In a refrigeration system, foaming of the crankcase oil may

第二组

Under normal operation, some lubrication oil mist may be discharged from the air compressor to the air start system. This oil may be from excess compressor cylinder lubrication, from faulty oil scraper rings, or may even be suspended oil vapor contaminating the engine room atmosphere and drawn in at the compressor suction. Oil discharge is kept to a minimum by draining the after cooler, air receiver and starting system. If small quantities of lubrication oil do get passed into the starting air system, they will deposit as thin moist film over internal pipe surfaces but are not readily combustible. If a cylinder non-return valve leak while the engine is in operation, some hot gas, possibly with unburned fuel and cylinder lubrication oil, may be blown through the valve to the adjacent air manifold. With further heating from the leaky valve, this, together with the already deposited oil film, will carbonize and form. incandescent carbon. If starting air is applied to the system while still hot, the high pressure air coming into contact with the burning carbon may cause an explosion. Such an explosion will cause a flame to pass back through the air start pipe system, evaporating the deposited oil film and igniting it in the presence of air. Very high velocities and shockwaves are generated which may rupture pipes and fittings.

Alternatively, if excessive oil has entered the air start system, a mixture of air and oil droplets may be discharged through the open cylinder non-return valve during starting. This spray may ignite due to high temperatures in the cylinder, causing a flame through the still open valve to the air manifold.

To prevent an explosion, air start valves must be correctly maintained and lubricated to ensure correct timing and free movement with positive closing. Oil in the system must be kept to a minimum, pipe lines must be drained and cleaned internally when necessary and oil discharge from air compressors must be kept to a minimum by good maintenance.

The passage is mainly about

A.crankcase explosion

B.scavenge box fire

C.starting air pipe

D.the danger of explosion in the starting air system

Sweating of the refrigeration system compressor crankcase is caused by_______ .

A.too much superheat

B.insufficient superheat

C.suction pressure too low

D.excessive refrigerant returning to the compressor

Crankcase explosions in propulsion diesel engines result from ____.

A.the splashing of lubrication oil by the crankshaft

B.the dilution of crankcase oil with particles of combustion

C.broken fuel lines spraying oil on the crankcase

D.the ignition of unburned fuel and air in the crankcase

Sludge may be formed in the oil in the crankcase of a reciprocating air conditioning compressor as a result of ______.

A.refrigerant bubbles in the lube oil

B.refrigerant reducing the lube oil viscosity

C.oxidation(氧化) of the lube oil from overheating

D.reducing the floc or cloud point of the oil

Excessive oil foaming in the crankcase of a refrigeration compressor is most likely to occur when the compressor

A.has run continuously for a long period

B.suction pressure is below normal

C.oil level is below normal

D.starts after a long idle period

______continuously extract the crankcase atmosphere, via a pipe system, and move it past a sensitive and accurate opacity(不透明性) measuring track.

A.The oil mist detectors

B.The smoke detectors

C.An oily water monitor

D.Oil discharge monitoring and controlling system

If the refrigeration compressor crankcase is sweating, the cause may be due to

A.a shortage of refrigerant

B.the compressor running continuously

C.liquid refrigerant returning to the compressor

D.the compressor short cycling on the high pressure cutout