单选题Injectors on modern engines are cooled by a combination of the intensive bore cooling in the cylinder by a combination of the intensive bore pockets and by the fuel which is re-circulated through the injector when the follower is on the （）of the cam or when the engine is stopped.AslopeBbaseCtopDbottom
单选题
Injectors on modern engines are cooled by a combination of the intensive bore cooling in the cylinder by a combination of the intensive bore pockets and by the fuel which is re-circulated through the injector when the follower is on the （）of the cam or when the engine is stopped.
A
slope
B
base
C
top
D
bottom
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Each cylinder liner on the marine medium speed engines _____.A.is usually cooled by sea waterB.can be replaced when worn outC.is in direct contact with the water in the bore of the cylinderD.can t expand when heated
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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 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 headB.several injectors mounted around the external boundary of the cylinder headC.a single injector mounted at the external boundary of the cylinder headD.several injectors mounted in the center of the cylinder head
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
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Cylinders of marine diesel engines are normally cooled by ___ .A.sea waterB.fine mineral oilC.sanitary waterD.fresh water
Modern marine diesel engines equipped with mechanical fuel injection operate on a combustion phase within the cycle which is ______.A.entirely constant pressureB.entirely constant temperatureC.a combination of constant volume and constant pressureD.a combination of constant temperature and constant pressure
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