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In order to study the explosion suppression characteristics of LPG/air mixture by CO2 synergistic inert powder, explosion suppression experiments were conducted in a 20 L explosion device. The results show that the explosion suppression effect of NaHCO3 powder is prior to Al(OH)3 powder under the condition of no CO2 synergy. As the mass concentration of inert powder increases, the peak value of explosion pressure Pex and the peak value of the pressure rise rate (dP/dt)ex decrease, and the explosion suppression effect gradually enhances. Gas–solid two-phase inhibitors exhibit more significant inhibitory effects than single-phase inhibitors. Increasing the volume fraction of CO2 or the mass concentration of inert powder can improve the explosion suppression effect. The explosion suppression effect of CO2/NaHCO3 is significantly better than that of CO2/Al(OH)3. The research results have certain significance for the prevention and control of LPG explosion accidents. [ABSTRACT FROM AUTHOR]

Most of existing research analyze gas explosion limit from single component gas or parial component mixed gas of coal spontaneous combustion, while analysis of gas explosion limit from mixed gas produced at different stages of coal spontaneous combustion is insufficient, and there are few experimental research on coal spontaneous combustion and gas explosion coupling disaster. In view of the above problems, the characteristic laws of gas generation in process of coal spontaneous combustion were researched by simulating experimental device of coal spontaneous combustion.The 20 L spherical explosion device was used to conduct the experiment about methane mix gas from coal spontaneous combustion at different stages,and effects of coal spontaneous combustion on the lower limits of gas explosion were studied.The experiment results show that main flammable gases of the coal sample spontaneous combustion are CH4, CO, C2H4, C2H6, C2H2， etc. Among these gases, CH4 and CO have the highest volume fraction, and the maximum volume fraction can reach 0.75% and 0.37% respectively. The content of flammable gases produced in different stages of coal spontaneous combustion is increased with the increase of spontaneous combustion time and temperature. CH4 and CO flammable gases are mainly produced at temperatures below 80 ℃ at the initial of coal spontaneous combustion, CO can be used as a marker gas for the slow oxidation stage of coal spontaneous combustion. As the time of spontaneous combustion continues,it starts to produce C2H4 and C2H6 after the temperature exceeds 80 ℃, and then C3H8 gas is gradually produced. At this time, the appearance of C2H4 indicates that the oxidation of coal has entered the acceleration stage. C2H2 is produced on the temperatures of 220 ℃ after the late stage of coal spontaneous combustion, at this point, the coal enters the intense oxidation stage. Low concentration of CO inhibits gas explosion, however, high concentration of CO promotes gas explosion, explosion pressure becomes larger, and lower explosion limit decreases. The mixed gas produced during the spontaneous combustion of coal increases the pressure of gas explosion, decreases the lower explosion limit by 0.55%,so increases the risk of gas explosion.

At present，there are few researches on coal spontaneous combustion with different metamorphic degree under environment conditions of simulated gradually heated goaf. Taking 4 kinds of metamorphic coal samples, such as coke lean coal, gas-fat coal, anthracite coal and fat coke coal as example, the experiment of coal spontaneous combustion was carried out by using simulation system of coal spontaneous combustion to study combustion characteristics of coal and generation rules of spontaneous combustion gas under goaf environment. Experiment results show that when coke lean coal, gas-fat coal, anthracite and fat coke coal are warmed up, the temperature will rise 'S' type. The early temperature will have a slow accumulation process at first and then start to heat up quickly, and finally tend to balance at 300 ℃, and then slowly rising. Different coal samples produce volatile gases such as hydrocarbons and carbon oxides during the spontaneous combustion process and the rate of formation is affected by temperature, as well as the maximum and minimum two inflection points are present. The temperature rise curve of anthracite coal is similar to a straight line, and the gas curve does not fluctuate obviously with temperature. Large amounts of CO and CH4 are produced in spontaneous combustion of gas-fat coal and fat coke coal, the rate of CO production of gas-fat coal is the fastest, the maximum volume fraction of CO can reach 8%; and the rate of CH4 production of fat coke coal is the fastest, the maximum volume fraction of CH4 can reach 14%. The volume fraction of CO and CO2 produced by coke lean coal and anthracite is about 2% and 4% respectively.

