Showing posts with label IC engines. Show all posts
Showing posts with label IC engines. Show all posts

Sunday, 15 April 2018

DIESEL CYCLE

Q. EXPLAIN DIESEL CYCLE WITH DIAGRAM.


ANS: DIESEL CYCLE (constant pressure cycle)

The cycle was first analyzed by Rudolf Diesel
1-2:- is-entropic compression
2-3:- heat addition at constant pressure
3:- heat supply is cut-off
3-4: is-entropic expansion
4-1:- heat rejection at constant volume
Compression ratio=v1/v2
  • It is an ideal cycle. 
  • It must be made clear that this does not represent what actually happens inside the cylinder of a working diesel engine. 
  • It was developed to be able to model engine behavior and to analyze the effects of certain changes to the cycle without the complications of modeling an actual engine cycle.

Like an indicator diagram it is a graph of Pressure against Volume, but it makes certain assumptions:

(a) The mass of air within the cylinder remains the same: There are no inlet or exhaust valves.
(b) Fuel is not injected and burnt, but heat energy is added at constant pressure.
(c) At the end of the cycle the heat energy is rejected at constant volume.
(d) The compression and expansion of the air is adiabatic (no heat energy is added or lost) and follows the law (pv^y=c)
where c is a constant , for air Y is 1.4.
NOTE:- Thermal efficiency of diesel engine is always less then otto engine for same compression ratio.(mathematically can be shown)

Friday, 6 April 2018

OBJECTIVE QUESTIONS WITH ANSWER IC ENGINE

1. Which standards govern the specifications for supply of Residual Marine Fuels and Distillate Marine Fuels onboard merchant ships?
A. ISO 3012:1999
B. ISO 3648:1996
C. ISO 8216-1:2010
D. ISO 8217:2010
Answer-D

2. Crank web deflection readings will give a positive indication of
A. worn main bearing journals
B. torsional stress deformation
C. slack thrust bearings
D. bearing shells shim dimensions
Answer-A

3. ESD stands for which type of boiler
A. External superheater D-type
B. Emergency shutdown Boiler
C. Extreme Superheat type
D. External Superheat De-superheater type
Answer-A

4. The advantage of tie rods over an engine without tie rods is that:
A. The engine is very easily aligned after any misalignment has taken place between different components of the engine
B. The engine doesn???t require thrust pads for transmission of thrust to the ship???s hull as the same is being taken care of by the tie rods
C. The engine components are much lighter leading in overall reduction is engine weight with a high power generation with the elimination of fatigue stresses
D. There are no advantages of engines with tie rods, because tie rods require regular maintenance and replacement like connecting rods and overall engine becomes more expensive to operate
Answer-A

5. Which of the following is an example of a solid bearing?
A. Piston pin bushing
B. Turbo-generator turbine bearing
C. Spring bearing
D. Thrust bearing
Answer-A

6. In order for microbiological growths to thrive in a fuel tank it is necessary for
A. high temperatures to exist
B. low temperatures to exist
C. small amounts of water to be present
D. large amounts of water to be present
Answer-C

7. Marine boilers burning H.F.O. face a problem of cold corrosion due to high sulphur content. The minimum flue gas temperature within any boiler part is kept above due point of H2SO4. The actual dew point of H2SO4 in flue gases depends on the:
A. Boiler furnace temperature
B. Ambient air temperature
C. Boiler operating pressure
D. HFO sulphur content and moisture in combustion air
Answer-D

8. The purpose of an air cooler in a supercharging system is to:
A. Reduce temperature of supercharged air in order to condense and remove maximum possible moisture from the air prior entry to the engine
B. Reduce the temperature of the supercharged air in order to increase the density & also to cool down below dew point to remove moisture from air prior entry to the engine
C. Cool supercharged air to increase its density such that the dew point is not reached to avoid entry of moisture into the engine
D. Cool supercharged air to increase it???s density and also to keep the peak temperature and exhaust gas temperature within limits
Answer-B

9. Use of Halon as fire extinguishing medium has been discontinued because
A. It is highly toxic
B. It is expensive
C. It has high Ozone depleting potential
D. It leads to acid rains
Answer-C

10. In comparison to exhaust valves, intake valves of diesel engines may be fabricated from low-alloy steels because
A. the beveled edges of the intake valves provide forself-centering during seating
B. intake valves utilize stellite-coated valve seat insertswhich reduce wear
C. the volume of air passing through intake valves is less than the volume of air passing through exhaust valves
D. intake valves are less affected to the corrosive action of exhaust gases
Answer-D

11. Why is it essential to renew turbocharger bearings after a preset number of hours of running even if the bearings are in seemingly perfect condition?
A. Because they are prone to failure due to prolonged exposure to high temperature conditions.
B. Because they are subject to cyclic loading and are prone to failure due to metal fatigue.
C. It is not essential to renew if condition monitoring suggests perfect condition.
D. Lube oil contamination is bound to occur and affect the condition of the bearings.
Answer-B

12. Which of the following statements is true?
A. The rotary vane type steering gear generally operates at higher oil pressures than the ram type.
B. The ram type steering gear generally operates at higher oil pressures than the rotary vane type.
C. Both ram type and rotary vane type steering gears generally operate at similar oil pressures
D. None of the above
Answer-B

15. Modern marine turbochargers use a ___________ type of compressor
A. Radial flow
B. Axial flow
C. Mixed flow
D. Turbulent flow
Answer-A

16. Which of the following is a disadvantage of water as cooling medium for pistons, when compared to oil?
A. Chemical treatment is required
B. Higher thermal stresses in piston
C. Piston of more complicated design
D. All of the above
Answer-D

17 How is the concentration of dissolved oxygen in the feed water of an auxiliary boiler maintained at acceptable limits?
A. Feed water is cycled through a DC heater.
B. Feed water is treated with phosphates.
C. Oxygen is liberated in the three-stages of feed water preheating.
D. Oxygen is liberated by maintaining the highest practical feed water temperature
Answer-D

18. In a 2-stroke marine diesel engine if the o-ring for Jacket cooling water sealing is leaking then
A. The water will leak directly into the crankcase
B. The water will leak into the under piston space
C. The water will come out through tell-tale hole provided between the two o-rings
D. The water will come out from the top of cylinder jacket
Answer-C

19. The lube oil pump used in a diesel engine is a
A. volute pump
B. centrifugal pump
C. diaphragm pump
D. gear pump
Answer-D

20. Prior to lighting off a cold automatically fired auxiliary boiler, you should
A. check and regulate the water level
B. close the air cock once fires are lit
C. blow down the gage glass
D. crack the steam stop to assure protective steam flow
Answer-A

21. Steam temperature control for the ESD-II boiler is achieved by :
A. Fitting a de-superheater between 1st & 2nd passes of superheater
B. Fitting an attemperator between 1st & 2nd passes of superheater
C. Gas dampers in boiler uptake
D. Bypassing the superheater
Answer-C

22. The coating which is provided on the valve stem of exhaust valves of modern marine diesel engines is of:
A. Nickel
B. Stellite
C. Chromium
D. Nimonic
Answer-B

23. If the combustion control system of an automatically fired auxiliary boiler fails to sustain burner ignition after a normal shutdown, you should check for a/an
A. faulty photocell detector
B. low steam pressure
C. high voltage on the ignition electrode
D. open air damper
Answer-A

