单选题If a single cylinder relief valve on a diesel engine lists frequently while the engine is running, the cause may be an （）A excessively late injection timing for each cylinderB incorrectly adjusted intake valve timingC incorrectly adjusted fuel injector

Fuel is admitted to a diesel engine cylinder through the ______.

A.injector nozzles

B.carburetor

C.exhaust ports

D.intake valves

In a diesel engine, late fuel injection is indicated by black or gray exhaust smoke with ______.

A.low firing pressure

B.low exhaust temperature

C.mechanical knock in each cylinder

D.fuel knock in each cylinder

If the diesel engine fuel injection timing is changed to delay the start of injection until the pistons are at top dead center, the engine will_________.

A.backfire through the air intakes

B.develop less power under load

C.have high firing pressures

D.lift its cylinder relief valves

One cylinder of a diesel engine is persistently knocking and does not cease(停止) when the fuel supply to that cylinder is secured.Which of the following problems may be the cause?

A.Low loading of the cylinder

B.Excessive cooling of that piston

C.Sluggish ring action on the piston

D.A mechanical defect in a working part

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