Flammability Characteristics Flammability Characteristics of JP-8 Fuel Vapors Existing of JP-8 Fuel Vapors Existing

Within a Typical Aircraft Fuel Within a Typical Aircraft Fuel TankTank

Steven M. SummerDepartment of Mechanical & Aerospace Engg.

Masters Thesis DefenseDecember 21, 2000

Faculty Advisor: Prof. C. E. Polymeropoulos

Overview of ProblemOverview 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 ProblemOverview 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: Overview of Problem: Aircraft Fuel TanksAircraft Fuel Tanks

Fuel is typically is stored in two wing tanksLarger aircraft also use a Center Wing

Tank (CWT) located within fuselage

Definition: Fuel Mass Loading - (Mass of Liquid Fuel)/(Total Internal Tank Volume)

Overview of Problem: Overview of Problem: Aircraft Fuel TanksAircraft Fuel Tanks

In some cases, located directly underneath CWT is the Environmental Conditioning System (ECS)

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

Aviation Rulemaking

Advisory Committee

Fuel Tank Harmonization

Working Group

Overview of Problem:Overview of Problem:Aviation FuelAviation 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:Overview of Problem:Aviation FuelAviation 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 ProblemSummary of Problem

CWTs with adjacent heat sources (ECS)• Increases rate of fuel vapor generation

Typically small amount of fuel in CWT• Reduced impact on flammability because of

increased evaporation of light ends

Lack of a definitive composition of aviation fuels• Leads to fuels consisting of hundreds of

hydrocarbons, with varying properties

Result: Fuel Tank Flammability Potential is Increased Throughout

Flight Profile

Heated Fuel Vapor Testing• Determine the effects of

fuel mass loading,liquid fuel evaporative surface area andresidual fuel on tank walls and

on ullage vapor generation within an aircraft fuel tank environment

ObjectivesObjectives

Definition: Ullage - the unused internal portion of the fuel tank

ObjectivesObjectives

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

ObjectivesObjectives

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 VaporHeated Fuel VaporTesting: ObjectivesTesting: 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 VaporHeated Fuel VaporTesting: ApparatusTesting: Apparatus

88.21 ft3 vented, aluminum fuel tank• 14 K-type thermocouples

1 Fuel5 Surface (3 wall, 2 ceiling)5 Ullage

• 2 hydrocarbon sample ports150,000-Btu kerosene air heaterSeveral sized fuel pans

• 1 x 1 , 2 x 2 and one covering tank bottom

DoorT/C 5

T/C 2

Analyzer Port 2

T/C 1

T/C 0T/C 3

Analyzer Port 1

T/C 4

Heat InletHeat Outlet

Heated Fuel VaporHeated Fuel VaporTesting: ProceduresTesting: Procedures

Fuel measured and poured into fuel panFuel pan placed into tankTank door sealedKerosene air heater turned onFuel heated to 10° above flash point (125 °F)Hydrocarbon concentration monitored until

equilibrium is reached

Mass Loading ResultsMass Loading Results

Mass Loading ResultsMass Loading Results

Mass Loading ResultsMass Loading Results

Evaporative Surface Area ResultsEvaporative Surface Area Results

Evaporative Surface Area ResultsEvaporative Surface Area Results

Residual Fuel ResultsResidual Fuel Results

Residual Fuel ResultsResidual Fuel Results

Tank Wall Cooling:Tank Wall Cooling:ObjectivesObjectives

Determine the effects of cold tank wall temperatures on ullage vapor generation within an aircraft fuel tank environment

Tank Wall Cooling:Tank Wall Cooling:ApparatusApparatus

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:Tank Wall Cooling:ProceduresProcedures

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 ResultsTank Wall Cooling Results

LOLF Testing:LOLF Testing:ObjectivesObjectives

Determine the lowest oxygen level within the tank that would support ignition (i.e. the lower oxygen limit of flammability)

LOLF Testing: ApparatusLOLF 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

V i d e o C a m e r a

T o H C A n a l y z e r

R i g h t T e s t T r a c k

L e f t T e s t T r a c k

1 0 m P r e s s u r e V e s s e l3

A n a l y z e r B y p a s sS a m p l e L i n e O A n a l y z e r2H e a t e rH e a t e r

S p a r k S o u r c e F a n

= T h e r m o c o u p l e F e e d t h r o u g h

N L i n e s2

Video C am era

To H C A n a ly z e r

R igh t Test Track

Left Test Track

O A n a ly z e r

2H eater

Spark Source

Fan

= T h e rm o c o u p le F e e d th ro u g h

N L in e s2

R ig h t T /C T re eL e ft T /C T re e

L iq u id J P -8 F u e lF u e l P a n

= T h e rm o c o u p le B e a d6.

0"6.

0"

LOLF Testing: LOLF Testing: ApparatusApparatus

LOLF Testing: ProceduresLOLF 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 LOLF Testing Results (Preliminary Methane Tests)(Preliminary Methane Tests)

LOLF Testing ResultsLOLF Testing Results

ConclusionsConclusions

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

ConclusionsConclusions

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

RecommendationsRecommendations

Tank wall & ullage temperatures need to be treated carefully

Further LOLF experiments should include dynamic pressure instrumentation

LOLF at altitude