© COPYRIGHT, PROPRIETARY INFORMATION OF SMITHS AEROSPACE LTD AND SHAW AERO DEVICES
A Practical Approach For Inerting Systems on Commercial Aircraft and the Development of Industry Standards
Presented by Phil Jones & Brian Greenawalt
Shaw Aero Devices
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History of Recent Commercial Inerting
FAA proposed concepts for practical inerting of commercial aircraft fuel tanks
Storage of nitrogen enriched air in the ullage of the tank
Use of different flow modes in phases of flight
FAA proposed building of inerting system for 747SP
Team members from FTIHWG
Onboard ground inerting (OBGI) system
Designed for inerting fuel tank as well as cargo fire suppression
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OBGI System Schematic
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System Operation
Engine bleed air Pressurized air supply
Cooling air Reduce bleed air temperatures
Filter Remove contaminants found in bleed air
Heater Reheats air after run from heat exchanger to prevent condensation
Hollow fiber membrane Pressure device which reduces the oxygen level in air stream
Dual orifice valve Changes the back pressure on the hollow fiber membrane Different flow modes – high flow/low purity, low flow/high purity
Distribution system Injects nitrogen into tank
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747SP OBGI System (CATIA Model)
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Use of OBGI System
Converted to OBIGGS
Used as a flying test bed
Proved concepts Storage of nitrogen in fuel tank ullage Dual flow mode
Updating required for integration into commercial aircraft Pallet style design – space and weight restrictive
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Installation
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Installation Location
FAA 747SP large installation area available
Installation location was central on the aircraft
Benign environment & easily accessible
Relatively few personnel involved and highly aware of program
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747SP OBGI System
View from forward looking aft and up
Items visible include OEA permeate bleed manifold, ASM inlets and
supporting structure
View from forward looking aft and up
Items visible include inlet door control cable, ASM outlets, supporting structure and NEA termination point
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Installation Location
Space availability is rare on smaller aircraft Large open bays not available
Proximity to the following systems: Pressurized air – bleed air Cooling air Fuel tank
Environmental conditions in location No all available locations are contained within bays and may be
exposed to elements or near high temperature components May be difficult for maintenance actions
Human safety NEA leakage into pressurized areas or adjacent bays
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Installation Location
System size must be minimized for use in most applications
Installation in close proximity to interface locations a benefit Less weight required for connections
Location should be chosen for installation environment and ease of maintenance should also be considered
Health and safety of passengers/crew and maintenance personnel must be considered Potential leak and accumulation of nitrogen gas
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System Performance & Analysis
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Analysis Requirements
Flammability exposure model
Fuel tank thermal model
Inerting system performance model
Aircraft information required Configuration Systems performance Flight details
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System Performance
Aircraft configuration Ullage Volume Vent configuration Space availability Weight
Aircraft OBIGGS interface systems Bleed air pressure, temperature and flow profile Cooling air pressure, temperature and flow profile Maximum NEA flow Contaminants
Flight details Climb & descent rate Cruise altitude & duration
Other issues Allowable flammability exposure Reliability requirement Oxygen concentration
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Inerting Performance Model
Inerting performance model throughout flight profile Receives external aircraft inputs
Bleed air conditionsCooling air conditions
Uses performance of OBIGGSHeat exchangerFilterHollow fiber membraneDual orifice In-tank distribution
Calculates conditions within tankUllage spaceTemperaturePressure
Result of the model is O2% in the tankOxygen concentration in ullage space throughout flight profile
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Single Aisle Aircraft Performance Curve
Single Aisle Aircraft, Percentage of Oxygen in Ullage & Altitude
0
5
10
15
20
25
30
0 100
Time-Minutes
Par
tial
Pre
ssu
re-p
sia,
%O
2
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
Alt
itu
de
(ft)
CWT %O2( vol)
"12%"
Flight Profile
Case Details
Tank type
Init.Oxygen Level %
Fuel Oxygen Level % Initial Fuel Load %
CWT Landing Temp (F)
Tank Capacity(cu-ft)
Cruise Time (min)
ASM(s) Installed
12
21
CWT
0
-10
350
1
60
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Flammability Exposure Model
Reliability
Aircraft System Performance
(Bleed & cooling air, etc.)
OBIGGS Performance
(Ullage inert?)
Tank Conditions(Ullage & pressure)
Flight Details(Altitude,
temperature and flight profile)
Fuel tank thermal model
FlammabilityExposure
Model
Hollow Fiber Performance(NEA flow & purity)
Flammable
Conditions?
Inert?
