JET A VAPORIZATION IN AN EXPERIMENTAL TANK Part 1 computed results

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JET A VAPORIZATIONIN AN EXPERIMENTAL TANKPart 1
computed results
C. E. Polymeropoulos Department of Mechanical
and Aerospace Engineering Rutgers University 98
Bowser Rd Piscataway, New Jersey, 08854-8058,
USA Tel [phone], email poly_at_jove.rutgers.ed
u
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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 for the liquid fuel and tank walls
• Ambient pressure and temperature
• Time

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Previous Work

• Measurement of LFL of Jet A using different
  methods Nestor (1967), Ott (1970)
• Model of vaporization in a fuel tank using single
  component fuel Kosvic (1971)
• Jet A Explosion Studies Shepherd, 1997
• Review of Flammability Hazard DOT /FAA/AR-98/26
• Jet A multi-component, non-equilibrium model
  Polymeropoulos and Summer (2002)
• etc
• Other work not available in the open literature?
  

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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 gas and liquid phases
• Ralullageo(109)
• Raliquido(106)

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Approach

• Use of available empirical or experimental data
  on temporal variation liquid fuel, and tank wall
  temperatures
• Possible CFD modeling of the 3D coupled heat and
  mass transfer processes in the tank
• Advantages
• Detailed spacial information on conditions
  within the tank
• Disadvantages
• Uncertainties with turbulent modeling of the
  multi-component mixing processes
• Computational complexity with 3D flows
• Computational time
• Possible use of well mixed tank model with
  spatially uniform but temporally varying fluid
  temperatures and compositions
• Advantages
• Ease of implementation
• Globally correct results provided the fluids are
  well mixed
• Disadvantages
• Requires empirical correlations for heat and mass
  transport
• Uncertainties with respect to the degree of well
  mixedness

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Principal Assumptions

• Well mixed gas and liquid phases
• Uniformity of temperatures and species
  concentrations in the ullage gas 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 form published data from
  samples with similar falsh points ts those tested
  

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Heat and Mass Transport
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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 Wodrow (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 120 F
  lt F.P. lt 125 F
• Present results use compositions corresponding
  to samples with F.P. 120 F and F.P. 125 F
  from the Woodrow (2003) data

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Composition of the Fuels Usedfrom Woodrow (2003)
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Dry Tank Ullage Temperature Comparison with
Experiment (Ochs,2003), Ambient pressure
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Dry Tank Ullage Temperature Comparison with
Experiment (Ochs,2003), 30,000 ft
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Computed and Measured (Summer, 1992) Propane
Equivalent Hydrocarbon Concentrations
Atmospheric Pressure, 2.2 x1.22 x 0.93 m Vented
Test Tank with heated floor and unheated
walls Tmax fuel 52 C
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Model Predictions for a Given Flight
ScenarioTank Dimensions (m) 0.9 W x 0.9 D x
0.6 HJet A. Flash point 322.2 K (120 F)
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Example of Model Input ParametersTfi 325 K,
Tf-Ts 10 K
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Fuel Vapor Mass Account after LiftoffL32 Kg/m3,
Tfi 325 K, Tf - Ts 10 K
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F/A Variation during FlightL400 kg/m3, Tfi
315 K, Tf-Ts15 K
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F/A, Effect of Fuel Temperature
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Vapor Molecular Weight

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Conclusions

• The Jet A fuel to air ratio in a test tank can be
  estimated using spatially uniform but temporally
  varying properties in the tank
• Liquid Jet A can be assumed to consist of a
  mixture of C5-C20 Alkanes obtained from fuel
  samples with F.P. in the range of those tested
• The computed results appear to agree with
  previous atmospheric pressure data from a test
  tank
• The model was used for estimating the F/A
  variation during an example flight scenario.
  Examples of computed results demosntrate
• The strong effect of liquid temperature on ullage
  A/F
• The considerable temporal variation of ullage
  species composition
• The model results must be compared with
  measurements appropriate to different flight
  conditions