24. Which of the following statements is true, about slow speed engines?
A. A scavenge fire can lead to a crankcase explosion
B. A scavenge fire can lead to deformation of diaphragm plate
C. A scavenge fire can lead to damage to tie rods.
D. All of the above.
Answer-D

25. For a two stroke engine two o-rings are provided on the liner. The function of the top o-ring is to ___________ and function of the lower o-ring is to ____________
A. Seal jacket cooling water; act as secondary seal in case 1st o-ring leaks
B. Seal jacket cooling water, Seal scavenge air
C. Seal scavenge air, Seal Jacket cooling water
D. Seal combustion gases, Seal jacket cooling water
Answer-B

26. Even if there is an oil mist concentration inside a crankcase, and there is also a hot spot, crankcase explosion will only take place when
A. The hot spot provides the ignition temperature for the oil mist concentration
B. When the oil mist - air mixture is in the flammable range
C. Both A and B
D. None of the above
Answer-C

27. Which of the following conditions is responsible for the fuel oil to atomize when using a steam atomizer in an auxiliary boiler?
A. Expansion of the steam in the furnace.
B. Expansion of the steam in the whirling chamber.
C. Expansion of the steam in the orifice plate.
D. All of the above.
Answer-A

28. Some 4-stroke engines are fitted with a rotorcap on the cylinder head valves. For what reason?
A. Rotate the inlet valve during operation.
B. Distribute the exhaust gas or the air inlet better to improve combustion.
C. Improve the scaling surface function, increase the service time of the exhaust valve in the engine
D. To prevent the valve spindle from sticking
Answer-C

30. Shaft tunnel requires
a) drain
b) escape trunk
c) water tight door
d) all the above
Answer-D

31. What do you mean by surge limit of a turbocharger?
A. Characteristic curve of a turbocharger
B. Portion of compressor characteristic curve which lies on the left side of the point of maximum pressure
C. A line joining all the points of maximum pressure on compressor characteristic curves , drawn at various speeds of operation
D. Maximum rpm limit of T/C above which surging will start
Answer-C

32. A large, low-speed, main propulsion diesel engine uses sea water to directly cool the
A. cylinder heads
B. exhaust valves
C. scavenging air
D. injectors
Answer-C

33. Exhaust Grouping is required in case of ______________ turbocharging in order to
A. Constant pressure, prevents shockwave generation
B. Pulse pressure, prevent interference with scavenging of other cylinders
C. Constant pressure, prevent interference with scavenging of other cylinders
D. Pulse pressure, prevents shockwave generation
Answer-B

34. Function of a de-superheater is to.
A. Protect superheater from overheat
B. Control superheater steam outlet temperature
C. Increase the efficiency of the boiler
D. Reduce steam temperature for auxiliary uses after steam superheater
Answer-D

35. Which of the following statements is false?
A. Oxidation of lubricant leads to decrease in its viscosity
B. Formation of oxidation acids, sulfuric acid leads to depletion of TBN of lubricant
C. Contamination with water will lead to decrease in the load carrying capacity of a lubricant .
D. Build up of insolubles will lead to increase in viscosity of a lubricant
Answer-A

37. After prolonged operation, jerk type fuel pumps wear on the top edge of plunger and edges of spill ports and helix due to erosion by high pressure fuel as it spills. This wear would result in
A. Late start of injection and early end of injection
B. Early start of injection and late end of injection
C. Early start of injection and early end of injection
D. Late start of injection and late end of injection
Answer-A

38. Labyrinth seal fitted on the back surface of a compressor wheel of a turbocharger:
A. Prevents bearing lube oil contamination
B. Prevents bearing lube oil being sucked into the air stream
C. Helps to keep the shaft cool by controlled leakage of air
D. None of the above
Answer-C

39. It is a known fact that centrifugal pumps require priming for pumping liquids , as they cannot handle air and will lose suction due to air entry . But on the other hand T/Cs use centrifugal compressors for supercharging. Which of the following do you think makes a centrifugal compressor to pump air and behave differently than the centrifugal pumps?
A. Presence of air cooler
B. Presence of Labyrinth seal
C. High speed of rotation, very fine internal clearances and large impeller diameters
D. Difference in principle of operation
Answer-C

40. If an operating auxiliary boiler has a water pH reading of 7, you should
A. bottom blow the boiler
B. treat the water with caustic soda
C. treat the water with chemical scavengers
D. reduce the water alkalinity to recommended readings
Answer-B

41. In case of 2-stroke marine diesel engines, the top part of the liner forming the combustion chamber experiences very high pressure induced mechanical stresses as well as high thermal stresses. Which of the following is a correctly designed liner for catering both the above stresses?
A. Thick top portion with jacket cooling to take care of both the high mechanical and thermal stresses
B. Thick top portion to take care of high mechanical stresses while bore cooling to reduce thermal gradients
C. Thin top portion to reduce thermal gradients and hence thermal stresses while supporting ribs to take care of mechanical stresses
D. Thick top portion to take care of high mechanical stresses with jacket cooling combined with allowance for thermal expansion to minimize the thermal stresses
Answer-B

42. Which of these fuel oil impurities can cause maximum abrasive damage?
A. Water
B. Ash
C. Catalytic fines
D. Sodium
Answer-C

43. In modern marine 2-stroke diesel engines, ________________ is sometimes used as a coating on the underside of the exhaust valve disc, to reduce the rate of hot corrosion.
A. Monel
B. Chromium
C. Inconel
D. Cermet
Answer-C

44. Irregular circumferential wear of liner due to diminishing neutralizing capacity of cylinder oil away from lubricating holes is known as:
A. Micro seizure
B. Scuffing
C. Scoring
D. Clover leafing
Answer-D

45. Which of the following is a reasonable statement about water washing of turbine side of a T/C ?
A. It leads to thermal shock and reduces the life of the T/C
B. It leads to thermal shock and not so effective as solid washing
C. If properly carried out keeping rpm, load, temperature limits & other factors into account; it is quite safe and more effective than solid washing
D. It should never be carried out as most of the engine manufacturers recommend against the same
Answer-C

46. Which of the following statements correctly describes the phenomenon of surging in a 2-stroke crosshead type engine?
A. Due to sudden increase in engine load the exhaust gases may flow back through scavenge ports causing surge
B. Due to sudden decrease in engine load the turbocharger pressure ratio drops . This causes high pressure downstream of T/C in scavenge trunk causing flow reversal of scavenge air
C. Due to sudden increase in engine load , the T/C turbine rpm may increase suddenly increasing the compressor pressure ratio to surge
D. Due to sudden decrease in engine load , the turbocharger may stall as the higher pressure downstream in exhaust system may cause reversal of flow of exhaust gases
Answer-B

47. If the boiler tubes are scaled on the water side then
A. Heat conduction through the tubes will be very high leading to rapid evaporation
B. The boiler furnace can get damaged due to excessive temperatures
C. The surface of the tube will be overheated as heat transfer is impaired
D. The natural circulation of water within the boiler will be more efficient
Answer-C

