Дизельные двигатели. Эксплуатация и обслуживание = Diesel engines. Operation and maintenance. Практикум

7.LUBRICATING SYSTEM OF A DIESEL ENGINE

1.Read and translate the text. Pay attention to new phrases.

Lubricating System

A scavenge lubricating pump draws oil from the bedplate and delivers it to the external lubricating oil tank. The pressure pump draws oil from the tank and delivers it, under pressure, through the oil cooler and filter into the main lubricating oil distributor pipe, cast integrally with the bedplate, and to the engine bearings, etc. The engine is designed to work on the dry-sump system. However, in the event of a breakdown of one pump, the lubricating system can be adjusted to run on one pump as a wet-sump engine, by arranging the control cocks.

When running on a wet-sump system, it is important that the oil level in the bedplate is checked by means of the dipstick and the oil level should be kept between the highand low-level marks on the dipstick. There is a relief valve located on each pump. The valve prevents excessive pressure being built up in the system and oil cooler. The vital parts of the engine such as main bearings, connecting rod large end & small end bearings, camshaft bearings, governor and gear wheels are all force lubricated. Other parts such as pistons, cams and cam followers are amply splash lubricated and the valve gear grease lubricated.

draw oil from the bedplate

deliver it to the external lubricating oil tank

main lubricating oil distributor pipe

cast integrally with the bedplate

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work on the dry-sump system

adjust to run on one pump as a wetsump engine

run on a wet-sump system

arrange the control cocks

dipstick

keep between the highand lowlevel marks on the dipstick

relief valve

prevent excessive pressure

large (big) end bearings

small end bearings

camshaft bearings

governor

gear wheels

force lubricate

cam follower

splash lubricate

valve gear

grease lubricate

2. Complete sentences offered:

1.The scavenging lubricating pump draws oil from … and delivers it

to … .

2.The pressure pump draws oil from the tank and delivers it through … into … .

3.The engine is designed to work on … .

4.In the event of a breakdown of one pump, the lubricating system can be adjusted to run … .

5.When running on a wet-sump system, it is important to … .

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6.The important parts of the engine such as … are force lubricated.

7.Other parts such as … are splash lubricated.

8.The valve gear is … lubricated.

3. Ask your interlocutor and give answers:

•if the correct lubrication effects the life of the engine;

•from where the lubricating pump draws oil;

•about the path of lubricating oil;

•about two lubricating systems on which the engine works;

•about the method of checking the oil level;

•about the parts which are force (grease, splash) lubricated.

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8.SCAVENGING

1.Read and translate the text. Pay attention to new phrases.

Scavenging

In the two-stroke cycle engine the scavenge air is admitted through scavenging ports located at the bottom of the cylinder.

In the scavenging arrangement we describe, the exhaust ports are placed on one side of the cylinder and on the opposite side are scavenging ports. The exhaust ports are slightly higher than the scavenging ports so that the piston uncovers the exhaust ports first, thus allowing the pressure in the cylinder to fall before the scavenging ports are opened. By the time the scavenging ports are uncovered the pressure in the cylinder has fallen to atmospheric and the scavenging air rushes in. By inclining the scavenging ports and shaping the piston head, the entering air is deflected upward, as shown by the arrows, and sweeps the burned gases out of the upper part of the cylinder and out through the exhaust ports. When the piston covers the ports on its up stroke, the air is trapped in the cylinder and then is compressed. This arrangement of scavenging does away with the necessity for the scavenging valves in the cylinder head. The only cylinder head valves then required are the spray valve and air starting valve. This simplifies the head, makes cooling easier and reduces the liability to crack.

There are a number of different systems in use for admitting scavenge air.

In 2-stroke Diesel engines the following three methods are used for the scavenging of the cylinder: cross scavenging system (Sulzer), loop scavenging (M.A.N.) and uniflow scavenging system (B. & W.).

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Uniflow scavenging is of greater advantage when compared to the two other systems. It ensures better removal of all residues of the combustion products.

By giving the scavenging port an inclined shape, a rotary motion of the scavenging air is obtained, which means that the air ascends through the cylinder without mixing with the combustion gases, consequently, the latter are forced out of the cylinder, no residue being left.

As a consequence of the advantageous flow conditions, this system requires less surplus air and less scavenging work, too.