Various particle sizes and its explosive residues were tested using 20 L spherical explosive device, and the effect of particle size on the explosive conditions and explosive products of coal dust and solid residues was analyzed under different coal dust concentrations and ignition energy conditions. The results show that with the increase of coal dust particle size, the explosion of coal dust and its solid residue requires more stringent explosive critical conditions (higher coal dust concentration and higher ignition energy); the degree of hole development and particle fragmentation is much higher than that of large particle size coal dust and its explosive residue, compared with the explosive product of large particle size and its solid residue, and the content of O, Si two elements and the content of C element is lower in the explosive product of small particle size coal dust and its solid residue.

Secondary explosion experiments of coal dust were carried out by use of 20 L spherical explosion device under the conditions of different coal dust concentration, particle size and ignition energy separately, and influence of coal dust concentration, particle size and ignition energy on combustion duration and residual gas was analyzed. The results show that under the same conditions, the secondary explosion combustion duration(T2) of coal dust is greater than the first explosion combustion duration(T1). Ignition energy has the greatest influence on T2, and coal dust particle size has the least influence. With increase of coal dust concentration, T2 first decreases and then increases. With decrease of coal dust particle size or increase of ignition energy, T2 decreases continually. For the same kind of gas under the same conditions, volume fraction of residual gas after the secondary explosion of coal dust is smaller than that after the first explosion. In a certain range, with decreases of coal dust particle size, volume fraction of residual CO continuously decreases after the secondary explosion, ratio of volume fraction of CO to the one of CO2 decreases, and volume fraction of CH4 increases. With increase of ignition energy, volume fraction of residual CO or CH4 after the secondary explosion continuously increases, and ratio of volume fraction of CO to the one of CO2 shows an increasing trend.

Influence of concentration, particle size and ignition energy of coal dust on secondary explosion characteristic of coal dust were studied by use of 20 L spherical explosion device, and the secondary explosion characteristic of coal dust was compared with the first explosion characteristic of coal dust. The results show that with the increase of coal dust concentration, the maximum pressure and the maximum rising rate of pressure of secondary explosion of coal dust increase firstly and then decrease, the maximum pressure difference between the first explosion and secondary explosion decreases firstly and then increases, and the maximum rising rate difference of pressure between the first explosion and secondary explosion decreases firstly, then increases and decreases lastly; with the decrease of coal dust particle size, the maximum pressure and the maximum rising rate of pressure of secondary explosion of coal dust gradually increase, the maximum pressure difference and the maximum rising rate difference of pressure between the first explosion and secondary explosion increase firstly and then decrease; with the increase of ignition energy, the maximum pressure and the maximum rising rate of pressure of secondary explosion of coal dust, and the maximum pressure difference and the maximum rising rate difference of pressure between the first explosion and secondary explosion increase; the maximum pressure and the maximum rising rate of pressure of secondary explosion of coal dust is smaller than that of the first explosion; coal dust concentration is the main influence factor on the characteristic difference between secondary explosion and the first explosion of coal dust.

For the demand of automation and accuracy of coal and gas outburst early warning, a remote intelligent monitoring and warning system for coal and gas outburst was developed. The system constitution was introduced as well as key technologies including signal monitoring, interference recognition, signal transmission and early warning rules. The system takes sound acoustic emission, electromagnetic radiation and gas concentration as early warning indexes, and realizes remote monitoring and comprehensive early warning of sound acoustic emission, electromagnetic radiation and gas signals during outburst evolution process. Meanwhile, the system can automatically recognize and filter interference signals according to opening or stopping information of electromechanical equipments, so as to improve early warning accuracy of coal and gas outburst. The application result shows the system has high early warning accuracy, which can capture coal and gas outburst risk information in advance of 8-24 hours.

In order to assess effect of using coal seam water injection to control strong pressure of No.3 coal seam of Zhaozhuang Coal Mine, pre-evaluation research of using coal seam water injection to control strong pressure was carried out. Water injection parameters including moisture content, water absorption, firmness coefficient of coal sample and so on were tested to analyze feasibility of water injection of No.3 coal seam. Absolute variation and change rate of compressive strength of test sample before and after soaking were test to analyze expected pressure-relief effect of water injection and propose injection project. The analysis result shows that No.3 coal seam can meet the conditions of water injection, and after soaking, physical properties of coal and rock samples are changed, compressive strength is reduced greatly, which indicates water injection has desired expected pressure-relief effect.

