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Piston Engine Theory > Piston Engine Fundamentals > Flashcards

Piston Engine Fundamentals Flashcards

1
Q

What is Top Dead Centre (TDC)?

A

When the piston is at the top of its stroke

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2
Q

What is Bottom Dead Centre (BDC)?

A

When the piston is at the bottom of its stroke

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3
Q

Define what is “stroke” in piston engine theory.

A

The linear distance the piston travels inside the cylinder from TDC to BDC

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4
Q

Define “clearance volume”.

A

The volume of the area above the above the piston when at TDC

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5
Q

What is swept volume?

A

The volume of a cylinder between the TDC and BDC

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6
Q

What is swept volume also known as?

A

Displacement volume

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7
Q

Define piston displacement.

A

The total volume swept by all of the pistons as they move through one revolution of the crankshaft

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8
Q

What is compression ratio?

A

The ratio of cylinder volume at bottom dead centre and top dead centre

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9
Q

What is the formula for compression ratio?

A

(check answer with pg 15 of PDF)

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10
Q

What factors affect engine efficiency?

A

Thermal, volumetric and mechanical efficiency

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11
Q

What is thermal efficiency?

A

It is the ratio of useful work done to the heat energy of the fuel used

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12
Q

What is the formula for thermal efficiency?

A

(check answer with pg 16 of PDF)

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13
Q

What is volumetric efficiency?

A

It is the ratio of the amount of air the engine takes into the cylinder to the total volume of the cylinder

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14
Q

How do you calculate volumetric efficiency?

A

(check answer with pg 17 of PDF)

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15
Q

What factors affect volumetric efficiency? (List at least 3)

A

Part throttle operation, long intake pipes with small diameter, sharp bends in induction system, high carby air temps, high cylinder head temps, incomplete scavenging, improper valve timing

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16
Q

What is mechanical efficiency?

A

It is the ratio of brake horsepower to indicated horsepower

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17
Q

What is the formula for mechanical efficiency?

A

(check answer with pg 18 of PDF)

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18
Q

If an engine develops 160 BHP and 180 IHP, what is the ratio? And what is the mechanical efficiency expressed as a percentage? (use formula to calculate)

A

The ratio is 160:180
The mechanical efficiency expressed as a percentage is 89%.

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19
Q

What factor has the greatest affect on mechanical efficiency?

A

Friction

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20
Q

What is 1 BTU?

A

The quantity of heat energy required to raise the temperature of one pound of water by one degree Fahrenheit.

21
Q

How many joules is 1 BTU equal to?

A

1055 joules

22
Q

What is Brake Horsepower (BHP)?

A

It is the actual amount of power delivered to the propeller shaft

23
Q

What does effective combustion require?

A

A metered combustible gas, compression of the gas, a source of ignition and an avenue of escape for the burnt gas

24
Q

True or False: A two stroke engine fires on every second revolution of the crankshaft.

A

False. It fires on every rotation of the crankshaft.

25
Q

What are the strokes of a two-stroke engine called?

A

Compression and Power

26
Q

What are the strokes of an Otto Cycle engine (4-Stroke)?

A

Intake, compression, ignition and exhaust

27
Q

What is the number of crankshaft degrees that the intake valve opens BEFORE TDC called?

A

Inlet valve lead

28
Q

What could happen if the intake valve didn’t open at the correct time?

A

The air-fuel ratio will be affected causing the engine to run rough or not at all

29
Q

When does the intake valve open?

A

Approx. 15 degrees before TDC (inlet valve lead)

30
Q

When does the intake valve close?

A

Approx. 60 degrees past BDC (inlet valve lag)

31
Q

What are the advantages of inlet valve lag?

A

It helps improve volumetric efficiency by allowing a greater charge of air/fuel mixture into the cylinder.

32
Q

When does the exhaust valve open?

A

Approx. 60 degrees before BDC (exhaust valve lead)

33
Q

When does the exhaust valve close?

A

Approx. 10 degrees past TDC (exhaust valve lag)

34
Q

What are the advantages of exhaust valve lead?

A

Improve volumetric efficiency and help remove heat from the cylinder

35
Q

What are the advantages of exhaust valve lag?

A

Helps take advantage of exhaust gas inertia

36
Q

Why is does ignition occur before TDC? (ignition advance)

A

So that pressure can be applied to the cylinder at the correct angle.

37
Q

Approximately when is ignition initiated?

A

20-30 degrees before TDC

38
Q

What is valve overlap and for how long does it occur?

A

The point in time in which both valves are open. This happens for approximately 25 degrees.

39
Q

What is another term for a diesel engine?

A

Compression-ignition engine

40
Q

What is the difference between an Otto cycle engine and a Diesel engine?

A

Compressed hot air ignites the fuel rather than spark plugs

41
Q

What compression ratio is typical for a diesel engine?

A

Between 14:1 and 24:1

42
Q

Is premature detonation an issue for diesel engines? Why/Why not?

A

It is not an issue for diesel engines as the fuel is not introduced into the cylinder until shortly before TDC

43
Q

What are some advantages of diesel engines?

A

More fuel efficient, longer life span, absence of coils and spark plug leads eliminates a source of radio frequency emissions

44
Q

What are some disadvantages of diesel engines?

A

Heavier, more prone to vibration and higher initial cost.

45
Q

What configuration do opposed engines have?

A

Odd numbered cylinders on the right and even numbered cylinders on the left?

46
Q

What configuration do single row radials have?

A

They are numbered consecutively starting from the top cylinder and progressing clockwise (as viewed from the pilot’s seat)

47
Q

What configuration do double-row radial engines have?

A

Numbered consecutively starting from the top cylinder progressing clockwise. Odd numbered cylinders are in the rear and even numbers are in the front.

48
Q

What is the firing order for single row radials?

A

Odd numbers first then even numbers

49
Q
A

Piston Engine Theory (2 decks)

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