Дизельные двигатели. Эксплуатация и обслуживание = Diesel engines. Operation and maintenance. Практикум
.pdf4.CYCLE OF DIESEL ENGINES
1.Read and translate the text. Pay attention to new phrases.
Cycles of Diesel Engines
Any internal combustion engine, regardless of principle it operates on, is said to have a four-stroke cycle or a two-stroke cycle. According to the construction the engines may be single or double acting, trunk-piston type, crosshead type, opposed-piston type. According to the method of air supply the engines are supercharged and naturally aspirated.
The four-stroke cycle consists of: the suction stroke, compression stroke, combustion and expansion stroke and exhaust stroke. The piston starts a downward, suction stroke. The air inlet valve is open and air is being drawn into the cylinder through the air inlet pipe. The exhaust valve, fuel valve are all closed. As the piston reaches the end of the suction stroke the air inlet valve closes and as the piston rises on the second, or compression, stroke the air in the cylinder is compressed. At the end of this stroke the air has been compressed to about 480 pounds and its temperature has risen to about 1,000 degrees F. Ignites the fuel now opens and the fuel oil is sprayed into the cylinder under a pressure of 3,550 p.s.i. The high temperature of the compressed air in the cylinder ignites the fuel, and it continues to burn as long as injection is maintained. This burning raises the temperature of the gas to approximately 3,000 °F. In the meantime, the piston has started down on the third, or expansion, stroke with the gas expanding behind it. The injection valve closes shortly after the piston has started down on this stroke. At the end of this stroke the exhaust valve opens and the burned gases in the cylinder, now reduced to about 40 pounds pressure, and
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correspondingly reduced in temperature, start to flow out through the exhaust pipe. Returning on the fourth, or exhaust, stroke the piston pushes the remaining gas out of the cylinder. At the end of this stroke the exhaust valve closes, the air inlet valve opens and the cycle of operations starts again.
It is thus seen that one complete cycle requires four strokes of the piston; the four strokes comprise two complete revolutions of crankshaft.
In the 2-cycle, single acting Diesel engine instead of an exhaust valve there is a ring of exhaust ports around the bottom of the cylinder, communicating with the exhaust pipe. The spray valve and starting valve are the same as in the 4-cycle. In place of air inlet valves there are scavenging ports, in place of exhaust valves there are exhaust ports, in uniflow scavenging engines there are exhaust valves. The scavenging ports are in communication with a passage leading to a lowpressure scavenging air compressor, operated from the engine.
When the piston on its downward stroke uncovers the exhaust ports and the cylinder pressure drops to atmospheric, the scavenging ports open and the air, under pressure, flows into the cylinder and pushes the exhaust gases out through these ports. As the piston on its up stroke covers the scavenging ports, the exhaust ports close, leaving the cylinder full of fresh air. The piston moving upward on its compression stroke, compresses this air and at the end of compression fuel injection occurs, just as previously described for the 4-stroke cycle.
It is thus seen that the complete series of operations, including fuel injection and combustion, expansion, exhaust, filling cylinder with fresh air and compression, occurs in two strokes of the piston, or one revolution of the crankshaft.
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four-stroke cycle
two-stroke cycle
single acting engine
double acting engine
engine of trunk-piston type
engine of crosshead type
engine of opposed-piston type
method of air supply
supercharged engine
naturally aspirated engine
suction stroke
compression stroke
combustion stroke
expansion stroke
exhaust stroke
air is being drawn into the cylinder through the air inlet pipe
air inlet valve
exhaust valve
compress air
rise
raise temperature
degrees Fahrenheit
p.s.i. = pounds per square inch
ignite fuel
the fuel oil is sprayed into the cylinder under a pressure
as long as injection is maintained
approximately
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expand gas
burned gases
gas reduced to about 40 pounds pressure
flow out through the exhaust pipe
push the remaining gas out of the cylinder
it is thus seen that …
require four strokes of the piston
comprise two complete revolutions of crankshaft
instead of an exhaust valve
exhaust ports around the bottom of the cylinder
uniflow scavenging engine
uncover exhaust ports
pressure drops to atmospheric
cover scavenging ports
leave the cylinder full of fresh air
move upward on compression stroke
fuel injection occurs
2. Fill in the gaps in the sentences with words or word combinations from the word box: to maintain; combustion and expansion; scavenging ports; downward; exhaust; air inlet pipe; exhaust ports.
1.The piston moves ... on a suction stroke.
2.The air inlet valve opens, and the air being drawn into the cylinder through … .
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3.The high temperature of the compressed air in the cylinder ignites the fuel, and it continues to burn as long as the injection is … .
4.The piston starts down on the third or … stroke.
5.Returning on the fourth or … stroke, the piston pushes the remaining gases out of the cylinder.
6.In the 2-cycle Diesel engine instead of an exhaust valve there is a ring of …, in place of air inlet valves there is … .
