Transcript Document 7496898

Flammability Characteristics
of JP-8 Fuel Vapors Existing
Within a Typical Aircraft Fuel
Tank
Steven M. Summer
Department of Mechanical & Aerospace Engg.
Masters Thesis Defense
December 21, 2000
Faculty Advisor: Prof. C. E. Polymeropoulos
Overview of Problem
Threat of ignition of fuel vapors within
aircraft fuel tanks
• Has long been noted, but until recently, not
much data
• Several protection systems have been
researched and proposed, but none
implemented in commercial aircraft
Overview of Problem
July 1996, TWA 800 crashes over East
Moriches, NY
• NTSB cites an in-flight fuel tank explosion as
cause
• Numerous research projects undertaken by
CIT, UNR, ASU, SWRI and others
• Overall goal: generate enough data on aviation
fuel vapor generation/flammability to be able
to develop a means of protecting against
ignition
Overview of Problem:
Aircraft Fuel Tanks
Definition: Fuel Mass Loading Fuel is typically is stored in two wing tanks
(Mass of Liquid Fuel)/(Total Internal Tank Volume)
Larger aircraft also use a Center Wing Tank
(CWT) located within fuselage
Overview of Problem:
Aircraft Fuel Tanks
In some cases, located directly underneath
Aviation
Rulemaking
Fuel
Tank Harmonization
CWT
is the
Environmental
Conditioning
System
(ECS)
Advisory Committee
Working Group
Hot bleed air from the ECS heats CWT
fuel, resulting in an increase of the FAR
ARAC’s FTHWG determined that these
tanks are at risk 30% of the total flight time
compared to 5% for CWT’s without ECS
Overview of Problem:
Aviation Fuel
Specifications for commercial grade fuel
(Jet A/Jet A-1 & Jet B) set forth by ASTM
D1655
• Sets min/max values for things such as flash
point, boiling point, freezing point, etc.
• Very vague criteria for actual composition of
the fuel
Overview of Problem:
Aviation Fuel
“These fuels shall consist of refined
hydrocarbons derived from
conventional sources including crude
oil, natural gas liquids, heavy oil, and
tar sands”
-ASTM D1655
Summary of Problem
CWTs with adjacent heat sources (ECS)
• Increases rate of fuel vapor generation
Result:small
Fuelamount
Tank of
Flammability
Typically
fuel in CWT
•Potential
Reduced impact
on flammability
because of
is Increased
Throughout
increased evaporation of light ends
Flight Profile
Lack of a definitive composition of aviation
fuels
• Leads to fuels consisting of hundreds of
hydrocarbons, with varying properties
Objectives
Heated Fuel Vapor Testing
• Determine the effects of
fuel mass
loading,
Definition:
Ullage
- the unused internal
portion
of the fuel
tank area and
liquid
fuel evaporative
surface
residual fuel on tank walls and
on ullage vapor generation within an
aircraft fuel tank environment
Objectives
Heated Fuel Vapor Testing With Tank
Wall Cooling:
• Determine the effects of cold tank wall
temperatures on ullage vapor generation
within an aircraft fuel tank environment
Objectives
Lower Oxygen Limit of Flammability
Testing:
• Determine the lowest oxygen level
within the tank that will support ignition
of the ullage fuel vapors (i.e. LOLF)
Heated Fuel Vapor
Testing: Objectives
Determine the effects of
• fuel mass loading,
• liquid fuel evaporative surface area and
• residual fuel on tank walls and
on ullage vapor generation within an
aircraft fuel tank environment
Heated Fuel Vapor
Testing: Apparatus
88.21 ft3 vented, aluminum fuel tank
• 14 K-type thermocouples
1 Fuel
5 Surface (3 wall, 2 ceiling)
5 Ullage
• 2 hydrocarbon sample ports
150,000-Btu kerosene air heater
