Technical english for automotive engineering chapter 2 THE ENGINE

An individual cycle comprises four strokes: 1, intake stroke; 2, compression stroke; 3, power stroke and 4, exhaust stroke.. The intake stroke on the diesel engine draws only air into th

Chapter 2: The Engine

I. PRE-READING QUESTION

1 Name some kinds of engines you know

2 Do you have a four-stroke engine in your house? How powerful is it?

3 What type of fuel does a four-stroke engine run on?

II. READING

1 The reciprocating engine

The engine is the heart of a car although it is normally hidden under the bonnet The engine is exposed in a motorcycle but the detailed mechanisms are not visible

There are two main types of reciprocating engine, the four-stroke and the two-stroke engine:

1.1 The petrol engine

1.1.1 Four-stroke engine

Fig2.2: Basic operations of four-stroke cycle engine

Fig 2.1: Cutaway of four-stroke cycle petrol engine (courtesy of Volvo Car Corporation)

The four-stroke engine is also referred to as the Otto cycle engine after its inventor N.A Otto Most cars use the four-stroke engine An individual cycle comprises four strokes: 1, intake stroke; 2, compression stroke; 3, power stroke and 4, exhaust stroke These four strokes repeat to generate the crankshaft revolution

+ Intake stroke: the intake stroke draws air and fuel into the combustion chamber The piston

descends in the cylinder bore to evacuate the combustion chamber When the inlet valve opens, atmospheric pressure forces the air-fuel charge into the evacuated chamber As a result, the combustible mixture of fuel and air fills the chamber

+ Compression stroke: at the end of the intake stroke, both inlet and exhaust valves are

closed The inertial action of the crankshaft in turn lifts the piston which compresses the mixture The ratio of the combustion chamber volume before and after compression is called the compression ratio

+ Power stroke: when the piston ascends and reaches top dead center, an electric current

ignites the spark plug and as the mixed gas burns, it expands and builds pressure in the combustion chamber The resulting pressure pushes the piston down with several tons of force

+ Exhaust stroke: during the exhaust stroke, the inlet valve remains closed whilst the exhaust

valve opens The moving piston pushes the burned fumes through the now open exhaust port and another intake stroke starts again

During one cycle, the piston makes two round trips and the crankshaft revolves twice The inlet and exhaust valves open and close only once The ignition plug also sparks only once A

petrol engine, whether four- or two-stroke, is called a Spark Ignition (SI) engine because it

fires with an ignition plug The four-stroke-cycle engine contains the lubricating oil in the crankcase The oil both lubricates the crankshaft bearings and cools the hot piston

1.1.2 The two-stroke engine

The two-stroke engine is similar to that of the four-stroke-cycle engine in its reciprocating mechanism It uses the piston-crankshaft mechanism, but requires only one revolution of the crankshaft for a complete power-producing cycle The two-stroke engine does not use inlet and exhaust valves The gas exchange is implemented by scavenging and exhaust port-hole openings in the bore wall The upward and downward motion of the piston simultaneously opens and closes these port-holes The air-fuel mixture then goes in or out of the combustion chamber through the port-holes Combustion takes place at every rotation of the crankshaft

In the two-stroke engine, the space in the crankcase works as a pre-compression chamber for each successive fuel charge The fuel and lubricating oil are premixed and introduced into the crankcase, so that the crankcase cannot

be used for storing the lubricating oil When combustion occurs in the cylinder, the combustion pressure compresses the new gas

in the crankcase for the next combustion The burnt gas then exhausts while drawing in new gas The lubricating oil mixed into the air-fuel mixture also burns

Since the two-stroke engine does not use a valve system, its mechanism is very simple The power output is fairly high because it achieves one power stroke per two revolutions

of the crankshaft However, although the power output is high, it is used only for small motorcycle engines and some large diesel

applications Since the new gas pushes out the burnt gas, the intake and exhaust gases are not clearly separated As a result, fuel consumption is relatively high and cleaning of the exhaust gas by a catalytic converter is difficult

1.2 The diesel engine

The name diesel comes from the inventor of the diesel engine, R Diesel There are both four- and two-stroke-cycle diesel engines Most automotive diesels are four-stroke engines The intake stroke on the diesel engine draws only air into the cylinder The air is then compressed during the compression stroke At near maximum compression, finely atomized diesel fuel (a gas oil having a high flashpoint) is sprayed into the hot air, initiating auto ignition of the mixture During the subsequent power stroke, the expanding hot mixture works

on the piston, then burnt gases are purged during the exhaust stroke

Since diesel engines do not use a spark plug, they are also referred to as compression ignition (CI) engines In the case of petrol engines, too high a temperature in the combustion

chamber ignites the petrol spontaneously When this occurs, the plug cannot control the moment of ignition This unwanted phenomenon is often referred to as ‘knocking’

The diesel is an injection engine A petrol engine normally needs a throttle valve to control airflow into the cylinder, but a diesel engine does not Instead, the diesel uses a fuel injection pump and an injector nozzle sprays fuel right into the combustion chamber at high pressure The amount of fuel injected into the cylinder controls the engine power and

speed There are two methods by which

fuel is injected into a combustion chamber, direct or indirect injection

With direct injection engines (DI)

the fuel is injected directly into the cylinder and initial combustion takes place within the bowl that is machined

into the piston head itself With indirect injection engines (IDI) the fuel is

injected and initial combustion takes place in a small pre combustion chamber formed in the cylinder head The burning gases then expand into the cylinder where combustion continues