48. Fins are installed on the generating tube surfaces in waste heat boilers to
(A) Prevent soot fires in the exhaust system
(B) Prevent exhaust gas erosion of the tubes
(C) Increase the velocity of exhaust gas flow
(D) Increase the rate of heat transfer
Answer-D

49. Any steering gear system alarm can only be successfully acknowledged from
A. The bridge
B. The engine control room
C. The steering compartment
D. The ship's office
Answer-B

50. To check the setting of the over speed trip on a diesel powered generator, you would use a
A. tachometer
B. torsion meter
C. dynamometer
D. pony brake
Answer-A

51. Which of the following specifications/qualities of cylinder oils counter corrosive wear?
A. Viscosity
B. TBN
C. Detergency
D. Specific gravity
Answer-B

52. What is meant by elastohydrodynamic lubrication?
A. Formation of hydrodynamic film under high pressure with minor elastic deformation of mating surfaces, distributing load over a greater area
B. Addition of extreme pressure additive (EP) to the lubricant
C. Addition of Viscosity index improvement additive
D. Addition of elastomer based additives
Answer-A

53. In a bypass type filtering system for a medium or high speed diesel engine, the lube oil bypassing the filter
A. returns directly to the suction side of the pump
B. returns directly to the sump
C. flows to the engine bearings
D. flows through a second-stage strainer, reheater, and returns to the sump
Answer-C

54. Which type of boiler burner has max turn down ratio?
a. Pressure set
b. spinning cup
c. Spill type
d. Y-jet type
Answer-D

55. Most steam traps respond well to cleaning. But when a thermodynamic trap fails to operate after cleaning, the next course of action should be
A. throttle the steam outlet valve
B. renew the trap
C. lap the disc and seat the trap
D. throttle the steam inlet valve
Answer-C

56. Types of corrosion in fresh water of D/E
a. Stress
b. hot corrosion
c. bimetallic
d. selective phase corrosion
Answer-D

57. Which of the following types of damages are metal seatings of a valve subject to? Choose the correct alternative.
A. Corrosion, Erosion, Abrasion, Deformation
B. Corrosion, Fatigue failure, brittle fracture, caustic cracking
C. Erosion, caustic cracking, brittle fracture, Clover leafing
D. None of the above
Answer-A

58. When A/E stand by F.O.heater to be used for main engine
A. Sudden opening F.O. inlet valve pressurized and damage the heater
B. F.O. in vapor lock inside heater allow steam
C. F.O. inlet valve causes pressure drop M/E F.O. pressure standby water is not pressurized may cause sudden change in engine /per load/rpm
D. heater leaking.
Answer-C

59. Viscosity of fuel oil used for ME was 145cst, new fuel comes whose viscosity was more than earlier, what u should do
a) Increase temp setting
b) Change setting of viscotherm
c) Do nothing
d) Open steam valve manually more
Answer-C

60. Which of the following can be done to reduce the cold corrosion of Main Engine cylinder liners using high sulphur fuel oil
A. Increasing cylinder oil feed rate
B. Using high TBN cylinder oil
C. Increasing scavenge air temperature
D. Decreasing cylinder oil feed rate
Answer-B

61. When m/e is running in emergency condition which of the alarms can't be bypassed
1. LO low pressure
2. Jacket water high temp
3. Piston cooling water high temp
4. All the above
Answer-4

62. Which of the following will be required to be done in order to reduce sulphur corrosion of main Engine Components?
A. Increasing the atomization pressure of fuel injectors
B. Fitting exhaust valves with valve rotators
C. Running engine at or near normal sea load
D. Decreasing the F.O. purifier feed rate , running two purifier in series one acting as purifier and other as clarifier
Answer-A,B,C and D

63. Where boiler point temp high?
A) Riser
b) Superheater
c) Primary steam drum
d) Secondary steam drum
Answer-B


64. Sudden stop of diesel engine (multiple choices)
A. air in system
B. water in system
C. air filter chocked
D. water in air filter
Answer-A,B and C

65. Mixed lubrication consist of
1. Mix two lubes oil
2. Contimanitiön of hydrodynamic lube oil.
3. Mixed grease and oil
Answer-2

66. The muffling of exhaust gas noise in 4 stroke auxiliary engines in achieved by
(a) Allowing the gas to expand.
(b) Change the direction of their flow.
(c) Cool the gas with injected water. (d) Cool the gas with scavenge air.
Answer-A and B

67. An auxiliary engine turbo-charger makes strange noises when the load changes. The engine parameters however are absolutely fine. An external examination of turbocharger parameters as stated in the manual also reveals nothing. Would you
(a) Continue to run the engine and wait for some time
(b) Stop the engine for a while and make some checks
(c) Reduce the load of the engine
(d) Run it on steady load to make some checks.
Answer-B

68. To avoid the engine running too long on critical speed during start up it is necessary to
(a) Start at speeds above critical speed.
(b) Start at speeds just below critical speed and quickly move across the critical speed.
(c) Start at maximum speed and quickly bring down to just above critical speed.
(d) Eliminate totally the hazards of critical speed by ignoring it.
Answer-B

69. Supercharging an existing medium speed naturally aspirated engine will
(a) Reduce weight of the engine.
(b) Reduce bulk of the engine.
(c) Increase existing power.
(d) Increase piston speed.
(e) Reduce fuel consumption.
Answer-C and E

71. When using low sulfur fuel oil for Emission Control Areas (ECA???S), ideally the TBN of the cylinder oil used should be
A. Lower than normal
B. Higher than normal
C. Same as normal
D. Same as normal if the feed is kept higher
Answer-A

72. Which of the following functions is done by a cam operating an exhaust valve?
A. It governs the timing of opening and closing of the valve.
B. It governs the speed at which the valve operates
C. It governs the amount of opening of the valve
D. All of the above
Answer-D

73. In the latest concept of Variable Geometry Turbocharging, _______angle can be varied to match the turbocharger at varying engine loads
A. Compressor vane
B. Turbine blade
C. Nozzle ring blade
D. Diffuser ring blade
Answer-C

74. The primary function of a flame safeguard system, as used on an automatically fired auxiliary boiler, is to prevent
A. accidental dry firing and overpressure
B. uncontrolled fires in the furnace
C. explosions in the boiler furnace
D. explosions in the boiler furnace
Answer-C

75. Directional intake ports in diesel engines are used to
A. reduce air charge turbulence
B. induce air swirl
C. deflect hot combustion gas away from the valves
D. oppose the effects of piston induced squish
Answer-B

76. Why does a chain stretch in service?
A. Due to plastic elongation
B. Due to high temperature expansion
C. Due to wear on rollers and bushes
D. Due to the phenomenon of creep
Answer-C

77. Which of the following methods is normally used to lubricate bearings in a small high-speed diesel engine?
A. Splash lubrication
B. Pressure lubrication
C. Sight feed lubricators
D. Mechanical lubricators
Answer-B

78. External fouling of boiler tubes can lead to:
A. Greater steam generation
B. Tube corrosion
C. Tube Erosion
D. Protection of tube against corrosion
Answer-B

79. What is the purpose of the inlet grid provided within the exhaust gas casing in the gas flow path, prior entry to turbocharger ?
A. To filter out any unburned carbon
B. To absorb and dampen the pressure fluctuation
C. To reduce noise in the constant pressure exhaust piping
D. To prevent any broken piston rings finding their way to turbine
Answer-A

