1. LESSON 9 TEXT STARTING SYSTEM 第 9 课 起动系统

2. Diesel engines are started by supplying compressed air into the cylinders in the appropriate sequence for the required direction. Diesel engines are started by supplying compressed air into the cylinders in the appropriate sequence for the required direction.

3. A supply of compressed air is stored in air reservoirs or bottles or receivers at pressures about 30 or 40 bar ready for immediate use.

4. Some times compressed air pressure is dropped to a lower value by means of a reducing valve( 减压阀 ) for other uses. The receivers are charged by compressors.

5. The design of starting air systems, including the number and capacity of compressors and receivers, the provision （规定） of features and drainage facilities are the subject of stringent( 严格 ) requirements by Classification Societies( 船级社 ).

6. Up to 12 starts are possible with the stored quantity of compressed air. The starting air system usually has interlocks to prevent starting if any thing is not in order.

7. The compressed air is supplied by a large bore pipe to a remote operating non-return or automatic valve and then to the cylinder air start valves( 气缸起 动阀 ).

8. The opening of each cylinder air start valves will admit compressed air into the corresponding cylinder.

9. The automatic valve and the cylinder start valves are controlled by a pilot air system.

10. Each cylinder start valve will be opened immediately after the top dead centre(TDC) position has been passed and closed just before the exhaust ports are due to open according to the direction of rotation required.

11. Thus, when compressed air from the main supply is supplied to the starting system of an engine at rest it enters those cylinders in which the pistons are in a position corresponding to some part of the power stroke, the resulting pressure on the pistons causes the engine to rotate.

12. When a sufficiently high speed, say about 20 r/min, has been achieved the air supply is cut off and fuel is injected causing the cylinders to fire and continue to run in the normal way.

13. Cylinder air start valve start valve Air distributor Master valve ( automatic valve) Air bottle Air start lever a pilot air control valve

14. The pilot air is drawn from the large pipe and passes to a pilot air control valve which is operated by the engine air start lever.

15. When the air start lever is operated, supply of pilot air enables the pilot air control valve to open either manually or with a pneumatic cylinder when a bridge control system is fitted.

16. Pilot air for the appropriate direction of operation is also supplied to an air distributor( 空气分配器 ).

17. This device is usually driven by the engine camshaft and supplies pilot air to the control cylinders of the cylinder air start valves.

18. The pilot air is then supplied in appropriate sequence for the direction of operation required.

19. The cylinder air start valves are held closed by springs when not in use and opened by the pilot air enabling the compressed air direct from the receivers to enter the engine cylinder.

20. As soon as the engine fires the air starting lever is brought back. The pilot air control valve returns to the off position, venting the pilot air lines and the remote air starting valve and allowing it to close.

21. A number of interlocks are provided in connection with the air starting system to safeguard the engine and personnel. These are:

22. 1. The turning gear( 盘车机 ) interlock valve which is arranged to shut off the starting air pilot line when the turning gear is engaged( 啮合 ), thus preventing the engine being started.

23. 2. To prevent operation of the starting air system whilst the engine is running a pilot air interlock valve is operated by the main control lever.

24. The valve remains open during the starting sequence, i.e. until the main control lever is removed just beyond the starting position, but remains closed after this point and does not open again until the main lever is moved back to the stop position.

25. 3. A mechanical interlock is provided in the control box to prevent the main control lever being moved beyond the starting position while the starting air lever is either the ahead or astern starting position.

26. 4. Another mechanical interlock is provided to prevent the main control lever being moved until starting air is admitted to the cylinders. This prevents fuel being admitted to the cylinders when the engine is at rest.

27. Lubricating oil from the compressor will pass along the air lines and deposit on them. In the event of a cylinder air starting valve leaking, hot gases would pass into the air pipes and ignite the lubricating oil.

28. If starting air is supplied to the engine this would further feed the fire and could lead to an explosion in the pipelines.

