Sludge may form in the crankcase of an air conditioning comp

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

Sludge may form in the crankcase of an air conditioning compressor as a result of ______.

A.bubbling refrigerant

B.overheating and oxidation

C.lowered operating temperatures

D.reducing the cloud or floc point

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

Due to the large amount of heat picked up by the air in boiler and engine rooms, it would be impracticable to maintain ambient conditions within the comfort zone by air conditioning or any other means. The normal practice is to provide copious mechanical ventilation; in boiler rooms, the quantity is equated to the combustion requirements, while in a motor ship engine room the supply may be 25-50% in excess of the requirements of the engines.

The axial flow fan is particularly suited to handle these large air volumes at the moderate pressures required, while of course the “straight-through” flow feature places it at an advantage over the centrifugal fan.

The increasing adoption of automation, with the provision of a separate control room makes less significant the fact that comfort conditions cannot be maintained in the engine room all the time. Which of the following devices should be taken to maintain ambient conditions of the boiler and machinery space?

A.air compressor

B.air cooler

C.air-conditioning plant

D.mechanical ventilation plant

In an air conditioning system, moisture is removed from the air by ______.

A.filters

B.separators

C.ducted traps

D.dehumidifiers

According to this passage, which of the following statements is true?

A.In boiler and machinery spaces, there is the air conditioning.

B.In the boiler rooms the requirement of air volume should meet 25-50% of combustion requirement.

C.To maintain the comfort zone in the separate control room the air conditioning plant should be fitted.

D.The comfort conditions can be maintained in the engine room all the time.

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