80. The main function of tie rods in the construction of large, low speed diesel engines is to
A. stiffen the bedplate in way of the main bearings to increase the engine's longitudinal strength
B. accept most of the tensile loading that results from the firing forces developed during operation
C. mount the engine frame securely to the hull to prevent shaft coupling misalignment
D. connect the crosshead solidly to the piston rod
Answer-B

81. The fall in speed that occurs in a diesel engine equipped with governor, on increase of load is called:
A. Offset
B. Speed drop
C. Speed droop
D. Speed offset
Answer-C

82. Which of the following factors governs the lower limit of thrust bearing clearance?
A. To allow some oil leakage to prevent overheating
B. Reduction of oil viscosity
C. Alignment of crankshaft
D. To allow the thrust pads to tilt and generate the oil wedge
Answer-D

83. Which of the following can result in cracking of piston crown?
A. Deposits in cooling spaces
B. Impingement of fuel due to faulty injection
C. Insufficient piston cooling oil flow
D. All of the above
Answer-D

84. The boiler water alkalinity in a coil-type auxiliary boiler should be maintained at the pH recommended by the boiler manufacturer to
A. precipitate silica from solution
B. reduce corrosion in the heating coil
C. prevent clogging and erosion in the coil
D. maintain zero water hardness
Answer-B

85. What does the NLGI number of a grease indicate?
A. The oxidation resistance of the grease
B. The consistency of the grease i.e how fluid or non fluid
C. Demulsibility of the grease
D. The shelf life of the grease
Answer-B

86. Which of the following layers of a thin shell bearing gives it its fatigue strength?
A. The overlay
B. The interlay
C. The backing
D. The barrier layer
Answer-A

87. Which of the bearings listed is most widely used for main and connecting rod bearings of modern diesel engines?
A. Steel-lined
B. Poured babbitt, self-aligning
C. Split roller
D. Precision insert
Answer-D

88. Which of the following statements is false?
A. The fuel oil sulfur level is one of the important criteria for choice of TBN level of cylinder oil.
B. The use of anti-polishing rings or flame rings increases the consumption of cylinder oil
C. Excessive cylinder oil feed can lead to harmful deposits in piston top land area
D. None of the above
Answer-B

89. When preparing to light off a cold boiler equipped with a return flow fuel oil system, the recirculating valve directs the flow of oil
A. directly to the fuel oil heater inlet for further warm-up
B. back to the fuel oil settler for further filtration
C. back to the suction side of the service pump
D. directly to the deep tanks
Answer-C

90. Prompt correction of speed of diesel engines driving alternators, without having massive fluctuations is ensured by incorporating:
A. Load limiting devices
B. Load sharing devices
C. Load sensing devices
D. Load shedding devices
Answer-C

91. In a uniflow scavenged marine 2-stroke diesel engine, the scavenge ports in a cylinder liner are machined
A. Only for a part of the circumference, at an angle almost tangential to the circumference of the liner
B. All around the circumference at right angles to the circumference of the liner
C. only for a part of the circumference, at right angles to the circumference of the liner
D. All around the circumference at an angle almost tangential to the circumference of the liner
Answer-D

92. If the tappet clearance between the rocker arm tappet and exhaust valve stem is excessive then:
A. The valve will open early and close later
B. The valve will open later and close early
C. The valve will open and close later
D. The valve will open and close early
Answer-B

93. In order to reduce thermal loading on the upper part of the liner and increase the effectiveness of cylinder lubrication, modern 2-stroke marine diesel engines are designed to have:
A. Cermet coated piston rings, bore cooled liners and uniflow scavenging
B. High top land of piston crown and deeper cylinder cover with top land of crown extending into cylinder cover at TDC
C. Low top land of the piston crown with bore cooled cylinder liner
D. Bore cooled cylinder liner and bore cooled piston crown with toroidal shape combustion chamber
Answer-B

94. Which of the following conditions can lead to reduced power developed by a main engine?
A. High scavenge air temperature
B. Choked air suction filter of a turbocharger
C. Blow past in one or more units
D. All of the above.
Answer-D

95. Which of the following types of diagrams would give an indication of effectiveness of exhaust and scavenge processes?
A. Power card
B. Draw card
C. Light spring diagram
D. All of the above.
Answer-

C
96. The arrangement used to protect overheating of the superheaters under fluctuating loads is called
A. De-superheater
B. Attemperator
C. Steam dumping valve
D. Feed heater
Answer-B

97. Piston rod stuffing box scraper rings butt clearances should:
A. Not to be allowed to fall below 50% of original clearance
B. Not to be allowed to increase above 50% of original clearance
C. Not to be allowed to fall below manufacturer recommended value
D. Not to be allowed to increase above manufacturer recommended value
Answer-C

98. In a 2-stroke engine a ________________ separates the under piston space from the crankcase.
A. A-frame
B. Crosshead
C. Diaphragm
D. Scavenge space
Answer-C

99. Fusible plugs are installed in fire-tube boilers to
A. provide a means of draining the boiler
B. warn the engineer of low water level
C. cool the crown sheet at high firing rates
D. open the burners' electrical firing circuits
Answer-B

100. Which of the following gauges are generally used to evaluate main bearing clearances?
A. Poker gauge
B. Feeler gauge
C. Telescopic feeler gauge
D. Dial gauge
Answer-C

101. In a coil-type auxiliary water-tube circulation boiler
A. unevaporated feedwater collects in the bottom of the flash chamber
B. all generated steam is recirculated through heating coils in the boiler
C. heated water flashes to steam in the boiler heating coils
D. response to steam demand is slower than in a fire-tube boiler
Answer-A

102. For a continuous operation diesel engine, a duplex filter unit would be the best arrangement because
A. changing filter elements would not interrupt engine operation
B. filtering occurs twice in each pass of oil through the system
C. clogging will not occur
D. dropping pressure is half of that through a single filter unit
Answer-A

103. As per regulations, within how many hours before each departure, satisfactory working of the steering gear must be checked?
A. 2
B. 12
C. 24
D. None of the above
Answer-B

104. Modern 4-stroke medium speed, marine diesel engine exhaust valve spindles are rotated by providing
A. Nozzle rings
B. Tappet clearance
C. Spinners or vanes
D. Rotocaps
Answer-D

105. The purpose of economizer is to:
A. Decrease the capacity and size of the auxiliary boiler
B. Cooling down the exhaust gases in order to reduce NOx emission
C. Allowing Sox to react at low temperatures with water to form acids thus reducing Sox emission
D. Increasing the overall efficiency of the main propulsion plant
Answer-D

106. Microbiological growths in marine fuel are a common occurrence that can be
A. extremely detrimental to equipment and operating processes
B. prevented by maintaining proper storage temperatures
C. removed from emulsified fuel oil during the centrifuging processes
D. All of the above are correct.
Answer-A

107. The function of the tie rods is to:
A. Keep the engine components under tension at all the times
B. Just secure the engine parts together
C. Act as holding down bolts for the bedplate and keeps all the engine components together
D. Keep engine components under high compression, so that tensile stresses acting during firing stroke do not exceed this pre-compression to avoid fatigue failure
Answer-D

