I C ENGINES

1. I C ENGINES P R Venkatesh, Mech Dept, RVCE, B'lore

2. INTERNAL COMBUSTION ENGINES • Any type of engine which derives heat energy from the combustion of fuel and converts it into mechanical work is termed as a heat engine. Heat engines may be classified into two main types; • External Combustion engines (E.C engines) • Internal combustion engines (I.C engines) In an external combustion engine, the combustion of fuel takes place outside the engine cylinder. Ex: Steam engines P R Venkatesh, Mech Dept, RVCE, B'lore

3. In an internal combustion engine, the combustion of fuel takes place inside the engine cylinder. Ex: Petrol engines, Diesel engines. Advantages of I.C engines over E.C Engines • High efficiency • Simplicity • Compactness • Light weight • Easy starting • Comparatively low cost P R Venkatesh, Mech Dept, RVCE, B'lore

4. Classification of IC Engines: I.C. Engines are classified according to: 1. Nature of thermodynamic cycle • Otto cycle engine. • Diesel engine. • Dual combustion cycle engine. 2. Type of the Fuel used • Petrol engine. • Diesel engine. • Gas engine. • Bi-fuel engine. 3. Number of strokes • Two stroke engine. • Four stroke engine. P R Venkatesh, Mech Dept, RVCE, B'lore

5. Classification of IC Engines (continued): 4. Number of Ignition • Spark ignition engine, known as S.I. Engine. • Compression ignition engine, known as C.I engine. 5. Number of Cylinder as • Single cylinder engine. • Multicylinder engine. 6. Position of the Cylinder • Horizontal engine. • Vertical engine. • Radial engines • In-line engines 7. Method of Cooling • Air cooled engine. • Water cooled engine. P R Venkatesh, Mech Dept, RVCE, B'lore

6. PARTS OF I C ENGINE P R Venkatesh, Mech Dept, RVCE, B'lore

7. 1.Cylinder: • It is made of grey cast iron. • Fuel is burnt inside the cylinder and power is developed by action of hot gases on the piston. • To avoid wear & tear, cylinder liners are provided. CYLINDER WITH FINS P R Venkatesh, Mech Dept, RVCE, B'lore

8. 2.Cylinder head: • One end of the cylinder is closed by means of a removable cylinder head which is made of cast iron with alloying elements such as nickel, chromium, molybdenum, etc. • Cylinder head houses the inlet & exhaust valves. P R Venkatesh, Mech Dept, RVCE, B'lore

9. 3.Piston: • It is a close fitting hollow cylindrical plunger moving to & fro inside the cylinder. • It is made of aluminium alloys for light weight. • The power developed by the combustion of fuel is transmitted by the piston to the crank shaft through the connecting rod. P R Venkatesh, Mech Dept, RVCE, B'lore

10. 4. Piston rings: • These are metallic rings made of cast iron. They are inserted into the circumferential grooves provided at the top end of the piston. • Piston rings maintain a gas-tight seal between the cylinder & the piston. They also help in conducting the heat from piston to cylinder. PISTON , PISTON RINGS, GUDGEON PIN & CIRCLIP P R Venkatesh, Mech Dept, RVCE, B'lore

11. 5. Connecting rod: • It is the link that connects the piston and the crankshaft by means of pin joints. • It converts the linear motion of the piston into rotary motion of the crankshaft. • Connecting rods are made of alloy steels. CONNECTING ROD P R Venkatesh, Mech Dept, RVCE, B'lore

12. CRANK & CRANK SHAFT 6. Crank & Crankshaft: • Crank is a lever (made of carbon steel) that is connected to the end of the connecting rod by a pin joint. • The other end of the crank is rigidly connected to a shaft known as ‘crankshaft’. • As the connecting rod oscillates, the crank and hence the crankshaft rotate about an axis. P R Venkatesh, Mech Dept, RVCE, B'lore

13. VALVES 7. Valves: • Valves are devices which control the flow of intake and exhaust gases to & from the cylinder. • They are also called as ‘Poppet Valves’ and are operated by means of cams driven by the crank shaft through belts or gears. P R Venkatesh, Mech Dept, RVCE, B'lore

14. 8. Flywheel: • It is a heavy wheel mounted on the crankshaft of the engine to maintain uniform rotation of the crankshaft. • It absorbs kinetic energy during power stroke & delivers energy during other strokes. • Flywheel is made of cast iron. RIM TYPE FLYWHEEL DISKTYPE FLYWHEEL P R Venkatesh, Mech Dept, RVCE, B'lore

15. 9. Crank case: • It is the lower part of the engine serving as an enclosure for the crankshaft. • It also serves as a sump (reservoir) for lubricating oil. P R Venkatesh, Mech Dept, RVCE, B'lore

