1. ,
.
1. An engine produces power by burning air and fuel.
a. What is an engine supplied with?
b. Does fuel burn inside an engine?
c. How does an engine produce power?
2. At optimal point in the compression stroke a spark plug creates an electric spark that ignites the fuel.
a. The ignition of fuel takes place in the compression stroke, doesnt it?
b. How is the fuel ignited?
c. What does the ignition of fuel result in?
3. The outward linear motion of the piston is used by a crankshaft to produce circular motion.
a. When is circular motion produced?
b. What is the outward linear motion of the piston used by a crankshaft for?
c. How is a crankshaft constructed?
4. Diesel engines use less fuel and last longer than petrol engines.
a. What are the most common types of engine?
b. What kind of fuel is used in diesel engines?
c. What are the advantages of diesel engines?
5. Valves control the intake of air fuel mixture and allow exhaust gases to exit at the appropriate time.
a. Which valves control the intake of air fuel mixture?
b. What controls the flow of air fuel mixture into and out of the cylinder?
c. Where are valves fitted?
2. ,
.
1. The fuel is stored........
a. in a fuel tank
b. in a fuel pipe
c. in a carburettor
2. The burned fuel and air........
a. are expelled from the cylinder
b. are drawn into the engine cylinder by the piston
c. are compressed by the piston
3......... is controlled by two valves.
a. The burning of fuel air mixture
b. The flow of gases into and out of the cylinder
c. The fuel pump
4. The combustion of fuel........
a. results in the generation of heat
b. is used by a crankshaft to produce circular motion
c. is controlled by a throttle
5. Diesel engines are safer than petrol engines because........
a. they are lighter and smaller
b. they are less noisy
c. there is less danger of fire
3. .
. :
1) , ;
2) , .
, , . .
: 4 2 .
UNIT 3
TEXT A
TWO-STROKE ENGINE
The two stroke engine is simple in construction, but complex dynamics are employed in its operation.
The rising piston creates a partial vacuum in the crankcase. The inlet port is uncovered by the piston as it rises, and the air fuel mixture enters the crankcase. As the piston descends, it closes the inlet port and pressurizes the crankcase. The air fuel mixture is forced into the cylinder through the transfer ports. As the piston reaches bottom and then starts to rise again the transfer ports are closed by the piston and the air fuel mixture is compressed.
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When the piston reaches the top of its stroke, the mixture is ignited, and the piston is forced down by the rapidly expanding gases of combustion. As the piston descends, the exhaust port is opened, and the burned gases escape. The transfer ports are just a bit lower than the exhaust port, so there is a period of time when fresh air fuel mixture is coming in while exhaust gases escape out to the atmosphere.
WORD LIST
dynamics
employ
rise
create
partial
crankcase
descend
transfer port
as
reach
combustion
bottom
rapidly
expand
low
so
while
through
pressurize
exhaust gases
1.
:
to employ crankcase partial while(as)
to rise transfer port low through
to create dynamics rapidly
to descend bottom
to reach
to expand
2. .
force, employ, move down, move up, descend, use, rise, push, expand, fill up.
3. .
1. uncover 1. exhaust
2. rise 2. escape
3. enter 3. down
4. inlet 4. close
5. bottom 5. top
6. up 6. descend
4. ,
.
.
two stroke engine force down
force into the cylinder rapidly expanding
top of the stroke burned gases
5. , .
6. ,
.
.
7. .
1) In what way does the air fuel mixture enter the crankcase?
2) How does the air fuel mixture get into the cylinder?
3) When is the air fuel mixture compressed?
4) When is the mixture ignited?
5) What is the piston forced down by?
6) In what way are the burned gases removed?
TEXT B
FOUR-STROKE CYCLE
The four stroke cycle of an internal combustion engine is the cycle most commonly used for automotive and industrial purposes today. It was invented by Nikolaus Otto in 1876, and it also called the Otto cycle.
On the first (downward) stroke of the piston, fuel/air is drawn into the cylinder through the intake valve. The intake valve then closes and the following (upward) stroke compresses the fuel air mixture, which is then ignited, usually by a spark plug, at approximately the top of the compression stroke. The resulting expansion of burning gases then forces the piston downward for the third stroke, and the fourth and final (upward) stroke evacuates the spent exhaust gases from the cylinder through the then open exhaust valve.
The four stroke cycle is more efficient than the two stroke cycle, but requires considerably more moving parts and manufacturing expertise.
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WORD LIST
commonly
purpose
invent
call
intake valve
approximately
compression stroke
evacuate
efficient
require
considerably
expertise ,
1. :
1. where the 4 stroke cycle of an internal combustion engine finds its use;
2. what fuel/air is drawn into on the 1st stroke;
3. what the 2nd stroke makes with the fuel- air mixture;
4. what the expansion of burning gases results in;
5. what way the exhaust gases are evacuated;
6. whether the 4 stroke is more efficient than the 2 stroke cycle.
2. . .
1. On the 1st (induction) stroke of the piston fuel air mixture is drawn into the cylinder through the intake valve.
2. At the top of the 2nd (power) stroke the fuel air mixture is compressed and then ignited by a spark plug.
3. On the 3d (compression) stroke the resulting expansion of burning gases forces the piston upward.
4. On the 4th (exhaust) stroke the spent exhaust gases are evacuated from the cylinder through the open exhaust valve.
3. 1- 2, -
- ,
.
TEXT C
DIESEL CYCLE
The diesel cycle is the combustion process of a type of internal combustion engine in which the burning of the fuel is triggered not by a spark plug as in the four stroke cycle, but rather by the heat generated in compressing the fuel air mixture.
In the Diesel cycle only air is drawn into the engine and compressed. The fuel is then injected directly into the cylinder with a high pressure fuel injector when the piston reaches the top of its motion. The fuel is thicker and burns more slowly than petrol, so the piston is already moving down by the time the combustion completes. Thus the Diesel actually loses some of the potential energy of the charge, although it is less stressful on the engine. For example, in the 4 stroke cycle the fuel can cause the dreaded condition known as knock. Knock occurs when the fuel ignites at the wrong time, usually from heating while it is being compressed. In the Diesel this problem simply cant happen, because the fuel isnt in the engine until the exact moment it is needed. This allows the Diesel to be run at much higher compression ratios. Thus the Diesel engine is considerably more efficient than a similar 4 stroke engine.
WORD LIST
trigger while
rather happen
generate until .
directly run
injector compression ratio
reach considerable
thick efficient
complete similar
actually
charge
although
cause
dreaded condition
knock ;
occur
1. :
(a) ;
(b) ;
(c) 4 .
