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AMT 225 > Reciprocating Engines > Flashcards

Reciprocating Engines Flashcards

1
Q

What is a constant-volume cycle?

A

In a reciprocating engine heat energy is added to the air

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2
Q

What is a four-stroke also refereed to?

A

Otto-cycle

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3
Q

How many cycles are in a four stroke?

A

Five-event cycle

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4
Q

What are the five cycles of a stroke?

A

Intake, compression, ignition, power, and exhaust

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5
Q

What is a stroke?

A

The distance the piston moves inside the cylinder

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6
Q

How is the duration of a stroke measured?

A

In degrees of crankshaft rotation

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7
Q

How many degrees is each stroke?

A

180°

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8
Q

Why are more cylinders better?

A

More cylinders the more power and the smoother the operation

The firing impulses are closer together

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8
Q

What is the bore of a cylinder?

A

The inside diameter of a cylinder

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9
Q

Explain the five event cycles

A

-Intake-draws the fuel-air mixture into the cylinder
-Compression-compresses the mixture
-Ignition-ignites the mixture
-Power-the mechanical energy is produced
-Exhaust-spent gases are forced out of the cylinder

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10
Q

When does ignition occur?

A

Before the piston reaches TDC

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11
Q

What happens during the power stroke?

A

Both valves are closed. The piston is forced down by the pressure. The only time useful work is done

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12
Q

What happens if the ignition timing is correct?

A

The fuel-air mixture will completely burn shortly after the piston passes TDC on the power stroke

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13
Q

What is valve overlap and why is it important?

A

-The portion of the operating cycle of a four-stroke reciprocating engine during which both the intake and exhaust valves are open at the same time
-Its important for volumetric efficiency and proper cooling

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14
Q

When does the intake valve open?

A

During the exhaust stroke just before the piston reaches TDC

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15
Q

When does the exhaust valve closes?

A

During the intake stroke just after the piston passes TDC

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16
Q

When does the intake valve close?

A

During the compression stroke just after the piston passes BDC

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17
Q

When does ignition occur?

A

During the compression stroke just before the piston reaches TDC

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18
Q

When does the exhaust valve open?

A

During the power stroke just before the piston reaches BDC

19
Q

1hp equals?

A

550ft-lbs per second

20
Q

What are the three types of horsepower involved in recip engines?

A

Indicated horsepower
Friction horsepower
Brake horsepower

21
Q

What is brake horsepower?

A

The actual horsepower delivered to the propeller shaft

22
Q

What is torque?

A

The force that produces a twisting or rotational motion of the crankshaft

23
Q

What are the three major efficiency groups in a recip engine?

A

Thermal efficiency
Mechanical efficiency
Volumetric efficiency

24
Q

What is brake thermal efficiency?

A

The ratio of useful work done by an engine to the heat of the fuel it uses

25
Q

What is volumetric efficiency?

A

It’s the ratio of the volume of fuel-air charge inside the cylinder to the single cylinder displacement

26
Q

What factors affect engine power?

A

Piston displacement
Compression ratio
Valve timing
Ignition timing
Air density

27
Q

What is compression ratio?

A

The ratio of the volume of the cylinder with the piston at the BDC to the volume of the cylinder with the piston at TDC

28
Q

What is detonation?

A

An uncontrolled explosion inside the cylinder caused by fuel exceeding it’s critical temperature and pressure

29
Q

What is pre-ignition?

A

Ignition of the fuel-air mixture inside the cylinder before the normal spark occurs

30
Q

What major parts make up the top end of an engine?

A

Cylinders
Valve assemblies
Pistons

31
Q

What is choke-ground cylinder?

A

The barrels are ground so its diameter at the top is slightly smaller than diameter at the bottom
-The top of the barrel expands more than the rest

32
Q

What is cylinder honing?

A

-The barrel is honed with a 45° cris-cross finish
-holds oil for lubrication

33
Q

What are the two ways cylinder walls are hardened?

A

Chrome plating-orange
Nitriding-blue

33
Q

What is an interference fit?

A

The barrel is chilled and the head is heated and then screwed together

34
Q

How can you tell the difference between the exhaust and intake side of a cylinder head

A

The exhaust side has more fins

35
Q

Why does the exhaust valve hollow in the middle?

A

Its filled with metallic sodium that aids in cooling the valve

36
Q

To what degree are intake valves ground?

A

30° to provide for better airflow into the cylinder

37
Q

To what degree are exhaust valves ground?

A

45° to make sure of proper seating

38
Q

What is interference angle?

A

The difference between the angles of the valve seat and the valve face

39
Q

How are valves open and closed?

A

Opened by pressure from the camshaft and closed by the force of two or more coil springs

40
Q

Why are two springs used for valves?

A

So if a spring has a resonant frequency it will lose spring pressure

41
Q

What are cam-ground pistons?

A

The boss area absorbs more heat because of extra metal and expands more

42
Q

What are the function of piston rings?

A

-Sealing action to prevent gas leakage
-transfer heat from the piston to the cylinder wall
-oil control on the cylinder wall preventing oil entering the combustion chamber

43
Q

Why should you use a different material on piston rings from the piston

A

They will not wear out the rings initially to provide a good seal

44
Q

What are the three critical measurements for piston rings?

A

Eng-gap clearance
Tension
Side clearance

45
Q

Why should compression rings be staggered?

A

To minimize leakage

AMT 225 (8 decks)

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