单选题When a fuel injection nozzle overheats, which of the problems listed can be expected?（）A The fuel metering will varyB The fuel will explodeC The cylinder head will crackD The engine will stop

Which of the following problems is the main source of fuel pump and injection system malfunctions?

A.Improper lubrication

B.Air in the fuel system

C.Coated fuel lines

D.Excessive vibration

_______can be a direct cause of faulty operation of diesel engine fuel injection nozzles.

A.Excessive fuel nozzle holder cooling

B.Sediment in the fuel supply

C.Distortion of the fuel spray pattern

D.Improper atomization of the fuel

Because the timing of injection is crucial, _____ mounted on the camshaft, which is driven by the crankshaft are used to operate the fuel pumps, one of which is provided for each cylinder.

A.gears

B.rams

C.barrels

D.cams

第一组

Older loop scavenged engines may have a single injector mounted centrally in the cylinder head. Because the exhaust valve is in the center of the cylinder head on modern uniflow scavenged engines the fuel valves (2 or 3) are arranged around the periphery of the head. The pressure at which the injector operates can be adjusted by adjusting the loading on the spring. The pressures at which the injectors operate vary depending on the engine, but can be as high as 540 bar. Some injectors have internal cooling passages in them extending into the nozzle through which cooling water is circulated. This is to prevent overheating and burning of the nozzle tip. Injectors on modern engines do not have internal cooling passages. They are cooled by a combination of the intensive bore cooling in the cylinder head being close to the valve pockets and by the fuel which is re-circulated through the injector when the follower is on the base of the cam or when the engine is stopped. As well as cooling the injector, re-circulating the fuel when the engine is stopped keeps the fuel at the correct viscosity for injection by preventing it from cooling down. Fuel injectors must be kept in good condition to maintain optimum efficiency, and to prevent conditions arising which could lead to damage within the cylinder. Injectors should be changed in line with manufacturers&39; recommendations, overhauled and tested. Springs can weaken with repeated operation leading to the injector opening at a lower pressure than designed. The needle valve and seat can wear which together with worn nozzle holes will lead to incorrect atomization and dribbling.

Modern uniflow scavenged engines have______.

A.a single injector mounted in the center of the cylinder head

B.several injectors mounted around the external boundary of the cylinder head

C.a single injector mounted at the external boundary of the cylinder head

D.several injectors mounted in the center of the cylinder head

The plunger in a jerk pump is rotated until the release port is uncovered If the port remains uncovered all of the time, which of the listed operations will occur?

A.No fuel will be delivered

B.The maximum effective stroke will be attained

C.The fuel delivered to the cylinder will be excessive

D.The injection nozzle will overheat and carbonize