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AGK - Engines > The Piston Engine > Flashcards

The Piston Engine Flashcards

1
Q

The Otto cycle stages

A

Induction stroke

Compression stroke

Power stroke

Exhaust stroke

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2
Q

Induction stroke

A

As the piston goes down - creates low pressure - draws air in

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3
Q

Compression stroke

A

As the cylinder head goes up - air compresses and creates heat

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4
Q

Power stroke

A

The ignition of the fuel and air mix = rapid expansion

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5
Q

Exhaust stroke

A

Exhaust leans the cylinder

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6
Q

Why is more efficient at high altitude

A

Easier to push the end gasses out - less atmospheric pressure acting against it

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7
Q

Bottom dead centre

A

Lowest point the cylinder gets to

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8
Q

Top dead centre

A

Highest point the cylinder gets to

Crank and connected rod are perfectly aligned

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9
Q

Inline engine

A

Cylinders are aligned in a line on 1 crank shaft

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10
Q

Inverted inline engine

A

Turned upside down - could get puddles of oil in each of the cylinders

Pulling through get rid of these puddles by turning the engine before starting

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11
Q

Radial engine

A

Engine cylinders are arranged in a circle - equal cooling throughout - more surface area

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12
Q

Horizontally opposed

A

Cylinders on each side

Shorter engine - better cooling - no hydro locking

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13
Q

The crank case

A

2 parts bolted together - crank in the middle

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14
Q

Main journal

A

Main crankshaft centre

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15
Q

Big end journal

A

To the side of the main crankshaft centre - where the cylinders are joined onto it

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16
Q

Stroke

A

Full distance through which the piston moves

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17
Q

Throw

A

Half the stroke

From the centreline of the main journal to the centreline of the big end journal

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18
Q

Connecting rods

A

Connects piston to the crank shaft

Generally made of steel

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19
Q

Gudgen pin

A

Pin through the cylinder head which connects the connector rod to the cylinder head

20
Q

Cylinder head is generally made of

A

Aluminium alloy

21
Q

Piston rings

A

Will expand and contract to create a gas type seal
1st and 2nd = compression rings

3rd = oil control rings

Normally made of carbon steel

22
Q

How the valves operate

A

Cam shaft pushes the hydraulic tappet/ cam follower which pushes the push rod which moves the rocker arm to push the valve tip which pushes the valve open and close using the spring

23
Q

Camshaft

A

Moves at half the speed of the crank

Regulates the movement of the rocker - opening and closing the inlet and outtake valves

24
Q

Inlet and exhaust valves

A

Inlet is slightly wider than the exhaust

Exhaust valves are hollow and filled with sodium

25
Q

Boor area

A

Area on top of the cylinder

26
Q

Swept volume

A

The amount of volume displaced by the piston during a stroke

27
Q

Clearance volume

A

Residual volume left at the top of the cylinder at TDC

28
Q

Compression ratio

A

= total volume (stoke + clearance) / clearance

29
Q

Multi-cylinder stroke sequence

A

1-3-4-2

30
Q

1 horsepower =

A

33000 ft lbs/min

Based on 33lbs being lifted through 100 ft

31
Q

How to measure brake-horsepower

A

Torque x rpm

Pony brake - clamped to the shaft

BHP = indicated HP - friction HP

32
Q

Indicated horsepower

A

= PLANE/33000(ft lbs/min)

P= indicated mean effective power 
L= length of the stroke
A = area of the piston crown (pxa = force) 
N = number of power strokes/min 
E = number of cylinders
33
Q

Friction HP

A

Horsepower taken from the total HP for other things e.g air con

34
Q

Why does power decrease with altitude

A

Less pressure = less air in the piston = less fuel burn = less power

However at altitude it is easier for the inlet and outlier valve to work so it reduces the power loss - improves scavenging

35
Q

Efficiency equation piston engine

A

Ratio of work done by a measure of energy it gives

Thermal efficiency = work out (BHP)/ work contained within the fuel

36
Q

% of the fuel which gets turned into stuff

A

30% into work

40% in the exhaust

25% In the cooling system

5% on friction

37
Q

Mechanical efficiency

A

Ratio of BHP to IHP

Percentage of power in the engine to turn the prop

Typically 80 to 85%

38
Q

Volumetric efficiency

A

Ratio of volume of change drawn into the cylinder on the induction stroke compared to the swept volume

Indication of how well the engine is breathing

Typically 85%

39
Q

Theoretical cycle

A

All events happen at TDC or BDC

40
Q

Induction - practical cycle

A

Opens the net valve early - ensures the valve is fully open by TDC

Valve lead

41
Q

Compression

A

Inlet valve closes late - after BDC - allows the momentum of the incoming mixture to increase the the mas of the induced charge

Valve lag

42
Q

Ignition advanced - practical cycle

A

Takes a finite time to ignite and fir the flame to expand across the crown

Spark is initiated early to achieve max pressure at 10 degrees after TDC

43
Q

Power - practical cycle

A

Exhaust valve opens early

By the time the piston has passed 90 degrees on the power stroke most of the pressure energy has been expended

Exhaust valve opens early - prevents back pressure which resists upwards movement of the piston

44
Q

Exhaust - pratical cycle

A

Valve closes late

Remains open after TDC - momentum of the moving exhaust gasses removes the last of the burned gasses - allows more space for incoming air/fuel mix

45
Q

Valve overlap - practical cycle

A

A period where both valves are partially open

Exhaust gasses flowing out helps the air/fuel mix to flowing in

Improves old metric efficiency

Mass of the induced charge is increased

AGK - Engines (14 decks)

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