Home – Home – Jornals – Combustion, Explosion and Shock Waves 2022 number 4

The macrokinetic laws of combustion and the kinetics of thermal decomposition of energetic condensed compositions containing high-enthalpy polynitrogen compounds based on the system of furazan, furoxan, and azepine rings and poly-2-methyl-5-vinyltetrazole as an active binder. The linear rates of high-temperature transformations (combustion) of compositions with different ratios of components were determined in the nitrogen pressure range 1 ÷ 6 MPa. It was found that the burning rate of compositions of polycyclic compounds and poly-2-methyl-5-vinyltetrazole exceeds the burning rate of individual components, with the synergistic effect increasing with decreasing nitrogen pressure in the system. Kinetic studies of heat release during thermal decomposition of energetic compositions in the temperature range 50 ÷ 350 °С under isothermal and nonisothermal conditions have shown that in pressed compositions, reactants interact, leading to a significant increase in the rate thermal decomposition of the mixture relative to the rate of decomposition of individual components. The data obtained indicate that one of the reasons for an increase in the burning rate upon mixing of components may be a change in the leading combustion reactions as a result of the chemical interaction of components of the binary composition.

Combustion of high-energy condensed systems may include the formation of an intermediate structure (skeleton layer, which significantly affects the combustion process. The influence of binder solidification on the formation of such a structure is studied experimentally. It is demonstrated that the laws of the skeleton layer formation during binder solidification depend to a large extent on the polymer structure. A specific role of the substance acting as a binder is determined. The basic features of modeling phenomena in the surface layer with and without the skeleton layer are presented. The possibility of predicting a number of characteristics of the combustion process is demonstrated.

Distribution of plutonium and americium compounds in the combustion products of radioactive graphite in water vapor or air is analyzed. The study is carried out via thermodynamic analysis using the TERRA software package in a temperature range of 400÷3200 K. It is revealed that all carbon in water vapor passes into gas at temperatures above 900 K, and its transition temperature in air is 1000 K. Condensed plutonium compounds transform into vapor compounds in water vapor at temperatures above 1800 K and in air at 1700 K. Condensed americium compounds begin transforming into a vapor state at temperatures above 2000 K, and their transition temperature in air is 2200 K.

Powders of various metals and boron are widely used in mixed fuel compositions to increase the combustion temperature and specific impulse of rocket engines. The article presents the results of an experimental study of the oxidation and ignition in air of ultrafine aluminum powders Alex, amorphous boron and microsized aluminum powders μAl, aluminum borides AlB₂ and AlB₁₂. Metal and boron powders were heated and ignited by a cw CO₂ laser in the heat flux density range 65 ÷ 190 W/cm². Based on thermal analysis data, it was found that the powder reactivity parameters are arranged in the following sequence (in descending order of activity): Alex ® B ® AlB₁₂ ® AlB₂ ® μAl. During the oxidation of amorphous boron and aluminum dodecaboride AlB₁₂, the total specific heat release and the rate of mass change have maximum values. Alex, boron and AlB₁₂ powders ignite more easily in air under the action of an external radiant source. Power exponent n as a function of the ignition delay time t_ign on the heat flux density t_ign ( q ) = Aq ^{- n} for μAl powders, AlB₂ and AlB₁₂ are approximately the same and equal to »2.0, for ultrafine Alex and boron powders it is lower and amounts to n = 1.5 and 1.0, respectively.

Effect of furan (C₄H₄O) and tetrahydrofuran (C₄H₈O) additives in a mixture of ethylene (C₂H₄) with argon on soot formation during pyrolysis behind reflected shock waves in a pressure range p ₅ = 2.1 ÷ 4.4 atm and a temperature range T ₅ = 1 600 ÷ 2 580 K is studied. Temperature dependences for the volume fraction of the condensed phase and the sizes of forming carbon nanoparticles in the studied mixtures are obtained by laser extinction and laser-induced incandescence. It is revealed that adding these furans increases the volume fraction of soot and expands the temperature range of its formation. The effect of furan turns out to be more pronounced than that of tetrahydrofuran. It is shown by the kinetic modeling of ethylene pyrolysis processes with the selected additives that alternative pathways for the production of C₃H₃ propargyl are formed in the presence of C₄H₄O and C₄H₈O, which is the reason why soot formation improves.

The fraction of methane in gas hydrates is approximately 12 wt. %. Theoretically, the temperature of combustion of such a composition is rather low. Nevertheless, the measurements show that an appropriate organization of the process may ensure a much higher flame temperature. For this purpose, it is necessary to separate the regions of dissociation and combustion (i.e., eliminate water heating). On the other hand, for combustion to be stable, some part of the combustion heat should be returned to the hydrate region to maintain the dissociation rate at a needed level. Stability of methane hydrate combustion is naturally determined by the ratio of heat release and heat transfer. The present paper described experiments on methane combustion above a layer of a dissociating gas hydrate, and a simple mathematical model is proposed for estimating diffusion combustion stability. A comparison of the modeling results with experimental data allows one to determine the water vapor concentration and to find the thermal balance of hydrate combustion.

