Starting air for auxiliary engines may be taken directly fro

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

In an operating diesel engine, which of the following conditions is an indication of a leaking air starting valve?

A.Noise coming from that air starting valve

B.Continuous operation of the starting air compressor

C.Zero air pressure in the air starting system

D.Overheated starting air pipe to the cylinder head

A.filtering

B.centrifuging

C.depositing

D.operating

题干材料：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.

问题：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 a motor vessel, the air quantity which the engine room need is_______ of the requirements of the engines.A.less than 25-50%

B.more than 125-150%

C.more than 25-50%

D.less than 125-150%

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

At the middle pressure and large air quantity,_________ is more suitable.A.an axial flow fan

B.a radial flow blower

C.a centrifugal fan

D.an auxiliary blower

请帮忙给出每个问题的正确答案和分析，谢谢！

Vessels having main engines arranged for air starting are to be provided with at least__.

A.one automatic drain serving both containers

B.two air starting containers of approximately equal size

C.one control air container and one starting air container

D.one additional means of starting the main engine

If the engine does start on air, but combustion does not immediately begin, the cause may be _____.

A.failure of the fuel pumps

B.starting air pressure too low

C.stop valve in air line closed

D.the turning gear still engaged

If the engine does not start on air, it may be due to

A.low compression of the fuel pumps

B.incorrect timing of fuel pumps

C.the starting air valves stuck

D.air-locks in fuel oil pipeline