Home – Home – Jornals – Combustion, Explosion and Shock Waves 2026 number 2

Despite numerous studies, many aspects of ignition and propagation of combustion and detonation waves in combustible mixtures remain insufficiently understood, complicating the scientifically sound management of such processes. This paper presents new data on the various stages of ignition and flame front propagation in a flat (two-dimensional) channel of constant cross-section. The experimentally observed main flame instabilities (manifested in the significant non-uniformity and non-stationarity of the combustion front), the phenomenon of flame blowoff (disappearance of glow), and the effect of flame transition to a self-sustaining propagation mode are discussed. Attention is drawn to the problems of the emergence of new ignition sources in the flame front, including explosive micro-sources that facilitate the subsequent transition of combustion to detonation. A number of new features in the physics and dynamics of flame propagation are identified.

Despite extensive research, many aspects of ignition and propagation of combustion and detonation waves in combustible mixtures remain poorly understood, complicating scientifically sound control of such processes. The first part of this paper presented new experimental data on various stages of ignition and flame front propagation in a flat (two-dimensional) channel of constant cross-section. This paper presents results on the little-studied area of combustion wave behavior with changing channel geometric dimensions (so-called flame diffraction). Characteristic processes in the behavior of a turbulent flame as it transitions from a narrow channel to a wide one are established: from flame breakdown and loss of front glow with incomplete combustion of the mixture in a wide channel to the emergence of new explosive microcenters due to the development of expanding flame instabilities and collisions of turbulent flame tongues, leading to the generation of detonation-like waves.

The results of direct numerical modeling of combustion in a cone-shaped methane-air mixture flame directed at a flat, cold barrier are presented. Three cases with different distances between the burner nozzle and the barrier were considered. The study focused on analyzing nitrogen oxide formation in the wall region. It was found that when the barrier was positioned three calibers from the nozzle edge, a recirculation zone with an elevated concentration of nitrogen oxides (NO_x ) forms between the cone-shaped flame front and the cold wall. This increased NOx formation is offset in the downstream wall region.

Using a detailed kinetic mechanism of chemical interaction, the effect of adding ozone (or hydrogen peroxide) and helium as an inert diluent to a stoichiometric hydrogen-air mixture on the detonation wave parameters was numerically studied. It was found that the mole fractions of the additives can be selected such that the detonation wave cell size in the resulting mixture is close to the average cell size in the pure mixture, while the temperature of the detonation products is significantly reduced. It was shown that the introduction of hydrogen peroxide and helium reduces the stability of the detonation wave to disturbances caused by multiple obstacles (barriers) located in the channel, thereby contributing to the wave suppression. Conversely, detonation in a mixture with ozone and helium additives at selected concentrations is found to be more resistant to these disturbances than in the pure mixture.

A microscopic and diffraction study of detonation carbon in the products of benzotrifuroxane-based explosive compositions containing hexogen, octadecanoic acid, and TNT was conducted. Carbon species characteristic of pure benzotrifuroxane were observed in the detonation products of benzotrifuroxane-based compositions with individual benzotrifuroxane granules ranging in size from a few to tens of microns. No such species were detected in the submicron mixture of benzotrifuroxane and TNT.

Wide-range semiempirical equations of state for liquid and gaseous argon, krypton, and xenon are constructed, taking into account evaporation and thermal ionization, based on a modified van der Waals model for mixed substances. The empirical functions that specify the model have a simple form. They contain a small number of free parameters, selected based on the best possible description of the experimental data. A comparison of the model calculation results with experiment up to pressures of ≈1000 GPa and the results of calculations using other models at pressures above 1000 GPa is presented. In the limit of low density and high temperature, the model transforms into an equation of state for a mixture of ideal gases of atoms, ions of all multiplicities, and electrons with a concentration determined by the Saha system of equations.

The possibility of the existence of combustion waves in αCH₄/air gas mixtures and αCH₄/air/coal suspension dual-fuel heterogeneous mixtures (DGMs) with a methane volume concentration of α = 5 ÷ 8% was studied in a closed vertical shock tube and in a horizontal quartz tube open at one end. It was shown that the value of the lower concentration limit of methane flame propagation (LEL) α* and the flame stability are affected by the channel location relative to the gravity vector and the concentration of the coal suspension. In the vertical closed channel, combustion waves propagated from top to bottom in gas mixtures and DGMs at α ≥ 6%, but did not ignite at α ≤ 5.5%. In a horizontal tube, flame propagated in gas mixtures with α ≥ 6% and in a dual-fuel mixture with α ≥ 5.5%. Adding coal suspension to methane-air mixtures has little effect on flame velocity, increases brightness, and reduces the flame's LFL.

