Home – Home – Jornals – Combustion, Explosion and Shock Waves 2026 number 3

A reaction mechanism for the ignition and combustion of three-component C₃H₈/nC₄H₁₀/iC₄H₁₀ surrogates of alternative fuels based on liquefied petroleum gases has been developed. The mechanism describes the ignition of the surrogates at both high and low temperatures, as well as in the region of inverse temperature dependence of ignition delay time. The mechanism includes 442 reactions for 84 components. The results of testing the mechanism are presented using experimental data: ignition delay time of isobutane mixtures, hydrocarbon gas mixtures containing propane, n-butane, and isobutane (T₀ = 670 ÷ 1478 K, ρ₀ = 1 ÷ 30 atm, φ = 0.3 ÷ 2.0), normal flame propagation velocity in isobutane-air mixtures, and the concentration of the main isobutane oxidation products in a flat-flame burner.

The excitation and propagation of exothermic reaction waves in a closed channel filled with gaseous oxygen at initial pressures of 0.1 to 2 MPa was studied. The waves were excited by a hot nichrome coil coated with a small amount of VM-4 vacuum oil or melted fat. The wave parameters and initial pressures at which flame propagation occurs in the channel were determined.

The most interesting and important gas-dynamic and kinetic parameters of combustion, explosion, and detonation of ammonia/oxygen combustible systems of stoichiometric, lean, and rich compositions with the addition of molecular nitrogen (transition from fuel-oxygen to fuel-air mixtures) are presented. The same data are presented for fuel-air mixtures ranging from the lower to the upper concentration limit and with varying initial pressures. From an explosion safety perspective, the most important data are on the critical initiation energy, which allows for an analysis of the relative hazard of various mixtures. Critical energy E_* is defined as the minimum energy of the initiator that ensures the propagation of combustion and detonation waves in the mixture under study: the lower the E_*, the more hazardous the mixture. Data on the detonation cell size, which is used to determine the characteristic parameters of combustion chambers, which have the dimension of length, are also presented.

Continuous spin and multifront detonation modes of carbon-free ammonia/hydrogen-air fuel-air mixtures were implemented for the first time in a flow-through annular cylindrical combustion chamber with a diameter of 503 mm. Binary fuel (ammonia/hydrogen) with H₂ mass fractions in the fuel of 0.105 ÷ 0.485 was studied in the range of specific mixture flow rates of 22 ÷ 347 kg/(s ∙ m²) at an excess fuel coefficient of φ= 0.47 ÷ 1.55. In ammonia/hydrogen --- air mixtures with fuel of three compositions NH₃ + 8H₂, NH₃ + 4H₂ and NH₃ + 2H₂, single-wave and two-wave modes of continuous spin detonation with a velocity of 1.15 ÷ 1.59 km/s and a wave rotation frequency of 0.73 ÷ 1.81 kHz at φ= 0.73 ÷ 1.2 are realized, and for the NH₃ + H₂ composition --- continuous multifront detonation with two counter transverse detonation waves with a frequency of about 1.0 kHz at φ= 0.72 ÷ 1.0. The region of implementation of continuous spin detonation and continuous multifront detonation modes is determined depending on the ammonia content in the binary fuel and on the pressure in the air manifold. High-frequency sensors measured pressure profiles in the air manifold and in the combustion chamber in the region of rotation of transverse detonation waves. Thrust forces and specific impulses were determined. The highest thrust impulses obtained in the chamber were 2300, 1500, 1350, and 900 s for mixtures with hydrogen mass fractions in the binary fuel of 0.485, 0.32, 0.19, and 0.105.

A study was conducted on the detonation of oxyacetylene mixtures diluted with helium or argon in an extended channel with a flow-through feed of explosive mixture components at atmospheric pressure. The steady-state detonation velocity, temperature, and dynamic pressure of the products were calculated. The limits of self-sustaining detonation in a 26 mm diameter channel were determined. These limits are achieved by diluting an equimolar and stoichiometric mixture to 92% with both helium and argon. Near these limits, near-spin detonation is initiated without a noticeable transition from combustion to detonation by a booster charge of an equimolar oxyacetylene mixture, the volume of which does not exceed 180 cm³ or 13 channel calibers. Detonation coatings made of pure titanium were obtained using both helium and argon as the purging gas. Helium produces a dense coating with a porosity of <0.5% and a microhardness of 370 HV300. Argon can be used to produce coatings with a developed surface and high (tens of percent) porosity in the surface layer, which have potential for use in catalytic reactors and the production of medical implants.

