Jet Fuel Vaporization and Condensation:

Modeling and Validation

Robert Ochs and C.E. Polymeropoulos

Rutgers, The StateUniversity of NewJersey

International Aircraft Systems Fire ProtectionWorking Group MeetingGrenoble, FranceJune 21, 2004

Part I: Physical Considerations and Modeling

Motivation

• Combustible mixtures can be generated in the ullage of aircraft fuel tanks

• Need for estimating temporal dependence of F/A on:– Fuel Loading– Temperature of the liquid fuel and tank walls– Ambient pressure and temperature

Physical Considerations• 3D natural convection heat

and mass transfer– Liquid vaporization– Vapor condensation

• Variable Pa and Ta

• Multicomponent vaporization and condensation

• Well mixed liquid and gas phases– Rayleigh number of liquid

~o(106)– Rayleigh number of ullage

~o(109)

Principal Assumptions• Well mixed gas and liquid phases

– Uniformity of temperatures and species concentrations in the ullage and in the evaporating liquid fuel pool

• Use of available experimental liquid fuel and tank wall temperatures

• Quasi-steady transport using heat transfer correlations and the analogy between heat and mass transfer for estimating film coefficients for heat and mass transfer

• Liquid Jet A composition from published data from samples with similar flash points as those tested

Heat and Mass Transport

• Liquid Surfaces (species evaporation/condensation)– Fuel species mass balance– Henry’s law (liquid/vapor equilibrium)– Wagner’s equation (species vapor pressures)

• Ullage Control Volume (variable pressure and temperature)– Fuel species mass balance– Overall mass balance (outflow/inflow)– Overall energy balance

• Natural convection enclosure heat transfer correlations• Heat and mass transfer analogy for the mass transfer

coefficients

Liquid Jet A Composition• Liquid Jet A composition depends on origin and

weathering• Jet A samples with different flash points were

characterized by Woodrow (2003):– Results in terms of C5-C20 Alkanes– Computed vapor pressures in agreement with measured data

• JP8 used with FAA testing in the range of 115-125 Deg. F.

• Present results use compositions corresponding to samples with F.P.=120 Deg. F. and 125 Deg. F. from the Woodrow (2003) data

Composition of the Fuels Usedfrom Woodrow (2003)

Dry Tank Tests

• Tests run without fuel in the tank to check the accuracy of the heat transfer correlations without the added variable of mass transfer

• Ullage temperature was measured in three different locations to verify the well-mixed assumption

• The measured ullage temperature was compared with the calculated ullage temperature

Dry Tank Ullage TemperatureComparison of measured vs. calculated ullage temperature

Shows validity of well-mixed ullage assumption

290.0

295.0

300.0

305.0

310.0

315.0

0 1000 2000 3000 4000 5000 6000

Time, s

Tem

pera

ture

, K

Liquid fuel

Tank surface

Ullage, measured

Ullage, computed

Measured ullage temp

Calculated ullage temp

Part II: Experimental Validation of Modeling

Overview

• Fuel vaporization experimentation is performed at W.J.H. Technical Center at Atlantic City Airport, NJ

• Experimental data consists of hydrocarbon concentrations and temperatures as functions of time

• Data is input into computer model and compared to calculated vapor composition

Model Inputs

• Fuel and tank surface temperature profiles

• Pressure and outside air temperatures as functions time

• Fuel composition (volume fractions of C5-C20 Alkanes) from Woodrow (2003)

• Tank dimensions and fuel loading

Model Outputs

• Hydrocarbon concentration profile – Propane equivalent hydrocarbon concentrations– Parts per million or percent propane can be

converted into F/A ratio

• Ullage temperature profile

Experimental Setup• Fuel tank – 36”x36”x24”, ¼” thick aluminum• Sample ports

– Heated hydrocarbon sample line– Pressurization of the sample for sub-atmospheric pressure

experiments– Intermittent (10 minute intervals) 30 sec long sampling

• FID hydrocarbon analyzer, cal. w/2% propane, check w/4%

• 12 thermocouples • Blanket heater for uniform floor heating• Unheated walls and ceiling• JP-8 Fuel

Experimental Setup (continued)

• Fuel tank inside environmental chamber– Programmable variation of chamber pressure

and temperature using:• Vacuum pump system

• Air heating and refrigeration system

Experimental Setup (continued)

Thermocouple Locations

Experimental Procedure• Fill tank with specified quantity of fuel• Adjust chamber pressure and temperature to desired

values, let equilibrate for 1-2 hours• Begin to record data with DAS• Take initial hydrocarbon reading to get initial quasi-

equilibrium fuel vapor concentration• Set tank pressure and temperature as well as the

temperature variation• Experiment concludes when hydrocarbon

concentration levels off and quasi-equilibrium is attained

Experimental Results

Experimental Results

Experimental Results

Flight Profile Tests

Simulated Flight

Pure Component Fuel

• Use isooctane (C8H18) as test fuel

• Pure component removes the ambiguity of multi-component fuel composition

• Highly volatile at room temperature – need to cool fuel to approx 0 deg. F. to stay within range of hydrocarbon analyzer

Isooctane

Conclusions and Future Work

• Measure flammability with NDIR type hydrocarbon analyzer and compare results with FID type analyzer

• Use experimental data from flight tests to compare measured with calculated flammability

• Simulate flight test scenarios in the lab to compare flammability of flight tests, lab tests, and calculated results