Influence of particle size, concentration and ignition energy of coal dust on the maximum pressure and its rising rate of coal dust explosion were researched by use of 20 L spherical explosion equipment. The research results show that under the condition of certain particle size of coal dust, the maximum pressure and its rising rate of coal dust explosion will increase firstly and then decrease along with increasing of concentration of coal dust. When concentration of coal dust is in 400-480 g/m3, the maximum pressure and its rising rate of coal dust explosion achieve the maximal value of 0.94 MPa and maximum 28.79 MPa/s respectively. Under the condition of certain concentration of coal dust, the maximum pressure of coal dust explosion will not change in a similar tendency and its rising rate will increase along monotone with decreasing of particle size of coal dust. The maximum pressure and its rising rate of coal dust explosion will increase significantly along with increasing of ignition energy.

Understanding the damage evolution behavior of coal under stress wave can provide a theoretical basis for preventing rock burst. In this work, the impact experiments of coal samples were carried out by split Hopkinson pressure bar (SHPB); the stress wave propagation characteristics were recorded by dynamic strain acquisition instrument; the evolution behaviors of coal samples’ surface displacement were analyzed by digital image correlation (DIC); the correlation between stress wave and displacement were discussed based on the multi-fractal theory. The results proved the stress wave propagates in the non-linear attenuation mode of multiple incidences, reflection, and transmission. Among them, the attenuation velocity of the incident wave is the largest, followed by the reflected wave, and the transmitted wave is the smallest. The incident and reflected stress waves are mainly dominated by high amplitude signals, while the transmitted stress waves are mainly dominated by low amplitude signals. The horizontal displacement on the coal sample surface is changed in the form of variable velocity, acceleration, and direction during the process of the stress wave propagation. The impact velocity is favorably linked with the amplitudes and attenuation velocities of incident, reflected, and transmitted waves as well as the surface displacement, displacement velocity, and acceleration of coal samples. The multi-fractal characteristic parameters of stress wave and displacement show that the proportional relationship and difference between the large- and small-scale displacement are influenced by those between the high- and low-intensity signal of the stress wave, and the transmission wave can exert greater influence. [ABSTRACT FROM AUTHOR]

To investigate co-deflagration effect of a mixture of coal powder and corn starch, an air/methane atmosphere test was performed in a vertical explosion tube device and a 20-L spherical explosion device. Compared with pure coal powder and corn starch, the powder mixture undergoing deflagration in air was characterized by more uniform-distributed flame brightness, a more continuous flame structure, and less fluctuating flame propagation, approaching the fastest propagation velocity before mixing. Under the same mass concentration, the deflagration pressure of the powder mixture in methane atmosphere is related to the mixing proportion and is between the respective pressures of the two kinds of powder. Pm and (dP/dt)m of the mixtures of methane and different powders show overall consistency with increasing equivalence ratios, however, different powders with the same equivalence ratio still differ in their characteristic deflagration parameters. [ABSTRACT FROM AUTHOR]

Summary: This study is aimed at investigating the characteristics of CH4 explosion diffusion and propagation to the non‐methane area. The CH4 explosion pressure and flame were tested with the aid of a self‐built horizontal pipeline system. On this basis, the flame images, photoelectric signals, and pressure propagation laws during explosions of methane with different volume fractions in the pipeline were obtained. The experimental research results indicate that an obvious secondary explosion pressure occurs at L/D = 3.5. After the explosion pressures at different positions along the entire pipeline reach the peak values, they experience varying degrees of oscillations. The maximum explosion pressure in the non‐methane zone may occur at different length‐to‐diameter ratios. When the volume fraction of CH4 is larger, the maximum explosion pressure occurs farther. However, the explosion pressure at the end of the pipeline is lower than that at the explosion source. The flame intensity and flame duration of methane explosion are remarkably enhanced at L/D = 17.5 and then become gradually weakened in the non‐methane area. The variations of explosion pressure are always prior to those of flame signal. CO and CO2 are the main toxic and harmful gases produced by methane explosions, and high‐concentration (13% in this experiment) methane explosions produce a small amount of hydrocarbon gases such as C2H4 and C2H6. The volume fractions of the gases produced decrease with the increase in the distance from the explosion source. The research results boast great significance for suppressing methane explosions and their propagation in the pipeline. [ABSTRACT FROM AUTHOR]