supercharging ICE Course.pptxrtgdrttttyt5y

Ygsbhdybdnd

1. Course: Internal Combustion Engines Class:- Third Year, Semester VI ( B.Tech ) Mechanical Engineering

2. Unit IV Supercharging Contents Introduction to Supercharger Objectives & principles of supercharging Working diagram of supercharger Classification of supercharger Drives used in Supercharger Advantages & limitations

3. Introduction The Power Output Of Naturally Aspirated Engine Depends On Amount of air inducted into the cylinder Extent utilization of the inducted air The speed of the engine Quantity of fuel admitted and its combustion characteristics

4. About Supercharger A supercharger is an equipment that compresses the air being delivered to an engine, allowing the combustion chamber to be overfilled without enlarging the space. The method of supplying air higher than the pressure at which the engine naturally aspirates, by means of a boosting device is called the supercharging The higher concentration of oxygen provided by a super- charger is used to enhance the power output of an IC engine.

5. Concept of Supercharging The most preferred method for increasing the power output is by means of increasing mean effective pressure that is to supply air/fuel mixture at pressure higher than atm.

6. Objectives & principles of supercharging To increase the charge density of working medium To increase the power output of an existing engine to meet the greater power demand. To reduce the weight of an engine per kW power developed. To overcome the loss of power at high altitude either in case of static engines or in case of aircraft applications.

7. Why Supercharger? Increases the power of an engine. Increases the torque produced. An efficiently working supercharger can achieve the same speed in one third time. Necessary in aero-planes as they have less oxygen at high altitudes. Ensures complete combustion of the fuel. Reduces pollution to some extent

8. Principle of working Superchargers provides more air by compressing air above atmospheric pressure , hence providing more fuel into the charge & would make for a Greater horsepower. Hence it Increased Power , Torque and Speed is achieved.

9. Classification of Superchargers Supercharger is a pressure boosting devise which supplies air at a higher pressure. • There are three types of supercharger Centrifugal type Root’s type Vane type

10. Centrifugal type A centrifugal supercharger works by powering an impeller (a device similar to a rotor) at very high speeds to quickly draw air into a small compressor housing. Impeller speeds can reach ‘50,000 to 60,000 RPM’. Centrifugal superchargers are the most efficient and the most common induction systems. They are small, lightweight and attachable to the front of the Engine.

11. Working As the air is drawn in the hub of the impeller, centrifugal force causes it to radiate outward. The air leaves the impeller at high speed, but low pressure. A diffuser converts the high-speed , low-pressure air to low-speed , high-pressure air. Thus pressurized air is achieved

12. Root type

13. Working As the meshing lobes spin, air trapped in the pockets between the lobes is carried between the fill side and the discharge side & Large quantities of air move into the intake manifold and "stack up" to create positive pressure. Roots superchargers are usually large and sit on top of the engine.

14. Roots superchargers are the least efficient supercharger for two reasons:- They add more weight to the vehicle. They provide air in discrete bursts instead of providing in a smooth and continuous manner

15. Vane type 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.

16. Methods of Supercharging Independently driven compressor or blower usually driven by an electric motor. Under piston supercharging. Engine driven compressor or blower

17. 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 .

18. 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.

19. 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.

20. Turbocharger A turbocharger is a small radial fan pump driven by the energy of the exhaust gases of an engine. A turbocharger consists of a turbine and a compressor on a shared shaft. The turbine converts exhaust to rotational force, which is in turn used to drive the compressor. The compressor draws in ambient air and pumps it in to the intake manifold at increased pressure, resulting in a greater mass of air entering the cylinders on each intake stroke.

21. Therefore, the gas turbine and compressor used are independent of the engine and the total engine output is enhanced. Components of turbocharger Air compressor Turbine Intercooler

22. Supercharging Limit The degree of supercharging in SI engines is chiefly limited by the knock. This increase in pressure and usually in temperature also, because of supercharging reduces ignition delay and consequently the engine has a knocking tendency at these pressure. The knock limit is dependent upon the type of fuel used, mixture ratio, spark advance and the design features of the engine, of which the valve the valve timing and cooling system are important.

23. Supercharging limit in CI engine Unlike SI engines, the limits of supercharging for compression-ignition engines are not due to combustion. The factor which limit the output of a SI engine due to knock, result in quieter and smoother operation of a CI engine. An increase in pressure and temperature decreases the ignition delay and engine runs smoother. The limit of supercharging for CI engine is reached by thermal loading. The temperature of the piston and cylinder if very high results in scuffing of piston rings and heavy linear wear.

24. Effect of Supercharging Pressure on Compression and Firing Pressure

25. Advantages & Disadvantages 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 / m 3 of air handle is low. Disadvantages Space requirement is high. Increased temperature of fuel/air mixture increases risk of detonation.