Effect of Local Mixture Variations on Deflagration-to-Detonation Transition in Gaseous Hydrogen–Air Mixtures

Deflagration-to-detonation transition (DDT) is a critical process in propulsion and industrial safety applications. This transition involves interactions between shock waves, reaction fronts, and turbulent mixing, leading to complex flow behavior. In practical systems, the fuel–air mixture is rarely homogeneous. Local changes in mixture composition can strongly affect when and where DDT occurs by modifying the detonation cell size, hotspot formation, and flame–shock interactions. In this study, we analyze DDT in gaseous hydrogen–air mixtures with spatially varying composition in a two-dimensional channel. The multidimensional, reacting, fully compressible Navier–Stokes equations are solved, with chemical reactions and energy release represented using the Chemical-Diffusive Model (CDM). This reduced-parameter methodology uses a minimal set of calibrated reaction parameters to reproduce key combustion properties such as flame speed, detonation velocity and temperature. The CDM parameters are updated at each time step in every computational cell based on the local mixture composition. We examine how these variations influence the onset and structure of detonation during DDT.