Lecture 11 - Aero and Industrial Gas Turbines Flashcards

1
Q

When are emissions regulated for aircraft

A

during landing and takeoff situation - causes development to make gas turbines bigger diameter - more efficient at low amplitude

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2
Q

What is the emissions trade off faced in engine design

A

high pressure ratios = more efficient but need higher take off temp which increases smoke and NOx

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3
Q

NOx emissions are dependent on

A

Temperature of engine

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4
Q

Why is there such a small range of temperature for engines

A

minimum point - if you increase temp NOx increases

if you decrease temp CO increases

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5
Q

can we use water to reduce emissions

A

technically yes - reduce temp reduce NOx emissions - have to be careful where you input - cant do before compressor as cant compress, difficult to do after compressor as you require a lot of water

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6
Q

Why do fighter jets inject water in through combustor

A

when performing fast maneuvers - more mass flow rate from nozzle

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7
Q

Can we use steam to reduce emissions

A

yes technically - inject in combustor to reduce temp and reduce NOx but difficult to do pracitcally

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8
Q

What is the advantage variable geometry combustors

A

proposed concept to reduce NOx, pass more air through combustor or round outside
more air in combustor - high altitude, reduce temp reduce NOx
more air outside - stable flame, more thrust, for takeoff

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9
Q

What are catalytic Combustors

A

Combustors with catalysts in, not used as pressure drop too high

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10
Q

What would premixing fuel do

A

premixing fuel with air - better combustibility - burn leaner - lower temp - lower NOx

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11
Q

What is a rich burn quick quench combustor

A

RQL combustor - currently working on - burn very rich then burn very lean, need to closely control temperatures and inject air very quickly to prevent massive jump in temperatures
Intention to keep temperature very low

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12
Q

Options for improving combustor efficiency

A
variable geometry
catalytic 
premixing
rich burn quick quench 
Staged Combustor
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13
Q

What is a staged combustor

A

combust in stages - keep low temperatures

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14
Q

What type of aircraft uses twin spool GT

A

military

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15
Q

What type of aircraft uses triple spool

A

standard passenger jet

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16
Q

Design Drivers of GT

A
Low specific fuel consumption
High Reliability
Lowest possible emissions
Lowest Possible Cost
Pressure Ratios
17
Q

What leads to low specific fuel consumption

A

higher firing temperature - higher specifc power but requires complex cooling and can impact life and reliability
Higher pressure rations - increased cycle efficiency, increased number of compressor/turbine stages
Complex Cycles - Increased Cycle Efficiency, Can impact operability, cost and reliability

18
Q

What does higher reliability achieve

A

offset other advantages from TET increases

19
Q

What decreases cost of GT

A

smaller frame size, high specific power

20
Q

How do industrial gas turbines compare to aviation in emissions

A

Industrial can have very efficient cycle and make everything bigger to increase mass flow rate
aviation cant make bigger due to weight issues therefore increae temp and compression ratios (increase NOx)

21
Q

what basic parameters are available for adjustment to the engineer

A

compression ration rc

and turbine inlet temperature TIT

22
Q

What does a high TIT lead to

A

Expensive alloys and or complex/expensive cooling

23
Q

What does a high rc lead to

A

many stage compression - multi spool configurations

24
Q

Cycle selection of business jets

A

low cost by low pressure ratios and cheap turbine material
fuel consumption less important
noise restriction
higher SFC, light

25
Q

Cycle selection of lifting engines

A
high thrust - highest pressure ratios with one rotor
light as possible
cost not a criteria
short life
high SFC
26
Q

Cycle selection of long range subsonic

A

high pressure ratio, high bybass ratio turbofans
as efficient as possible
cost not an issue if efficient