Structure and dynamics of hexagonal cells in H$_2$/CO$_2$ flames

Transition from fossil fuels to sustainably produced hydrogen remains an important goal to achieve current
climate targets. Hydrogen from gasification and steam reforming is produced alongside CO$_2$. Instead of
separating the CO$_2$, it can be kept in the product gas, leading to possible reductions in NO$_x$ and improved
safety aspects. However, the addition of CO$_2$ makes hydrogen flames more prone to cellular instabilities, which
can lead to problems when designing burners for hydrogen-based flames. To understand the formation and
dynamics of these instabilities, fully resolved 3D simulations of H$_2$/CO$_2$ cellular flames on a heat flux burner
are performed. The numerical configuration follows an experimental setup that observed cellular and band-like
structures stabilizing on the burner plate. With the simulations employing finite rate chemistry and detailed
diffusion models, hexagonal flame structures are identified and characterized. The simulations show good
qualitative agreement of the flame structure with the measurements. The influence of mass flow rate, burner
plate temperature and equivalence ratio on the flame structure is investigated. ... mehrA transition from band-like to hexagonal structures is described in terms of cusp formation, which become the corner points of the hexagonal
cells, and the stabilization mechanism is explained via the high local flame stretch above holes in the burner plate. A Markstein number-based correlation for the cell size with respect to the burner plate temperature is proposed and the simulation data is provided as a public database for further analysis.