Using the Euler equations in a two-dimensional plane, we numerically study the incidence of a shock wave on a near-wall gas bubble (a transverse cylinder) filled with a hydrogen-oxygen mixture doped with xenon. Gas combustion is modeled using detailed kinetics, taking into account 19 reversible reactions. A high-order finite-difference method of the WENO class is applied. The processes of shock wave refraction and reflection, as well as the focusing of secondary shock waves, are described. Various modes of detonation initiation in the bubble are discovered: direct detonation, refraction and reflection of the wave from the wall, and focusing of shock waves on a plane of symmetry near the wall. Based on a series of calculations, the dependence of ignition modes and threshold Mach numbers of the incident wave on the bubble shape is determined. It has been shown that the combination of wave focusing on the bubble and reflection from the wall leads to a significant reduction in threshold Mach numbers, both compared to a flat layer of combustible gas in front of the wall and compared to a free bubble without a wall.

The results of an experimental study of the ignition of electrode carbon samples heated by an integrated thermal radiation flux are presented. The experiments were conducted using a Uran-1 radiation heating system in an oxygen atmosphere at different pressures (0.1 and 1.1 MPa) with a heat flux density of 75 to 314 W/cm² incident on the sample surface. Ignition temperatures and the dependence of the ignition delay time on the heat flux density were obtained. The measured dependences were used to determine the formal kinetic constants of the process within a heterogeneous ignition model.

Using a coupled combustion model of a metallized composite solid propellant, this study examines transient fuel combustion under harmonic pressure variations above the fuel surface. The combustion model takes into account chemical reactions in the condensed and gas phases. Above the fuel surface, convection and diffusion of gas mixture components, two-phase flow, velocity and thermal nonequilibrium of the phases, and combustion of aluminum particles are considered. Boundary conditions for equal mass and energy fluxes are imposed on the fuel surface. The results of a computational and theoretical study of the dependence of the fuel combustion rate on the amplitude and frequency of pressure oscillations are presented. The study was conducted for two reaction orders in the gas phase. The influence of pressure oscillation frequency on the amplitude of fuel combustion rate variations is determined.

A method based on a genetic algorithm and a reaction rate equation is proposed to determine the parameters of the Lee - Tarver trinomial ignition and growth model for explosives. The method involves extracting characteristic points from the experimental pressure-time curve. The physical flow data is then analyzed and processed using a proprietary program implementing the genetic algorithm, and the Lee - Tarver model parameters are calibrated. The results show that the calculated pressure curve obtained using the model parameters determined by the genetic algorithm is in good agreement with the curve calculated using reference parameters. The maximum error for peak pressure is 6.3%, demonstrating the high accuracy and efficiency of the proposed calibration method.

In self-propagating high-temperature synthesis processes, one of the key issues is the availability and reproducibility of the combustion mode. It is well known that different grades and even different batches of the same grade of powder metals, incorporated during synthesis and obtained from particles of different shapes and sizes, contain varying amounts of gasifiable impurities. Therefore, the combustion rate of powder mixtures of the same composition produced from them can vary severalfold. Previously, the authors of articles for a granulated mixture of 5Ti + 3Si, and in this study for Ti + C mixtures, determined the combustion rate of mixtures with titanium of a single grade in narrow fractions for wide particle sizes of the original titanium powder. These values are well approximated by power laws with a determination coefficient of R² > 0.97. The resulting approximating dependences are presented as baselines. These dependences were used to compare the combustion rates of other titanium grades. For subsequent narrow fractions of other titanium grades, the combustion rate components of powder and granulated mixtures of 5Ti + 3Si, Ti + C were analyzed. Experiments show that the basic dependences of combustion rate on titanium particle size allow us to predict the combustion rate of granulated SHS mixtures of the same composition for narrow fractions of other titanium grades with a level of at least 30%.

