Internal combustion engines
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Internal combustion engines

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Internal combustion engine

Internal combustion engine

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Internal combustion engines Internal combustion engines Document Transcript

  • EXPERIMENT NO: DATE: STUDY OF INTERNAL COMBUSTION ENGINES OBJECTIVES: At the end of this experiment students are able to know  About heat engine  Various components of IC engine & its functions  Basic nomenclature of IC engine  Application of IC engine. Theory: In general, an engine is defined as a device, which converts one form of energy into mechanical work. Heat engine is a device, which transforms heat energy into mechanical work. Transformation of one form of energy into another required form is always associated with losses. Therefore efficiency of conversion plays an important role. In every heat engine, some form of fuel (solid, liquid, gas or nuclear) is used. The chemical energy of fuel is converted into thermal or heat energy & that is further used to perform useful work. Heat engines are mainly classified as • External Combustion Engines. (E.C.engine) • Internal Combustion Engines. (I.C.engine) In E. C. engine as name suggest its combustion process takes place outside of the prime mover (power producing machine). In E.C. engine working fluid is not mixed with fuel, therefore, the same working fluid is used again & again. Steam engine / Steam turbine falls under this category. In I.C. engine, fuel is mixed with the air & burned, the combustion of fuel takes place inside the engine cylinder and power is produced. These types of engines are used in trucks & buses, scooters & cars, ships & locomotives, agricultural & earth moving machinery, many industrial applications & for power generation. Various components of I C Engine: Depending upon the design & application, one I.C.engine may be different from the other I.C.engine, as regards its size, shape & dimensions. But it becomes necessary to understand the purpose of various components for complete understanding of I.C.engine. So now we shall discuss the purpose of main components of I.C.engines (Refer figure 1). Frame: It generally consists of base plate, crankcase. This serves as a tool to mount engine and different systems of engine. It is skeleton of an automobile. It also supports different moving parts. The base plates are rigidly fixed to the foundation of the floor. The lower part of crankcase contains oil for lubrication purpose. Cylinder and Cylinder Block: Single cylinder engine has a single cylinder block. Multi cylinder engine has no. of cylinder blocks as per type of engine (i. e. four cylinder engine, six cylinder engine etc.) which contains cylinder bores and openings for the valves. To avoid wear and tear of cylinder block surface, cylinder liners are provided. It may contain passage for flow of cooling water in case of water cooling and fins on its outer surface to enhance cooling in case of air cooling. The cylinder of I.C.engine is considered as main body of the engine in which
  • piston reciprocates to develop power. It has to withstand very high pressure and temperature (about 2200 o C) because there is direct combustion inside the cylinder. Due to this its material should be such that it can retain strength at high temperature, should be good conductor of heat and should resist to rapid wear and tear due to reciprocating parts. Generally ordinary cast iron is used, but in case of heavy duty engines, alloy steels are used. Sometimes, when engine blocks are heavy & for easy maintenance sleeves or liners are inserted into cylinder, which can be replaced when worn out Liners, are generally made of nickel chrome iron. Cylinder head: The cylinder head closes one end of cylinder. It houses inlet and exhaust valves through which charge is taken inside the cylinder and burned gases are exhausted to atmosphere from the cylinder. Cylinder head is usually cast as one piece and bolted to the top of the cylinder. Copper and asbestos gaskets are provided between the cylinder & cylinder head to obtain a gas tight joint. The material used for cylinder head is also cast iron. Like cylinder block it also consists of water jackets and or fins for cooling purpose. Water jacket: The jackets are the integral opening/passage provided around the cylinder & other hot spots through which water is passed for cooling the engine. Piston & Piston Rings: The functions of piston are to compress the charge during compression stroke and to transmit the gas force to the connecting rod and then to the crank during power stroke. The piston of I.C.engines is made of cast iron, cast steel and aluminum alloy. The aluminum alloy has the advantage of higher thermal conductivity and lower specific gravity. Piston is the heart of the engine. The piston rings: These are housed in the circumferential grooves provided on the outer surface of the piston. It gives gas tight fitting between piston and cylinder prevents the leakage of high pressure gases. These are made of special grade cast iron. This material retains its elastic property at very high temperature. The upper piston rings are called the compression rings and the lower piston rings are called the oiling or oil control ring (oil scrapper rings). Piston pin or wrist pin: Piston pin connects the piston and small end of connecting rod. It provides the bearing for the oscillating small end of connecting rod. Connecting rod: It is usually a steel forging of circular, rectangular, I, T or H section (Generally I section) and is highly polished for increased endurance strength. Its small end forms a hinge and pin joint with piston and its big end is connected to crank by crank pin. It has a passage for the transfer of lubricating oil from the big end bearing to small end bearing (gudgeon pin). Crank & Crank shaft: Both crank and crankshafts are steel forged and machined to a smooth finish. These are held together by means of a key. Crankshaft is supported in main bearings and has a heavy wheel called flywheel, to even out the fluctuation of torque. The power required for any useful purpose is taken from crankshaft only. The crankshaft is the backbone of the engine. Camshaft: The function of the camshaft is to operate the intake and exhaust valves through the cams, cam followers, push rods and rocker arms. The camshaft is driven positively from the crankshaft at half speed of the crankshaft. Cam & Cam follower: It gives the desired motion to the valves through the follower.
