MEK (Motor) asked Questions Part 4

151. 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

152. 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

153. 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

154. 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

155. Which of these fuel oil impurities can cause maximum abrasive damage?

A. Water

B. Ash

C. Catalytic fines

D. Sodium

answer c

156. 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

157. 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
d

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