A hot air start pipe indicates that there is （）.

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

Man has always wanted to fly.Even as long as eight hundred years ago, an Englishman had tried.He made a (1)of wings from chicken feathers and fixed them to his shoulders.Then he jumped om a tall building.As you can imagine, he did not fly very far.(2) he fell to the ground and broke several bones.The first real attempt at flying took place in France in 1783.The two Mongolian brothers knew that hot air rose.If they could

fill a large balloon(3)hot air, they thought it would rise into the air and fly.They were right.They made a very large hot air balloon of cloth and paper.It measured ten meters it diameter.They filled it with hot air and the balloon got two hundred meters into the air.It fell into earth about three kilometers away.

At the next attempt, they (4) passengers use a bal loon to rise into the air and fly.We do not know what the passengers fell about the trip as they were a cock, a duck, and a sheep But we (5) know that the trip lasted eight minutes and the animals landed safely.(完型填空)

A.Instead

B.Pair

C.Do

D.Arranged

E.With

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