# Presentation: 489836

## Jet Fuel Vaporization and Condensation: Modeling and Validation 

- 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

## Part I:  Physical Considerations and Modeling

## 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

## 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)

**Notes:**
Pa and Ta are ambient pressure and temperature, will change with varying flight conditions

Multicomponent vaporization and condensation – species with different boiling points and dew points 

Well  mixed assumption based on high order Rayleigh numbers, proven experimentally with spatially stratified sample locations for hydrocarbon and ullage temperature measurement

## 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

**Notes:**
These are the assumptions made in the computational model to simplify the calculations.  

## 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

## 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

## Composition of the Fuels Usedfrom Woodrow (2003)

## 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

## Dry Tank Ullage TemperatureComparison of measured vs. calculated ullage temperatureShows validity of well-mixed ullage assumption

- Measured ullage temp

- Calculated ullage temp

## Part II:  Experimental Validation of Modeling

## 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

## 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

## 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

## Experimental Setup

- Fuel tank – 36”x36”x24”, 1⁄4” 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

## Experimental Setup (continued)

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

## Experimental Setup (continued)

## Thermocouple Locations

## 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

## Experimental Results

## Experimental Results

## Experimental Results

## Flight Profile Tests

## Simulated Flight

## 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

## Isooctane

## 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