ENGINE AND ITS COMPONENTS

ENGINE AND ITS COMPONENTS

Engine is heart of an automobile. Its role is very important. It converts the Chemical Energy (heat energy) to Mechanical Energy. This energy is utilized for vehicular movement. There are different ways of igniting fuel in an auto engine. Accordingly engines are called Internal Combustion (IC) OR external combustion Engines. Even within the IC engine category ignition can be by a spark or by high compression.

Automotive engines are called internal-combustion (IC) engines because the fuel that runs them engine burned internally, or inside the engines. There are two types engines – reciprocating engine and rotary engine. Reciprocating means moving up and down, or back and forth. Almost all automotive engines are of the reciprocating type. This type of engine is called a piston engine. have rotors that spin, or rotate. Wankel has invented the Rotary engine, hence it is named as Wankel engine and these are slowly coming up in use today. There are two kinds of piston engines (IC Engines).

 1. Spark-ignition (Petrol or gas) engine.

2. Compression ignition (diesel) engine.

 The differences between these two engines are: The type of fuel used. The way the fuel gets into the engine cylinders. The way the fuel is ignited. The spark-ignition engine uses a highly volatile fuel which turns to vapor easily, such as gasoline or gasohol. The fuel is mixed with air before it enters the engine cylinders. The fuel turns into a vapor and mixes with the air to form a combustible air-fuel mixture. This mixture is then enters the cylinders and is compressed. Next, an electric spark produced by the ignition system to ignite the combustible mixture, which is already being compressed into the combustion chamber of engine. In the compression-ignition engine or diesel engine, only fresh air enters the cylinder, which is then compressed to a very high temperature and pressure. The air is compressed so much that its temperature goes up to 10000F (5380C) or higher. Then the diesel is injected (sprayed) into the engine cylinder. This spray contains very very fine and tiny cloud of diesel known as atomized form in automobile jargon. The hot air, or heat of compression, ignites the fuel. This is why the diesel engine is called a compression ignition engine. Rotary engines The spark-ignition engine (petrol or gas engine).

The spark-ignition engine uses a highly volatile fuel which turns to vapor easily, such as gasoline or gasohol. The fuel is mixed with air before it enters the engine cylinders. The fuel turns into a vapor and mixes with the air to form a combustible air-fuel mixture. This mixture is then enters the cylinders and is compressed. Next, an electric spark produced by the ignition system to ignite the combustible mixture, which is already being compressed into the combustion chamber of engine. In the compression-ignition engine or diesel engine, only fresh air enters the cylinder, which is then compressed to a very high temperature and pressure. The air is compressed so much that its temperature goes up to 10000F (5380C) or higher. Then the diesel is injected (sprayed) into the engine cylinder. This spray contains very very fine and tiny cloud of diesel known as atomized form in automobile jargon. The hot air, or heat of compression, ignites the fuel. This is why the diesel engine is called a compression ignition engine.

Components of engine

1. Cylinder: The cylinder of an I.C. engine is considered as the main body of the engine in which piston reciprocates to develop power. It has to withstand very high pressures (about 70 bar) and temperatures (about 22000C) because there is direct combustion inside the cylinder. Therefore, its material should be such that it can retain strength at high temperatures, 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 or aluminum alloy are used.

   

2. Cylinder Head: The cylinder head closes one end of the cylinder. It houses the inlet and exhaust valves. The charge (fuel and air mixture for SI engine and only air for CI engine) enters through inlet valves and after producing power the exhaust gases escapes through the exhaust valves to the atmosphere. Cylinder head is usually cast as one piece and bolted to the top of the cylinder (engine block). A copper and asbestos gaskets are provided between the cylinder and cylinder-head to obtain a gas-tight joint. The material used for the cylinder-head is also cast iron or aluminum alloy.

   

3. Piston and Piston Rings: Piston is the heart of the engine. The functions of the 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 pistons of I.C. engines are usually made of cast iron, cast steel and aluminum alloy. The aluminum alloy has the advantage of higher thermal conductivity and lower specific gravity. The piston rings are housed in the circumferential grooves provided on the outer surface of the piston. It gives gas tight fitting between the piston and the cylinder and 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 rings.

   

4. Connecting Rod: It is usually a steel forging of circular, rectangular, I,T, or H section and is highly polished for increased strength. Its small end forms a hinge and pin joint with the piston and its big end is connected to the 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).

   

5. Crank and Crankshaft: Both crank and crankshaft are steel forged and machined to a smooth finish. The two 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 fluctuations of torque. The power required for any useful purpose is taken from crankshaft only. The crankshaft is the backbone of the engine.

   

6. Piston Pin or Wrist Pin: The piston pin provides the bearing for the oscillating small end of the connecting rod.

   

7. Inlet Valve: This valve controls the admission of the charge into the petrol engine or air into diesel engine during suction stroke of the engine.

8. Exhaust Valve: The removal of exhaust gases after doing work on the piston, is controlled by this valve.

9. Valve Spring:The valves are kept closed by the valve springs.

10. Inlet Manifold: It is the passage which carries the charge from carburetor to the petrol engine or only air to the diesel engine.

    

11. Exhaust Manifold: It is the passage which carries the exhaust gases from the exhaust valve to the atmosphere.

    

12. Camshaft: The function of the camshaft is to operate the intake and exhaust valves through the cams, cam followers, pushrods and rocker arms. The camshaft is driven positively from the crankshaft at half the speed of the crankshaft.

13. Cam and Cam Follower: It is made of a required profile to give desired motion to the valve through the follower.

14. Push Rod and Rocker Arm: The motion of the cam is transmitted to the valve through the push rod and rocker arm. These links together are also known as valve gear.

15. Crank Case: It is the base which holds the cylinder and crankshaft. It also serves as the sump for the lubricating oil.

16. Water Pump and Water Jacket: The function of water pump is to draw water from the radiator and supply it to water jacket at certain pressure for the purpose of proper circulation of coolant between engine water jacket and radiator. The jackets are provided in the crankcase (cylinder block) for the circulation of coolant to carry away the excessive heat of the engine.

17. Radiator: It has two tanks located at top and bottom. It is the storage of coolant for cooling the engine. It has a pressure cap to increase the boiling point of coolant.

    

18. Bed Plate: The lower portion of the crank case is known as bedplate. The bed plates are held by the bed bolts to concrete foundations.

19. Flywheel: It is a wheel mounted on the crankshaft which stores the energy during the power stroke and transmits the energy through transmission to the wheels when the clutch is engaged.

20. Governor: It is run by drive from the crankshaft. The function of the governor is to regulate the 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.  

21. Carburetor: The function of the carburetor is to supply the uniform air-fuel to the cylinder of a petrol engine through the intake manifold. The mass of the mixture entering the cylinder in controlled by a special valve called as throttle valve will be described in later sessions.

22. Spark Plug: The function of the spark plug is to ignite the mixture after completing the compression in the petrol engine. It is generally mounted in the cylinder head. This is only used in petrol engine.

    

23. Fuel Injection Pump: It forces the fuel oil at high pressure in automized condition through fuel nozzle into the cylinder at the end of compression stroke in diesel engine.

24. Fuel Injector: The function of fuel injector is to break up the oil into fine spray (atomized condition) as it enters the cylinder of diesel engine