MULTI-COMPONENT FUEL VAPORIZATION IN A SIMULATED AIRCRAFT FUEL TANK

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MULTI-COMPONENT FUEL VAPORIZATION IN A SIMULATED
AIRCRAFT FUEL TANK
C. E. Polymeropoulos Department of Mechanical
and Aerospace Engineering, Rutgers University 98
Bowser Rd Piscataway, New Jersey, 08854-8058,
USA Email poly_at_jove.rutgers.edu
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MOTIVATION

• Generation of a flammable mixture within aircraft
  center fuel tank may result in explosion hazard
• Experimentation with Jet A vaporization in an
  instrumented laboratory tank has been used to
  assess the effect of different test conditions on
  the resulting fuel vapor concentrations (Summer,
  1999)
• Evaluation of the experimental results (Summer,
  1999) requires analytical consideration of
• the influence of different experimental
  parameters
• the multi-component fuel vaporization

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OUTLINE

• Brief discussion of the experiment and of the
  results (Summer, 1999)
• Description of the semi-empirical model
• Results and comparison with data
• Conclusions

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SCHEMATIC DIAGRAM OF APPARATUS SUMMER (1999)
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EXPERIMENTAL CONDITIONS/DATA

• Mass loading (mass of liquid/tank volume)
  0.08 - 5.46 kg fuel/m3
• Fuel pan area 0.09 m2 - 2.05 m2
• Mean liquid temperature 52 C
• Unheated tank walls
• Data Temporal evolution of the liquid, gas, and
  wall temperatures, and of the total propane
  equivalent HC concentration

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Temporal Variation of Gas, Liquid and Mean Wall
Temperatures, and of Propane Equivalent
Hydrocarbon Concentration
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PREVIOUS EXPERIMENTAL FINDINGS(Summer, 1999)

• Propane equivalent hydrocarbon concentration
  reached a maximum steady value which increased
  with mass loading
• The time for reaching maximum hydrocarbon
  concentration decreased with increasing mass
  loading
• Measured hydrocarbon concentrations were lower
  than those expected with equilibrium vaporization
  at the liquid temperature (Woodrow, 1977,
  Shepherd, 1977)

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PHYSICAL CONSIDERATIONS

• 3D natural convection heat and mass transfer
  within the tank.
• Tank dimensions W/D 2.4 , H/D 1.3
• Liquid vaporization
• Vapor condensation
• Multicomponent vaporization and condensation

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PREVIOUS WORK

• Numerous previous investigations of heat
  transfer within enclosures
• Review papers Catton (1978), Hoogendoon (1986),
  Ostrach (1988), etc.
• Correlations
• Few studies of heat and mass transfer within
  enclosures
• Single component fuel evaporation in a fuel tank,
  Kosvic et al. (1971)
• Computation of single component liquid
  evaporation within cylindrical enclosures,
  Bunama, Karim et al. (1997, 1999)

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MAJOR ASSUMPTIONS

• Well mixed gas and liquid phases
• Uniformity of temperatures and species
  concentrations the gas and evaporating fuel
• Rag 109 , Ral 105-106
• Use of experimental liquid, gas, and wall
  temperatures
• Mass transport using heat transfer correlations
  and the analogy between heat and mass transfer
  for estimating film mass transfer coefficients
• Low evaporating species concentrations
• Approximate liquid Jet A composition based on
  previous published data and and adjusted to
  reflect equilibrium vapor data

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PRINCIPAL MASS CONSERVATION AND PHYSICAL PROPERTY
RELATIONS
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Mass Transfer Correlations
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Assumed Jet A Composition Based on data by
Clewell, 1983, and adjusted to reflect for the
presence of lower than C8 components
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Assumed Jet A Composition by no. of Carbon Atoms
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Computed and Measured Equilibrium Vapor MW
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Computed and Measured Equilibrium F/A
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Computed and Measured Equilibrium Vapor Pressure
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Effect of Fuel Loading on Measured and
ComputedPropane Equivalent Fuel Vapor
Concentrations
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Evolution of Fuel Vapor in the Tank
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Effect of Fuel Loading on ComputedFuel Vapor to
Air Mass Ratio
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Effect of Fuel Loading on ComputedFuel to Vapor
Molecular Weight
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Effect of Fuel Loading on the Steady State Vapor
Mole Fraction
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Results for the Floor Area Covered with Fuel
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Results with a 30.5 x 30.5 cm Pan
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CONCLUSIONS

• A semi-empirical model of Jet A vaporization
  together with previous experimental temperature
  data were used to compute the evolution of
  multi-component fuel vapor within the test tank
  ullage
• The liquid species composition was based on
  previous data adjusted to yield reasonable
  agreement with measured equilibrium vapor
  compositions at different fuel loadings
• There was good agreement between computed and
  experimental total vapor concentrations
• Computed results showed that steady state vapor
  concentration in the test tank was reached when
  the rate of vaporization equaled the rate of
  condensation on the tank walls

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CONCLUSIONS (continued)

• Condensation on the tank walls had a strong
  influence on the ullage vapor concentration
• Depletion of light components as the fuel
  loading was decreased resulted in increase of the
  molecular weight of the resulting mixture
• For the cases considered computed vapor to air
  mass ratios ratios were in good agreement with
  those calculated from experimental propane
  equivalent PPM data using a constant fuel vapor
  MW of 132.4 and a carbon ratio of 3/9.58
• The approach will be further tested to include
  current data with with a different size tank,
  sub- atmospheric pressures, and a spark igniter
• Extension using data with a full size tank when
  available

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ACKNOWLEDGMENT

• The work was supported by the Fire Safety
  Division of the FAA William J. Hughes Technical
  Center, Atlantic City, New Jersey, USA.
• Helpful discussions with Richard Hill and Steven
  Summer of the Fire Safety Division are gratefully
  acknowledged