6/13/02IASFPWG – London, UK Ongoing Fuel Flammability Work at the FAA Technical Center International Aircraft Systems Fire Protection Working Group London, UK June 13 – 14, 2002 Steve Summer Project Engineer Federal Aviation Administration Fire Safety Branch, AAR-440

6/13/02IASFPWG – London, UK Agenda  Fuel vaporization computer model – validation experiments  Theoretical flammability limits as a function of MIE, FP, and O 2 content  Fuel vapor simulant for use in future ignition testing  Reports to be published

6/13/02IASFPWG – London, UK Fuel Vaporization Model – Validation Experiments

6/13/02IASFPWG – London, UK Acknowledgements  Professor C. E. Polymeropolous of Rutgers University  David Adkins of the Boeing Company

6/13/02IASFPWG – London, UK Introduction  The original model proved a good method of predicting the evolution of hydrocarbons. Results were presented by Prof. Polymeropolous (10/01 Fire Safety Conference)  Could prove to be a key tool in performing fleet flammability studies.  Fortran code has been converted to a user-friendly Excel spreadsheet by David Adkins of Boeing.

6/13/02IASFPWG – London, UK Physical Considerations  3D natural convection heat and mass transfer within tank Fuel vaporization from the tank floor which is completely covered with liquid Vapor condensation/vaporization from the tank walls and ceiling  Multi-component vaporization and condensation  Initial conditions are for an equilibrium mixture at a given initial temperature Gas, T g Liquid, T l Walls and Ceiling, T s

6/13/02IASFPWG – London, UK Major Assumptions  Well mixed gas and liquid phases within the tank Uniform temperature and species concentrations in the gas and within the evaporating and condensing liquid Ra g ≈ 10 9, Ra l ≈  Externally supplied uniform liquid and wall temperatures. Gas temperature is then computed from an energy balance  Condensate layer is thin and its temperature equals the wall temperature.

6/13/02IASFPWG – London, UK Major Assumptions (cont’d)  Mass transport at the liquid – gas interfaces was estimated using heat transfer correlations and the analogy between heat and mass transfer for estimating film mass transfer coefficients  Low evaporating species concentrations  Liquid Jet A composition was based on previous published data and and adjusted to reflect equilibrium vapor data (Polymeropoulos, 2000)

6/13/02IASFPWG – London, UK Assumed Jet A Composition  Based on data by Clewell, 1983, and adjusted to reflect for the presence of lower than C8 components

6/13/02IASFPWG – London, UK Assumed Jet A Composition Number of Carbon Atoms MW: 164 % by Volume

6/13/02IASFPWG – London, UK User Inputs  Equilibrium Temperature  Final Wall and Liquid Temperatures  Time Constants  Mass Loading  Tank Dimensions Note: For comparison with experimental results, recorded wall and liquid temperature profiles were entered directly in lieu of the final temperatures and corresponding time constants

6/13/02IASFPWG – London, UK Program Outputs  Equilibrium gas & liquid concentrations/species fractionation  Species fractionation as a function of time  Ullage, wall and liquid temperatures as a function of time  Ullage gas concentrations as a function of time FAR, ppm, ppm C 3 H 8

6/13/02IASFPWG – London, UK Experimental Setup  17 ft 3 vented tank placed inside environmental chamber.  Thermocouples used to monitor ambient, ullage, surface and fuel temperatures.  Blanket heater attached to bottom of tank used to heat fuel.  Hydrocarbon analyzer used to monitor ullage fuel vapors.

6/13/02IASFPWG – London, UK

6/13/02IASFPWG – London, UK

6/13/02IASFPWG – London, UK Future Testing  Future tests to consist of: Constant surface temperature tests. Various steady state pressure (cruise) tests. Varying pressure tests (flight profile). Varying wall to wall temperature tests. Varying fuel distribution tests.

6/13/02IASFPWG – London, UK Future Model Improvements  Capability of varying tank pressure.  Capability of varying wall to wall temperature calculations.  Capability of varying fuel distribution.

