SuperchargingThe power output of a naturally aspirated engine depends

mainly on the following five factors:1 Amount of air inducted into the cylinder.2 Extent of utilization of the inducted air.3 The speed of the engine.4 Quantity of fuel admitted and its combustion characteristics.5 Thermal efficiency of the engine.

SuperchargingSupercharging of internalcombustion engines is in

practice for a long time as a method for improving engine power output.

The purpose of supercharging an engine is to raise the density of the air charge, before it enters the cylinders.

Supercharging increases the power output of the engine. It does not increase the fuel consumption, per brake kW hour.

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 an engine of the same capacity, without supercharging.

The engine should be designed to withstand the higher forces due to supercharging.

The increased pressure and temperature as a result of supercharging, may lead to detonation, Therefore the fuel used must have better anti-knock characteristics.

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

SuperchargersA supercharger is an engine-driven air pump that

supplies more than the normal amount of air into the intake manifold and boosts engine torque and power.

A supercharger provides an instantaneous increase in power without the delay or lag often associated with turbochargers.

However, a supercharger, because it is driven by the engine, does require horsepower to operate and is not as efficient as a turbocharger

Types Of SuperchargersSupercharger is a pressure-boosting device which supplies

air (or mixture) at a higher pressure.If the supercharger is driven by the engine crankshaft,

then it is called mechanically driven supercharger. Some su perchargers are driven by a gas turbine, which derives its power from the engine exhaust gases.

Centrifugal type.Root's type.Vane type.

Centrifugal Type Supercharger

Root's type

Vane type

METHODS OF SUPERCHARGINGIndependently driven compressor or blower, usually

driven by an elec tric motor.Ram effect.Under piston supercharging.Kadenacy system (applied to two stroke engines).Engine driven compressor or blow

Electric Motor Driven SuperchargingIn this type the compressor is driven

independently usually by an electric motor. The speed of the supercharger can be varied independent of engine speed and therefore control is comparatively easier.

Ram Effect of SuperchargingThe ram effect of supercharging system consists primarily

of tuned inlet pipes. These pipes induce resonant harmonic air oscillations. The kinetic energy of these oscillations provides a ramming effect. For the efficient operation of this system, the engine speed must be kept constant

Under Piston SuperchargingUnder piston method of supercharging has so far been

confined to large marine four stroke engines of the crosshead type. It utilizes the bottom side of the piston for compressing the air. The bottom ends of the cylinder are closed off and provided with suitable valves. This system gives an adequate supply of compressed air, as there are two delivery strokes to each suction stroke of the cycle.

Kadenacy System of SuperchargingThe kadenacy system utilizes the energy in the exhaust system to

cause a depression of pressure in the cylinder. This depression makes the scavenge air to flow.

The kadenacy system is based on the following principle: When the exhaust ports or valves are opened rapidly during the end of expansion stroke, there is, within the first interval of a few thousandths of a second, an urge or impulse in the gases to escape very rapidly from the cylinder. The escaping gases leave behind a pressure depression.

At the above moment, the fresh charge of air (or mixture) is allowed to enter the cylinder behind the exhaust gases by suitable timing of the admission valve or ports. For the best result a proper timing and skillful design of the exhaust system is a must.

EFFECTS OF SUPERCHARGINGHigher power output.Greater induction of charge massBetter atomization of fuel.Better mixing of fuel and air.Better scavenging of products.Better torque characteristic over the whole speed range.Quicker acceleration of vehicle.

More complete and smoother combustion.Inferior or poor ignition quality fuel usage.Smoother operation and reduction in diesel knock

tendency Increased detonation tendency in SI engines.Improved cold starting.Reduced exhaust smoke.Reduced specific fuel consumption, in turbo charging

Increased mechanical efficiency.Increased thermal stresses.Increased heat losses due to increased turbulence

Increased gas loading.Increased valve overlap period of 60 to 160° of crank

angle Increased cooling requirements of pistons and valves .

GEAR DRIVEN AND EXHAUST DRIVEN SUPERCHARGING ARRANGEMENTS

Figure shows an engine with free exhaust driven compressor. The engines, so equipped are said to be turbo-supercharged. In this case the exhaust energy of the engine is used to drive the turbine which is coupled to a compressor. There is no mechanical coupling of compressor or turbine with the engine. The exhaust pipe of engine is however connected to inlet of turbine. In this case engine output is not utilized to drive the compressor.

shows the compressor coupled to the engine with step up gearing to increase the rotational speed of compressor. In this case a certain percentage of engine output is utilized to drive the compressor. The net output increase due to supercharging is obtained by subtracting this power from the engine gross output.. After cooler is also shown, by which the cool air to the engine can be sent if so desired. This will further increase the density of the intake air.

compressor, engine, and turbine are all geared together. The Wright Turbo-compound air plane engine is an example. In this case, if the turbine output is insufficient to run the compressor particularly at part loads, the engine power takes care of the remaining load of compressor. Also, the additional power from the turbine can be fed to the engine

shows the gas generator type of arrangement. In this case engine drives only the compressor. Air from the compressor flows through the engine and the exhaust gases drive a power turbine. Most free-piston engines work on this principle.