3. Choose the correct word:
1.The exhaust valve is ... .
a) close b) closing c) closed
2.The fuel continues to burn as long as injection is … . a) maintenance
b) maintained c) maintaining
3.The piston moves downward with the gas ... behind it. a) expand
b) expansion c) expanding
4.The scavenging ports are in … with a passage leading to a lowpressure compressor.
a) communication b) communicating c) communicated
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5. The scavenging air compressor is … from the engine.
a)operation
b)operating
c)operated
4. Make up sentences using their parts (use verbs in the correct Tense and Voice):
1)to spray / the fuel / under / the cylinder / into / pressure;
2)to reduce / pressure / the gas / and / during / temperature / in / the expansion stroke;
3)to be / there / an exhaust pipe / the cylinder / connected / to;
4)to operate / a scavenging air compressor / the engine / from;
5)the 2-cycle engine / in / only / revolution / one / crankshaft / to
require.
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5.THE FUEL SYSTEM OF A DIESEL ENGINE
1.Read and translate the text. Pay attention to new phrases.
The Fuel System of a Diesel Engine
If the engineer wants to do his job effectively, he must have a good knowledge of the engine fuel system. The functions of this system are taking on, transferring, storing, settling, heating, filtering and supplying fuel oil into the engine’s cylinders.
The fuel is taken from the storage tank by means of fuel transfer pump and delivered to the settling tank where it is preheated and settled then passed through the centrifugal purifier for efficient cleaning and delivered to the service tank for using in operational process. The fuel is then led to one of the two electrically driven supply pumps which deliver it under pressure through a flow metre to the fuel circulating pump and through the oil heater — viscosity regulator — to the filter. Then the fuel is supplied by high pressure fuel pump to the fuel injection valve of each cylinder for combustion process.
The fuel piping system consists of three main pipelines: fuel supply lines, high pressure fuel lines and fuel heating piping. The fuel supply line connects the fuel transfer pump and preheating arrangements with fuel filters and fuel pumps. The high-pressure fuel lines connect HP fuel pumps with fuel valves and are under very high intermittent pressure. The preheating system is led along the fuel supply lines, high pressure fuel lines and filters.
The fuel system fittings are: fuel pressure maintenance / pressure retaining valve, fuel shut-off valve, fuel non-return valve. The function of the fuel pressure retaining valve is to maintain adjustable back pressure, which is to be so high that there is no formation of vapor
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on the suction side of the fuel pump. The fuel shut-off valve opens during operation, and its function is to isolate the main pipe for dismantling of the fuel pump or preheating. It is provided with a double-cone seat to prevent leakage. The non-return valve is placed between the fuel pump and the overflow line which is used for leakage of surplus fuel. The fuel pump may be isolated from the overflow line by the non-return valve for dismantling.
The high-pressure fuel pumps discharge fuel through the discharge line to the fuel valve under high pressure. Then finely atomized fuel is sprayed into the combustion chamber through nozzle orifices.
Grade of fuel oil effects the engine performance. Fuel requirements for operating conditions are specified in a document called certificate of quality or fuel specifications. The most frequent items in this document are the following: Specific Gravity or Density, Viscosity in cst, Flashpoint, Ash Content, Sulphur Content, Water Content, Sediments, Carbon Residues, Calorific Value, Water Soluble Acids, Pour Test, Cloud Point and Alkalis.
storage tank
fuel transfer pump
settling tank
centrifugal purifier
service tank
supply pump
flow metre
viscosity regulator
fuel injection valve
fuel supply lines
high pressure fuel lines
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preheating arrangement
intermittent pressure
pressure maintenance valve / pressure retaining valve
fuel shut-off valve
fuel non-return valve
adjustable back pressure
formation of vapor
to prevent leakage
overflow line
to discharge
finely atomized fuel
nozzle orifice
engine performance
Specific Gravity
Density
Viscosity
Flashpoint
Ash Content
Sulphur Content
Sediments
Carbon Residues
Calorific Value
Water Soluble Acids
Alkalis
Cloud Point
Pour Test
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2.Fill in the gaps in the sentences with words or word combinations from the word box: intermittent; preheating arrangement; heavy fuel; fuel shut-off valve; welding; non-return valve; fuel transfer pump:
1.The fuel system comprises fuel supply line, high-pressure line and fuel heating pipes, if … is used.
2.High-pressure lines are under high …pressure.
3.Defective HP fuel lines must not be repaired by … .
4.… employs steam up to 7 kg/sq.cm.g.
5.… is driven separately by an electric motor.
6.… … isolates the main pipe temporarily for dismantling the fuel pump or preheating.
7.... isolates the fuel pump from the overflow line, into which the surplus fuel runs off during operation.
3. Choose the correct word:
1. The drain lines for leakage fuel are also partially … .
a)heating
b)heated
c)heat
2.Filter elements can be … over during operation. a) switch
b) switching c) switched
3.The fuel pressure-retaining valve is designed for … back pressure. a) adjustment
b) adjustable c) adjusting
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