The rotary motion of the scavenging air ensures a very even mixture of air and oil, and this in its turn will ensure an unusually good combustion of the oil.

scavenging

uncover the exhaust ports

shape the piston head

the entering air is deflected upward

the air is trapped in the cylinder

simplify the head

reduce the liability to crack

admitting scavenge air

cross scavenging system

loop scavenging

uniflow scavenging system

be of greater advantage

ensure better removal of all residues

rotary motion of the scavenging air is obtained

the air ascends through the cylinder

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as a consequence

system requires less surplus air and less scavenging work

even mixture of air and oil

ensure an unusually good combustion of the oil

2. Complete the sentences. Use suitable words from the list.

1.In the two-stroke cycle engine the scavenge air … through scavenging ports … at the bottom of the cylinder.

2.When the piston covers the ports on its up stroke, the air … in the cylinder and then … .

3.By giving the scavenging port an inclined shape, a rotary motion of the scavenging air … .

4.Combustion gases … out of the cylinder, no residues being left.

5.By inclining the scavenging ports and shaping the piston head, the entering air … upward.

6.The burned gases … through the exhaust ports.

7.Due to advantageous flow conditions less surplus air … .

8.The loop scavenging … in M.A.N. engines.

9.The cross scavenging … in Sulzer engines.

10.The uniflow scavenging system … in B&W engines.

11.The air … in the cylinder.

3. Answer question on the text.

1.Where are the scavenging ports located?

2.Where are the exhaust ports located in the two-cycle Diesel engine?

3.What can you say about the pressure when the piston uncovers the exhaust ports?

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4.By means of what method is the air deflected upward?

5.When is the air trapped in the cylinder?

6.What valves are located on the cylinder head?

7.Name different systems of scavenging in Diesel engines.

8.Enumerate advantages of uniflow scavenging. Does it ensure better removal of gases? What does rotary motion of scavenging air give?

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9.SUPERCHARGING

1.Read and translate the text. Pay attention to new phrases.

Supercharging

Supercharging, or pressure charging, is a means of increasing the power output of a given engine. It is the process of filling the engine cylinder before the compression stroke begins, with air at a pressure several pounds (2.0–2.5 kg) above atmospheric; this is done for the purpose of getting a greater weight of air into the cylinder than can be obtained by the ordinary method. Since the ratio of air at beginning and end of compression for any condition is fixed, it follows that, if we start with a higher pressure, the final compression pressure will be higher. This means that if the engine is supercharged, the volume of the compression space must be enlarged if the compression pressure is to be kept the same.

Having a greater weight of air in the cylinder we can burn more fuel. Although more oil is burned there is more air present and the ratio of oil to air is the same as without supercharging. Exhaust occurs at a higher pressure, but the temperature of the exhaust is even lower than with ordinary operation. The reason for this is that the valve timing is so arranged that the inlet valve opens before the exhaust valve closes; and the inlet air being higher in pressure than the exhaust gases at the time the inlet valve opens, the air is blown through the compression space, scavenging out the gases and cooling them, as well as cooling the piston and cylinder walls. This action also completely fills the compression space, i.e. cylinder space with fresh air. The net increase in power developed in the engine may be as much as 50 %.

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In modern Diesel engines exhaust gas turbocharging is widely used. The exhaust-driven turbochargers operate on the pulse system or on the constant-pressure principle, and are independent of the crankshaft. Their speed changes with the load on the engine. No auxiliary drive or blower is required for starting or for operation at partial loads. The air compressed by the turbochargers flows into the scavenging air receiver and through non-return valves into the chambers below each cylinder. Here it is further compressed by the pistons on their downward stroke before flowing into combustion space when the pistons uncover the scavenging ports. The pumping action of the lower piston surfaces is quite sufficient to scavenge out and charge the cylinders when the engine is being started up, before the turbochargers come into operation. In fact even if all the turbochargers should be out of action, the ship could still be run at 75 % of her normal speed. Another consequence of this arrangement is that the exhaust remains completely clear even down to low partial load.

supercharging

pressure charging

means of increasing power output

ratio

valve timing

the engine is supercharged

gas turbocharging

lower piston space

to come into operation

to be out of action

greater weight of air in the cylinder

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to blow through

to change with the load of the engine

auxiliary drive

pumping action (surging)

exhaust-driven turbocharger

engine operation at partial loads

the cylinder volume is enlarged

net increase

humming

snoring

howling

gulping

overspeed (engine racing)

hunting

2. Complete the following sentences:

1.Supercharging or pressure charging is … .

2.Supercharging is the process of … .

3.Having a greater weight of air in the cylinder we can burn … .

4.In modern diesel engines … is widely used.

5.The exhaust-driven turbochargers operate on … system or on … principle.

6.The speed of exhaust-driven turbochargers changes with … .

7.… is required for starting or for operation at partial loads.

8.The air compressed by the turbochargers flows into … and through … into … .

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