|| What is Supercharging? || What is supercharger and Turbocharger? | TYPES | Differences || METHODS || Ram effect || Blower || knowledgeaboutautomobile

What is Supercharging? 

The method of increasing the inlet air density is called Supercharging.

"MORE FUEL + MORE AIR = BIGGER EXPLOSION = GREAT HORSEPOWER"

Supercharging can be done both for SI engine as well as in CI engine.

The purpose of supercharging an engine is to raise the density of the air charge, before it enters the cylinders.Thus, the increased mass of air will be inducted which will then be compressed in each cylinder. This makes more oxygen available for combustion than the conventional method of drawing the fresh air charge into the cylinder. Consequently, more air and fuel per cycle will be forced into the cylinder, and this can be effectively burnt during the combustion process to raise the engine power output to a higher value than would otherwise be possible.

Supercharging of an engine can be done using either one of the following components:
1.)SUPERCHARGERS
2.)TURBOCHARGERS
 If the supercharger is driven by the engine crankshaft, then it is called mechanically driven supercharger. Some superchargers are driven by a gas turbine, which derives its power from the engine exhaust gases. Such a supercharger is called turbocharger. 

WHY SUPERCHARGING ??

• Supercharging increases the power of an engine. It does not increase the fuel consumption, per brake kW hour.
• Increases the Torque produced.
• Necessary in aero-planes as they have less oxygen at high altitudes.
• Ensure complete combustion of the fuel.
• Reduce pollution to some extent.
• The engine should be designed to withstand the higher forces due to supercharging.

In practice, racing car engines use supercharging. The most important are as where supercharging is of vital importance are :

(i) Marine and automotive engines, where weight and space are important.

(ii) Engines working at high altitudes. The power loss due to altitude can be compensated by supercharging.

Superchargers:

A supercharger is an equipment that compress the air being delivered to an engine, and allowing the combustion chamber to be overfilled without enlarging the space.

The higher concentration of oxygen provided by a supercharger is matched with a large amount of fuel from the fuel injectors thus boosting the power of the engine.

Types of Superchargers:

There are two main types of superchargers defined according to the method of gas transfer:

1.  positive displacement
2.  Dynamic compressors

Positive displacement type which deliver a nearly fixed volume of air per revolution at all speeds and a fairly constant level of boost regardless of engine speed.

 Dynamic compressors relay on accelerating the air to high speed and then exchanging that velocity for pressure by diffusing or slowing it down & deliver increasing boost with increasing engine speed.

Positive displacement:

Positive-displacement pumps deliver a nearly fixed volume of air per revolution at all speeds.

• Roots
• Lysholm twin-screw
• Sliding vane
• scroll-type supercharger, also known as the G-Lader

Dynamic

Dynamic compressors rely on accelerating the air to high speed and then exchanging that velocity for pressure by diffusing or slowing it down.

Major types of a dynamic compressor are:

• Centrifugal
• Multi-stage axial-flow

commonly using types of superchargers in Automobile are -

(i) Centrifugal type

(ii) Root’s type

(iii) Vane type

    

Supercharger drive types:

Superchargers are further defined according to their method of a drive.

• Belt (V-belt, Synchronous belt, Flat belt, Toothed belt)
• Direct drive
• Gear drive
• Chain drive
• Variable speed ratio

METHODS OF SUPERCHARGING:

(i) Independently driven compressor or blower, usually driven by an electric motor.

(ii) Ram effect.

(iii) Underpiston supercharging.

(iv) Kadenacy system (applied to two stroke engines).

(v) Engine driven compressor or blower.

