Home – Home – Jornals – Combustion, Explosion and Shock Waves 2021 number 1

The effect of SO₂ on the oxidative conversion of hydrogen and methane over a wide range of temperatures of 400 ÷ 1 500 ^oC at a pressure of the reacting mixture of 1 atm has been studied by numerical kinetic analysis. The analysis has shown that sulfur dioxide can have both accelerating and inhibitory effects on the oxidative conversion of hydrogen and methane, which is due to the participation of SO₂ and the products of its chemical transformation in conjugated processes. The accelerating effect of SO₂ on the oxidative conversion of hydrogen and methane is observed at low temperatures, and the decelerating effect at elevated temperatures.

New data on parameters of combustion and detonation of two-fuel mixtures of methane and hydrogen with oxygen and air are presented. The data are obtained with variations of both the ration between CH₄ and H₂ and also the ratio between the fuel components and oxidizer. Results for the critical energy of detonation initiation, characteristic size of detonation cells, detonation velocity, and energy release in detonation waves are included. New information on parameters of combustion and detonation of methane mixtures diluted by water, including situations with gas hydrates, is reported.

A CCDS2000 detonator for acetylene, ethylene, propylene, and a multicomponent methylacetylene-allene fraction (MAF) propellant is used to perform experiments on measuring the detonation rate and recording a detonation front cell in a tube 26 mm in diameter and 2 m in length. The experiments are carried out at atmospheric pressure in stoichiometric mixtures diluted by nitrogen to air concentrations and in air-propellant mixtures with a varying propellant content in them. In the case where the explosive mixture components are fed as a flow by stratifying an explosive charge in an initiation zone, a self-sustaining detonation is stably excited up to limiting (spin) regimes. The concentration limits of the detonation existence are determined. In the propellant-air mixtures of acetylene and ethylene, as the values become lower than the limits, there is multifront detonation. For propylene and MAF, a tube diameter of 26 mm is near-critical: only one- and two-headed spin is observed in the entire range of existence. Calculation results are in good agreement with the experiment.

A model of unsteady homogeneous nucleation of boron oxide vapors in chemically reacting gas mixtures is developed. This model is applied to perform a numerical study of homogeneous nucleation of boron oxide vapors in Laval nozzles with different geometric configurations. Typical values of the sizes of boron oxide condensation cores and their concentrations are determined. The potential barrier of nucleation, nucleation rate, and nucleation delay time are estimated. Important qualitative features of homogeneous nucleation evolution along the nozzle are identified. Based on the data obtained, recommendations on model application and its further development are formulated.

Difference in the molar masses of a combustible gas and its combustion products has a strong effect on a flame temperature and a burning rate. Instead of a molar mass difference, one may consider a heat capacity difference at a constant pressure. There are two heat sources in a combustion zone. One of them is chemical, and the other one is similar to heat release (heat absorption) during a first-order phase transition, but, depending on the process, it can be partially chemical. The higher the heat capacity of the fuel in comparison with the heat capacity of the combustion products, the higher the burning rate and the flame temperature. For the physical completeness of the issue under discussion, an ideal thermodynamic cycle is considered, and it is shown that Carnot's formula should contain a correction factor that takes into account a change in heat capacity.

Combustion of mechanically activated mixtures in 2Co-Ti-Al and Co-2Ti-Al is investigated, and alloys based on them are synthesized in self-propagating high-temperature synthesis. Microstructural, X-ray, and differential-thermal studies are performed. A Heusler phase Co₂TiAl-based alloy is obtained for the first time by means of mechanical activation. Conditions for the mechanical activation of a reacting powder mixture for the formation of a single-phase material is experimentally selected.

Dependence of the combustion of a Ti + C granular charge on a granule size is experimentally studied.It is revealed that the burning rate of a granular mixture of all fractions used in the work is higher than the burning rate of a bulk-density powder mixture. It is shown that, with a decrease in the granule size, the burning rate of the charge in the absence of gas decreases due to an increase in the number of boundaries between the granules per unit length of the sample. A strong influence of the nitrogen flow on the burning rate of both large and small granules is established. It is shown that, in contrast to small granules, an increase in the nitrogen flow rate of large granules up to 600 l/h leads to a transition to convective combustion. The studies performed indicate that, despite the structural analogy between mechanically activated and granular mixtures, the relationship between the combustion time and the front transition time in granular mixtures is completely different. This means that the combustion of granular mixtures even in the absence of a gas flow cannot be explained within the framework of a microheterogeneous model.

