Question

(a) Explain how the build-up of residue in the scavenge space of a large slow speed two stroke engines minimised by design, operation and maintenance.

(b) Explain the possible damage which could be caused by a scavenge fire

Answer 1

Part (a)

To avoid scavenge fires, scavenge trunking must be periodically inspected & cleaned, any buildup of the contamination noted & remedied. The drain pockets should also be cleaned regularly to remove the thicker carbonised oil sludges which do not drain down so easily & which are a common cause of the choked drain pipes. Scavenge drains should be blown regularly & any passage of oil from them noted.

The piston rings must be within wear down limits & lubricated suitably so that ring blow-by is avoided. At the same time one must guard against excess cylinder oil usage. With timed cylinder oil injection the timing should be periodically checked.

The piston-rod packing rings & scraper rings should be measured according to intervals in PMS so that oil is prevented from entering the scavenge space because of the butted ring segments. This may & does occur irrespective of the positive pressure difference between the scavenge trunk & the crankcase space.

Fuel injection equipment must be kept in good condition, timed correctly, & the mean indicated pressure in each cylinder should also be carefully balanced so that individual cylinders are not overloaded.

If cylinder liner wear is up to maximum limits the possibility of the scavenge fires will not be materially reduced till the liners are renewed.

Part (b)

Component affected by scavenge fire involves piston rod, cylinder liner, stuffing box, piston and rod alignment, marking or cracking of the liner and tie rod. Inspect the affected area thoroughly for any damage and cause of scavenge fire.

✓ Verified Model Answer (Text Solution)

Component affected by scavenge fire involves piston rod, cylinder liner, stuffing box, piston and rod alignment, marking or cracking of the liner and tie rod. Inspect the affected area thoroughly for any damage and cause of scavenge fire.