29. In order to prevent such an occurrence, cylinder starting valves should be properly maintained and the pipelines regularly drained. Also oil discharged from compressors should be kept to a minimum, by careful maintenance.

30. reduce the effects of an explosion, flame traps( 阻焰器 ), relief valves( 安 全阀 ) and bursting caps or discs ( 防爆帽 ) are fitted in the pipelines. In an attempt to reduce the effects of an explosion, flame traps( 阻焰器 ), relief valves( 安 全阀 ) and bursting caps or discs ( 防爆帽 ) are fitted in the pipelines.

31. In addition an isolating non- return valve (the automatic valve) is fitted to the system, which prevents further compressed air by the engine into system.

32. The loss of cooling water from an air compressor could lead to an overheated air discharge and possibly an explosion in the pipelines leading to the air reservoir.

33. A high temperature alarm or a fusible plug( 易溶塞 ), which will melt( 融化, 熔化 ), is used to guard against this possibility.

34. Reading material A. STARTING

35. As previously explained, the ignition of the fuel in diesel engine is caused by the heat of compression of the air previously admitted into the cylinder.

36. Thus, for the engine to begin firing, air must first be drawn or pumped into the cylinder and this air must be compressed by the upward movement of the piston to obtain the high temperature necessary to burn the fuel when it is injected.

37. Hence the engine must be driven for a few revolutions by some outside source before allowing the fuel into the cylinders.

38. In heavy marine engine the practice is to drive the engine on compressed air which has previously been stored (at pressure ranging from 20 to 40 bar depending upon the type of engine) in starting-air reservoirs.

39. The compressed air is admitted to each cylinder through a cam operated starting-air valve when the piston has just passed its top center and commence its power stroke and remaining open until the piston has traveled part of that stroke.

40. The period of opening depends upon(on) the number of cylinders and whether it is four-stroke or two-stroke engine.

41. When the starting-air valve closes on one cylinder, another starting-air valve already opened on another cylinder whose piston has just commenced its downward stroke.

42. Thus no matter in what position the engine stops there will always be at least one of the cylinders with its starting- air valve open to admit compressed air to start the engine.

43. When the engine obtains sufficient speed, the fuel pumps and valves are brought into operation and the starting air valves put out of commission.

44. B. Engine reversing Where running at maneuvering speed 1. Where manually operated auxiliary blowers are fitted they should be started.

45. 2. The fuel supply is shut off and the engine will quickly slow down. 3. The direction handle is positioned astern. 4. Compressed air is admitted to the engine to turn it in the astern direction.

46. 5. When turning astern under the action of compressed air, fuel will be admitted. The combustion process will take over and air admission cease.

47. When running at full speed 1. The auxiliary blowers, where manually operated, should be started. 2. Fuel is shut off from the engine.

48. 3. Blasts of compressed air may be used to slow the engine down. 4. When the engine is stopped the direction handle is positioned astern.

49. 5. Compressed air is admitted to turn the engine astern and fuel is admitted to accelerate the engine. The compressed air supply will then cease.

50. Speed regulation In order to control the engine speed, it is now common practice to fit a speed regulator or governor to make balance between the fuel injected into the engine and the engine load.

51. The governor maintains the engine speed at the desired value by continually positioning the metering device in the fuel system to control the amount of fuel being injected into each cylinder per cycle.

52. Most governors are hydraulic actuating types and self- contained( 独立的 ) units. The mechanism can be divided into two parts, a speed sensing portion and an actuating portion.

54. A common form of sensing devices is the ball head. It consists of a revolving carrier( 旋转支架 )on which are mounted two weights having cranked levers.

55. They are pivoted( 装在枢轴上 ) so that the levers compress a spring as the weights fly out under centrifugal force.

56. The force exerted by the spring is controlled by the pressure of an adjustment on its other end which is decided by the main control lever mechanism of the engine.

57. This adjustment is the speed control for the engine. Wherever this is set the weights will assume a corresponding position according to the speed at which they are rotated.

