A numerical investigation of deflagration propagation and transition to detonation in a microchannel with detailed chemistry: Effects of thermal boundary conditions and vitiation

We numerically investigate the premixed flame acceleration (FA) and the subsequent deflagration to detonation transition (DDT) of pure and vitiated fuel/oxidizer mixtures in a microchannel under two extreme wall thermal conditions—an adiabatic wall and a hot, preheated isothermal wall. The numerical simulations are conducted using AMReX-Combustion PeleC, an exascale compressible reacting flow solver that leverages load-balanced block-structured adaptive mesh refinement to enable high-fidelity direct numerical simulation. We perform these simulations for a hydrogen combustion system. While it is widely known that adiabatic walls strongly promote the occurrence of DDT via FA, such a mechanism of DDT is found to be strongly limited by the flame speeds of the unreacted mixture and hence is intrinsically tied to the mixture composition. We demonstrate that the addition of water (i.e., vitiation) to the unreacted mixture leads to a significant reduction in the flame speed, thereby slowing down the FA process and subsequent DDT. With isothermal preheated walls, the pure fuel cases preferentially propagate along the wall after an auto-ignition event, leading to the formation of a “secondary” finger-flame. This secondary front subsequently undergoes transverse expansion, following which deceleration of the flame is observed. The vitiated fuel cases also exhibit a similar behavior, nonetheless exhibit much longer time-scales of auto-ignition and propagation, in addition to stronger deceleration. In summary, this study presents one of the very few simulations in the FA and DDT literature that employ detailed chemical kinetics for both adiabatic and isothermal walls.