2 Advantages and disadvantages of reciprocating engines

-> An engine with a piston-cylinder mechanism has the following advantages:

a It is possible to seal the gap between the piston and the cylinder, resulting in high compression ratio, high heat efficiency and low fuel consumption

b The piston ring faces the cylinder bore wall, separated by an oil film The resulting hydrodynamic lubrication generates low friction and high durability

c The piston loses speed at the dead-center points where the travelling direction reverses, which gives enough time for combustion and intake as well as for exhaust

-> However, the reciprocating engine also has disadvantages:

a The unbalanced inertial force and resulting piston ‘slap’ can cause noise and vibration

b It is difficult to reuse the exhaust heat

Fig 2.4: Basic parts of a diesel engine

3 The rotary engine (Wankel engine)

The rotary-piston engine (or Wankel engine, named by its inventor) generates power by the compression, ignition, and expansion of gasoline/air mixture in a 4-stroke cycle in the same way as conventional internal combustion engines The completely different mechanical design allows all moving parts to have a continuous rotary motion instead of a reciprocating movement The rotor (or piston) is roughly triangular shaped and rotates on an eccentric on the output shaft within a housing of epitrochoid shape The term is given to the path described

by a point within a circle rolling around another circle

Fig 2.5: The Wankel rotary engine cycle

III. NEW WORDS

Look up for the new words

Valve lifter Lambda sensor Valve spring Inlet valve

Camshaft Catalytic converter Fuel injector Spark ignition (SI)

engine Valve seat Exhaust manifold Intake manifold Ignition plug

Cylinder Connecting rod Crank case Air-fuel mixture

Compression ignition

Knocking Injector nozzle Direct injection

engines (DI)

Indirect injection engines (IDI)

IV. COMPREHENSION QUESTION

1 What is the role of engine in cars?

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2 How many types of reciprocating engine?

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3 Name 4 strokes of the 4-stroke engine?

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4 How are the air and fuel mixture drawn into combustion chamber in intake stroke?

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5 In compression stroke, how the mixture is compressed?

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6 Why is the piston pushed down in power stroke?

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7 Why can we call a petrol engine as a Spark Ignition (SI) engine?

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8 What is the same feature of the two-stroke engine and the four-stroke-cycle engine?

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9 Does two-stroke engine use inlet and exhaust valves?

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10 In the two-stroke engine, what is the function of the space in the crankcase?

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11 Why is a two-stroke engine mechanism very simple?

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12 How about a two-stroke engine power? Is it more than or less than the same capacity of four-stroke engine? Why?

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13 Why isn’t a two-stroke engine as popular as four-stroke one?

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14 What kind of mixture is intaken in intake-stroke of a diesel engine?

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15 Why doesn’t a diesel engine have a spark plug?

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16 How many methods for injecting fuel into a combustion chamber in diesel engine?

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17 Advantages and disadvantages of reciprocating engines?

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V. QUIZ

1 Most automobile engines are

a large and heavy

b gasoline-fueled, spark-ignited, liquid-cooled internal combustion type

c unable to run at elevations that are below sea level

d able to operate with any fuel other than gasoline

2 An exhaust valve is

a a hole in the cylinder head

b a mechanism for releasing the combustion products from the cylinder

c the pipe connecting the engine to the muffler

d a small opening at the bottom of a piston

3 Power is produced during

a intake stroke

b compression stroke

c power stroke

d exhaust stroke

4 The air–fuel ratio is

a the rate at which combustible products enter the engine

b the ratio of the mass of air to the mass of fuel in a cylinder before ignition

c the ratio of gasoline to air in the exhaust pipe

d intake air and fuel velocity ratio

5 An SI engine is

a a type of internal combustion engine

b a Stirling engine

c always fuel injected

d none of the above

VI. TRUE/FALSE

Decide if these statements are True or False:

1 We can see the detailed mechanisms of a engine in a car ( True False)

2 The four-stroke engine is also referred to as the Otto cycle engine when petrol is used as fuel ( True False)

3 In four-stroke petrol engine, only air is intaken in induction stroke ( True False)

4 Two-stroke engine uses inlet and exhaust valves ( True False)

5 The name diesel comes from the inventor of the diesel engine, R Diesel ( True False)

6 The intake stroke on the diesel engine draws air/diesel mixture into the cylinder ( True False)

7 A diesel engine uses a spark plug for ignition ( True False)

8 A petrol engine normally needs a throttle valve to control airflow into the cylinder and a diesel engine does ( True False)

9 In DI engine, the fuel is injected directly into the cylinder ( True False)

10 In IDI engine, the fuel is injected and initial combustion takes place in a small pre-ombustion chamber formed in the cylinder head ( True False)

VII. SUBSTITUTION

1. “The engine is the heart of a car although it is normally hidden under the bonnet” (paragraph 1) It refers to:

a the man’s heart

b The engine’s heart

c The car’s heart

d All correct

2 “Power stroke: when the piston ascends and reaches top dead center, an electric current

ignites the spark plug and as the mixed gas burns, it expands and builds pressure in the combustion chamber” (paragraph 2, part 1.1.1) It refers to:

a spark plug

b air

c Fuel

d Air/fuel mixture

3 “Compression stroke: at the end of the intake stroke, both inlet and exhaust valves are

closed The inertial action of the crankshaft in turn lifts the piston which compresses the mixture” (paragraph 2, part 1.1.1) Which refers to:

a The inertial action

b the crankshaft

c the piston

d the mixture

4 “There are two methods by which fuel is injected into a combustion chamber, direct or indirect injection” (paragraph 4, part 1.2) Which refers to:

a the way to control engine power

b the way to inject fuel into cylinder

c the way to control engine speed

d All correct

5 “The piston loses speed at the dead-center points where the travelling direction reverses,

which gives enough time for combustion and intake as well as for exhaust” (paragraph 3, part 2) Which refers to:

a the travelling direction reverses

b the dead-center points

c the loosen speed of the piston

d all correct