Impact of local flame quenching on the flame acceleration in H2-CO-air mixtures in obstructed channels

In accident scenarios originating from weak ignition, flame acceleration preconditions the fresh gas ahead of the flame front and provides the necessary conditions for deflagration-to-detonation transition to occur. Strong shear layers, which form at the rear edge of obstacles in the accelerated flow of fast flames, isolate fresh gas pockets. Vortices in the intense shear layer have the potential to locally quench the flame, limiting the integral heat release and delaying the onset of detonation. This study investigates the potential of local turbulent quenching in H-2-CO-air mixtures. First, the presence of locally reduced heat release is visualized in highly resolved simulations for H-2-air and H-2-CO-air flames. Efficient simulation methods are of great importance for risk analysis studies. In connection with the results from highly resolved simulations this justifies a more detailed look at RANS-based combustion models for said flames. Thus, three different treatments of turbulent quenching are investigated, in which the geometrical configuration (blockage ratio and obstacle spacing) and the geometry size is varied. The results indicate that quenching does not need to be considered in RANS-based combustion models for H-2-CO-air flames in explosion scenarios. But since quenching does eventually occur at very high turbulence intensities, the authors suggest limiting the flame turbulence interaction to flame stretch values obtained from 1D counter-flow flame simulations with detailed chemistry.