Combustion of ethylene and kerosene in flows with Mach numbers M ≤ 2 is numerically studied. Flow throttling with the use of a side jet of compressed air is provided for igniting the fuel injected through an axial injector and for supporting its combustion. The Reynolds-averaged Navier - Stokes equations closed with the k-ε turbulence model are solved. Fuel combustion is modeled by one reaction. The possibility of formation of a transonic flow is considered. The gas-dynamic structure of the flow in the channel in the case of kerosene combustion is investigated for the Mach number M = 1.7 and stagnation temperatures of 1 400 and 1 500 K. The computations are performed for various values of the limiter of turbulent kinetic energy generation.

The characteristics of combustion of liquid hydrocarbons in the presence of a mixture of superheated water vapor with a diluent gas in a vaporizing burner are studied by an example of diesel fuel. Carbon dioxide is used as a diluent gas. The experiments reveal regimes of injection of superheated water vapor or carbon dioxide, as well as their mixture in various proportions, that ensure similar profiles of the mean flame temperature, thermal power, and air-to-fuel ratio. It is demonstrated that fuel burning in the presence of superheated water vapor, carbon dioxide, and their mixture allows reaching low concentrations of CO and NO _x in combustion products. In the case of CO₂ injection, these values are at the boundary of admissible concentrations for class 3 in accordance with the EN:267 norms. In the case of injection of only superheated water vapor, the nitrogen oxide emissions in flue gases are smaller than those in the case of carbon dioxide injection: reduction of NO _x emissions can reach 15 %.

A mathematical model based on macrokinetics is proposed for the numerical simulation of the auto-ignition period of fuel in a local volume of a hydrogen diesel engine with high pressure fuel injection equipment. Hydrogen auto-ignition in homogeneous chemical reactors for operating conditions of real hydrogen diesel engine at the moment of the start of hydrogen gas injection was simulated using a chosen detailed kinetic mechanism of hydrogen oxidation and a special software package. The results of these simulations for reactors of constant volume and constant pressures were used to derive an equation for the macrokinetics of hydrogen oxidation at high pressures. Using this equation, various operation modes of a hydrogen diesel engine with heating of air and hydrogen were investigated by numerical methods. Ways to reduce the induction period and increase the reliability of the engine are discussed.

Detonation waves in gaseous two-fuel systems CH₄/H₂/O₂ and heterogeneous three-fuel systems CH₄/H₂/O₂/coal suspension are experimentally studied. The experiments are performed with coal particle sizes 0 < d ≤ 200 μm and mean-volume densities of 160 ÷ 400 g/m³. The velocities along the tube and the pressure profiles in incident detonation and reflected waves are measured. The influence of the fuel components on the wave parameters is analyzed. The experimental detonation parameters are compared with the predicted thermodynamic equilibrium detonation parameters.

The results of a comprehensive assessment of the characteristics of combustion of fuels based on coal sludge with the addition of (5 % wt.) waste turbine oil and wood biomass using the method of multivariate (multicriteria) analysis are presented. The results of experimental studies of the processes of ignition and combustion of fuels, data on the calorific value, ash content, cost, composition of flue gases were used. The mixtures were burned in the form of tablets, layers and drops of an aqueous suspension. A positive effect of the use of additives on the indicators of energy, environmental and complex efficiency of coal sludge combustion was noted. The group of fuels burned in the form of pellets is characterized by the minimum indicators of energy, environmental and complex efficiency. The greatest environmental potential was found in fuels burned in the form of droplets of aqueous suspensions. The results of the study confirm the prospects for energy utilization of a wide range of wastes of coal, oil and vegetable origin as part of mixed fuels.

This paper presents the results of computational and experimental studies of the spark plasma gasification of technogenic carbon-containing wastes in order to obtain high-calorific-value syngas (H₂ + CO) for power generating devices. The composition of the syngas obtained in the process of gasification of organic waste was experimentally determined. The change in the composition and calorific value of the syngas was studied depending on the time of gasification of organic materials. The change in the calorific value of the syngas during waste gasification is shown.

Technological approaches to the reduction of carbon dioxide emissions in energy production are considered. Three levels of carbon dioxide generation by fuel power plants are identified. Fuel power plants were analyzed in terms of the most sensitive parameters in carbon capture, utilization and storage technologies: pressure, purity, and the amount of generated carbon dioxide. Ranging the carbon dioxide outlet parameters makes it possible to divide power plants into three groups: A, B, and C. Using the screening analysis method developed within a life cycle analysis system, the integral characteristics of the main technologies for utilization CO₂ emissions from energy production are considered depending on the level of technological maturity and market attractiveness. The groups of geological recycling, mineralization, carbonization, and bioutilization that are promising for the Russian industrial and energy complex are identified.