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

• Laminar flame speeds are computed for a wide set of H 2 /CO/CO 2 /CH 4 /air mixtures. • Weak influence of CO concentration on lean flammability limit of H 2 /CO/air mixtures. • In H 2 /CO/CO 2 /CH 4 blends, methane can mitigate fire risk better than inert CO 2 . • For H 2 /CO/CO 2 /CH 4 /air mixtures with large volume fraction of CO 2 there is fire risk. 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 H 2 /CO/CO 2 /CH 4 /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, CO 2 , and CH 4 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 H 2 /CO blends. Second, an increase in ϕ * and a decrease in S L ( ϕ ) in lean mixtures are more (less) pronounced when adding CH 4 (CO 2 , respectively) to H 2 /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 CH 4 (CO 2 , respectively) to H 2 /CO blends but retaining the same (low) equivalence ratio. Finally, results show that a large volume fraction of CO 2 in gases vented out a battery does not exclude fire risks.