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Mod 15: Engines > John's Notes > Flashcards

John's Notes Flashcards

1
Q

Gas turbine engine is what kind of cycle?

A

Gas Turbine Engine is the brayton cycle

meaning combustion occurs at constant pressure

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2
Q

What type of cycle is a piston engine?

A

Constant volume cycle

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3
Q

A turbojet engine has no _____

A

fan

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4
Q

Do fan blades change pitch like propeller blades?

A

No, fan blades are fixed pitch blades (always even number and typically 40)

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5
Q

What is ram ratio?

A

Ram ratio = compressor inlet pressure / ambient pressure

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6
Q

What is Ram temperature rise?

A

Ram temperature rise = compressor inlet temperature / ambient temperature

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7
Q

What is the simplest, most effective and most common type of inlet?

A

pitot type

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8
Q

What is a bifurcated intake?

A

2 inlets for the one engine

used on military aircraft

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9
Q

All subsonic ducts are ______ ducts

A

divergent

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10
Q

Dump and spill valves are used in which type of intake?

A

Moveable wedge intake

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11
Q

Bellmouth intake is gently ______ (divergent/convergent)

what is it used for?

A

convergent

helicopters and engine test cells

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12
Q

Compressor primary and secondary functions are

A

Primary = increase pressure

Secondary = cool engine hot parts, pressurise bearings, engine anti ice

Also supply customer service bleed air

CUstomer is airframe (pneumatics etc)

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13
Q

Compressor pressure ratio =

A

Outlet pressure / inlet pressure

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14
Q
A
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15
Q

What is the vaneless space in a compressor?

A

It is the space that exists between the impeller vane tips and the diffuser

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16
Q

What are the methods of securing compressor blades and why is a little bit of play given?

A

Fir tree and dove tail

To relieve stress and strains

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17
Q

Compressor stators and rotors are ________
while the overall compressor casing is _______

(convergent or divergent)

A

divergent

convergent

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18
Q

What is the compressor rise of an axial compressor vs centrifugal compressor?

A

1 or 2:1 per rotor/stator compressor but able to fit more on engine

Centrifugal is 10 or 15:1 but can only fit max 2 on engine

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19
Q

What is high aspect ratio means in relation to compressor blades?

A

Long and thin blades

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20
Q

What is a wide chord type compressor blade?

A

short and stubby

(type of aspect ratio)

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21
Q

There is always an ______ number of blades on a compressor for balancing reasons

A

even

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22
Q

Blade scatter is what?

A

Blades moving against each other

'’The blades , on moving, lean their shrouds onto the adjacent blades shroud’’

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23
Q

Compressor surge is what?

