonation, therefore the fuel used must have better antiknock characteristics
  • The engine should be designed to withstand the higher force 
In practice, the racing car engine used supercharging. 

The most important area where supercharging is of more importance are :
  1. Marine and automotive engine where weight and space are important
  2. Engines working at high altitudes
Types of supercharging :
There are three types of superchargers used in supercharging :
  1. Centrifugal type 
  2. Root's type
  3. Vane type
Methods of supercharging : 
  1. Ram effect
  2. Under piston supercharging
  3. Independently driven compressor or blower
  4. Kadenacy system ( applied to the two-stroke engine )
Effects of supercharging :

Before supercharging one should understand its effect and its effect given below :
  • Higher power output
  • Greater induction of charge mass
  • Better atomization of fuel
  • Better scavenging of products 
  • Better mixing of fuel and air
  • Better torque characteristics over the whole speed range
  • Quicker acceleration of the vehicle
  • More complete and smoother combustion
  • Poor ignition quality fuel usage
  • Smoother operation and reduction in diesel knock tendency
  • Increased detonation tendency in SI engine
  • Improved cold starting
  • Reduced exhaust smoke
  • Reduced specific fuel consumption
  • Increased mechanical efficiency
  • Increased thermal stresses
  • Increased heat losses due to increase turbulence
  • Increased gas loading
  • The increased valve overlap period
  • Increased cooling requirements of pistons and valves
Limitations to supercharging :
  • Thermal load on the various parts of the engine increases
  • The valve overlap usually greater it may vary about 80 to 160 degree of crank angle
  • The engine internals will be exposed to higher pressures and temperatures, which will, of course, affect the longevity of the engine.