Options:
Non-flammable & not inert
Non-flammable & inert
Flammable & inert
Flammable ¬ inert
Contributes to fleet wide flammability
No
No
No
Yes
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Flammability Exposure Model
Determines fleet average flammability exposure Total flammable time divided by the total operating time including
ground operations Flight profile randomly selected
Monitor inputs throughout flight profileTemperature & pressure conditions in tank – flammable?Tank ullage oxygen concentration – inert?
OBIGGS performance Producing required purity and flow of NEA Reliability – operating?
Flammable time during flight profile adds to fleet wide exposure Time flammable conditions exist and tank is not inert
Process is restarted until number of flights representative of fleet usage is reached
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System Performance & Analysis
Flammability exposure analysis
Fuel tank conditionsTemperaturePressureFuel vapor contentOxygen concentration
Inerting system performancePurity & flow rate of NEAReliability of inerting system
Total flammable time (when flammable and not inert) divided by the total operating time including ground operations
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Modular Inerting System
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Modular Inerting System
Current system Pallet system requires large installation area
Extra weightPallet-airframe mounting & component-pallet mountingPallet structure & component housingDucting runs between components Interstitial heater
Approach not acceptable for narrow body aircraft Space availabilityWeight penalty
New configuration required for each aircraft
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Modular Inerting System
Modular inerting system Package all major components in one housing
Hollow fiber membraneFilterHeat exchanger
Individual housings & mountings not required
Modular housing replaces need for tubing runs between components
Close communication between heat exchanger and hollow fiber membrane removes need for interstitial heater
Same Shaw Aero patented “Module” interchangeable across aircraftSingle aisle requires 1 module, twin aisle requires 3 modulesSingle & twin aisle module interchangeable - Stock 1 module part number
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Modular Inerting System
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Modular Inerting System
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Modular Inerting System
Reduced weight over distributed components
Removal of interstitial heater
Fits within space availability of smaller aircraft
One common designed component that is used across many aircraft
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Health Monitoring
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Health Monitoring
System required to measure the health of the inerting system
Options include:
Measurement of O2 in-tank
Measurement of O2 from inerting system
Measurement of flow of NEA from inerting system
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Health Monitoring
Current oxygen sensors Test bed measurement of O2% in tank accomplished with FAA system
Sensors have a short lifeEquipment requires large space availability
Commercially available oxygen sensors cannot be placed in tankSensing elements superheat sample, that may contain fuel vapors
Measurement of O2% of NEA stream prior to tank infers tank O2%
Purity of NEA produced by inerting system
Should be used in conjunction with flow sensor
Tight measurement tolerances required
Failures in the following systems will not be detected
NEA distribution
Tank vent system
Previous flight assumed inert
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Health Monitoring
Non-oxygen sensing methods
Measure pressure or flow downstream of inerting systemLatent hollow fiber membrane failures not detected
Measure O2% of inerting system with GSE at lengthy intervals
Tank O2% should be measured
Tank O2 level measured directly by sampling a few times during the flight at critical tank location
Not inferred – total loop closure
Can we reduce the life cycle costs of the inerting system?
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Health Monitoring
Current sensing methods are:
Too large
Not compatible with environment
Flawed
Currently working on developing system that will measure the O2% in-tank
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Industry Standards
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Industry Standards
Industry standards are needed to define
System performance
System design
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Industry Standards
AIA Document Defines problem tanks Methods of defining flammability Sets flammability exposure limits
Fleet wide average levelsSpecial case of 80°F days
Methods of reducing flammabilityManaging heat transferDisplacing the flammable zoneUllage sweeping InertingFoam
Monte Carlo Analysis
Document submitted to FAA
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Industry Standards
SAE
Group made up of cross-section from two SAE groupsAE-5 Aerospace Fuel, Oil and Oxidizer SystemsAC-9 Aircraft Environmental Systems
Document encompases commercial and military aircraftBackground
Requirements
System Design
Validation & Verification
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Industry Standards
Background Lessons learned Gasses used Definition of inert
Requirements Types of aircraft Fuels Environmental conditions
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Industry Standards
System Design Architectures Air sources Distribution methods Tank types Performance Impact to and from other systems System Control and monitoring Analysis methods Installation RMTS
Validation & Verification
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Industry Standards
AIA document submitted to FAA
SAE document currently in progress
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The Fourth Triennial The Fourth Triennial International Aircraft Fire and Cabin Safety International Aircraft Fire and Cabin Safety Research ConferenceResearch Conference
The Fourth Triennial The Fourth Triennial International Aircraft Fire and Cabin Safety International Aircraft Fire and Cabin Safety Research ConferenceResearch Conference
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