A

Surge is a reversal of airflow at the high pressure end

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24
Q

Another word for a mild stall is

A

transient stall

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25
Another word for a severe stall is
Hung stall
26
The most efficient angle of attack of a compressor blade is _____ degrees The AOA is based on what 2 vectors?
4 Engine RPM Air Inlet velocity
27
Stoichometric ratio is what?
Stoichometric ratio is the ideal ratio to burn fuel in air and is 15:1, note it is by _weight_ 15:1 represents 15 pounds of PRIMARY AIR and 1 pound of fuel
28
Name the 4 types of combustors?
1. Multiple Combustion chambers 2. Can-annular or tubo-annular combustion chambers 3. Annular combustion chambers (most common) 4. Annular reverse flow (turboprops)
29
There is only ever _____ (#) of igniters in a combustion section There is fuel nozzles in every chamber however (2 sets of 10)
2
30
Primary air is what?
Primary air is that portion of air which mixes with the fuel for combustion purposes.
31
Tertiary air is what?
Tertiary air is air which acts as a cooling agent. It takes no part in combustion
32
Secondary air is what?
Secondary air is that part of the air, which is metered into the combustion chamber to complete combustion
33
Swirl vanes do what and are located where?
Swirl vanes are located in the compressor section and act to slow down the air
34
Compressor blades are made of what material?
alluminium alloy, titanium or steel (cold section)
35
Turbine blades are made of what material? Turbine casing is made of what material?
Turbine blades are made of nickel or nimonic based super alloy Turbine casing is made of incanel
36
In general, describe Turbine nozzle guide vanes
Turbine nozzle guide vanes are convergent ducts that accelerate gases onto turbine blades Internally cooled with compressor bleed air (generally whether NGV's are either straight or convergent is determined by if they are reaction or impulse, respectively)
37
Are turbine stators before or after the rotors?
Turbine stators are located in front of the rotors (turbine blades) and they are generally convergent increasing their velocity while reducing temp and press. **_NOTE:_** Compressor stators are behind the compressor rotors(blades) and both are divergent to increase pressure
38
What is convection cooling in terms of Turbine blades?
Convection cooling is where compressor bleed air comes from the very bottom of the blade (fir tree area) and exits out the tip of the blade or at the trailing edge into the airflow. The air makes a couple of passes through the blade to cool it
39
What is film/impingement cooling in terms of Turbine blades?
Film/impingement cooling is where compressor bleed air comes from the blade bottom (fir tree area) and passes through blade cooling it before being released through the leading edge of the blade forming a heat shield around it. The more advanced version is called **''Transpiration''**
40
What is the more advanced version of Film/impingement turbine blade cooling called?
**''Transpiration''**
41
What is turbine blade creep?
Turbine blade creep is the elongation of turbine blades It is divided into primary, secondary and tertiary creep
42
Single crystal construction is a turbine blade manufacturing method used to stave off \_\_\_\_\_\_\_\_\_
tertiary creep
43
Turbine blades are made out of what material?
Nimonic alloy, nickel based alloy
44
The future of turbine blade manufacture will be blades manufactured from reinforced \_\_\_\_\_\_\_
ceramics
45
Blisk is a combination of what?
A Blade and a Disk both made as one
46
What are Reaction Turbine Blades?
Nozzle guide vanes are straight ducts that change the direction of the airflow onto the blades The blades are convergent meaning they accelerate the airflow, reducing its pressure and temp
47
Describe Impulse Turbine Blades
Nozzle guide vanes or stator vanes are convergent to accelerate airflow onto blades Turbine blades are straight ducts so velocity of airflow remains the same These are usually found in pnuematic air starters
48
What are Impulse reaction turbine blades?
A combination of impulse and reaction turbine blades, varies with designer how much of each
49
What type of turbine blades are used with pnuematic air starters?
Pnuematic air starters = Impulse Turbine blades
50
Exhaust is a _____ duct
convergent also called propelling nozzle
51
What is the only way to get more gas out of a ''choked'' nozzle?
To increase the gases temperature and thus its mach number
52
Afterburner of reheat is what?
Surplus oxgen convergent-divergent duct always increasing velocity as starts supersonic Area of nozzle opens up
53
As a basic rule, any sound over _____ dB is considered intense Human earss can evalualte noise up to _____ dB Anything over this is \_\_\_\_\_\_\_
100 120 damaging
54
What is a corrugated nozzle?
Cold air goes from fan duct across exhaust and mixes with hot air from core to get rid of thermal shock noise
55
Describe Multi-lobe nozzle?
splits exhaust into mulitple smaller exhausts increasing frequency of sound above what human ears can hear
56
The greatest reduction in noise level is achieved by the \_\_\_\_\_\_\_\_\_\_\_\_\_
high by-pass ratio turbo-fan engine
57
Honeycomb structure in an engine is used for what?
noise supression
58
Name the hot thrust reversers Name the cold thrust reversers
Hot = Bucket doors and clamshell doors cold = translating sleeve and blocker doors cascade vanes are incorporated into both
59
What is a meant by pour point of an oil?
The lowest temperature at which oil will gravity flow
60
Which has a lower freezing point: Jet A1 or Jet A fuel
Jet A1
61
Explain flash point Does fuel need a high or low flash point?
Flash point is the lowest temperature at which a liquid can give off vapor to form an ignitable mixture in air near the surface of the liquid. The lower the flash point, the easier it is to ignite the material Fuel needs a high flash point
62
\> _____ parts per million of free water (entrained water) is damaging and can cause engine flame out
30
63
If the amount of water detected in a fuel water test kit, the kit should turn \_\_\_\_\_\_ but in reality it will turn _______ \_\_\_\_\_\_\_
blue greenish torquoise
64
Which type of water is dangerous in fuel? Entrained (free) undissolved water _or_ dissolved water
Free water = entrained water or undissolved water and blobs of it in fuel are visible and problematic as if they freeze, they will block filters etc Dissolved water is not a problem
65
Kerosene is 'Hydroscopic', explain
It absorbs moisture into itself, the warmer it is the more moisture it will absorb
66
What is meant by a 'wet sump' system?
Oil reservoir located at the lowest part of the engine as it uses gravity to return oil. Oil reservoir is integrated into bottom of engine
67
What is meant by ''dry sump'' system?
The oil reservoir is located away from the engine near compressor or fan case (cold sections) Needs scavenge return filters
68
Scavenge pumps are of atleast \_\_\_\_\_% capacity of the pressure system as ____ also comes back with oil in addition to oil expanding as hotter
150 air
69
Name and briefly describe the 3 types of oil pump?
1. Gear pump (drive and driven pumps) 2. Gerotor pump (male and female gears, cocentric, male has 1 less tooth) 3. Vane pump (more tolerant of debris, prone to high rates of vane tip wear)
70
Filters are filtered _________ as greater surface area outside
Out-to-In
71
A micron is ________ of a meter
one millionth

Mod 15: Engines (28 decks)

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