EFFECTS OF SUPERCHARGING:

(i) Higher power output

(ii) Greater induction of charge mass

(iii) Better atomization of fuel 

(iv) Better mixing of fuel and air

(v) Better scavenging of products

(vi) Better torque characteristic over the whole speed range

(vii) Quicker acceleration of vehicle

(viii) More complete and smoother combustion

(ix) Inferior or poor ignition quality fuel usage

(x) Smoother operation and reduction in diesel knock tendency

(xi) Increased detonation tendency in SI engines

(xii) Improved cold starting

(xiii) Reduced exhaust smoke

(xiv) Reduced specific fuel consumption, in turbocharging

(xv) Increased mechanical efficiency

(xvi) Increased thermal stresses

(xvii) Increased heat losses due to increased turbulence

(xviii) Increased gas loading

(xix) Increased valve overlap period of 60 to 160◦of crank angle

(xx) Increased cooling requirements of pistons and valves

Advantage of Superchargers Over a Turbocharger:

• Supercharger do not suffer lag which is a serious problem in turbocharger.
• Modification of the exhaust system- Installing a turbocharger requires extensive modification of the exhaust system, but supercharger can be bolted to the top or side of the engine, that makes them cheaper to install and easier to service and maintain.
• Shutdown procedure- No special shutdown is required with superchargers as they are not lubricated by engine oil. They can be shut down normally. Turbochargers must idle for about 30 seconds or so prior to shutdown so the lubricating oil has a chance to cool down.

Disadvantages of Superchargers:

• It derives power from the engine itself crankshaft drives superchargers so they steal some of the engine's total power output.
• An added total power of the engine Supercharger puts an added strain on the engine, which needs to be strong to handle the extra boost and bigger explosion.
• Since some of the supercharger are larger in size the efficiency of the engine decreases as it is the additional component bolted on to it.
• Detonation is serious problem.

TURBOCHARGERS:

• Turbochargers are a type of forced induction system whose function is same as that of Supercharger.
• The major parts of a turbocharger are turbine wheel, turbine housing, turbo shaft, compressor wheel, compressor housing  and bearing housing. In order to achieve the boost,the turbocharger uses the exhaust flow the engine to spin a turbine, which in turns spins  an air pump.

• During engine operation, hot exhaust gases blowout through the exhaust valve opening into the exhaust manifold. The exhaust manifold and the connecting tubing route these gases into the turbine housing. As the gases pass through the turbine housing, they strike on the fins or blades on the turbine wheel. When the engine load is high enough, there is enough gas flow and this makes the turbine wheel to spin rapidly. The turbine wheel is connected to the compressor wheel by the turbo shaft. As such, the compressor wheel rotates with the turbine which sucks air into the compressor housing. Centrifugal force throws the air outward. This causes the air to flow out of the turbocharger and into the engine cylinder under pressure.
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•  In the case of turbocharging, there is a phenomena called turbolag. It refers to the short delay period before the boost or manifold pressure increases. This is due to the time the turbocharger assembly takes the exhaust gases to accelerate the turbine and compressor wheel to speed up.
• In the turbocharger assembly, there is a control unit called waste gate.This unit limits the maximum boost  pressure to prevent detonation in SI engines and the maximum pressure and engine damage. It is a diaphragm operated valve that can bypass part of the gases around the turbine wheel when manifold pressure is quite high.
• The computer controlled turbocharging system uses engine sensors, a microprocessor and a waste gate solenoid. The solenoid when energized or deenergized by the computer, can open or close the waste gate.  By this way, the boost pressure can be controlled closely. The exhaust smoke comparison for a diesel engine for a naturally aspirated and turbocharged version, for different loads.There is an appreciable reduction in smoke in the case of turbocharged engine in the overload operation.

Important Parts of supercharger

Turbine

Compressor

Ball bearing & fluid bearings

Intercooler: When air is compressed, it heats up, and when air heats up, it expands.So some of the pressure increases from a turbocharger is the result of 

 Difference between supercharger and Turbocharger: 

• The key difference between a turbocharger and a supercharger is its power supply. 
• Something has to supply the power to run the air compressor. 
• In a supercharger, there is a belt that connects directly to the engine. It gets its power the same way that the water pump or alternator does. 
• A turbocharger, on the other hand, gets its power from the exhaust stream. The exhaust runs through a turbine, which in turn spins the compressor
• There are trade offs in both systems. 
• In theory, a turbocharger is more efficient because it is using the "wasted" energy in the exhaust stream for its power source. 
• On the other hand, a turbocharger causes some amount of back pressure in the exhaust system and tends to provide less boost until the engine is running at higher engine speeds. 
• Superchargers are easier to install but tend to be more expensive.