Effects of dimethyl ether and ethanol additions on soot transition in ethylene counterflow diffusion flames

This paper investigates the effect of blending dimethyl ether(DME)and ethanol on the soot transition periods in ethylene counterflow diffusion flames by using a novel optical diagnostic method.The soot critical transition point in different conditions is identified experimentally and numerically.Two kinds of flames are carried out to gain the soot critical transition point in counterflow diffusion flames by changing oxygen fraction(Xo)and changing volume flow rates of fuel and oxidizer(Qv).The red-green-blue(RGB)ratio method is used to precisely identify the soot critical transition point,and chemical kinetic simulations are performed to analyze the detailed reaction paths.The results show that compared to the ethylene flame,the soot critical transition point occurs at a higher Xoand a lower Qvwhen DME or ethanol is blended.The addition of DME and ethanol can inhibit soot formation,due to the degree of soot formation reaction being lower than the degree of the oxidation reaction in the blending flames.

Inhibition Effects of CH_(4)/CH_(3)OH on Dimethyl Ether Cool Flames

CH_(4)/DME mixtures can be used for engines and gas turbines,and have already been studied for many years.However,DME has a strong cool flame phenomenon,which will greatly influence the ignition and combustion characteristics of following hot flames.Therefore,the cool flame characteristics of CH_(4)/DME mixture are very important for their utilization.Recently,the inhibition effect of CH_(4)on DME cool flames has been discovered,but the mechanisms of the inhibition effects lack further verification and research.In this study,the inhibition effects were investigated via both experiments and simulations.In order to validate the inhibition effects,a comparison fuel of CH_(3)OH/DME was also used in this study.The extinction limits,flame temperatures and combustion products of the cool flames of the CH_(4)/DME and CH_(3)OH/DME mixtures were measured using a counterflow burner,and the reaction paths and heat release rate were derived from the HPMech-v3.3.The results indicate that CH_(4)and CH_(3)OH will both inhibit the cool flame of DME via competing with DME for OH and O radicals,and CH_(3)OH has stronger inhibition effects than CH_(4),because it is more competitive and produces more CH2O,which inhibits the oxidation of DME.The HPMech-v3.3 closely agrees with the experimental data,but still needs to be improved.

Hysteresis and Multi-state Behavior of Counterflow Flame in a Blowing Cylindrical Burner

This study focuses on flame hysteresis over a porous cylindrical burner. The hysteresis results from different operation procedure of the experiment. Gradually increasing inflow velocity can transform the envelope flame into a wake flame. The blow-off curve can be plotted by determining every critical inflow velocity that makes an envelope flame become a wake flame at different fuel-ejection velocities. In contrast, decreasing the inflow veiocity can transform the wake or lift-off flame into an envelope one. The reattachment curve can be obtained by the same method to explore the blow-off curve, but the intake process is reverse. However, these two curves are not coincident, except the origin. The discrepancy between them is termed as hysteresis, and it results from the difference between the burning velocities associated with both curves. At the lowest fuel-ejection velocity, no hysteresis exists between both curves owing to nearly no burning velocity difference there. Then, raising the fuel-ejection velocity enhances hysteresis and the discrepancy between the two curves. However, as fuel-ejection velocity exceeds a critical value, the intensity of hysteresis almost keeps constant and causes the two curves to be parallel to each other.