16. I.C Engine Terminology P R Venkatesh, Mech Dept, RVCE, B'lore

17. Bore:It is the inner diameter of the engine cylinder. Stroke: It is the distance travelled by the piston when it moves from one end of the cylinder to the other end. Stroke is twice the radius of crank. Top dead center (TDC): • In a vertical engine, it is the topmost position of the piston towards the cover side of the cylinder. • In a horizontal engine, it is called the inner dead center. (IDC) P R Venkatesh, Mech Dept, RVCE, B'lore

18. Bottom dead center (BDC): In a vertical engine, it is the lowest position of the piston towards the crank end side of the cylinder. In a horizontal engine, it is called the outer dead center. (ODC) Clearance Volume: It is the volume contained in the cylinder above the piston in the top dead center position. Compression ratio:It is the ratio of total volume of the cylinder to the clearance volume. P R Venkatesh, Mech Dept, RVCE, B'lore

19. FOUR STROKE CYCLE PETROL ENGINE P R Venkatesh, Mech Dept, RVCE, B'lore

20. Petrol engines work on the principle of theoretical Otto cycle. • It is also known as constant volume cycle, shown in fig. • The piston performs four strokes (one each in half revolution of crankshaft) to complete the working cycle. (in 2 revolutions of crank shaft) • The four strokes are • Suction • Compression • Working (or) Power stroke • Exhaust stroke FOUR STROKE CYCLE PETROL ENGINE P-V diagram of theoretical Otto cycle P R Venkatesh, Mech Dept, RVCE, B'lore

21. During suction stroke, the inlet valve is open and exhaust valve is closed. • The piston moves from cover end to crank end during half revolution of crankshaft. • The air-petrol mixture is drawn into the cylinder and completely fills the cylinder. • Suction takes place at atmospheric pressure and is indicated by horizontal line AB in the p-v diagram. • The process is initiated by ‘cranking’ using external energy source. SUCTION STROKE SUCTION STROKE P R Venkatesh, Mech Dept, RVCE, B'lore

22. During this stroke, both inlet & exhaust valves are closed. The piston moves from crank end to cover end during half revolution of crankshaft. • The air fuel mixture in the cylinder will be compressed adiabatically as shown by curve BC in the p-v diagram. • At the end of compression stroke, the air-petrol mixture is ignited by an electric spark given out by the spark plug. • The combustion of the mixture causes increase in pressure as shown by line CD in P-V diagram. COMPRESSION STROKE COMPRESSION STROKE P R Venkatesh, Mech Dept, RVCE, B'lore

23. During this stroke, both inlet & exhaust valves are closed. • The expansion of gases due to heat of combustion exerts a pressure on the piston forcing it to move towards the crank end. • The expansion of gases is indicated by adiabatic process DE in the P-V diagram. • At the end of this stroke, the exhaust valve will open release the burnt gases to the atmosphere thus bringing down the pressure as indicated by vertical line EB in the P-V diagram. POWER STROKE POWER STROKE P R Venkatesh, Mech Dept, RVCE, B'lore

24. EXHAUST STROKE • During this stroke, the inlet valve remains closed & the exhaust valve remains open. • The piston moves from crank end to cover end forcing exhaust gases out of the cylinder. • The process is indicated by the horizontal line BA in the P-V diagram, thus completing the cycle. • Thus the cycle is completed in four strokes of the piston or two revolutions of the crankshaft. • Thereafter, the entire process repeats itself. P R Venkatesh, Mech Dept, RVCE, B'lore

25. FOUR STROKE ENGINE ANIMATION P R Venkatesh, Mech Dept, RVCE, B'lore

26. FOUR STROKE CYCLE DIESEL ENGINE P R Venkatesh, Mech Dept, RVCE, B'lore

27. Diesel engines work on the principle of theoretical Diesel cycle. • It is also known as constant pressure heat addition cycle, shown in fig. • In diesel engines the spark plug is replaced by a fuel injector & the fuel ignites due to high pressure & temperature of the compressed air. • Hence the name CI engines. (Compression Ignition engines) FOUR STROKE CYCLE DIESEL ENGINE P-V diagram of theoretical Diesel cycle P R Venkatesh, Mech Dept, RVCE, B'lore

28. During suction stroke, the inlet valve is open and exhaust valve is closed. • The piston moves from cover end to crank end during half revolution of crankshaft, and draws only air into the cylinder. • The energy required for this stroke is obtained by ‘cranking’ only at the time of starting & by the flywheel while running. • Suction takes place at atmospheric pressure and is indicated by horizontal line AB in the p-v diagram. SUCTION STROKE P R Venkatesh, Mech Dept, RVCE, B'lore

29. During this stroke, both inlet & exhaust valves are closed. The piston moves from crank end to cover end during half revolution of crankshaft. • The air in the cylinder will be compressed adiabatically as shown by curve BC in the p-v diagram. • At the end of compression stroke, diesel is injected into the hot compressed air as a fine spray by the fuel injector. • The fuel will be burnt at constant pressure as shown by line CD. COMPRESSION STROKE P R Venkatesh, Mech Dept, RVCE, B'lore

