Study On Dynamic Characteristics Of Coal Dust-methane Premixed Flame

For a comprehensive understanding of the occurrence and development process of coal mine accidents, we establish a set of experimental equipment to observe coal dust- methane mixing combustion flame dynamics process. We use high-speed photographic optical system, data acquisition machine and temperature sensor to analyze Coal dust- methane mixing combustion flame propagation characteristics and different coal particle size and the methane concentration on the influence of combustion flame propagation characteristics. Summed up the following conclusions.(1) The propagation morphology and combustion intensity of coal dust-methane mixture's combustion flame are closely related with dust particle size and methane concentration. When methane concentration was 3.7%, the front combustion flame was discrete and irregular; When the methane concentration was increased to 4.5%, 6.7%, he front combustion flame is a smooth plane or paraboloid; when the size of dust particle is small, the front combustion flame, with bright white light is smooth and continuous, which showed that the combustion was severe, and when the size of dust particle increases, the front combustion flame, with red and yellow light is discrete and irregular, which showed that the combustion intensity reduced.(2) During the propagation of coal dust-methane mixture's combustion flame, the heat of methane's combustion flame and particle size influenced the thermocouple temperature's rise time, and methane concentration mainly determined the thermocouple temperature's rise time; the combustion of coal dust determined the maximum flame temperature. When the coal dust particle size is relatively large(54-74?m), the temperature's rise time is very different under different methane concentration; when the coal dust particle size decreases, the temperature's rise time is little different with the methane concentration of 3.7% and 4.5% and the temperature's rise time is very different with the methane concentration of 6.7%; the combustion flame's temperature with the methane concentration of 6.7% rises soon after the mixture was burned. When the coal dust particle size increases, the reaction rate and energy released reduced, so flame's temperature reduced on the whole, but with slight fluctuation.(3) The propagation velocity of flame is determined by methane and coal dust, and the effects of methane on flame's propagation speed is far greater than that of coal dust. The propagation velocity of coal dust's flame decreased with the increase of coal particle size. When the coal particle size is little than 30-38.5?m, the propagation of composite flame is mainly affected by methane concentration, and the composite flame's propagation velocity with methane concentration of 6.7% is far more than that with methane concentration of 3.7% and 4.5%; When the coal particle size is large than 30-38.5?m, the coal particle size affects the propagation characteristics of composite flame, which leads to the reduce of flame's propagation velocity.At the moment, the single kinetic rate model and the kinetics/diffusion-limited rate model was used to reproduce the combustion process of coal dust-methane mixture. Through the analysis of flame image and flame temperature of coal dust- methane mixture in combustion tube, and numerical simulation, it concluded that:(4) The numerical simulation result of coal dust- methane mixture's combustion shows that the front composite flame is produced by methane, and, for coal dust, a little part of heat is released in front flame, but the coal dust still burned for a long time after front frame, and released most heat.(5) The preheating zone thickness can be obtained from the temperature and chemical reaction rate's numerical simulation cloud chart in the front of coal dustmethane mixture's combustion frame. The preheating zone thickness of coal dustmethane mixture's combustion frame ranged between 2mm and 16 mm under different experimental condition, and with the increase of coal particle size, frame's propagation velocity decreases, the time of heat propagation increased, and the preheating zone thickness increased under the same heat transfer rate. When the methane concentration increases, the reaction rate of methane combustion and the heat released increases, which transfer more heat to the preheated zone and make the preheating zone thickness increase.