Lecture 11 - Aero and Industrial Gas Turbines Flashcards
When are emissions regulated for aircraft
during landing and takeoff situation - causes development to make gas turbines bigger diameter - more efficient at low amplitude
What is the emissions trade off faced in engine design
high pressure ratios = more efficient but need higher take off temp which increases smoke and NOx
NOx emissions are dependent on
Temperature of engine
Why is there such a small range of temperature for engines
minimum point - if you increase temp NOx increases
if you decrease temp CO increases
can we use water to reduce emissions
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
Why do fighter jets inject water in through combustor
when performing fast maneuvers - more mass flow rate from nozzle
Can we use steam to reduce emissions
yes technically - inject in combustor to reduce temp and reduce NOx but difficult to do pracitcally
What is the advantage variable geometry combustors
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
What are catalytic Combustors
Combustors with catalysts in, not used as pressure drop too high
What would premixing fuel do
premixing fuel with air - better combustibility - burn leaner - lower temp - lower NOx
What is a rich burn quick quench combustor
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
Options for improving combustor efficiency
variable geometry catalytic premixing rich burn quick quench Staged Combustor
What is a staged combustor
combust in stages - keep low temperatures
What type of aircraft uses twin spool GT
military
What type of aircraft uses triple spool
standard passenger jet
Design Drivers of GT
Low specific fuel consumption High Reliability Lowest possible emissions Lowest Possible Cost Pressure Ratios
What leads to low specific fuel consumption
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
What does higher reliability achieve
offset other advantages from TET increases
What decreases cost of GT
smaller frame size, high specific power
How do industrial gas turbines compare to aviation in emissions
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)
what basic parameters are available for adjustment to the engineer
compression ration rc
and turbine inlet temperature TIT
What does a high TIT lead to
Expensive alloys and or complex/expensive cooling
What does a high rc lead to
many stage compression - multi spool configurations
Cycle selection of business jets
low cost by low pressure ratios and cheap turbine material
fuel consumption less important
noise restriction
higher SFC, light
Cycle selection of lifting engines
high thrust - highest pressure ratios with one rotor light as possible cost not a criteria short life high SFC
Cycle selection of long range subsonic
high pressure ratio, high bybass ratio turbofans
as efficient as possible
cost not an issue if efficient