The influence of the component ratio, mechanical activation and preliminary compression of the samples on the burning rate and elongation of uncompressed samples during synthesis, on the phase composition and morphology of the combustion products in the (5Ti + 3Si) + (Ti + 2B) system was studied. The combustion front did not reach the lower end of the sample from the initial 5Ti + 3Si mixture. Preliminary compression of the sample, as well as mechanical activation of the 5Ti + 3Si mixture, or the addition of a Ti + 2B mixture allowed the sample to burn to completion. The burning rate and elongation of samples from (100 - x)(5Ti + 3Si) + x(Ti + 2B) mixtures increased after mechanical activation. A tendency towards a decrease in the burning rate with an increase in the 5Ti + 3Si content in the mixtures was recorded. The combustion rate of samples from mechanically activated mixtures increased after compression and remained virtually unchanged for the initial mixtures (except for the Ti + 2B mixture). For some initial mixtures, shrinkage of the product samples was observed after preliminary compression. The maximum combustion rate was measured for samples containing 20% of the 5Ti + 3Si mixture. The dependence of the elongation of samples from the initial (100 - x)(5Ti + 3Si) + x(Ti + 2B) mixtures on their composition exhibited extremes. The phase composition of the combustion products remained unchanged after compression of the samples and mechanical activation of the mixtures.

The effect of preliminary mechanical activation (MA) of carbon black powder on the properties, compaction, and combustion patterns of Ti + C mixtures in an equiatomic ratio of components was studied. It was shown that during the MA process, the arched structure is destroyed and agglomerates of carbon black particles are crushed, which leads to an increase in bulk density by more than three times. It was found that during compaction, carbon black powder behaves as a solid non-plastic material with a high elastic aftereffect (up to 14%). It was shown that in Ti + C mixtures above a relative density of 0.52, a framework of titanium particles is formed, which is responsible for the strength properties of the compacts. It was found that compaction of Ti + C mixtures to a pressure of 50 MPa corresponds to the stage of structural deformation, and above this pressure, the stage of elastic-plastic deformation begins. It is shown that the relative density of compacts from Ti + C mixtures at the onset of the elastic-plastic deformation stage depends on the degree of MA of the carbon black powder. At the same pressure of 50 MPa, mixtures with more dispersed carbon black compact to a higher relative density of 0.65. It is shown that the dependences of the combustion temperature of compacts made from Ti + C mixtures on pressure and density have maxima. Increasing the density of Ti + C mixtures at the structural deformation stage (pressure up to 50 MPa) ensures an increase in the contact surface between the reactants and, consequently, an increase in the combustion temperature. With a further increase in compaction pressure at the beginning of the elastic-plastic deformation stage, the increase in the contact surface between the titanium particles leads to a decrease in the combustion temperature. It was found that the absolute value of the combustion temperature peaks increased with increasing density: for the mixture with the original soot, T_max ≈ 2900 °C at a relative density of 0.58; for the mixture with soot after 3 hours of MA, T_max ≈ 3000 °C at a density of 0.63; for the mixture with soot after 20 hours of MA, T_max ≈ 3200 °C at a density of 0.65. With increasing pressing pressure, the combustion rate decreases due to deterioration in the conditions for removing impurity gases from the volume of the original compacts. The appearance of delamination cracks is shown to lead to a sharp increase in the combustion rate.

An experimental study of the electrical resistance of copper foil under repeated shock compression up to a pressure of 40 GPa was performed in several explosive systems: in a reflected shock wave, under compression in a rigid cage, and in a layered system producing a sequence of waves of increasing amplitude. An improved measuring cell design is proposed, significantly reducing the influence of parasitic eddy currents on the recorded voltage. Under shock compression, the electrical resistance of copper increases monotonically, but the rate of increase depends on the loading history. Under compression by a sequence of shock waves, the electrical resistance of the metal is lower than under compression by a single shock wave (at the same incident wave pressure in a dielectric cage). In this case, the main change in copper's electrical resistance occurs in the first shock wave. In subsequent waves, the electrical resistance also increases, but the final value is lower than in a single shock wave. An assessment of the concentration of defects in the crystalline structure of a copper specimen under complex loading was performed. With repeated compression, the defect concentration is lower than with a single compression (at the same wave pressure or deformation). This means that under complex shock loading, defects are generated predominantly in the early stages of compression, with only a relatively small increase in the number of defects occurring subsequently. Qualitatively, the defect concentration during complex shock loading is determined by the deformation of the material in the first shock wave.