Numerical Investigation of Detonation Cell Size in Hydrogen and Hydrocarbon Fuels

Detonation cell size is one of the main characteristic scales of a multi-dimensional detonation, which plays an important role in the design of practical systems due to its empirical correlation with essential design metrics, such as minimum channel size and critical tube diameter. Despite the advances in modeling of multidimensional detonations, accurate prediction of the experimental detonation cell size remains elusive, except under specific conditions and for certain fuel mixtures. The underlying causes of this discrepancy and the fundamental mechanisms, which determine the cell size, are not fully understood. This study systematically compares numerical and experimental cell sizes across a wide range of pressures, temperatures, equivalence ratios and fuel mixtures. The simulation are performed using a fully compressible, adaptive mesh refinement, reacting flow solver Athena-RFX++ with complex chemical kinetics and mixture-averaged molecular transport. The effect of the ignition time and its temperature sensitivity on the cell size is investigated, with particular emphasis on the relative importance of different shock overdrives present in a multidimensional detonation front. Further, the impact of the simulation dimensionality and numerical resolution on the cell size is explored. Finally, the findings are used to identify potential limitations in the existing physio-chemical models, which may contribute to the inaccuracies in the predicted detonation structure.