108. Which of the following types of crankshafts is much lighter at similar power requirements?
A. Fully built type
B. Semi built, all welded type
C. Semi built type
D. Solid forged type
Answer-B

109. After an engine has been started using a Bendix drive unit, the drive gear, or pinion disengages from the flywheel due to
A. the action of a spring
B. rotation of the starting cam
C. the higher rotating speed of the flywheel
D. accumulator pressure
Answer-C

110. Fuels as produced in a refinery are generally sterile, however, contamination can occur as fuels are
A. stored at the refinery
B. stored on the vessel
C. transported to the distribution sites
D. All of the above are correct.
Answer-D

111. Which of the following statements is false?
A. Excessive cylinder liner lubrication can aggravate scuffing.
B. Use of anti polishing ring reduces scuffing.
C. Deep honing of liner fails to give an ideal liner surface.
D. None of the above
Answer-

112. In a fully built or semi built type crankshaft, how can any slippage at shrink fit be identified?
A. By inspecting the locking arrangement provided
B. By checking the dowel provided.
C. By checking the witness mark provided for reference .
D. By checking the performance of the engine
Answer-C

113. Which of the following is one of the major advantages of resin choking over cast iron choking, in holding down arrangements of modern diesel engines?
A. Better vibration damping properties.
B. Better compressive strength
C. 100% contact, no need for surface preparation
D. None of the above
Answer-C

114. In a 2-stroke crosshead type of engine, the side thrust generated due to rolling and connecting rod and fore-aft thrust due to pitching motion of the ship is taken care of by the:
A. Piston and the liner
B. Connecting rod and the piston rod
C. Crosshead shoes and guides
D. Crankpin and thrust bearing
Answer-C

115. In a VIT equipped jerk type fuel pump:
A. Raising the barrel delays beginning of injection
B. Lowering the barrel delays beginning of injection
C. Raising the barrel delays end of injection
D. Lowering the barrel delays end of injection
Answer-A

116. The over speeding of the diesel engine driving an electric generator could cause
A. low voltage trip to trip
B. reverse power trip to trip
C. damage to windings
D. excessive exhaust temperatures
Answer-C

117. In a large, slow-speed, main propulsion diesel engine, which of the parts listed is under tension when the engine is running?
A. Bed plate
B. Column
C. Entablature
D. Tie rod
Answer-D

118. A diffuser is provided at the end of a mechanical atomizer in boiler onboard
A. To prevent blow back of the flame
B. To mix the air and fuel properly
C. To prevent blow out of the flame
D. To eject the excess fumes from the atomizer
Answer-A and B

119. Steam stop valve is eased of its seat during boiler start up from cold
A. To allow thermal expansion of parts
B. To allow steam flow during start up
C. To prevent water hammer
D. All of the above
Answer-D

120. Which of the following statements about the design of D- type boilers, is false ?
A. The heavier water in top drum flows back to the bottom drum through the down- comers outside the furnace
B. Inside the furnace the water is heated up in the risers
C. The upper drum is the steam/water drum and the lower one is the water drum.
D. The feed water is pumped into the lower drum
Answer-D

121. Presence of catalytic fines in fuel oil is significant to engineers on board because
A. Catalytic fines tend to impair proper operation of purifiers
B. Catalytic fines lead to abrasive wear in liners, piston rings and fuel injection equipment
C. Catalytic fines necessitate increase in injection temperature
D. Catalytic fines necessitate increase in storage temperature
Answer-B

122. With reference to the data logger for a refrigerate sys. Which of the parameters should be noted?
A. Sea water temp, pressure
B. Condenser temp
C. Refrigerant leakage
D. Evaporator temp.
Answer-A,B and D

123. Which of the following factors affect penetration of fuel droplets during injection?
A. Quality of atomization
B. Injection temperature
C. Scavenge air pressure
D. All of the above.
Answer-D

124. Lube oil pumps taking suction from the sump of most small marine engines are usually
A. of the diaphragm type
B. of the centrifugal type
C. positive displacement type
D. independently driven by electric motors
Answer-C

125. Telescopic pipes to the piston of a large slow-speed main propulsion diesel engine are designed to prevent
A. excessive crankcase pressure
B. excessive lube oil temperature
C. contamination of the lube oil by water
D. contamination of the cooling water by lube oil
Answer-C

126. Excessive axial thickness of a piston ring can lead to ____________________
A. Scraping off of oil from liner surface
B. Increased wear
C. Twisting in the groove
D. Difficulty in formation of oil wedge
Answer-D

127. Which of the following is an adhesive?? type wear of a cylinder liner?
A. Clover- leafing
B. Scoring
C. Scuffing
D. Ovality
Answer-B

128. Cylinder heads of marine diesel engines are provided with _________ to relieve any excessive pressure within the combustion chamber
A. Safety valves
B. Indicator cocks
C. Relief valves
D. Bursting discs
Answer-C

129. Working of a pulse pressure turbocharger depends upon the ___________ that can be safely created in the exhaust system.
A. Enthalpy drop
B. Pressure difference
C. Turbocharger rpm
D. Pressure pulses
Answer-D

130. The maximum elongation of timing chains in service is limited to ___________ of original chain length.
A. 2%
B. 1%
C. 5%
D. 3%
Answer-A

131. Duplication of power units, fittings and pipings where each unit is capable of providing 100% steering power, and automatic isolation of one unit in the event of a leakage(single failure) in that unit would constitute 100% redundancy for the steering gear system. Such system is mandatory on ____________
A. All tankers
B. Tankers above 10000 GT
C. Tankers above 100000 Dwt
D. All ships above
Answer-B

132. Routine cleaning of air side of air cooler of main engine is done by:
A. Circulating fresh water
B. Circulating cold chemical solution
C. Circulating warm chemical solution
D. Circulating hot water
Answer-C

133. What prevents rotation and fretting between a thin shell bearing and its housing?
A. Location tangs or pegs
B. The nip or crush of the bearing
C. A special kind of adhesive
D. Any of the above
Answer-B

134. Microbial degradation of main engine sump oils can lead to:
A. Increased clogging of lube oil filters
B. Corrosive attack on journals and bearings
C. Formation of stable emulsions
D. All of the above.
Answer-D

135. In case of constant pressure turbo charging, the exhaust of the cylinders goes into :
A. Small diameter exhaust pipes with exhaust grouping
B. Exhaust compensators
C. Nozzles
D. Large diameter pipes
Answer-B

136. Which of the following is a limiting factor in cylinder liner cooling?
A. Maximum combustion temperature
B. Minimum liner temperature
C. Exhaust temperature
D. Dew point for formation of sulfuric acid
Answer-D

137. Which of the following is not a consequence of over lubrication of a cylinder liner?
A. Deposits in piston top land which can not only consume lube oil but always lead to increased abrasive wear
.B. Sticking and jamming of piston rings due to increased deposits.
C. Unburnt lube oil in scavenge spaces posing increased risk of scavenge fire .
D. Increased corrosive wear
Answer-A

138. Variable geometry turbocharging is the preferred choice over conventional turbochargers because :
A. T/C efficiency is very high at high engine loads
B. T/C has good starting characteristics while efficiency at full loads is slightly compromised
C. T/C efficiency is optimized for different engine loads by changing nozzle ring geometry
D. T/C is much cheaper and simple to manufacture and is virtually maintenance free
Answer-C

139. As a thumb rule, ovality in crankpins of medium speed engines should not exceed _____________ of bearing clearance.
A. 10%
B. 15%
C. 25%
D. 30%
Answer-

140. In a naturally aspirated diesel engine, the volume of air intake is directly related to engine
A. compression ratio
B. valve size
C. fuel pressure
D. cylinder clearance volume
Answer-B

Wednesday, 14 March 2018

crankshaft

Lets learn all about CRANKSHAFT- an important engine component.

