UNIT III MACHINERY

1. UNIT IIIMACHINERY MAIN ENGINE

4. Steam engines were used almost until 1900s. • Later the steam turbine and the internal combustion engine replaced steam engines.

5. Gas turbines have been used in merchant ships and navy. • Some submarines, merchant ships, and icebreakers have nuclear power plants.

6. STEAM ENGINE The steam engines convert heat energy into mechanical energy by using steam.

8. Steam engines operate by having superheated steam force a piston to reciprocate in a cylinder.

9. The piston is attached by a crosshead to a crankshaft that converts the reciprocating (back-and-forth) motion of the piston to rotary motion for propulsion.

10. In a steam engine, hot steam supplied by a boiler expands under pressure, and the heat energy is converted into work.

11. STEAM TURBINE • In the steam turbine, high pressure steam is discharged at high velocity through nozzles and then flows through a series of stationary and moving blades, causing a rotor to move at high speeds.

12. Steam turbines are more compact and usually permit higher temperatures and greater expansion ratios than steam engines.

13. The turbine is used to generate large quantities of electric power with steam.

14. Nowadays the steam turbine is used as cargo pump driving source in tankers.

15. INTERNAL COMBUSTION ENGINE • An internal combustion engine operates by burning its fuel inside the engine. • It converts chemical energy of the burning fuel into mechanical energy.

16. The common internal combustion engines are; • gas turbine • diesel engine

17. The compression ignited internal combustion engine has two main designs: • two stroke cycle • four stroke cycle

18. The two stroke and four stroke terms refer to the mechanical action of the piston within the cylinder.

19. TWO STROKE CYCLE

20. FOUR STROKE CYCLE

21. DIESEL ENGINE • Diesel engine uses the heat produced by compression to ignite the mixture of air and diesel fuel.

22. Diesel engine appears in three types, • low-speed engine, • medium-speed engine • high-speed engine

23. The low-speed engine is characterized by rated speeds in the range of 0-400 rpm. • It is a two-stroke engine supercharged by exhaust-gas turbochargers

24. The medium-speed engine runs in the range of 400–1000 rpm. It is a four-stroke engine supercharged by exhaust-driven turbochargers.

25. High-speed engine runs in the range of 1000-2000 rpm.

26. Diesel engines are also of two types according to their pistons; • trunk piston • barrel piston

27. Trunk piston

28. Barrel piston

29. Diesel engines are heavier than gasoline engines because of the extra strength required to contain the higher temperatures and compression ratios.

30. The diesel engine differs from the gasoline engine in that the ignition of fuel is caused by compression of air in its cylinders instead of by a spark.

31. The speed and power of the diesel are controlled by varying the amount of fuel injected into the cylinder, not the amount of air admitted as in the gasoline engine.

32. GAS TURBINE Gas turbine engines are extremely simple and has three main parts; • a compressor to compress the incoming air to high pressure, • a combustion chamber to burn the fuel and produce high pressure and • a turbine to extract the energy from the high pressure, high velocity gas flowing from the combustion chamber

34. The gas turbine is used as main propulsion engine at naval ships and supertankers because of the high power but • it has low manoeuvring capability. Therefore, it is combined with a diesel engine for high capability of manoeuvring.

35. ANSWER THE QUESTIONS 1-What are the main types of engine?

36. 2-How does an internal combustion engine work?

37. 3-What do the two stroke and four stroke terms refer to?

38. 4-Can you compare diesel engine with gas turbine?

39. Etymology • Diesel<Rudolf Diesel, who is a German inventor, invented the diesel engine • Energy< Latin, energia <Greek, energeia, active, at work < en, in +ergon, work • Machine<Latin, machine <Greek, mechane, engine <Indo-European, magh, to be able to, may, might

40. SOME WORDS Combustion (n)-Burning Expand (v) -To become larger in size, volume or quantity Ignite (v) -Start to burn or burst into flames

41. Reciprocate (v) -To move back and forth Rotary (n) -Occurring around an axis Rotate (v) -Turn around an axis Velocity (n) -Speed

42. Complete the diagram showing diesel engine types.

43. B- Complete the definitions using the words below. Internal combustion engine / boiler / compressor / crankshaft / diesel engine 1- A…………….is a device that supplies hot steam for steam engine. 2- A…………… is a device that converts the back-and-forth motion of the piston to rotary motion for propulsion 3- ………………is an engine type that converts chemical energy of the burning fuel into mechanical energy. 4- A ……………is an engine that uses the heat produced by compression. 5-A………….…is a device that compresses the incoming air to high pressure

44. 1-What statement is not true regarding the steam engines? a. Steam engines uses steam. b. Steam engines convert heat energy into work. c. Piston rotates in a cylinder to reciprocate the crankshaft d. Boilers supply hot steam. e. Steam engines are not common.

45. 1-What statement is not true regarding the steam engines? c. Piston rotates in a cylinder to reciprocate the crankshaft

46. 1-Which one is used for propulsion on ships? a. steam engine b. steam turbine c.gas turbine d.diesel engine e.all

47. 1-Which one is used for propulsion on ships? e.all

48. 3-‘combustion, compression, stroke’. The terms are related to a. steam turbine b. turbine c. boiler d. internal combustion engine e. reciprocating steam engine

49. 3-‘combustion, compression, stroke’. The terms are related to d. internal combustion engine

50. 4-What does the term ‘stroke’ refer to? a. combustion b. piston motion in the cylinder c. ignition d. compression e. rotary motion