# Presentation: 325731

## Jet Fuel Vaporization and Condensation: Modeling and Validation 

- C.E. Polymeropoulos
- Robert Ochs
- Rutgers, The State
- University of New
- Jersey

- International Aircraft
- Systems Fire Protection
- Working Group Meeting

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

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

## Part II:  Experimentation

## 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

## Measuring Input Parameters for the Model

- Heat Transfer

- Thermocouples on tank surface, ullage, and liquid fuel.

- Mass Transfer

- Fuel Properties

- Fuel tested in lab for flashpoint
- Used fuel composition from published data of fuels with similar flashpoints

- FID Hydrocarbon analyzer used to measure the concentration of evolved gasses in the ullage
- Pressure measurement for vaporization calculations

## Experimental Setup

- Fuel tank – 36”x36”x24”, 1⁄4” 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

## Experimental Setup

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

## 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

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## 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

## Test Matrix

- Temperature, pressure profiles created to simulate in-flight conditions

## Dry Tank Ullage Temperature

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

## Fuel Vaporization:Constant Ambient Conditions at Atmospheric Pressure

- Calculated vs. Measured Ullage Vapor Concentration

## 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

## 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

## Simulated Flight Profile up to 30,000’:

- Fuel Tank Temperatures and Ambient Pressure

- Calculated vs. Measured Ullage Vapor Concentration

## Varying T & P:Modeled Transport Processes

## 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

## 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.