轮机英语【轮机长】题库

问答题 6分

In one type of large bore MC engines with high cylinder numbers, we have experienced longitudinal vi...

In one type of large bore MC engines with high cylinder numbers, we have experienced longitudinal
vibrations of exhaust receiver of a magnitude that caused local overstressing around the fixed supports.
Measurements revealed that the vibrations were caused by gas pulsation inside the receiver at a frequency,
which, at certain engine speeds, coincided with the natural frequency of the mechanical vibrations of the
receiver. The problems were solved by redesigning the receiver and its supports, so as to change the natural
frequency. The fixed support for the exhaust receiver was modified from our single spring plate type to a
double spring plate type. The double spring plate type reduces the local deformation of the receiver and
because of the greater rigidity, also the natural frequency of the support is increased.

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参考解析:
1. The MC engine_____. A. is a new type of diesel engine discovered and used on board not long ago B. is a new type of diesel engine designed on the basis of MAN and B&W engine C. came to use before the MAN and B&W engine D. has no advantages over the MAN and B&W engine 2. The vibration caused by_____. A. the natural frequency of the fixed support B. the different engine speeds C. the gas pulsating within the receiver D. the gas exhausting inside the receiver 3. The aim at redesigning the receiver and its supports is to_____. A. keep the frequency down B. convert the natural frequency C. reduce the mechanical vibration D. exhaust much gas 4. The fixed support of the receiver of double spring plate type is_____. A. modified from that of the receiver of single spring plate type B. to reduce the local deformation of the receiver C. to produce less natural frequency of the support D. both A and B

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1 问答题 6分

The lubrication system of an engine provides a supply of lubricating oil to the various moving parts in
an engine. Its main function is to enable the formation of a film of oil between the moving parts, which
reduces friction and wear. The lubricating oil is also used as a cleaner and in some engines as a coolant. The
usual method of bearing lubrication is by forced feed system, which supplies oil to all bearings, so that a
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2 问答题 6分

This sequence of events is made possible by substituting ports in the bottom of the cylinder wall for
the inlet and exhaust valves. There are two groups of these ports, one for exhaust and the other for
scavenging air, usually on the opposite sides of the cylinder, but in some designs both groups are arranged
on the same side. The exhaust ports connect with the exhaust manifold, while the scavenging ports
communicate with the scavenging air receiver in which low-pressure air is stored. The exhaust ports are
slightly higher than the scavenging ports, so that they are uncovered by the piston while the scavenging
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3 问答题 6分

Spark erosion is caused by a voltage discharge between the main bearing and journal surface. The
cause of the potential is the development of a galvanic element between the ship’s hull, sea water,
and the propeller shaft/crankshaft.

The oil film acts as a dielectric. The puncture voltage in the bearing depends on the thickness of the oil
film. With increasing engine ratings, the specific load in the main bearing is increased. This will reduce the
oil film thickness, and enable the discharge to take place at a lower voltage level.

Since the hydrodynamic oil film thickness varies through a rotation cycle, the discharge will take place at
roughly the same instant during each rotation cycle, i.e. when the film thickness is at its minimum. The
roughening will accordingly be concentrated in certain areas on the journal surface. In the early stages, the
roughened areas can resemble pitting erosion. but later, as the roughness increases, the small craters will
scrape off and pick up white metal-hence the silvery white appearance.

Therefore, to ensure protection against spark erosion, the potential level must be kept at maximum 80
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4 问答题 6分

Pressurized oil atomization is used for smaller capacity burners. The nozzle is located at the end of the
oil gun. In the nozzle a number of small holes are oriented to assure the rotating flow for atomizing and
spraying the oil in the most efficient way.

As the geometry of the nozzle is fixed the velocity in the small holes and slits in the nozzle depends
upon the load on the burner. The higher load the higher velocity and thereby the better atomization. On the
other hand this means that the lower load the lower velocity and thereby the poorer atomization. Typically
pressurized jet atomization is efficient for a turndown ratio 1:2, i.e. 50 % load. At lower load, the
atomization will not be satisfying and this means non-satisfying combustion quality eventually causing soot
formations. The oil pressure varies between 0.5 and 2.0 MPa. As mentioned ensuring the correct
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specific nozzle. For the pressurized jet burners the swirl of the combustion air is created by means of a
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5 问答题 6分

For a certain provision cooling plant, the capacity regulator is generally controlled depending on
pressure, temperature or relative humidity. The pulse emitter is therefore either a pressostat(压力继电器),
thermostat or hygrostat. The switching difference of the control units should be rated as large as possible.
This applies in particular to control by means of the pressure, because change to the load in the
refrigeration circuit results in relatively quick pressure changes compared to temperature, which can in turn
lead to inadmissible oscillation of the regulator.

Under partial load, the suction volume and thus the gas speed can undergo marked changes depending on the
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In order to guarantee sufficient oil return, neither full load nor partial load operation may allow the gas speed
to fall below a minimum level: 4 m/s in horizontal pipe sections; 8 m/s in vertical pipes.

For this reason we recommend that vertical pipes bestaggered into two separate sections (as illustration).
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blocked by an accumulation of oil. This increases the gas velocity in pipe section A. In order to guarantee adequate
oil return, both cross sections must be rated so large that the velocity does not fall below the minimum level
in full and partial load operation. In plants with extensive pipe systems it is recommended at least for R22 and NH3
to install an additional oil separator. This reduces the oil circulation period and can have positive effects above
all for cold starts with relatively high oil ejection.

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第一章船舶主推进装置

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第三章船舶电气和自动化

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第五章国际公约、规则

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