INTRODUCTION:

  • The working of other components of the engine, such as camshaft for fuel timing, firing order of each unit, opening of inlet valve and exhaust valve, operation of air start distributer etc depends on correct rotation of the crank shaft.
  • Failure of crankshaft can stall the engine/ship.
  • The parts forming a crankshaft are : journals( crankshaft), crank webs and the crankpins.
  • They are too big to make a single unit and so they are constructed by joining together individual forgings.(will be discussed below how it is done).


MATERIAL:
  1. For slow speed marine diesel engines:
      steel castings or forgings
  2. For medium and high speed M.D.E
      Alloy steel

WEIGHT:
For 2-stroke crosshead engines- over 300 tonns.

CLASSIFICATON:
 They are divided into four depending upon the methods of construction-
(a) Fully built
(b) Semi-built
(c) Welded crankshaft
(d) Solid single piece used in very small engines.

Now we will know the above mentioned classifications one by one in a simple way.

(A) FULLY BUILT
  • As already mentioned above the parts which forms a crankshaft: journal, webs,      crankpins.
  • Journals and crankpins are made from forgings, and the webs may be forged or cast.They are made separately.
  • These parts are shrink-fitted.
  • Webs were heated up and the crank pin and journals fitted into the holes.The holes gets expanded due to heating.
  • Were used on older engines. 
  Let's see the diagram:


BEARING


BEARING

Classification
1) Main bearing
2) Top end bearing = Cross Head / Gudgeon Pin bearing
3) Bottom End Bearing / Crank pin bearing
4) Thrust Pad bearing
5) Pedestal bearing (generator alternator side insulated bearing)

1. MAIN  BEARINGS 
Function : Support crankshaft and keep it aligned.
  To remove heat produced by friction

2. TOP  END  BEARINGS 
Cross head Engines: Transmit load from cross head pin to connecting rod
   Allows relative movement of con rod & cross head pin
Trunk Piston Engines: Transmit load from gudgeon pin to connecting rod
   Allows relative movement of con rod & gudgeon pin

3. BOTTOM  END / CRANKPIN  BEARINGS 
Function: Transmit load from con rod to crankshaft
  Allows relative movement of con rod & journal

Bearing Operation: Depends on  
`  Operating temperature of bearing
`  Working temperature of bearing
`  Minimum oil film thickness
`  Rate of oil flow
`  Rate of heat production
`  Power loss of bearing.

Bearing Loads:
  • Combustion forces, Inertia forces & Centrifugal force of rotating masses 
  •  Varying resultant load from gas forces & inertia forces 
  •  Two stroke engine  No load reversal
  •  Four stroke engine  Load reversals at the end of exhaust stroke hence, wear uniform   & lubrication better.     
  •  Fluctuating gas force results fatigue failure in bearing 

Bearing Material Properties
 Mechanical Strength 

  • Fatigue & compressive strength to carry load – depends upon thickness 0.3 mm white metal can withstand 141 bar pressure and 0.08 mm white metal can withstand 211 bar pressure.
  • Thin lining has poor conformability and too soft material tends to flatten under heavy loads
  • Too hard material withstands high loads, posses high frictional characteristics & may be brittle with poor fatigue characteristics.


 Soft & low melting point material 

  • Softness & modulus of elasticity of bearing alloy should be as low as possible but hard enough to withstand heaviest continuous loading or chock loading without plastic deformation
  • Soft metal flows locally without damaging the harder steel called conformability
  •  Allows abrasive particles to embed to prevent damage to journal 

 Corrosion resistance
To withstand corrosive attack from lub oil

 Antifriction & wear properties –depends upon type of oxide film that material forms on reaction without lube additives.

Bearing Material 
 White Metal = Tin (Sn) +_ Antimony (Sb) + Copper (Cu)

  • Thin walled bearings, stiff cross head assembly    88% Sn + 8% Sb + 4% Cu
  • Thick walled bearing, flexible crosshead & Bottom end bearing  87% Sn + 9% Sb + 4%Cu 

  1. Tin forms soft matrix to accommodate misalignment
  2. Antimony forms hard cubes to withstand load of journal. Tends to float and segregate during  casting
  3. Copper holds antimony in evenly dispersed pattern, solidifies first. 

Sunday, 7 January 2018

AIR STARTING SYSTEM

Friends, lets know what exactly happens in AIR STARTING SYSTEM in simple way:

  1. It consists of 2 air reservoirs
  2. Reservoir used for storage of air at high pressure of 30 bar.
  3. Each reservoir has a capacity of 45 cubic meter.
  4. A stop valve is positioned next to the air reservoir.  This is manual isolation valve of the system.To prevent pressure surge this valve is opened manually.
  5. Turning gear interlock is an important interlock of any manouvering system.It prevents attempted start and admission of air to the control lines while the gear is engaged.
  6. AIR start lever in the engine room actuates pre-starting valve. It permits 30 bar to actuate the pilot valve.
  7. The pilot valve allows the passage of control air to operate automatic valve and load up distributor slide valve.
  8. The automatic valve opens and closes automatically to fill up start air manifold while starting .It conserve air during starting. often it includes  NR valve.
  9. Air distributor control valve regulates the admission of pilot air to operate cylinder air start valve in correct sequence.
  10. Cylinder air start valve admit starting air to individual cylinders.
  11. Distributor air operates this air start valve according to the firing order.
  12. An air manifold relief valve relieves excess pressure in the manifold.
  13. A flame trap prevents passage of flame from cylinder to manifold in the event of a jammed cylinder air start valve.
  14. A bursting cap ruptures to relive excess pressure in the event of start air line explosion.
  15. Pressure trips block the starting of engine if main engine and camshaft lube oil pressure are low.
Image result for Diagram of air starting system

QUESTIONS ON AIR STARTING SYSTEM:
Q1. To start a main propulsion 2s engine when the starting air is admitted into cylinder.
Ans: after TDC(affrox 15 degree).
Q2. D.E air start valve timing is controlled by ?
Ans: air start distributor
Q3. in operating condition what is the indication of leaking air starting valve?
Ans: overheating starting pipe to the cylinder head
Q4. The sequence of admitting starting air into the engine depends on?
Ans: normally the firing order
Q5. name some interlocks
Ans: turning gear interlock
        telegram interlock
         main lubricating oil pressure low interlock
          jacket water temperature high interlock
           control air pressure low

Thursday, 2 November 2017

crankcase inspection

       List the items to be checked during crankcase inspection of a large Marine Diesel Engine

      Safety Precautions carried Out before Crankcase Inspection:
·         Inform bridge and chief engineer.
·         If in port take immobilization certificate.
·         Get propeller clearance from duty officer.
·         Shut off starting air valve.
·         Put man at work tag
·         Stop lube oil pump.
·         Indicator cocks to be opened.
·         Turning gears to be engaged.
·         Ventilate crankcase door properly.

checks 
  • Firstly check oil condition for any smell, discoloration or degradation.
  • Check the piston rod surface for scoring marks and roughness.
  • Check piston palm bolts and locking device for slackness and fretting.
  •      CHECK THE guide shoe and area around it.
  •          Check cross head bearing general condition.
  •          Evaluate top and bottom end of connecting rod bolt, nut and locking device for       slackness, signs of fretting, etc.
  •          Check for slip of web and journal by checking the reference mark.
  •          Check crankcase relief door spring tension, wire mesh and & sealing ring.
  •          Check the axial movement of bottom end bearing.
  •          Check and clear O.M.D sampling pipe.

