Influence of air supply on coal spontaneous combustion during support withdrawal in fully mechanized coal mining and its prevention

It is necessary to change the air supply rate of the working face during the withdrawal of fully mechanized mining, making it important to study the oxidation characteristics of coal samples under different air supply rates. Through a self-made temperature-programmed experimental device, our focus was on studying the change laws of indicator gases released during the low-temperature (303.15–473.15 K) oxidation stage when the air supply rates of the coal samples were 0.67, 1.33, 2, 2.67, and 3.33 mL/s. The experimental results showed that the air supply increased, the concentrations of CO, C2H6, C3H8, C2H4, and C2H2 generated by the coal sample at the same temperature decreased, and the oxidation process decelerated. The initial temperatures of the four hydrocarbon gases were delayed to varying degrees with the increase in the air volume, and C2H4 was found to be more suitable as a hydrocarbon gas for the early warning of coal spontaneous combustion. Surface fitting was applied to analyze the change law of the CO generation rate under the combined effect of temperature and air supply; the change was divided into three stages. The CO concentration model at the upper corner of the working face during the withdrawal period was deduced, and comprehensive safety measures were put forward to prevent coal spontaneous combustion during the withdrawal period.

Methodology for Testing High-Energy Materials Under Low Temperature Conditions

The methodology developed for testing gun propellants at low temperatures according to PN-EN ISO 604:2006 is presented in the paper. Brief characteristics are given of the materials tested and the most important static compression test conditions, such as specimen dimensions, deformation velocity and temperature range for selected propellants, i.e. JA-2 and SC. To verify the methodology developed, preliminary strength tests were performed at selected temperatures (25, 0, -25 and -50°C). Tests were carried out on specimens fabricated by shortening the propellant grain to the dimensions required by the reference standard. The results obtained confirmed the expected strength properties for both propellants (tensile strength and brittleness). Due to its chemical composition, the JA-2 propellant is a material of low brittleness even at -50°C. It does not crack completely and only its yield point increases. The results obtained for the JA-2 propellant were consistent with those published in reference literature. The SC propellant proved to be very brittle even at room temperature. At temperatures below 0°C, it fractures completely after reaching the desired deformation. The results obtained confirm that the adopted strength test conditions and the way the tests were prepared and performed enable acquisition of comparable and reliable results. It can be seen by analysing the results for the JA-2 propellant, which are consistent with the data in the available references. In contrast, the tests on the SC propellant proved the validity of strength tests on this type of material. Brittleness of propellant grains is a very undesirable phenomenon. A change in the combustion surface of low explosives caused by the process of propellant grain fracturing can adversely affect the magnitude and course of the pressure pulse, leading to failure of a cartridge chamber or gun barrel.

Controlling changes in the combustion surface of solid fuel charges through the use of heat-conducting elements

On the basis of experimental data on the local values of the combustion rate of condensed systems along the heat-conducting filaments placed therein, regression models were constructed to relate the value of the local combustion rate with such characteristics of heat-conducting filaments as the thermal diffusivity and melting point. The obtained regression model was used to assess a possible expansion of the variation range of the local combustion rate when using various crystalline forms of CVD diamonds as heat-conducting filaments. It was shown that a local increase in the combustion rate could exceed the baseline value by 200 times. The possibility of controlling the transformation of the combustion surface by using heat-conducting filaments with variable characteristics was confirmed.

Synergistic Flame-Retardant Mechanism of Dicyclohexenyl Aluminum Hypophosphite and Nano-Silica

The flame retardant dicyclohexenyl aluminum hypophosphite (ADCP) and nano-silica are added to PA66 to improve flame retardant property of the composite. The flame-retardant property of the composite is tested via oxygen index test, vertical burning test, and cone calorimetry test. Combustion residues are tested using scanning electron microscopy, EDS spectroscopy, and Fourier infrared analysis. Results show that flame-retardant ADCP can effectively promote the formation of a porous carbon layer on the combustion surface of PA66. Nano-silica easily migrates to the material surface to improve the oxidation resistance of the carbon layer and the density of the carbon layer’s structure. It can also effectively prevent heat, flammable gases, and oxygen from entering the flame zone and enhance the flame retardant properties of ADCP.

Al2O3-CeO2 Oxides: Synthesis, Characterization and Evaluation as Catalytic Supports in Benzene Combustion. Surface Ceria Effects

Al2O3-CeO2 sol-gel oxides were obtained at ceria loadings of 2, 5, 10, 20 and 50 wt.%, calcined at 700 °C and characterized by N2 physisorption, XRD, TEM, 27Al MAS-NMR, and TPR. All samples present high amounts of surface ceria species and bulk ceria has significant presence from 20 wt.% of ceria. The sample with 50 wt.% presents both the reduction of bulk and interfacial ceria species and X-ray diffraction peaks corresponding to cerianite phase. Surface ceria dispersion degree (surface ceria/total reduced ceria) was determined to be 100 % for samples with 2 and 5 wt.% CeO2, with a slight decrease to ca. 90 % and 75 % for samples with 10 and 20 wt.% CeO2 respectively, and a lower value of 41 % for the sample with 50 wt.% CeO2. It was found the amount of surface ceria has a good correlation with the amount of AlV sites, indicating that incorporated Ce ions distorts the alumina matrix and restricts the amount of surface ceria. Platinum supported on these materials showed that the catalytic activity in benzene combustion for oxygen-depleted environments increased as the surface ceria concentration increased.

Impact of the Surface Morphology on the Combustion of Simulated Solid Rocket Motor

An advanced and intensive computational solution development is integrated with an asymptotic technique, to examine the impact of the combustion surface morphology on the generated rotational flow field in a solid rocket chamber with wide ranges of forcing frequencies. The simulated rectangular chamber is closed at one end and is open at the aft end. The upper and lower walls are permeable to allow steady and unsteady injected air to generate internal flow mimicking the flow field of the combustion gases in real rocket chamber. The frequencies of the unsteady injected flow are chosen to be very close or away from the resonance frequencies of the adapted chamber. The current study accounts for a wide range of wave numbers that reflect the complexity of real burning processes. Detailed derivation for Navier-Stokes equations at the four boundaries of the chamber is introduced in the current study. Qualitative comparison is performed with recent experimental work carried out on a two-inch hybrid rocket motor using a mixture of polyethylene and aluminum powder. The higher the percentage of aluminum powder in the mixture, the more the corrugations of the combustion surface. This trend is almost similar to the computational and analytical results of a simulated solid rocket chamber.

Study on Combustion Behavior of TC4 and Ti40 Alloys

OM, XRD, SEM, EDS were used to test. and analyze the combustion products of TC4 and Ti40 alloys by layer-by-layer from reaction frontier to matrix The result shows that: titanium alloy can be divided into 4 sections, combustion surface (CS), molten zone (MZ), transitional zone (TZ) and influence zone (IZ). The CS is mainly consist of TiO2, and with oxide of V. Cr2O3 and SiO2 are detected on CS of Ti40. MZ of TC4 is in loose and porous state. There are lots of cracks and holes in the TZ and IZ; MZ of Ti40 is compact, between MZ and IZ there is a TZ which is rich of V and Cr, it can stop oxygen diffusing effectively. From the MZ to matrix, oxygen content reduces gradually, and oxide of Ti with different valence state is detected. Because of effect of oxygen, the hardness of the two alloy increase after combustion, increment of Ti40 is much greater than that of TC4.