Ignition and cool flame interactions of DME/H2/air blends in a micro-channel with a wall temperature gradient

Two-dimensional numerical simulations are performed to study the flame dynamics of DME/H₂/air mixtures in a microchannel with a controlled wall temperature profile. The characteristics of premixed stoichiometric DME/H₂/air flames at various H₂ compositions (% by volume) are analyzed in a 1 mm diameter tube of 120 mm length for a mixture inlet velocity of 0.15 m/s at 300 K temperature and 1 bar pressure. For every mixture composition under investigation, flame repetitive extinction and ignition (FREI) instability is noted. When the hydrogen percentage in the mixture rises, the frequency of FREI considerably decreases. The effect of hydrogen addition is nonlinear when the H₂ composition in the mixture is above 40 %. Throughout the FREI cycle, a stable, weak flame is observed at the upstream side of the combustor. When the H₂ composition in the mixture is increased to 80 %, the hot flame interacts with the weak flame, resulting in an increased rate of weak flame reactions. The weak flame shifts further upstream in this condition. The CH₂O and H₂O₂ produced at the weak flame region are being consumed downstream, resulting in another peak in heat release rate between the cool flame and hot flame regions. This intermediate peak disappears during the propagation phase.