Experimental Investigation on combustion characteristics of DME lean side mixtures under micro-gravity

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Experiments have been carried out to elucidate the fundamental combustion characteristics of DME fuel-air mixtures. The main results obtained for the study are as follows that, for the measurement of burning velocity on DME fuel-air mixtures using microgravity technique, □The micro-gravity technique is the most suitable method to extract the essential combustion characteristics of DME fuel-air mixtures, especially, near the very lean side of mixtures, The burning velocity of DME fuel-air mixtures monotonically decreases with decre4asing equivalence ratio and these values are nearly the same with those4 of methane-air mixtures at all the equivalence ratios studied, for instance the burning velocity is 44.2cm/s and 16.5cm/s, respectively, at equivalence of 1.1 and 0.65 under room temperature and atmospheric pressure and □The decrease of burning velocity of lean side of DME fuel-air mixtures is larger than that of rich side of mixtures, for the fundamental analysis an combustion behavior … More of DME laminar premixed burner flames, The burning velocity of DME premixed flames is approximately 34cm/s at 1.0 of equivalence ratio. As comparison of the burning velocity of DME with those of methane and propane-air mixture, the burning velocity of propane-air mixtures are larger than those of DME-air mixture and DME-air mixture are larger than methane-air mixtures. The blow off velocity and flashback velocity of DME are always larger than those of methane. □The stable region of the flame is easily to examine by the boundary velocity gradients(g). In case of circular tube laminar flow, the boundary velocity gradients can be expressed as g=4V/πR^3. Where V is the volume flow rate and R is the burner radius. Combustion of DME fuel-air mixtures is more stable than that of methane-air mixtures. In this study, we have tried to obtain the lower flammability limit using the burner method with the flame histories. The lower flammability limits of DME-air premixed flame obtained by this method are approximately Φ=0.34 and that of methane-air premixed flame are approximately Φ=0.55. From these data it may be predicted that the application to the engine combustion of DME is an effective alternative fuel for the future and, for measurement of quenching distance on combustion of DME fuel-air mixtures by flat flame propagation method, (1) Both of the quenching distance of DME fuel-air mixtures measuring by parallel plate and circular tube increase with decreasing equivalence ratio and these values are almost identical with the corresponding value for methane-air and propane-air mixtures. □The relationship between the quenching distance of parallel plate L_q, and circular tube d_q may be expressed by L_q=0.65・d_q. (3) The effect of buoyancy makes flame propagation speed increase and quenching distance decrease in upward flame propagation. (4) The quenching distance also depends on the ratio of surface area S to internal volume V of cylindrical long tube and the quenching distance becomes smaller as the S/V decreases.From these experimental data it may be predicted that the application to the engine combustion of DME fuel is not impossible. Less