mae 4261 air breathing engines
Download
Skip this Video
Download Presentation
MAE 4261: AIR-BREATHING ENGINES

Loading in 2 Seconds...

play fullscreen
1 / 28

MAE 4261: AIR-BREATHING ENGINES - PowerPoint PPT Presentation


  • 145 Views
  • Uploaded on

MAE 4261: AIR-BREATHING ENGINES. Gas Turbine Engine Combustors Mechanical and Aerospace Engineering Department Florida Institute of Technology D. R. Kirk. COMBUSTOR LOCATION. Commercial PW4000. Combustor. Military F119-100. Afterburner. MAJOR COMBUSTOR COMPONENTS. Turbine. Compressor.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'MAE 4261: AIR-BREATHING ENGINES' - chesmu


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
mae 4261 air breathing engines

MAE 4261: AIR-BREATHING ENGINES

Gas Turbine Engine Combustors

Mechanical and Aerospace Engineering Department

Florida Institute of Technology

D. R. Kirk

combustor location
COMBUSTOR LOCATION

Commercial

PW4000

Combustor

Military

F119-100

Afterburner

major combustor components4
MAJOR COMBUSTOR COMPONENTS
  • Key Questions:
    • Why is combustor configured this way?
    • What sets overall length, volume and geometry of device?

Fuel

Combustion Products

Turbine

Air

Compressor

combustor requirements
COMBUSTOR REQUIREMENTS
  • Complete combustion (hb→ 1)
  • Low pressure loss (pb → 1)
  • Reliable and stable ignition
  • Wide stability limits
    • Flame stays lit over wide range of p, u, f/a ratio)
  • Freedom from combustion instabilities
  • Tailored temperature distribution into turbine with no hot spots
  • Low emissions
    • Smoke (soot), unburnt hydrocarbons, NOx, SOx, CO
  • Effective cooling of surfaces
  • Low stressed structures, durability
  • Small size and weight
  • Design for minimum cost and maintenance
  • Future – multiple fuel capability (?)
chemistry review
CHEMISTRY REVIEW
  • General hydrocarbon, CnHm (Jet fuel H/C~2)
  • Complete oxidation, hydrocarbon goes to CO2 and water
  • For air-breathing applications, hydrocarbon is burned in air
  • Air modeled as 20.9 % O2 and 79.1 % N2 (neglect trace species)
  • Complete combustion for hydrocarbons means all C → CO2 and all H → H2O

Stoichiometric Mass fuel/air ratio

Stoichiometric Molar fuel/air ratio

  • Stoichiometric = exactly correct ratio for complete combustion
comments on challenges
COMMENTS ON CHALLENGES
  • Based on material limits of turbine (Tt4), combustors must operate below stoichiometric values
    • For most relevant hydrocarbon fuels, ys~ 0.06 (based on mass)
  • Comparison of actual fuel-to-air and stoichiometric ratio is called equivalence ratio
    • Equivalence ratio = f = y/ystoich
    • For most modern aircraft f ~ 0.3
  • Summary
    • If f = 1: Stoichiometric
    • If f > 1: Fuel Rich
    • If f < 1: Fuel Lean
variation of flame temperature with f
VARIATION OF FLAME TEMPERATURE WITH f

Flame Temperature

Flammability Limits

Still too hot

for turbine

why is this relevant
WHY IS THIS RELEVANT?
  • Most mixtures will NOT burn so far away from stoichiometric
    • Often called Flammability Limit
    • Highly pressure dependent
      • Increased pressure, increased flammability limit
    • Requirements for combustion, roughly f > 0.8
  • Gas turbine can NOT operate at (or even near) stoichiometric levels
    • Temperatures (adiabatic flame temperatures) associated with stoichiometric combustion are way too hot for turbine
    • Fixed Tt4 implies roughly f < 0.5
  • What do we do?
    • Burn (keep combustion going) near f=1 with some of compressor exit air
    • Then mix very hot gases with remaining air to lower temperature for turbine
solution burning regions
SOLUTION: BURNING REGIONS

