# Presentation: 900684

## Fuel Tank Inerting Modeling

- Ivor Thomas
- Consultant to FAA
- 1 425 455 1807
- fuelsguy@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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## Slide 6

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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

***Ground Based Inerting***

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## Ground Based Inerting

***Ground Based Inerting***

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## Dual-Flow On Board Inerting 

***Dual-Flow On Board Inerting***

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## Dual Flow On board Inerting

***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

***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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## Slide 19

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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.

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