卷 42, 编号 3 (2023)

The ignition of microparticles of low-metamorphosed (long-flame gas grade (LFGG)) coal for fractions with a distribution in the size range d = 0.4–33 µm under the action of laser pulses (1064 nm, 120 µs, 1.3 J) is studied. The coincidence of the kinetic characteristics of coal ignition under the action of laser pulses with different energy densities on samples in both narrow and wide particle size ranges is established. The minimum values of the three threshold planes of laser energy studied for the stages of ignition are obtained for the fraction of coal particles with a size of 2.2 μm. When working with coal dust, it should be taken into account that when exposed to thermal energy sources, particles of 1 to 10 microns are the most easily flammable.

Various methods for obtaining a combustible gas with a low tar content during the gasification of wood in superadibatic regimes are experimentally investigated: by adding catalysts to the gasified fuel (1), oxidative conversion of wood gasification products (2), and a combination of these two methods. It is established that the conversion of products of the catalytic gasification of wood makes it possible to obtain a tar-free combustible gas, which can be used in power engineering, but is unsuitable for chemical synthesis.

Experimental study of the process of combustion of a premixed acetylene–oxygen mixture diluted with either nitrogen or argon in a circular cross-section tube is conducted by high-speed photography. The behaviour of flame front at the early stage of acceleration is identified. The experimental findings are compared with the theoretical models available in the literature. It is demonstrated that at the initial stage of the accelerated propagation of flame extended along the channel walls—until deceleration—the velocity of the leading tip of the front is effectively described by the exponential relationship proposed in (Clanet and Searby, 1996). The normal (laminar) burning velocity of the stoichiometric acetylene–oxygen mixture diluted with either nitrogen or argon at a reduced initial pressure (8–21 kPa) is identified.

The hot-spot mechanism of double-base gunpowder combustion at atmospheric pressure is studied using film photography and thermocouple measurements. The dynamics of the development of the hot spot, a transverse wave of limited extent, propagating along the surface of the sample, is studied. The local frontal and normal propagation velocities of the transverse combustion wave are measured as a function of time. From the analysis of temperature distributions in the condensed phase of the wave, obtained with the use of thermocouples, the normal combustion rates are determined and the corresponding combustion surface temperatures are calculated. The resulting spread of velocities is explained by the evolution of the profile of the transverse wave front passing through the thermocouple. Taking into account the time variation of these combustion rates, the observed temperature distribution of the heated layer of the condensed phase is plotted. When analyzing the mechanism of propagation of transverse waves, data on the wave parameters and their dependence on pressure and the average combustion rate from the previous works of the authors were used.

Based on the data of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), the kinetic characteristics of the thermal decomposition of urotropine in flows of N2 and CO2 are determined. The sample heating rates are 20, 60, and 90 K/min. The values of the kinetic rate constants of the decomposition of urotropine are determined by the Kissinger method. During gasification in nitrogen, the activation energy of the thermal decomposition of urotropine increases from 106 to 139 kJ/mol under conditions of an increase in the degree of conversion of the substance. The preexponential value also increases from 0.35 × 109 up to 145 × 109 s–1. The decomposition of urotropine proceeds by an exothermic reaction with a heat of 368, 339, and 275 kJ/kg for heating rates of 20, 60, and 90 K/min, respectively. During gasification in carbon dioxide, the activation energy of the thermal decomposition of urotropine first increases from 110 to 132 kJ/mol as the degree of conversion increases, and then decreases to 120 kJ/mol. The heat of decomposition of urotropine in a flow of CO2 is 382, 327, and 303 kJ/kg for heating rates of 20, 60, and 90 K/min, respectively.

Simulations of the effect of addition of atoms, molecules, and radicals on autoignition of lean (14%) and ultra-lean (6%) hydrogen–air mixtures are performed in the temperature range of 800 to 1700 K at initial pressures of 1 and 6 bar. Computed results demonstrate that adding H, O, OH, HO2, and H2O2 reduces ignition delay time τ. Common tendencies are revealed in the temperature-dependent effects of the added species. For each additive, the corresponding effect is found to be the strongest at temperatures near 900 and 1100 K at pressures of 1 and 6 bar, respectively. It is shown that the effects of addition of O and H are similar in magnitude. The effect of НО2 is much weaker compared to other additives, and its temperature dependence is qualitatively analogous to that of Н2О2. While the extent of ignition-delay reduction decreases towards the endpoints of the temperature interval explored for all additives, significant effects persist in its high-temperature part for OH and in the low-temperature one for HO2 and H2O2. Addition of water up to 1% does not affect the value of τ.

The transition of layer-by-layer burning to convective burning is studied on samples of 5/7 pyroxylin powder granules with a density of 1.34 to 1.47 g/cm3 and porosity 7–15%. The experiments were carried out in a manometric bomb and a model rocket engine. We use the original particles and particles coated on the side surface with a film of polyvinyl butyral (PVB) in an amount of 4.1%. On samples with the initial particles, the transition to the convective regime occurs at a close-to-constant or slightly increasing pressure. The breakdown pressure of layer-by-layer burning increases with decreasing porosity. The use of coated particles leads to an increase in the duration of layer-by-layer burning. The transition of layer-by-layer burning to convective burning occurs at a falling pressure. The breakdown pressure decreases with decreasing porosity.