Laminar burning velocities and lean flammability limits of H2/CO/CH4/CO2/air mixtures associated with gases vented out Li-ion batteries after thermal runaway

Journal article, 2025

To explore major combustion characteristics of mixtures relevant to gases vented out Li-ion batteries, complex-chemistry simulations of laminar flames are performed for a wide range of H2/CO/CO2/CH4/air mixtures by varying equivalence ratio and mole fractions of these species. The simulations are done for different temperatures of unburned reactants, using three state-of-the-art chemical mechanisms and multicomponent diffusion model with Soret effect. The focus of the study is placed on the influence of concentrations of CO, CO2, and CH4 on the computed laminar flame speeds S_L and a surrogate of lean flammability limit, i.e., equivalence ratio ϕ^∗ associated with a small speed S_L(ϕ^∗) = 5 cm/s. Results show that, first, both S_L(ϕ) in lean mixtures and ϕ^∗ depend weakly on mole fraction of CO in H2/CO blends. Second, an increase in ϕ^∗ and a decrease in S_L(ϕ) in lean mixtures are more (less) pronounced when adding CH4 (CO2, respectively) to H2/CO blends. Accordingly, under certain conditions, fuel can reduce S_L(ϕ) more than diluent. These observations are attributed to a larger (smaller) increase in the mole fraction of inert species when adding CH4 (CO2, respectively) to H2/CO blends but
retaining the same (low) equivalence ratio. Finally, results show that a large volume fraction of CO2 in gases vented out a battery does not exclude fire risks.