supercharging | internal combustion engine
Post on 21-Feb-2017
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Internal Combustion EngineSupercharging
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The Process of Increasing the inlet air or charge density in order to increase the power output of the engine is called supercharging. The device used for increasing the pressure of air above atmospheric pressure is called supercharger.
The include charge by the supercharge during suction helps in better mixing of fuel and air during its compression stroke due to the turbulent effect created by the supercharger and the increased temperature helps in vaporization of fuel. The increase in temperature of charge, however, reduces the charge density and it is detrimental in case of S.I. engine since it develops the tendency to detonation
Fig. shown the difference between the theoretical (p v ) diagrams of an naturally aspirated (un supercharged) engines the difference between the two are: Increased pressure over the naturally aspirated engine cycle. Pumping loop of supercharged engine is positive, therefore, the work output equivalent to this area is be added instead of being subtracted.
To increase the power output of the engine by increasing the density of charge at intake. To reduce the weight to power ratio. It is very useful in case of aircraft, racing cars and marine applications. To overcome the loss of power at high altitude either in case of static engines or in case of aircraft applications. The loss of power of an engine is estimated to be 1% per 100 metre of altitude. To reduce the bulk of the engine where weight and space are important considerations like in case if locomotives and marine engines.
Centrifugal SuperchargerRootes SuperchargerVane Supercharger
Centrifugal supercharger :-A centrifugal supercharger is similar to a turbocharger but is mechanically driven by the engine instead of being powered by the hot exhaust gases. Roots-type supercharger :-The roots-type supercharger is called a positive displacement design because all of the air that enters is forced through the unit. A roots-type supercharger uses two lobes to force the air around the outside of the housing into the intake manifold.
Fig.: Roots Supercharging
Vane type Supercharger :- It consists of spring loaded vanes mounted eccentrically inside the casting.The vanes are usually made of non metallic fibers or carbon. The action of vane type blower is similar to root blowers.
Advantages :- Power required is less for given pressure ratio. Can handle small to large volumes of air. Initial cost and maintenance cost is low. Weight / of air handle is low.Disadvantages :- Space requirement is high.Increased temperature of fuel/air mixture increases risk of detonation.
Gear Driven Supercharger :- The arrangement of compressor (supercharger) driven by engine shaft through gearing to increase the speed of the compressor.In this method, the power required to drive the compressor is supplied from the engine output. Therefore, net power output of the supercharged engine is equal to the difference of power output of engine and power required to drive the compressor.
2. Turbocharger :- In this arrangement the exhaust energy if engine is utilized to run a gas turbine. The output of the gas turbine is used to drive the compressor directly coupled to it. Therefore, the gas turbine and compressor used are independent of the engine and the total engine output is enhanced.
3. Coupled Engine, Compressor and Turbine Supercharger :- In this method, the turbine is coupled to engine through step up gearing which drives the compressor mounted on the same shaft. The advantage of this system is that if the turbine output is not sufficient to run the compressor particularly at part load running of the engine, the extra power required to run the compressor is taken from the engine.
4. Gear Driven Supercharger and Free Turbine :- In this method, the compressor is driven through step up gearing by the engine and the engine exhaust gases drive the power turbine separately.Such plants are also called as free piston engine. The thermal efficiency of the plant depends on the boost pressure ratio. Due to this its thermal efficiency is reduced at part loads. Also, at low loads the engine exhaust has to be blown off to surroundings since the power turbine cannot run below certain compressor pressures.