6/13/02IASFPWG – London, UK Theoretical Flammability Limits as a Function of MIE, FP & O 2 Content

6/13/02IASFPWG – London, UK Background  Present thinking in fuel tank inerting is that above x% O 2, the tank is at risk throughout the entire flammability envelope, below x% O 2 it is inert.

6/13/02IASFPWG – London, UK Background  Previous work has shown how flammability limits vary as a function of ignition energy.

6/13/02IASFPWG – London, UK Background  It follows intuitively that flammability limits will shift in a similar manner as inert gas is added to the fuel tank.  Thus, if your fuel tank is only partially inerted, the flammability exposure time has still been reduced by a significant amount.  How can this be quantified, validated and built into the flammability model?

6/13/02IASFPWG – London, UK Computed Flammability Limits as a Function of O 2  Similar methodology as that in DOT/FAA/AR-98/26 to compute flammability limits as a function of MIE.

6/13/02IASFPWG – London, UK Computed Flammability Limits as a Function of O 2  Correlation of the variation of LOC with altitude. Previously determined with a large (~20 J) spark source.

6/13/02IASFPWG – London, UK Computed Flammability Limits as a Function of O 2 , where T min is the minimum of the parabola given by T min = T fp + 22 – 1.5Z. a is a constant, determined by matching the curve as best as possible to the calculated 21% O 2 curve for the given ignition energy.

6/13/02IASFPWG – London, UK Resultant Curves for a 20 J Calculation

6/13/02IASFPWG – London, UK Flammability Limits as a Function of MIE, O 2 and FP  Combining this with the parabolic MIE calculations and LOC curves for various ignition energies, results in flammability limits which vary as a function of ignition energy, O 2 concentration and flashpoint. The sum of this work was put together into a working MS Excel model by Ivor Thomas, using the following LOC curves.

6/13/02IASFPWG – London, UK

6/13/02IASFPWG – London, UK Conclusions  By a set of simple calculations, one can obtain varying flammability limits as a function of ignition energy, O 2 concentration and flashpoint.  Once validated, this data can be used in the flammability model to show reduction in fleetwide fuel tank flammability as a function of the amount of inert gas added to the tank.  Future tests to validate these calculations are planned at the technical center.

6/13/02IASFPWG – London, UK Fuel Vapor Simulant for use in Future Ignition Testing

6/13/02IASFPWG – London, UK Background  Our current method for ignition testing of Jet-A fuel vapors is extremely time consuming (up to as long as 2 hours per test).  If a gaseous mixture was available to simulate the flammability properties of Jet A, it would allow us to perform more tests quicker.

6/13/02IASFPWG – London, UK Background  Availability of said mixture would also have applicability to other issues (e.g. explosion proof testing of pumps, etc.)  Subcommittee of SAE AE-5 currently being formed to look at this issue.

6/13/02IASFPWG – London, UK Past Simulants - Hexane

6/13/02IASFPWG – London, UK Past Simulants – Caltech Mixture  NTSB Docket No. SA-516, Exhibit No. 20O  Volumetric Ratio of H 2 :C 3 H 8 of 5:1  Examined the effect of fuel concentration, vessel size and ignition source on pressure history.

6/13/02IASFPWG – London, UK Past Simulants – Caltech Mixture

6/13/02IASFPWG – London, UK Proposed Research Activity at Tech Center  20 L combustion vessel to be constructed within 4 – 6 weeks.  Variable energy (0.5 mJ – 5 J) spark source to be obtained within 8 – 10 weeks.  Tests to be conducted in a manner similar to the procedures layed out in ASTM flammability standards (e.g. E582, E2079, etc).

6/13/02IASFPWG – London, UK Proposed Research Activity at Tech Center

6/13/02IASFPWG – London, UK Reports to be Published

6/13/02IASFPWG – London, UK Reports  Summer, S. M., Fuel Flammability Characteristics of JP-8 Fuel Vapors Existing Within a Typical Aircraft Fuel Tank, DOT/FAA/AR-01/54  Summer, S. M., JP-8 Ignition Testing at Reduced Oxygen Concentrations, DOT/FAA/AR-xx/xx