Several sized fuel pans
• 1 x 1 , 2  x 2  and one covering tank bottom
Analyzer
Port 2
Door
T/C 5
T/C 4
T/C 2
T/C 1
Analyzer
Port 1
T/C 0
T/C 3
Heat Inlet
Heat
Outlet
Heated Fuel Vapor
Testing: Procedures
Fuel measured and poured into fuel pan
Fuel pan placed into tank
Tank door sealed
Kerosene air heater turned on
Fuel heated to 10° above flash point (125 °F)
Hydrocarbon concentration monitored until
equilibrium is reached
Mass Loading Results
Mass Loading Results
Mass Loading Results
Evaporative Surface Area Results
Evaporative Surface Area Results
Residual Fuel Results
Residual Fuel Results
Tank Wall Cooling:
Objectives
Determine the effects of cold tank wall
temperatures on ullage vapor
generation within an aircraft fuel tank
environment
Tank Wall Cooling:
Apparatus
Same tank as Heated Fuel Vapor Testing
with some modifications:
• 3-in. shell surrounded the two side and rear
walls for CO2 cooling
• Kerosene air heater replaced with a
thermostatically controlled hot plate
Tank Wall Cooling:
Procedures
 Fuel measured (1.5 gallons) and poured into fuel
pan
 Fuel pan placed into tank & tank door sealed
 Hot plate turned on
 Fuel heated to 10° above flash point (125 °F) and
maintained for 2 hours
 Walls were cooled to desired temperatures and
maintained until significant decrease in HC
concentration was observed
Tank Wall Cooling Results
LOLF Testing:
Objectives
Determine the lowest oxygen level
within the tank that would support
ignition (i.e. the lower oxygen limit of
flammability)
LOLF Testing: Apparatus
 9 ft3 vented, aluminum fuel tank placed inside of
10 m3 pressure vessel equipped with:
• 12 K-type thermocouples
1 Fuel
7 Surface (3 floor, 1 on each side wall)
4 Ullage
•
•
•
•
•
•
•
9.5" x 9.5" fuel pan located in center of tank
Thermostatically controlled hot plate
6" diameter mixing fan
2 hydrocarbon sample ports
1 oxygen sample port
Spring loaded blow-out plate
Two tungsten electrodes powered by a 20,000 VAc, 20
mA transformer
LOLF Testing:
Apparatus
= Thermocouple Feedthrough
= Thermocouple Bead
Left T/C Tree
Right T/C Tree
6.0"
Left Test Track
Fan
Spark
Source
= Thermocouple Feedthrough
Left Test Track
Fan
3
10 m Pressure
Vessel
To HC
Analyzer
Spark
Source
N Lines
2
Heater
Sample
Li
Analyzer ne
Bypass
Video
Camera
O
Analyzer
2
Right Test Track
Fuel Pan
N Lines
2
6.0"
Liquid JP-8 Fuel
Heater
To HC
Analyzer
Sa m
p le
Line
Ana
lyze
r By
pas
s
Right Test Track
Video
Camera
O
Analyzer
2
LOLF Testing: Procedures
 Fuel measured (3/8-gallon) & placed in pan
 Fuel pan placed in center of tank
 Nitrogen injected until desired O2 concentration
reached
 Hot plates turned on
 Fuel heated to and maintained at ~150°F until HC
concentration leveled off at ~25000 ppm C3H8
 Spark initiated for 1, 2 & 3 second durations
LOLF Testing Results
(Preliminary Methane Tests)
LOLF Testing Results
Conclusions
Heated Fuel Testing
• At mass loading of 0.08 – 0.15 kg/m3
significant reduction in HC concentration
• Evaporative surface area has no effect on HC
concentration
• As evaporative surface area decreases, longer
time necessary to obtain maximum HC
concentration
• Residual fuel has no effects
Conclusions
Tank Wall Cooling Testing
• As tank wall temperatures decrease, the rate of
decrease in HC concentration increases
LOLF Testing
• Methane LFL of 5.3 – 5.35% determined
• LOLF determined to be 12% O2
Recommendations
Tank wall & ullage temperatures need to be
treated carefully
Further LOLF experiments should include
dynamic pressure instrumentation
LOLF at altitude