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