  • Push rod and Rocker arm: The motion of cam is transmitted to the valve through push rod and rocker arm. These links together are also known as valve gear. Inlet valve: It controls the admission of charge into the petrol engine or air into diesel engine during suction stroke of the engine. Exhaust valve: It allows exhaust of cylinder gases after doing work on piston. Valve spring: Valves are kept closed by the valve spring (compression spring). Inlet manifold: It is the passage, which carries the charge from carburetor to the petrol engine. It connects all the inlet valves in case of multi-cylinder engine to the carburetor. Exhaust manifold: It is the passage, which carries the exhaust gases from the exhaust valve in case of single cylinder engine or exhaust valves in case of multicylinder engines, to the atmosphere. Crankcase: It is the base, which holds the cylinder and crankshaft. It also serves as sump for lubricating oil. Flywheel: It is a wheel mounted on the crankshaft, which stores excess energy during power stroke and returns that energy during other strokes and maintains a fairly constant output torque on the crankshaft. Governor: It is run by a drive from the crankshaft. The function of governor is to regulate charge in case of petrol engine and amount of fuel in case of diesel engine to maintain the speed of the engine constant, when the load requirement varies. Carburetor: The function of carburetor is to supply the uniform air fuel to the cylinder of a petrol engine through the intake manifold. A throttle valve controls the mass of mixture entering the cylinder. Spark plug: To ignite the compressed charge in petrol engine. Fuel pump: It forces fuel oil at high pressure through fuel nozzle into the cylinder at the end of compression stroke in diesel engine. Fuel nozzle: The function of fuel nozzle is to break up the oil into a fine spray as it enters the cylinder of diesel engine.
  • Figure 1 Outline of Petrol/Diesel Engine
  • Basic Engine Nomenclature: Figure 2 shows general nomenclatures of internal combustion engine. 1. Bore: Inside diameter of cylinder is known as bore. 2. Stroke: The maximum linear distance traveled by the piston in cylinder in one direction is known as stroke and it is equal to twice the crank radius. 3. Top dead centre (TDC): The extreme position of the piston at the top of the cylinder (head end side) is called Top dead center position. In case of horizontal engines this is known as Inner dead center (IDC) position. 4. Bottom dead centre: The extreme position of piston at the bottom of cylinder is called Bottom dead center (BDC) position. In case of horizontal engine this is known as (ODC) Outer dead centre position. The distance between these two extreme positions is known as stroke length. 5. Clearance Volume: The volume contained in cylinder above top of piston when the piston is at TDC is called the clearance volume. It is denoted by Vc. 6. Piston displacement or swept volume: The volume swept through by the piston in moving between TDC & BDC is defined as piston displacement or swept volume and it is denoted by Vs. Vs = ∏/4 ×D2 ×L Where, L =Length of stroke in m N =Speed of the engine in RPM. The cylinder volume = Swept volume (Vs) + Clearance volume (Vc). 7. Compression Ratio: The ratio of volume when the piston is at BDC to volume when piston is at TDC is called compression ratio & It is denoted by r = (Vs+Vc) / Vc. Or It is the ratio of volume, of working fluid, before compression to volume of working fluid after compression. For petrol engine the compression ratio varies from 5:1 to 9:1. For diesel engine the compression ratio varies from 12:1 to 22:1 8. Piston speed: The distance travelled by the piston in one minute is known as piston speed. Piston speed = 2LN m/min Where, L =Length of stroke in m N =Speed of the engine in rpm.
  • Figure 2 Basic nomenclature of I. C. Engine
  • Details of Application of I.C. Engine: Application Power (kW) SI or CI 2-S or 4-S Cooling method 1 Road Vehicles 1.Mopeds 2.Scooters and Motor cycles 3.Small car 4.Large car 5.Lawn movers 0.75-1.5 3-7 15-75 75-200 0.75-3 SI SI SI SI SI 2 2,4 4 4 2,4 A A W W A 2 Locomotives 400-4000 CI 2,4 W 3 Small Air crafts 1.Helicopters 2.Airplanes 40-1500 40-3000 SI SI 4 4 A A 4 Marine Applications 1.Motor boats 2.Ships 0.5-75 3000-20000 SI, CI CI 4 2,4 W W 5 Industrial Applications 1.Electric power 2.Gas Pipe lines 40-25,000 700-5000 CI SI 2,4 2,4 W W 6 Off-Road Vehicles 1.Light vehicles 2.Agriculture 3.Earthmoving machinery 4.Military purpose 1.5-15 3-150 40-800 40-2000 SI SI,CI CI CI 2,4 2,4 2,4 2,4 A A,W W A,W S. I. = Spark ignition engine C. I. = Compression ignition engine 2-S = Two stroke 4-S = Four stroke A= Air cooled W = Water cooled A Assignment: 1. Define heat engine? How energy is liberated? 2. Why compression ratio of Diesel Engine is more than compression ratio of Petrol engine? 3. Piston is having how many piston rings? Name it and write its function? 4. Why governor is not kept in road vehicles? 5. “If size of crank radius is increased to twice then original value piston speed also increases to twice then its original value”. State this statement is true or false? Justify your answer? 6. We studied various components of I. C. engine, mention which components are not there in Petrol engine? Assessment: Involvement & Participation (03) Quiz/Viva (03) Discipline (02) Total (08) Date: Signature of faculty: