Modeling and Validation of Jet Fuel Vaporization and Condensation

1. C.E. Polymeropoulos Robert Ochs Rutgers, The State University of New Jersey International Aircraft Systems Fire Protection Working Group Meeting Jet Fuel Vaporization and Condensation: Modeling and Validation

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 • 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

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

8. Composition of the Fuels Usedfrom Woodrow (2003)

9. Part II: Experimentation

10. 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

11. Measuring Input Parameters for the Model HeatTransfer 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.

12. Experimental Setup • Fuel tank – 36”x36”x24”, 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

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

14. 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 10 9 6 7 8 5 4 3 2 11 1 12

15. 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

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

17. Dry Tank Ullage Temperature Comparison of measured vs. calculated ullage temperatureShows validity of well-mixed ullage assumption: Calculated vs. Measured Ullage Gas Temperature

18. Fuel Vaporization:Constant Ambient Conditions at Atmospheric Pressure Calculated vs. Measured Ullage Vapor Concentration

19. 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

20. Sea Level Vaporization:Flammability Assessment Flammability Assessment using the FAR rule, 0.033<LFL<0.045 Flammability Assessment using LeChatelier’s Rule, Flammable if LC>=1

21. Simulated Flight Profile up to 30,000’: Fuel Tank Temperatures and Ambient Pressure Calculated vs. Measured Ullage Vapor Concentration

22. Varying T & P:Modeled Transport Processes

23. Varying T & P:Flammability Assessment Flammability Assessment using the FAR rule, 0.033<LFL<0.045 Flammability Assessment using LeChatelier’s Rule, Flammable if LC>=1

24. 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 LeChatelier’s Flammability Rule • The calculations show that flammability is dependent on the composition of the ullage gas.