Flame Acceleration in Stoichiometric Methane/Hydrogen/Air Mixtures in an Obstructed Channel: Effect of Hydrogen Blend Ratio

Experiments and numerical simulations were conducted to study the flame acceleration (FA) in stoichiometric CH4/H2/air mixtures with various hydrogen blend ratios (i.e., Hbr = 0%, 20%, 50%, 80%, and 100%). In the experiments, high-speed photography was used to record the FA process. In the calculations, the two-dimensional, fully-compressible, reactive Navier-Stokes equations were solved using a high-order algorithm on a dynamically adapting mesh. The chemical reaction and diffusive transport of the mixtures were described by a calibrated chemical-diffusive model. The numerical predictions are in good agreement with the experimental measurements. The results show that the mechanism of FA is similar in all cases, that is the flame is accelerated by the thermal expansion effects, various fluid-dynamic instabilities, flame-vortex interactions, and the interactions of flame with pressure waves. The hydrogen blend ratio has a significant impact on the propagation speed and the morphological evolution of the flame during FA. A larger hydrogen blend ratio leads to a faster FA, and the difference in FA mainly depends on the increase of flame surface area and the interactions between flame and pressure waves. In addition, as the hydrogen blend ratio increases, there are fewer pockets of the unburned funnels in the combustion products when the flame propagates to the end of the channel.