Saturday, 14 October 2017

PISTON RINGS

PISTON RINGS

Types: 
1. Compression rings
2. scrapper rings

Compression rings

  • Fitted into grooves provided in the piston crown.
  • serves to prevent blow-bys.


Higher speed engine uses less rings then low-speed engines because of the fact that higher piston speeds lessen the possibility of a blow-by.

Q. HOW SEALING EFFECT IS PROVIDED BY COMPRESSION RING?
A. due to the pressure of the gases entering the so-called back clearance b/w the piston and ring and partly due to ring tension.

Maximum gas pressure comes onto the first and second rings next to the combustion chamber.
Pressure decreases for the lower rings due to the throttling effect of the labyrinth formed by the back clearance.

TYPE OF LUBRICATION FOR COMPRESSION RING
Hydrodynamic Lubrication


  • To ensure ring tension and allow for the expansion of the rings as they become hot, joints are provided in the rings.
  • Ring diameter in a free state is always larger then the bore.

SHAPE OF JOINT

  1. Straight
  2. Bevelled
  3. Stepped



  • Low speed diesel engines employ bevelled and stepped joints
  • High speed diesel engines employ straight joint.



  • Experiment proves that the piston rings rotates in the operation.
  • On the other hand it is desirable that on 2-stroke engines the piston ring retain their original position so that no joint would appear against the ports in the cylinder liner and become trapped and broken when the engine is running.
  • Special retainers are integrally made with the piston ring serve to secure this in place.



Friday, 13 October 2017

FUEL BOOSTER PUMP


  • To induce continuous flow of fuel from service tank to the fuel injection pumps, booster pump is used which is incorporated in fuel line
  • A booster pump must supply oil at pressure sufficient to overcome frictional resistance of filters, lines.
  • For marine practice booster pumps are of reciprocating, vane and centrifugal type.
  • Usually gear pump is used as a booster pump capable of creating suction lift of 1-1.5 m h2o.

Tuesday, 26 September 2017

FUEL SYSTEM

RELATED QUESTIONS:-


  1. WHAT ARE THE MAIN COMPONENTS OF FUEL SYSTEM?
  2. IN WHICH WAY FUEL IS SEPARATED FROM SEDIMENTS?
  3. WHAT IS THE FUNCTION OF FUEL BOOSTER PUMP? WHAT TYPE OF FUEL BOOSTER PUMP DO YOU HAVE? DISCUSS THEIR OPERATION.
  4. WHAT PURPOSE DOES THE FUEL-INJECTION PUMP SERVES?
  5. WHAT IS THE FUNCTION OF FUEL INJECTOR?
  6. DISCUSS THE OPERATION OF FUEL INJECTOR.
  7. WHAT IS THE PRINCIPAL MALFUNCTIONS OF THE FUEL EQUIPMENT?
  8. TEST AND OVERHAUL OF FUEL INJECTION VALVES.
  9. REASONS FOR FUEL VALVE SEIZURE.
  10. HOW FUEL INJECTOR IS BEING COOLED COMPARE BETWEEN OLDER ENGINE AND NEWER ENGINE.
  11. HOW TO CHANGE THE TIMING OF FUEL INJECTION?
  12. OPERATION OF VIT AND SUPER VIT?
  13. REQUIREMENTS OF CRANKCASE OIL AND CYLINDER LUBRICATION OIL.
  14. DIFFERENT TYPES OF TEST CARRIED OUT ON LUBE OIL?
  15. HOW TO UPKEEP THE QUALITY OF LUBE OIL ONBOARD SHIP?
  16. CATEGORIZE CRUDE OIL?
  17. DEFINE MICROBIAL DEGRADATION OF FUEL OIL.
  18. MICROBIAL DEGRADATION OF LUBE OIL , ITS CAUSE AND EFFECT AND THE METHOD OF INDICATION?

Monday, 18 September 2017

DIESEL CYCLE

DIESEL CYCLE (constant pressure cycle)















The cycle was first analysed by Rudolf Diesel
1-2:- isentropic compression
2-3:- heat addition at constant pressure
3:- heat supply is cut-off
3-4: isentropic expansion
4-1:- heat rejection at constant volume
Compression ratio=v1/v2

  • It is an ideal cycle. 
  • It must be made clear that this does not represent what actually happens inside the cylinder of a working diesel engine. 
  • It was developed to be able to model engine behaviour and to analyze the effects of certain changes to the cycle without the complications of modelling an actual engine cycle.

Like an indicator diagram it is a graph of Pressure against Volume, but it makes certain assumptions:
(a) The mass of air within the cylinder remains the same: There are no inlet or exhaust valves.
(b) Fuel is not injected and burnt, but heat energy is added at constant pressure.
(c) At the end of the cycle the heat energy is rejected at constant volume.
(d) The compression and expansion of the air is adiabatic (no heat energy is added or lost) and follows the law (pv^y=c)
where c is a constant , for y air is 1.4.
NOTE:- Thermal efficiency of diesel engine is always less then otto engine for same compression ratio.(mathematically can be shown)

Sunday, 17 September 2017

FEATURES OF 4 STROKE MARINE DIESEL ENGINES

  •          4 STROKE ENGINES
  •          HIGHER OUTPUT
  •          HIGHER MEAN EFFECTIVE PRESSURE
  •           HIGH DEGREE OF TURBOCHARGING
  •           LOW WEIGHT OF ENGINE AND REDUCED SPACE REQUIREMENT
                         - AS A RESULT OF TURBOCHARGER
                      - 30% SAVING IN SPACE
                       -300% SAVING IN WEIGHT 
  •          comparison   W.R.T SLOW ENGINES

                                         - LOW HEAD SPACE
                                          - LOCATION OF ENGINE AS AFT AS POSSIBLE.
                                           -ENGINE SPEED AND PROPELLER SHAFT SPEED INDEPENDENT OF EACH OTHER.
                                            -LOW INSTALLATION COST.

  •          HIGH LUBRICATING OIL CONSUMPTION.
  •          SHORT LIFE OF EXHAUST VALVE

STUFFING BOX

STUFFING BOX




Image result for stuffing box of piston
fig.:-stuffing box







FUNCTION



  •                   TO PREVENT PISTON ROD TAKING OIL FROM CRANKCASE.
  •                  COUNTERACT THE LEAKING OUT OF SCAVENGE AIR


              

LOCATION

  •               AT THE BOTTOM OF SCAVENGE AIR BOXES   

               
          

HOW TO CHECK DURING ENGINE RUNNING

  •                 BY WATCHING THE OUTLET FROM TEST COCK ON MANOUVERING    PLATFORM.
  •                 LEAKAGE OF AIR INDICATES THAT SEALING RINGS ARE DEFECTED.
  •                 EXCESSIVE OIL OUTLET MEANS THAT SCRAPPER RING NEED OVERHAUL.

