Jet Fuel Vaporization and Condensation: Modeling and Validation

1. 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 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.=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 – 36”x36”x24”, 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