Jet Fuel Vaporization and Condensation: Modeling and Validation

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Jet Fuel Vaporization and Condensation Modeling
and Validation

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

• International Aircraft
• Systems Fire Protection
• Working Group Meeting

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Part I Physical Considerations and Modeling
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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

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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)

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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

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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

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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.115 Deg. F. and 120 Deg. F.
  from the Woodrow (2003) data

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Composition of the Fuels Usedfrom Woodrow (2003)
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Part II Experimentation
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Requirements for Experimental Setup

• Ability to vary fuel tank floor temperature with
  uniform floor heating
• Setup with capability of changing ambient
  temperature and pressure with controlled profiles
• Measurement of temporal changes in liquid,
  surface, ullage, and ambient temperatures
• Ability to asses the concentration of fuel in the
  ullage at a point in time

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Measuring Input Parameters for the Model
Heat Transfer
Mass Transfer
Fuel Properties

• FID Hydrocarbon analyzer used to measure the
  concentration of evolved gasses in the ullage
• Pressure measurement for vaporization calculations

• Fuel tested in lab for flashpoint
• Used fuel composition from published data of
  fuels with similar flashpoints

• Thermocouples on tank surface, ullage, and liquid
  fuel.

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Experimental Setup

• Fuel tank 36x36x24, ¼ aluminum
• Sample ports
• Heated hydrocarbon sample line
• Pressurization of the sample for sub-atmospheric
  pressure experiments by means of a heated head
  sample pump
• Intermittent (at 10 minute intervals) 30 sec long
  sampling
• FID hydrocarbon analyzer, cal. w/2 propane
• 12 K-type thermocouples
• Blanket heater for uniform floor heating
• Unheated tank walls and ceiling
• JP-8 jet fuel

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Experimental Setup

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

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Thermocouple Locations

• Thermocouple Channel
• Left Fuel
• Center Fuel
• Right Fuel
• Left Ullage
• Center Ullage
• Right Ullage
• Rear Surface
• Left Surface
• Top Surface
• Ambient
• Heater
• Heater Temperature Controller

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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

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Test Matrix

• 5 gallon fuel load for every test
• Temperature, pressure profiles created to
  simulate in-flight conditions

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Dry Tank Ullage Temperature
Comparison of measured vs. calculated ullage
temperatureShows validity of well-mixed ullage
assumption Calculated vs. Measured Ullage Gas
Temperature
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Fuel VaporizationConstant Ambient Conditions at
Atmospheric Pressure
Calculated vs. Measured Ullage Vapor Concentration
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Sea Level Vaporization
Calculated Temporal Mass Transport Occurring
within the Tank
-As fuel temperature increases, mass of liquid
evaporated, and hence stored in the ullage,
increases -As gas concentration in ullage
increases, condensation is seen to occur -As
condensation increases, mass of fuel stored in
the ullage decreases due to fuel condensing
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Sea Level VaporizationFlammability Assessment
Flammability Assessment using the FAR rule,
0.033ltLFLlt0.045
Flammability Assessment using LeChateliers Rule,
Flammable if LCgt1
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Simulated Flight Profile up to 30,000 Fuel Tank
Temperatures and Ambient Pressure
Calculated vs. Measured Ullage Vapor Concentration
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Varying T PModeled Transport Processes
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Varying T PFlammability Assessment
Flammability Assessment using the FAR rule,
0.033ltLFLlt0.045
Flammability Assessment using LeChateliers Rule,
Flammable if LCgt1
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Summary of Results

• Experiment was well designed to provide usable
  model validation data
• Model calculations of ullage gas temperature and
  ullage vapor concentration agree well with
  measured values
• Model calculations of mass transport within the
  tank give a good explanation of the processes
  occurring in a fuel tank
• Model can be used to determine the level of
  flammability using either the FAR rule or
  LeChateliers Flammability Rule
• The calculations show that flammability is
  dependent on the composition of the ullage gas.