            

CHECK POINTS DURING OVERHAUL

  •               CHECK CLEARANCE OF RINGS (VERTICAL, GAP)
  •               CHECK SPIRAL SPRING TENSION
  •               ALL DRAIN HOLES CLEANED
  •               CHECK THE FITTING BOLT. RENEW LOCKING WASHER, RENEW ‘O’ RING.

Image result for stuffing box of piston
overhauling of stuffing box











TURBOCHARGER

BY TURBOCHARGING AN ENGINE, THE FOLLOWING ADVANTAGES ARE OBTAINED:

  • INCREASED POWER FOR AN ENGINE OF THE SAME SIZE OR REDUCTION IN SIZE FOR AN ENGINE WITH THE SAME POWER OUTPUT.
  • REDUCED SPECIFIC FUEL OIL CONSUMPTION - MECHANICAL, THERMAL AND SCAVENGE EFFICIENCIES ARE IMPROVED DUE TO LESS CYLINDERS, GREATER AIR SUPPLY AND USE OF EXHAUST GASSES.
  • THERMAL LOADING IS REDUCED DUE TO SHORTER MORE EFFICIENT BURNING PERIOD FOR THE FUEL LEADING TO LESS EXACTING CYLINDER CONDITIONS.
CONSTRUCTION DETAILS:-

  • THE TURBOCHARGER CONSISTS OF A SINGLE STAGE IMPULSE TURBINE CONNECTED TO A CENTRIFUGAL IMPELLER VIA A SHAFT.

  • THE TURBINE IS DRIVEN BY THE ENGINE EXHAUST GAS, WHICH ENTERS VIA THE GAS INLET CASING. THE GAS EXPANDS THROUGH A NOZZLE RING WHERE THE PRESSURE ENERGY OF THE GAS IS CONVERTED TO KINETIC ENERGY. THIS HIGH VELOCITY GAS IS DIRECTED ONTO THE TURBINE BLADES WHERE IT DRIVES THE TURBINE WHEEL, AND THUS THE COMPRESSOR AT HIGH SPEEDS (10 -15000 RPM). THE EXHAUST GAS THEN PASSES THROUGH THE OUTLET CASING TO THE EXHAUST UPTAKES.


      · ON THE AIR SIDE AIR IS DRAWN IN THROUGH   FILTERS, AND ENTERS THE     COMPRESSOR WHEEL AXIALLY WHERE IT IS ACCELERATED TO HIGH VELOCITY. THE AIR EXITS THE IMPELLER RADIALLY AND PASSES THROUGH A DIFFUSER, WHERE SOME OF THE KINETIC ENERGY GETS CONVERTED TO PRESSURE ENERGY. THE AIR PASSES TO THE VOLUTE CASING WHERE A FURTHER ENERGY CONVERSION TAKES PLACE. THE AIR IS COOLED BEFORE PASSING TO THE ENGINE INLET MANIFOLD OR SCAVENGE AIR RECEIVER.


     ·THE NOZZLE RING IS WHERE THE ENERGY IN THE EXHAUST GAS IS CONVERTED INTO KINETIC ENERGY. IT IS FABRICATED FROM A CREEP RESISTANT CHROMIUM NICKEL ALLOY, HEAT RESISTING MOLY-CHROME NICKEL STEEL OR A NIMONIC ALLOY WHICH WILL WITHSTAND THE HIGH TEMPERATURES AND BE RESISTANT TO CORROSION.
  •  LABYRINTH SEALS OR GLANDS ARE FITTED TO THE SHAFT AND CASING TO PREVENT THE LEAKAGE OF EXHAUST GAS INTO THE TURBINE END BEARING, OR TO PREVENT OIL BEING DRAWN INTO THE COMPRESSOR.
      

Image result for labyrinth gland in turbochargerImage result for labyrinth gland in turbocharger
     

  • A LABYRINTH ARRANGEMENT IS ALSO FITTED TO THE BACK OF THE COMPRESSOR IMPELLER TO RESTRICT THE LEAKAGE OF AIR TO THE GAS SIDE

           Image result for labyrinth gland in turbocharger


  • DISCOLORING OF THE OIL ON A ROTOR FITTED WITH A ROLLER BEARING WILL ALSO INDICATE A FAILURE IN THE TURBINE END GLAND.


TURBOCHARGER TYPES

(A) AXIAL FLOW :-


  •     SINGLE STAGE IMPULSE REACTION TURBINE IS USED.
  •     TURBINE DRIVES A CENTRIFUGAL COMPRESSOR.
  •     EXHAUST FLOW IN AND OUT OF TURBINE BLADE IS ALONG THE AXIS OF THE SHAFT.
  •     MOST COMMONLY USED IN MARINE APPLICATION


(B) RADIAL FLOW

·         EXHAUST FLOW INTO THE TURBINE BLADE IS ALONG THE RADIAL DIRECTION.
·         OUTLET OF TURBINE IN ALONG THE AXIX OF ROTOR.
·         USED IN SMALL HIGH SPEED ENGINES.  
MATERIALS USED IN T/C
TURBINE WHEEL, NOZZLE RING, ROTOR SHAFT AND BLADES:

·  NICKEL-CHROME ALLOY (NI 75%, CO 18%, TI 3%, AL 2%, CR 2%)

TURBINE CASING:
  • CAST IRON WITH CORROSION PREVENTIVE PLASTIC COATINGS IN CASE OF WATER COLED T/C.

COMPRESSOR IMPELLER, VOLUTE CASING, DIFFUSER, & INDUCER:
  • ALUMINIUM ALLOY FOR LIGHT WEIGHT AND STRENGTH OR MORE EXPENSIVE TITANIUM 
TURBOCHARGER SURGING
·     WHEN THE DISCHARGE PRESSURE EXCEED THE PRESSURE BUILD UP IN THE DIFFUSER AND IMPELLER.
·     IT PRODUCES A BACK FLOW OF AIR FROM DISCHARGE TO SUCTION.
·     BACK FLOW FROM SCAVENGE AIR MANIFOLD TO THE T/C DIFFUSER.
·     CHARACTERISED BY NOISE AND VIBRATION.

RASONS FOR T/C SURGING

  • ·     SCAVENGE SPACE FIRE
  • ·         DIRTY NOZZLE AND BLADE
  • ·         INDIVIDUAL CYLINDER MISFIRE
  • ·         CHOCKED SCAVENGE/EXHAUST PORT
  • ·         INCORRECT MATCHING OF T/C TO ENGINE
  • ·         POOR SCAVENGING OR LEAKY EXHAUST VALVE
  • ·         SUDDEN LOAD CHANGE BY BAD WEATHER
  • ·         POOR POWER BALANCE

SURGING REMEDY AND ACTION


  • REDUCE ENGINE SPEED
              -IT WILL REDUCE SCAVENGE AIR PRESSURE
              -HENCE LESS TENDENCY OF REVERSE FLOW