单选题The rising of the exhaust temperature in manifold pipe may NOT result from （）.A too great a loadingB fouled turbochargerC bad combustionD excessive air

High firing pressures and low exhaust temperature in a diesel engine may resultfrom( ).

A.decreased piston to cylinder head clearance

B.increased exhaust system back pressure

C.early fuel injection timing

D.low scavenge air temperature

Maintaining the lowest possible scavenging air temperature at all times is not recommended due to the possibility of the ______.

A.air charge density becoming too high

B.piston crown surfaces becoming too cold

C.formation of excessive quantities of condensate

D.compression pressure being greatly reduced

High cylinder firing pressure, accompanied by low exhaust temperature, can result from ___.

A.improper fuel rack positing

B.lengthy exhaust valve duration

C.extend operation at light load

D.excessively early injection timing

In many areas "atoll" clouds (clouds of vertical development) are produced over small islands. These are the result of ______.

A.rising air currents produced by the warm islands

B.warm air from the sea rising over higher land areas

C.cool land air mixing with warm sea air

D.descending air over the islands

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

The relative air pressure in the inlet manifold of a turbocharged diesel engine is usually______.

A.greater than the average exhaust manifold pressure

B.less than the average exhaust manifold pressure

C.greater at the turbine wheel than at the impeller

D.greater at reduced engine speed

A.Close the inlet and outletvalves for diesel oil

B.Open the air nozzles in the secondary combustion chamber until it stops

C.Open the air nozzles in the primary combustion chamber until it stops

D.Close inlet valve for pressurized air

The exhaust pipe must be gas tight throughout its entire length otherwise ______．

A.Bilge water may enter the exhaust pipe

B.Entry of air may cause vapor lock

C.Carbon monoxide may enter the interior of the vessel

D.The joint gaskets may be blown