Turbine

Air

Primary

Zone

f~0.3

f ~ 1.0

T>2000 K

Compressor

combustor zones more details
COMBUSTOR ZONES: MORE DETAILS
  • Primary Zone
    • Anchors Flame
    • Provides sufficient time, mixing, temperature for “complete” oxidation of fuel
    • Equivalence ratio near f=1
  • Intermediate (Secondary Zone)
    • Low altitude operation (higher pressures in combustor)
      • Recover dissociation losses (primarily CO → CO2) and Soot Oxidation
      • Complete burning of anything left over from primary due to poor mixing
    • High altitude operation (lower pressures in combustor)
      • Low pressure implies slower rate of reaction in primary zone
      • Serves basically as an extension of primary zone (increased tres)
    • L/D ~ 0.7
  • Dilution Zone (critical to durability of turbine)
    • Mix in air to lower temperature to acceptable value for turbine
    • Tailor temperature profile (low at root and tip, high in middle)
    • Uses about 20-40% of total ingested core mass flow
    • L/D ~ 1.5-1.8
combustor design
COMBUSTOR DESIGN
  • Combustion efficiency, hb = Actual Enthalpy Rise / Ideal Enthalpy Rise
    • h=heat of reaction (sometimes designated as QR) = 43,400 KJ/Kg
  • General Observations:
    • hb↓ as p ↓ and T ↓ (because of dependency of reaction rate)
    • hb↓ as Mach number ↑ (decrease in residence time)
    • hb↓ as fuel/air ratio ↓
  • Assuming that the fuel-to-air ratio is small
combustor types lefebvre
COMBUSTOR TYPES (Lefebvre)

Single Can

Tubular

or Multi-Can

Tuboannular

Can-Annular

Annular

examples
EXAMPLES

CAN-TYPE

Rolls-Royce Dart

ANNULAR-TYPE

General Electric T58

examples20
EXAMPLES

CAN-ANNULAR-TYPE

Rolls-Royce Tyne

chemical emissions
CHEMICAL EMISSIONS
  • Aircraft deposit combustion products at high altitudes, into upper troposphere and lower stratosphere (25,000 to 50,000 feet)
  • Combustion products deposited there have long residence times, enhancing impact
  • NOx suspected to contribute to toxic ozone production
    • Goal: NOx emission level to no-ozone-impact levels during cruise
afterburner augmenter
AFTERBURNER (AUGMENTER)
  • Spray in more fuel to use up more oxygen
    • Main combustion can not use all air
  • Exit Mach number stays same (choked Mexit = 1)
    • Temp ↑
    • Speed of sound ↑
    • Velocity = M*a ↑
    • Therefore Thrust ↑
  • Penalty:
    • Pressure is lower so thermodynamic efficiency is poor
    • Propulsive efficiency is reduced (but don’t really care in this application)
  • As turbine inlet temperature keeps increasing less oxygen downstream for AB and usefulness decreases
  • Requirements
    • VERY lightweight
    • Stable and startable
    • Durable and efficient
relative length of afterburner
RELATIVE LENGTH OF AFTERBURNER

J79 (F4, F104, B58)

Afterburner

Combustor

  • Why is AB so much longer than primary combustor?
    • Pressure is so low in AB that they need to be very long (and heavy)
    • Reaction rate ~ pn (n~2 for mixed gas collision rate)
burner turbine burner itb concepts
BURNER-TURBINE-BURNER (ITB) CONCEPTS
  • Improve gas turbine engine performance using an interstage turbine burner (ITB)
    • With a higher specific thrust engine will be smaller and lighter
    • Increasing payload
    • Reduce CO2 emissions
    • Reduce NOx emissions by reducing peak flame temperature
  • Initially locate ITB in transition duct between high pressure turbine (HTP) and low pressure turbine (LPT)

Conventional

Intra Turbine Burner (schematic only)

slide27
UNDERSTANDING BENEFIT FROM CYCLE ANALYSISFrom “Turbojet and Turbofan Engine Performance Increases Through Turbine Burners, by Liu and Sirignano, JPP Vol. 17, No. 3, May-June 2001

Conventional

Intra Turbine Burner

slide28
UNDERSTANDING BENEFIT FROM CYCLE ANALYSISFrom “Turbojet and Turbofan Engine Performance Increases Through Turbine Burners, by Liu and Sirignano, JPP Vol. 17, No. 3, May-June 2001

Continuous burning

in turbine

2 additional burners

5 additional burners

ad