The role of intense reactant-product mixing in distributed turbulent premixed combustion *

Distributed turbulent premixed combustion (DTPC) is a combustion regime in which reduced chemistry is disrupted by small, fast turbulence scales and is characterized by a suppression of radical concentrations. However, the mechanisms of and leading to DTPC and the regime boundaries of DTPC in terms of the Karlovitz number remain elusive. To better understand the radical behavior in and approaching this combustion regime, a series of direct numerical simulations (DNS) has been conducted for a recirculating model combustor that promotes intense mixing of premixed hydrogen-air reactants and products. This configuration has been used in the study of moderate and intense low-oxygen dilution (MILD) combustion and flameless oxidation (FLOX). As the global Karlovitz number increases, a suppression of chemical reactivity is observed. Radical concentration profiles in terms of progress variable are compared with a manifold-based combustion model to better understand the nature of the progress variable dissipation rate in DTPC and the role of intense reactant-product mixing.