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Recent Reports

Title: Effect of Airflow and Measurement Method on the Heat Release Rate of Aircraft Cabin Materials in the Ohio State University Apparatus
Author: Richard E. Lyon, Matthew Fulmer, Richard Walters, and Sean Crowley
Abstract:

Materials for aircraft cabin interiors must meet the flammability requirements of Title 14 Code of Federal Regulations (CFR) Part 25.853. The 14 CFR 25.853 requirement includes a test for large-area materials that measures the heat release rate (HRR) during burning using a fire calorimeter originally developed at Ohio State University (OSU). In the standard 14 CFR 25 procedure, a sample is inserted into the combustion chamber of the OSU apparatus and subjected to a calibrated radiant heat flux of 35 kW/m2 and an impinging pilot flame. Room temperature air is forced through the combustion chamber and exits through the exhaust duct at the top of the apparatus where a thermopile senses the temperature of the exhaust gases. The HRR during the test is deduced from the sensible enthalpy rise of the air flowing through the combustion chamber using the temperature difference between the exhaust gases and the ambient incoming air to calculate the amount of heat released by burning after suitable calibration using a metered methane diffusion flame. Limits of 65 kW/m2 and 65 kW/m2-min for the maximum (peak HRR) and the total heat release (HR) up to 2 minutes into the test (2-min HR), respectively, are placed on large-area materials used in passenger cabins of transport category airplanes carrying more than 19 passengers.

Results from multi-laboratory studies of the same materials tested for HR and HRR according to 14 CFR 25.853 indicated that the laboratory-to-laboratory variation of the test results was relatively high. There are many factors that can contribute to poor agreement between OSU fire calorimeter results obtained in different laboratories (i.e., reproducibility), including the accuracy of the heat flux calibration, contaminated temperature sensors, thermal inertia of the apparatus and its components, and changes in the convective environment in the combustion and bypass chambers caused by airflow and airflow distribution. This study focused on the effect of the airflow through the 14 CFR 25.853 fire calorimeter on the repeatability and reproducibility of the HR and HRR by the sensible enthalpy (temperature rise) of the standard method, compared to HR and HRR measured simultaneously by the oxygen consumption method.

Report: DOT/FAA/TC-TN15/34 Pages: 20 Size: 870 KB
Title: Thermal Dynamics of Bomb Calorimeters
Author: Richard E. Lyon
Abstract:

The validated solution to a two-term heat transfer model of a bomb calorimeter allows direct calculation of the heat released in an arbitrary process from the recorded temperature history without the need to correct for non-adiabatic behavior. The heat transfer coefficients and thermal capacities of the bomb calorimeter used in the heat calculation are determined parametrically from the temperature response to a known heat impulse (i.e., benzoic acid combustion). This methodology allows accurate measurement of heat released intermittently or during an extended period of time in a bomb calorimeter, as occurs during electrical resistance heating and subsequent thermal runaway of lithium ion batteries.

Report: DOT/FAA/TC-TN16/16 Pages: 20 Size: 408 KB
Title: Energy Release by Rechargeable Lithium-Ion Batteries in Thermal Runaway
Author: Richard E. Lyon and Richard N. Walters
Abstract:

The energy released by failure of rechargeable 18-mm diameter by 65-mm long cylindrical (18650) lithium-ion cells/batteries was measured in a bomb calorimeter for four different commercial cathode chemistries over the full range of charge using a method developed for this purpose. Thermal runaway was induced by electrical resistance (Joule) heating of the cell in the nitrogen-filled pressure vessel (bomb) to preclude combustion. The total energy released by cell failure, ?Hf, was assumed to be comprised of the stored electrical energy E (cell potential x charge) and the energies of mixing, chemical reaction, and thermal decomposition of the cell components, ?Urxn. The contribution of E and ?Urxn to ?Hf was determined, and the mass of volatile, combustible thermal decomposition products was measured in an effort to characterize the fire safety hazard of rechargeable lithium-ion cells.

Report: DOT/FAA/TC-TN16/22 Pages: 26 Size: 652 KB