Introduction to Supercharger:
The purpose of supercharging is to raise the volumetric efficiency above that value which can be obtained by normal aspiration.
Since the I.H.P. produced by an I.C. engine is directly proportional to the air consumed by the engine. And greater quantities of fuel to be added by increasing the air consumption permit and result in greater power produced by the engine. So, it is, therefore, desirable that the engine should take in the greatest possible mass of air. The supply of air is pumped into the cylinder at a pressure greater than the atmospheric pressure and is called supercharging. When greater quantity of air is supplied to an I.C. engine it would be able to develop more power for the same size and conversely a small size engine fed with extra air would produce the same power as a larger engine supplied with its normal air feed.
Supercharging is used to increase rated power output capacity of a given engine or to make the rating equal at high altitudes corresponding to the unsupercharged sea level rating. Installing a super charger between engine intakes does supercharging and air inlet through air cleaner super charger is merely a compressor that provides a denser charge to the engine thereby enabling the consumption of a greater mass of charge with the same total piston displacement. Power required to drive the super charger is taken from the engine and thereby removes from over all engine output some of the gain in power obtained through supercharging
Since the main object of supercharging is to increase the power output of these engine without
increasing its rotational speed or the dimensions of the cylinder. This is achieved by increasing the
charge of air, which results more burning of the fuel and a higher mean effective pressure.
TYPES OF SUPERCHARGER
Supercharging is done by means of compressor; there are two types of compressors that may be
used as super chargers. They are as follows:
1. Positive displacement type super chargers.
(a) Piston Cylinder type
(b) Roots blowers
(c) Vane blower
2. Centrifugal type super chargers or turbo type.
3. Turbo type super chargers.
|Types Of Supercharger|
The blowers are usually driven from the engine cranks shaft by mean of Spur, helical or herringbone
gears, silent chains or V-belts at a speed 2-3 times the engine speed. In the case of turbo-supercharger, the super charger is coupled to a gas turbine in which the exhaust of the engine is expanded.
The positive displacement types are used for low and medium speed engines with speeds not over 4000 rev/min. Positive displacement type used with many reciprocating engines in stationary plants, vehicles and marine installations.
The piston cylinder type is used on large and slow speed stationary engines, but their use is limited since they are bulkier, more expensive and less dependable than the rotary type blowers.
Centrifugal blowers are used both on low speed and high-speed engines. Centrifugal blowers
driven by exhaust gas turbine are small and light and are used for stationary, locomotive, and marine and aircraft engine. The speed of the centrifugal type of blowers is high about 10000 to 15000 rev/min for low speed engines and 15000 to 30000 rev/min for high-speed engines such as aircraft engines.
ADVANTAGE OF SUPERCHARGING
The various advantages of supercharging are as follows:
1. Power Increase. Mean effective pressure of the engine can be easily increased by 30 to 50% by supercharging which will result in the increase the power output.
2. Fuel Economy. Due to better combustion because of increased turbulence, better mixing of the fuel and air, and of an increased mechanical efficiency, the specific fuel consumption in most cases, though supercharging reduces not all.
3. Mechanical Efficiency. The mechanical efficiency referred to maximum load is increased since the increase of frictional losses with a supercharger driven directly from the engine is quite smaller as compared to the power gained by supercharging.
4. Fuel Knock. It is decreased due to increased compression pressure because increasing the inlet pressure decreases the ignition lag and this reduces the rate of pressure rise in the cylinder resulting in increasing smoothness of operation.
5. Volumetric Efficiency. Volumetric efficiency is increased since the clearance gases are compressed by the induced charge that is at a higher pressure than the exhaust pressure.