Influence of micromilling on air conversion of pulverized coal fuel is under study. On the basis of these experiments, computational fluid dynamics methods are used to perform simulation determining the conditions of the process under study. Conversion of coarse coal in a medium of combustion products of fine coal with the following parameters: a flow rate of primary and secondary coal is 0.82; a corresponding air flow rate is 0.35; the excess ratios of primary, secondary, and total air are 0.8, 1.87, and 1.39; temperatures in the active zone are higher than 1 200 ^oC. According to the computational results for this regime, conversion for the primary and secondary coal is 100 % and 60 %, respectively, and the total conversion is »80%. The results obtained suggest that it is possible to increase the efficiency of coal combustion due to micromilling technologies as applied to oil-free ignition and torch illumination systems on steam pulverized coal boilers at TPPs.

An experimental method for determining the limiting pressure perturbations initiating acoustic instability in liquid rocket engine combustors has been developed which can be used to estimate of the stability of the working process. The method involves a statistical processing of the recorded noise pressure pulsations in the vicinity of natural resonance frequencies for all normal modes of acoustic vibrations in cylindrical combustion chambers and gas generators. The vibration damping coefficient (decrement), characterizing the difference between the generated and dissipated energy, is adopted as a diagnostic predictive criterion of the stable or unstable state of a dynamic system. The method is based on the theory of self-oscillating dynamic systems and one-dimensional Markov random processes using the apparatus of the Fokker-Planck-Kolmogorov equation. Analysis of the nonlinear differential equation with a symmetrized stochastic right-hand side describing white noise for experimentally determined amplitudes of pressure pulsations and their statistical processing using Mera software allows the state of the self-oscillating system to be identified a stable or unstable. The method is passive and applicable used without using standard external pulsed disturbing devices.

This paper presents a method and results of an experimental study of the ignition characteristics of samples of high-energy materials by multimode laser radiation. An even distribution of the radiation flux density on the end surface of a cylindrical sample is obtained by its rotation around the axis of symmetry with a given angular velocity. The effect of convective heat transfer of the end surface of the sample with the environment on ignition characteristics is eliminated by placing the sample in a cylindrical container. The results of experiments on ignition of pyroxylin samples by a CO₂ laser with and without rotation rotation of the sample are presented.

Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is extensively employed in military weapons as the main constituent of HMX-based polymer-bonded explosives (PBXs). It is known that the safety of PBXs is closely related to their microstructures. Discontinuities in PBXs, such as micron-sized pores, air bubbles, and interfaces between the explosive crystal and polymer bonds, may transform into hot spots when subjected to impact. Herein, a three-dimensional mechanical-thermal-chemical coupled mesoscopic model is proposed to study the collapse of an air bubble in an HMX crystal under impact. A viscoplastic constitutive model and the Birch-Murnaghan equation of state are employed for the HMX crystal to predict its mechanical response. Thermal decomposition of HMX is taken into account by using multistep thermal decomposition equations. The viscoplastic model yields results that reasonably agree with data obtained in the plane shock experiment. The influence of the edge length of the mesh elements on simulation results is analyzed. Then more simulations are conducted for studying the feasibility of using the viscoplastic model for different orientations of the HMX lattice. Afterwards, the coupled model is applied to study the collapse of an air-bubble/pore in the HMX crystal for different impact velocities.

RDX containing a small amount of single-walled carbon nanotubes is obtained by the method of codeposition from a solution. The detonation of this composition is studied by an electromagnetic method of mass velocity measurement and by a high-resolution electroconductivity method. A clearly expressed chemical spike is observed. Preliminary indications of reaction acceleration in the presence of nanotubes are obtained. The electroconductivity measurements are difficult because of the noticeable conductivity of the original material; if this factor is taken into account, the electrical conductivity profiles behind the detonation front are similar to those observed for pure RDX. Possible reasons for the influence of nanotubes on detonation characteristics are discussed.

The results of a study of the dynamic compression of plastic-bonded PETN by the method of Hopkinson's composite rod (HCR) are presented. The test procedure and some aspects of this method are described. The advantages of the HCR method in comparison with drop weight tests of explosives are briefly discussed. In experiments, the strain rates were 7 500 ÷ 12 000 s^-1. Load-strain and load-displacement diagrams are plotted, and the amount of energy required to initiate an explosive transformation are estimated. It is proposed to use this method as an additional one to the existing methods for studying the characteristics of explosives.

Pipe sticking is one of technical challenges in the drilling industry that has a major impact on the drilling efficiency and well costs. In order to eliminate deep water stuck pipe hazards, a new type of the jet cutter cartridge is designed. The main structure of the cartridge is a linear shaped charge including hydrogen-based emulsion explosives and copper tubes. During the detonation process of emulsion explosives, the copper tubes form several linear jet cutters along the ring direction to penetrate the stuck drill pipe. Experimental results indicate that the properties of hydrogen-based emulsion explosive meet the requirement to the explosive for the environment of the stuck point. This annular jet cutter cartridge is successfully applied in a copper mine to solve a stuck pipe incident.