单选题Injectors for use with heavy fuel oil must be cooled by either water or light oil to （）A prevent heat corrosion to internal componentsB increase fuel delivery rate and economyC prevent pre-ignitionD avoid carbonization of the nozzle tips

Injectors for use with heavy fuel oil must be cooled by either water or light oil to_____.

A.prevent heat corrosion to internal components

B.increase fuel delivery rate and economy

C.prevent pre-ignition

D.avoid carbonization of the nozzle tips

Which product is volatile ________．

A.Benzene

B.Diesel fuel

C.Coal tar

D.Heavy industrial fuel oil

A.viscosity a heated to reduce its

B.cooled to reduce its temperature

C.heated to reduce its density

D.heated to reduce its gravity

A ship which is required to carry an Oil Record Book must log in the book ______.

A.discharge of ballast or cleaning water from fuel tanks

B.sounding levels of all fuel tanks on a daily basis

C.the grade and specific gravity of all fuel oil carried

D.fuel consumption rates on a weekly basis

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