30. During this stroke, both inlet & exhaust valves are closed. • The expansion of gases due to heat of combustion exerts a pressure on the piston forcing it to move towards the crank end. • The expansion of gases is indicated by adiabatic process DE in the P-V diagram. • At the end of this stroke, the exhaust valve will open release the burnt gases to the atmosphere thus bringing down the pressure as indicated by vertical line EB in the P-V diagram. POWER STROKE P R Venkatesh, Mech Dept, RVCE, B'lore

31. EXHAUST STROKE • During this stroke, the inlet valve remains closed & the exhaust valve remains open. • The piston moves from crank end to cover end forcing exhaust gases out of the cylinder. • The process is indicated by the horizontal line BA in the P-V diagram, thus completing the cycle. • Thus the cycle is completed in four strokes of the piston or two revolutions of the crankshaft. • Thereafter, the entire process repeats itself. P R Venkatesh, Mech Dept, RVCE, B'lore

32. As the name itself implies, two stroke engine performs only two strokes of the piston or one revolution of the crankshaft to complete one cycle. • The suction & exhaust strokes take place while the suction & compression strokes are in progress. • The theoretical Otto cycle & Diesel cycles are followed respectively for two stroke petrol & two stroke diesel engines. TWO STROKE CYCLE ENGINE P R Venkatesh, Mech Dept, RVCE, B'lore

33. TWO STROKE CYCLE PETROL ENGINE P R Venkatesh, Mech Dept, RVCE, B'lore

34. UPWARD STROKE fig (a) fig (b) • During the upward stroke, the piston moves from bottom dead center to top dead center, compressing the air-fuel mixture in the cylinder. • The cylinder is connected to a closed crank chamber. • Due to upward motion of the piston, a partial vacuum is created in the crankcase, and fresh charge is drawn into the crank case through the uncovered inlet port. • The compressed charge is ignited in the combustion chamber by a spark plug. P R Venkatesh, Mech Dept, RVCE, B'lore

35. DOWNWARD STROKE fig (d) fig (c) • As soon as the charge is ignited, the hot gases force the piston to move downwards, rotating the crankshaft, thus doing useful work. • Further downward movement will uncover the exhaust port & transfer port. • The burnt gases escape through the exhaust port. The fresh charge entering through the transfer port will be deflected by the hump provided on the piston . • It helps in removing the burnt gases completely from the cylinder and this process is known as ‘Scavenging’. The cycle repeats itself thereafter. P R Venkatesh, Mech Dept, RVCE, B'lore

36. In a two stroke diesel engine, only air is compressed in the cylinder and diesel is injected by the fuel injector. • There is no spark plug in the engine. • The remaining operations of the engine are same as that of a petrol engine. TWO STROKE CYCLE DIESEL ENGINE UPWARD STROKE P R Venkatesh, Mech Dept, RVCE, B'lore

37. DOWNWARD STROKE P R Venkatesh, Mech Dept, RVCE, B'lore

38. TWO STROKE ENGINE ANIMATION P R Venkatesh, Mech Dept, RVCE, B'lore

39. Comparison between Petrol Engine & and Diesel Engine P R Venkatesh, Mech Dept, RVCE, B'lore

40. Comparison between 4-stroke & 2-stroke Engines P R Venkatesh, Mech Dept, RVCE, B'lore

41. I C Engine Calculations P R Venkatesh, Mech Dept, RVCE, B'lore

42. Indicated power (IP) : It is the power produced inside the cylinder and calculated by finding the actual mean effective pressure. P R Venkatesh, Mech Dept, RVCE, B'lore

43. Brake power (BP) : It is the net power available calculated at the crank shaft is called Brake Power. P R Venkatesh, Mech Dept, RVCE, B'lore

44. P R Venkatesh, Mech Dept, RVCE, B'lore

45. P R Venkatesh, Mech Dept, RVCE, B'lore

46. BRAKE DYNAMOMETER P R Venkatesh, Mech Dept, RVCE, B'lore

47. PROBLEM 1 A single cylinder two stroke cycle I.C. Engine has a piston diameter 105 mm and stroke length 120 mm. The mean effective pressure is 6 bar. If the crank shaft speed is 1500 rpm. Calculate the indicated power of the engine. P R Venkatesh, Mech Dept, RVCE, B'lore

48. P R Venkatesh, Mech Dept, RVCE, B'lore

49. PROBLEM 2 On a single cylinder four stroke petrol engine, the following readings were taken: Load on the brake drum = 40 kg. Spring balance reading = 5 kg. Diameter of the brake drum = 120 cm. Fuel consumption = 3 kg/hour. Calorific value of the fuel = 42000 kJ/kg. Engine Speed = 500 rpm. Find the brake thermal efficiency. P R Venkatesh, Mech Dept, RVCE, B'lore

50. P R Venkatesh, Mech Dept, RVCE, B'lore