in-situ-gas-analysis-fire-characterization-lithium-ion-cells-during

<em>In Situ</em> Gas Analysis and Fire Characterization of Lithium-Ion Cells During Thermal Runaway Using an Environmental Chamber

An experimental apparatus and a standard operating procedure (SOP) are developed to collect time-resolved data on the gas compositions and fire ...

Case Western Reserve University

Thermodynamic equilibrium calculations, as well as perfectly-stirred reactor (PSR) simulations with detailed reaction kinetics, are performed for a potential halon replacement, CHFBr (2-BTP, CHFBr, 2-Bromo-3,3,3-trifluoropropene), to understand the reasons for the unexpected enhanced combustion rather than suppression in a mandated FAA test. The high pressure rise with added agent is shown to depend on the amount of agent, and is well-predicted by an equilibrium model corresponding to stoichiometric reaction of fuel, oxygen, and agent. A kinetic model for the reaction of CHFBr in hydrocarbon-air flames has been applied to understand differences in the chemical suppression behavior of CHFBr vs. CFBr in the FAA test. Stirred-reactor simulations predict that in the conditions of the FAA test, the inhibition effectiveness of CHFBr at high agent loadings is relatively insensitive to the overall stoichiometry (for fuel-lean conditions), and the marginal inhibitory effect of the agent is greatly reduced, so that the mixture remains flammable over a wide range of conditions. Most important, the flammability of the agent-air mixtures themselves (when compressively preheated), can support low-strain flames which are much more difficult to extinguish than the easy-to extinguish, high-strain primary fireball from the impulsively released fuel mixture. Hence, the exothermic reaction of halogenated hydrocarbons in air should be considered in other situations with strong ignition sources and low strain flows, especially at preheated conditions.

Understanding overpressure in the FAA aerosol can test by CHFBr (2-BTP).

Computations of cup-burner flames in normal gravity have been performed using propane as the fuel to reveal the combustion inhibition and enhancement by the CFBr (halon 1301) and potential alternative fire-extinguishing agents (CHF, CHFCl, and CHFBr). The time-dependent, two-dimensional numerical code used includes a detailed kinetic model (up to 241 species and 3918 reactions), diffusive transport, and a gray-gas radiation model. The peak reactivity spot (i.e., reaction kernel) at the flame base stabilizes a trailing flame, which is inclined inwardly by a buoyancy-induced entrainment flow. As the volume fraction of agent in the coflow increases gradually, the -like reaction kernel weakens, thus inducing the flame base detachment from the burner rim and blowoff-type extinguishment eventually. The  flame structure (with two heat-release-rate peaks) is formed in the trailing  flame. The HO formed in the inner zone is converted further, primarily in the outer zone, to HF and CFO through exothermic reactions most significantly with the CHF addition. The total heat release of the entire flame decreases (inhibiting) for CFBr but increases (enhancing) for the halon alternative agents, particularly CHF and CHFCl. Addition of CHF results in unusual (non-chain branching) reactions.

A Computational Study of Extinguishment and Enhancement of Propane Cup-Burner Flames by Halon and Alternative Agents.

The effects of phosphorus-containing compounds (PCCs) on the extinguishment and structure of methane-air coflow diffusion flames, in the cup-burner configuration, is studied computationally. Dimethyl methylphosphonate (DMMP), trimethyl phosphate (TMP), or phosphoric acid is added to either the air or fuel flow. Time-dependent axisymmetric computation is performed with full gas-phase chemistry and transport to reveal the flame structure and inhibition process. A detailed chemical-kinetics model (77 species and 886 reactions) is constructed by combining the methane-oxygen combustion and phosphorus inhibition chemistry. A simple model for radiation from CH, CO, CO, HO, and soot based on the optically thin-media assumption is incorporated into the energy equation. The inhibitor effectiveness is calculated as the minimum extinguishing concentrations (MECs) of CO (added to the oxidizer) as a function of the PCC loading (added to the oxidizer or fuel stream). The calculated MEC of CO without an inhibitor is in good agreement with the measured value. For moderate DMMP loading to the air (<1 %), the measured value becomes significantly smaller, presumably due to particle formation in the experiment. An inhibitor in the oxidizer flow is an order of magnitude more effective compared to that in the fuel flow in gas-phase inhibition of co-flow diffusion flames. The three PCCs studied behave similarly with regard to flame inhibition, lowering radical concentrations and the heat-release rate at the flame-stabilizing peak reactivity spot (i.e., reaction kernel) in the base, promoting flame blow-off. The three compounds behave differently, however, with regard to the trailing flame. While all three raise the maximum temperature in the trailing flame, DMMP and TMP, which contain three methyl groups, result in higher maximum flame temperature and combustion enhancement there, with a unique two-zone flame structure, whereas phosphoric acid does not.

Fumiaki Takahashi

Department of Mechanical and Aerospace Engineering

Case Western Reserve University

In Situ Gas Analysis and Fire Characterization of Lithium-Ion Cells During Thermal Runaway Using an Environmental Chamber

Fumiaki Takahashi

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Mechanical and Aerospace Engineering

Case Western Reserve University

In Situ Gas Analysis and Fire Characterization of Lithium-Ion Cells During Thermal Runaway Using an Environmental Chamber

Department of Mechanical and Aerospace Engineering