Influence of the reactant temperature on particle entrained laminar methane-air premixed flames

This study investigates the laminar burning velocity of premixed methane-air mixtures, entrained with micron-sized (75-90 μm) coal dust particles over a range of gas phase equivalence ratios (0.9-1.2), dust concentrations (0-250 g/m3) and reactant temperatures (297, 350, 400 K) using a novel Bunsen-burner type experimental design. The experimental results show that, the laminar burning velocity is enhanced by the increase in the reactant temperature, irrespective of the equivalence ratio of the mixture. Addition of coal particles in fuel lean (ϕ < 1) mixtures increases the laminar burning velocity initially, but after a certain concentration of dust addition this trend is altered. The dust concentration value, where this variation is observed, increases with increase in reactant temperature. In other words, the reactant temperature plays a significant role in the trend of increase in laminar burning velocity with dust addition. For ϕ ⩾ 1, at a given reactant temperature, a linear decay of burning velocity with dust addition is observed. When a combustible dust particle interacts with the flame zone, it extracts energy from the flame and releases volatiles, thereby changing the equivalence ratio. This local increase in the equivalence ratio and the heat sink effect, are found to be influenced by the reactant temperature. A mathematical model including these effects is developed and the model predictions are compared with the experimental results. The results are in a good agreement for fuel lean and stoichiometric mixtures; whereas the model is found to under predict results for fuel rich cases.