Turbulent burning velocity of methane–air–dust premixed flames

Abstract

Investigation of turbulent burning velocity (ST) of methane–air–dust premixed flames with different dust types (coal, sand and sodium bicarbonate) and dust concentrations (λp = 0–75 g/m3) were conducted at three methane–air pre-mixture equivalence ratios (ϕg = 0.8, 1.0 and 1.2) and different turbulent intensities (urms′ = 0.65, 0.72 and 0.88 m/s). Experiments were conducted in a dust Bunsen burner set-up at constant pressure conditions to study stabilized premixed flames. The results indicate that based on the particle type, the variation of turbulent burning velocity with an increase in the particle concentration differs. In general, coal and sodium bicarbonate result in the heterogeneous effect of absorbing heat and releasing volatiles; whereas sand particles just absorb heat from the flame zone. The detailed time scale analysis conducted shows that the presence of particles in the concentration range considered tends to slightly enhance the cold flow turbulence whereas with the presence of flame zone, an increase in the turbulent intensity results in increasing the vaporization rate of the particles. This effects in decreasing the turbulent burning velocity of methane–air mixtures with coal and sodium bicarbonate particles at higher concentrations and turbulent intensities. Out of three dusts examined, sodium bicarbonate addition results in the lowest ST due to the release of CO2 and H2O. Between coal and sand, at fuel lean and stoichiometric conditions, ST values with coal are greater than sand due to the equivalence ratio promotion with the release of CH4. But, as the turbulent intensity increases and for ϕg = 1.0–1.2, ST values with sand becomes comparable to or greater than that of coal. Model coefficients are generated from the experimental data to estimate the turbulent burning velocity in these conditions and the results show a clear distinction in the model coefficients for gaseous and gas–dust mixtures.