58. This position is signaled to the actuating portion of the governor by the position of the control spindle.

59. The control spindle is connected to a pilot valve which admits oil as required to the actuating piston and cylinder.

60. The position taken up by this actuating piston is ‘fed back( 反 馈 )’to pilot valve so that the oil is controlled to give the actuator the desired final position.

61. The actuator spindle is connected to a lever output from the governor. This lever is connected to the linkage which controls the fuel quantity.

62. For any speed setting of the governor there will be a range of fuel output according to whether the load torque( 扭矩 ) is high or low.

63. It will vary from full at one end of the travel of the actuator piston to no fuel at the other.

64. These two positions correspond to two slightly different values of the speed. The difference between these values is known as the governor drop. It is usually expressed as a percentage of the set speed.

65. Electronic governors are coming into use on modern engines. They give quicker response and a more powerful output.

66. The speed-sensing device is a small electric generator( 发生器 ) or small machine which produce a signal, usually in the form of a pulsed current or voltage having a frequency proportional to engine speed.

67. This is compared with a desired speed setting and any difference produces an output signal. The output signal energizes( 激活， 使 … 活跃 ) the actuating equipment which operates the fuel control mechanism.

68. With all governors it is usual practice to provide a manual over-ride( 优势，优先权 ) by which the linkage can be returned to the no fuel position in an emergency or should the governor fail in any way.

69. The engine is stopped for normal maneuvering purposes by bringing the main control lever to the no fuel position.

70. Automatic shutdown systems are also provided to stop the engine in the case of failure of lubricating oil or of cooling water or if the engine speed exceeds the maximum allowable r/min.

71. c. Starting air system The engine is started with compressed air of max. 30 bar. Minimum pressure required is 15 bar.

72. A pressure transmitter( 变送器 ) PT301 mounted on the starting air line before the main starting valve has an indicator in the instrument panel.

73. The supply line from the starting air bottle is provided with a non- return valve and a drain valve.

74. The solenoid valve( 电磁阀 ) is electrical (remote control) or manual (on the engine) operated and sends after activation( 带电 ) a pilot air signal to the main starting air valve.

75. Interruption( 阻断, 中断 ) of the control air closes the main starting air valve.

76. After the main starting air valve is activated, the air flows through the flame arresters(trap) to the starting air valves in the cylinder heads.

77. Part of air flows via the starting air distributor to each of the main starting air valves in the cylinder heads. The starting air distributor controls the timing of opening and closing of the main starting air valves.

78. On the moment the main starting air valve is operated the governor booster( 调速器升 压器 ) is also energized.

79. The main starting air line is provided of a safety valve. Interlock valve is a safety device to avoid an engine start with engaged turning gear.

80. Starting air distributor The starting air distributor is of the piston type with precision-machined inter- changeable liners.

81. The liners as well as the pilot pistons are of corrosion resistant materials. The pilot pistons are controlled by a cam connected to the camshaft end.

82. When the main starting valve opens, the pilot pistons are pressed onto the cam, whereby the pilot piston for the engine cylinder which is in starting position admits control air to the main piston of the starting valve.

83. The starting air valve opens and admits compressed air into the engine cylinder forcing that piston down.

84. Shortly before the exhaust valves are opened the pilot valve interrupts the control air to the starting air valve and starting air to that cylinder is stopped.

85. This procedure will be repeated as long as the main starting valve is activated or until the engine speed is so high that the engine fires.

86. After the main starting air valve is closed, the main starting air system is deaerated( 释放，泄压 ), the pressure drops quickly and the springs will lift the pilot plungers off the cam.

87. This means that pilot plungers touch the cam only during the starting process and thus wear is insignificant( 可忽略的 ).

88. If a pilot liner is worn out, press it out. It may be necessary to heat the distributor up till about 200 ℃ as Loctites (a sealing agent) is used for fixing and sealing.