Flame Propagation And Temperature Distribution Characteristics Of Magnesium Dust Cloud Explosion

Magnesium powder is widely used in military,aviation,chemical and metallurgical industries.In the processes of manufacturing and application,magnesium powders will form dust cloud in local open space,which is very prone to dust explosion accident under the external stimulation of ignition source.How to accurately evaluate its explosion severity to develop the corresponding prevention and control measures,is of great significance to the work safe of magnesium powder.In this paper,the flame propagation and temperature distribution characteristics of magnesium dust explosion were studied based on contour detection and the two-color pyrometer technique,and the deflagration characteristic and influence factors of magnesium dust induced by hydrogen explosion was studied,which provides an important reference for the study of the explosion mechanism and explosion prevention of magnesium dust.This paper sets magnesium dust explosion as the main line of research.Using the experimental systems of dust explosion in an open space and a semi-open space to study the influence of particle size,dust concentration and particle size polydispersity on the flame propagation characteristics and temperature characteristics of the magnesium dust cloud.At the same time,the experimental system of explosion in a 27 L cubic chamber was used to study the deflagration characteristics of magnesium dust induced by a hydrogen explosion,and the effects of different ignition positions and different hydrogen contents were discussed.The main conclusions are as follows:（1）Based on the contour detection technique,the flame propagation velocity of magnesium dust cloud was measured and the influence factors of flame propagation were studied.The flame structures of magnesium dust clouds were closely related to the particle sizes,and the dust flame shapes of the small particle sizes were more spherical than those of the large particle sizes.When the concentration of magnesium dust cloud was 830 g/m³,the flame propagation velocity increased as the particle size decreased.The average flame propagation velocities of-400,-325,-200 and 100-200 mesh magnesium dust cloud were 2.27,1.68,0.64 and 0.38 m/s,respectively.The stable flame propagation velocities of small particle sizes were 2～6 times than those of large ones.With the decrease of particle size polydispersity,the structure of flame became more spherical before reaching the tube wall,the time of flame reaching the wall and top of tube increased.Before the flame reached the wall of tube,the average flame propagation velocities of magnesium dust cloud with the particle size polydispersity of 1.00,1.72 and2.45 were 2.07,3.42,and 4.22 m/s,respectively.（2）Based on the two-color pyrometer technique,the influence factors of magnesium dust cloud on flame temperature characteristics were studied.When the dust cloud concentration of-400 mesh magnesium powder was in the range of 830-1328 g/m³,with the increase of dust concentration,the low-temperature zone inside the flame expanded continuously,the leading edge of the flame maintained at a high temperature,and the average flame temperature decreased gradually.The flame temperature of magnesium dust cloud was related to the particle size.As the flame continuously propagated outward,the average flame temperature of magnesium dust clouds with different particle sizes gradually decreased over time.The average flame temperatures of-400 and-325 mesh magnesium dust clouds dropped quickly,while decreased relative slowly for the-200 and100-200 mesh magnesium dust clouds.In addition,the particle size polydispersity also has an obvious effect on the flame temperature of magnesium dust cloud.When the particle size polydispersity was middle（σ_D=1.72）,the flame surface of magnesium dust cloud maintained a relatively high temperature on the whole,and there was an obvious discrete flame at the lower part of the flame.However,when the particle size polydispersity was the biggest（σ_D=2.45）,the leading edge of the flame kept at a high temperature,and the low-temperature zone expanded with the flame propagation in the flame temperature mapping of magnesium dust cloud.The average flame temperature of magnesium dust cloud withσ_D=1.00 and 2.45 showed a decreasing trend during the flame propagation.At the initial stage of flame propagation,the average flame temperature of magnesium dust cloud withσ_D=1.72 was slightly lower than that of magnesium dust cloud withσ_D=2.45.Nevertheless,the average flame temperature maintained a high temperature at the later stage.（3）The deflagration characteristics of magnesium powder induced by hydrogen explosion were studied using the experimental system of explosion in a 27 L cubic chamber.And the experiments of different ignition positions and different hydrogen contents were compared.When ignited at the top（I_T）,center（I_C）,and bottom（I_B）,the propagation height of magnesium deflagration flame induced by hydrogen explosion decreased in turn.The ignition positions had an effect on the maximum explosion pressure of magnesium deflagration induced by a hydrogen explosion.When ignited at the top,the explosion pressure trends at P2 and P3 were similar,and P_1ex was minimum.When ignited at the center,both P_2ex and P_3ex were greater than P_1ex.When ignited at the bottom,the peak pressure was in the order of P_2ex>P_1ex>P_3ex.The（d P/dt）_ex value was maximum with the ignition position I_C,followed by the ignition position I_T,and minimum with the ignition position I_B.When the hydrogen content was between 24%-60%,as the hydrogen content increased,the peak pressure at P1,P2 and P3 increased first and then decreased,reaching the maximum value at the hydrogen content of 34%.Figure[45]Table[6]Reference[118]...