Fuel Tank Inerting Modeling

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Fuel Tank Inerting Modeling

• Ivor Thomas
• Consultant to FAA
• 1 425 455 1807
• fuelsguy_at_msn.com

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Background

• Following TWA 800 the FAA undertook to examine
  fuel tank inerting to determine if a system could
  be made practical.
• Two ARAC studies
• FAA lab, ground and flight test programs
• Computer simulations of system performance

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Computer simulations of system performance

• Initial model to verify system performance in a
  single bay tank, using FAA Technical Center tests
  to confirm model.
• Flight simulation model to look at performance of
  an inerting system throughout a flight
• Air Separation Module (ASM) performance in flight
  (effects of available bleed air, system pressure
  drop etc.)
• Multi-bay simulations to examine in-tank
  performance (potential for one or more high
  oxygen bays when the tank average is
  satisfactory)

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Initial Model

• Model Features
• Simple one bay tank,
• Single source of Nitrogen Enriched Air, at a
  fixed level of O2
• Single vent overboard
• Sea level conditions only

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Initial Model

• Model Results
• Mixing was very rapid, and could be assumed to be
  instantaneous
• Starting from 21 O2 model would predict test
  results accurately

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Flight Model

• Model Features
• Simple one bay tank,
• Single source of Nitrogen Enriched Air, at a
  variable level of O2 and flow rate
• Changeable for different flight conditions
• Could add results of ASM performance for given
  airplane/engine combination
• Single vent overboard
• Ground and Flight profiles can be simulated.
• Fuel O2 Evolution and Fuel consumption included

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Flight Model

• Model Results
• Very useful in determining effectiveness of
  inerting options
• Ground based inerting
• Various sizes of ASM and flow modes
• Substantiated concept of variable flow technique,
  low flow in climb and cruise, high flow in
  descent

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Ground Based Inerting
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Ground Based Inerting
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Dual-Flow On Board Inerting
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Dual Flow On board Inerting
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Air Separation Module (ASM)

• ASM performance strongly affected by available
  pressure and temperature
• Airplane bleed flow affected by airplane flight
  conditions.
• Model combined airplane/engine bleed data with
  ASM performance data to predict ASM performance
  in flight, which could then be used in the
  inerting flight model.

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Screen Dump of ASM Model
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Typical Single ASM Performance
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Multi-bay simulations

• Background
• The performance of an inerting system can be
  estimated with the inerting flight model at a
  gross tank level.
• In-tank effects needed to be examined to
  understand the potential for bays of a tank to be
  left at a high O2 state even though the tank
  average O2 was acceptable.

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Multi-bay simulations

• Model Features
• Specific airplane /tank set-up
• Bay sizes
• Interconnect flow areas
• vent geometry,
• Multiple NEA insertion points
• Ground and Flight Operation
• Leakage

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Multi-bay simulations

• Model Approach
• Establish bay to bay flow paths, vent flow paths
  and any leakage flows
• Determine mass changes in each bay for each time
  increment, based on NEA flow and altitude change
  and temperature change
• Solve for flows between bays and compute
  resultant O2 level in each bay
• Iterate along flight path

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Current Status

• FAA Multi-bay model developed for specific tanks
• NOT available to public as the model uses
  specific airplane data
• Specific model allows examination of different
  distribution techniques to minimize bay-to-bay O2
  variation, particularly at Landing.

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Conclusions

• FAA computer models, together with a large amount
  of testing to verify the assumptions in the
  models have allowed the FAA to understand the
  potential for On-board inerting systems and has
  allowed FAA to go forward towards an NPRM to
  address high flammability fuel tanks.