Jet Fuel Vaporization and Condensation: Modeling and Validation

1
Jet Fuel Vaporization and Condensation Modeling
and Validation

• Robert Ochs and C.E. Polymeropoulos
• Rutgers, The State
• University of New
• Jersey

• International Aircraft
• Systems Fire Protection
• Working Group Meeting
• Grenoble, France
• June 21, 2004

2
Part I Physical Considerations and Modeling
3
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

4
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)

5
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

6
Heat and Mass Transport

• Liquid Surfaces (species evaporation/condensation)
  
• Fuel species mass balance
• Henrys law (liquid/vapor equilibrium)
• Wagners 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

7
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

8
Composition of the Fuels Usedfrom Woodrow (2003)
9
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

10
Dry Tank Ullage TemperatureComparison of
measured vs. calculated ullage temperatureShows
validity of well-mixed ullage assumption
Measured ullage temp
Calculated ullage temp
11
Part II Experimental Validation of Modeling
12
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

13
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

14
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

15
Experimental Setup

• Fuel tank 36x36x24, 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

16
Experimental Setup (continued)

• Fuel tank inside environmental chamber
• Programmable variation of chamber pressure and
  temperature using
• Vacuum pump system
• Air heating and refrigeration system

17
Experimental Setup (continued)
18
Thermocouple Locations
19
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

20
Experimental Results
21
Experimental Results
22
Experimental Results
23
Flight Profile Tests
24
Simulated Flight
25
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

26
Isooctane
27
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