An experimental study of the ignition and combustion processes of composite liquid fuel (CLF) droplets based on coal cleaning waste in a high-temperature oxidizer environment at 700 ÷ 900 °C was performed. The effect of adding waste motor oil as a component of the CLF and as a feedstock for generating syngas, which was fed to the CLF combustion zone, was investigated. The feasibility of co-combustion of CLF with syngas was experimentally confirmed. The gas-phase ignition delay of CLF droplets with the addition of syngas to the combustion zone is 1.1 ÷ 1.2 times shorter compared to CLF combustion without the addition of syngas. Under these conditions, the heterogeneous ignition delay is 1.3 ÷ 1.7 times shorter, and the fuel burnout duration is 1.2 ÷ 1.5 times shorter. The use of waste oil as a component of composite fuel is characterized by a significant improvement in energy performance, which, combined with the increased combustion temperature, makes this strategy the most attractive for practical implementation.

The development of advanced technologies, such as oxy-drip-torch combustion, will solve a number of problems and improve the environmental situation associated with the combustion of hydrocarbon fuels (including waste) at power plants. In this study, experiments were conducted on a laboratory rig to study the autoignition of droplets of coal-water slurry in a tubular reactor. The dependence of the ignition induction period on the oxygen and carbon dioxide concentrations under adiabatic conditions was investigated. It was shown that increasing the O₂ concentration by 1% (volume) reduces the ignition time by 5.14% under the experimental parameters considered. It was found that increasing the CO₂ concentration in the flow at the same oxygen concentration does not significantly affect the ignition time under these conditions.

Tests of model solid propellants based on aluminum dodecaboride AlB₁₂ revealed significant discrepancies between the experimental values of the exhaust coefficient and the temperature of the primary combustion products in the model gas generator chamber compared to their values calculated from thermodynamic equilibrium conditions. A computational and experimental method for determining the thermodynamic characteristics of the primary combustion products for model boron-containing propellants characterized by a low content of oxidizing elements (α < 0.2) is proposed. The method involves experimentally determining the combustion product temperature and exhaust coefficient, followed by calculating the gas constant and adiabatic index of the combustion products. The ranges of possible values of the thermodynamic characteristics and their pressure dependences are determined.

The ignition of pine sawdust (d < 200 μm) and mixed compositions of brown coal particles (d < 3 mm) and pine sawdust in a fluidized bed was studied using localized radiation from a continuous-wave semiconductor laser (λ = 450 nm) with a power of ≤23 W with an exposure time sufficient for ignition and flame propagation over the fuel surface until self-sustaining combustion was established. The dependences of the time to establish self-sustaining combustion and the mass of sawdust burnt out in 60 s at a fixed radiation power on the air flow rate through the fluidized bed were determined, as well as the dependence of the time to establish self-sustaining combustion of sawdust on the radiation power at a fixed air flow rate and the dependence of the time to establish self-sustaining combustion of a sawdust and coal mixture on the mass content of coal in the mixture of 30 ÷ 80% at a fixed radiation power of 23 W. Optimal conditions for establishing self-sustaining combustion of solid fuel in a fluidized bed under laser radiation exposure were determined.

The oxidation properties of unmodified boron powders and boron modified with vanadium pentoxide gels were studied using X-ray phase analysis (XPA) using a synchrotron radiation source at a heating rate of 10°C/min in air. It was established that the mechanism underlying the activation of boron oxidation by vanadium pentoxide is the ability of vanadium pentoxide to transfer electrons and deliver oxygen to the boron surface upon dissolution in molten B₂O₃.

The principles of gasless combustion wave transition through an air gap separating two cylindrical samples of different diameters, prepared from a Ti--Si mixture, are examined. Critical conditions of the transition process are investigated using experimental and computational methods. A mathematical model is proposed, based on which the effective emissivity from the combustion surface is calculated in correlation with experimental data. The emissivity of titanium silicide is estimated.

Using mathematical modeling methods, we analyzed combustion failure of a cylindrical sample undergoing radiant heat transfer. A method is proposed for estimating critical parameters-the critical diameter, temperature, and velocity at the combustion limit-under conditions of predominantly radiant heat loss, typical of high-temperature SHS systems. The results are compared with similar values for maximum heat loss, cooling the cylinder surface to ambient temperature. The calculation results can be used to estimate the critical cylinder radius and the effective activation energy of the reaction. A method is proposed for estimating the effective activation energy of the heat release rate during gasless combustion of condensed media.

Stage separation is a critical event in multi-stage aerospace vehicles, demanding precise, reliable, and debris-free performance. Flexible Linear Shaped Charges (FLSC) have emerged as an effective solution due to their high cutting efficiency, low weight, and ability to conform to structural interfaces. This study presents a comprehensive numerical and experimental investigation into an FLSC-based separation mechanism, with a focus on optimizing cut quality, minimizing debris, and validating simulation results through testing. Three distinct configurations were modelled using hydrocode software: a baseline flat plate setup (Case A) with an 8.4 g/m FLSC, a modified geometry with an R8 notch to guide fracture (Case B), and a reduced-charge configuration with 4.2 g/m FLSC for shock minimization and single plane cutting (Case C). The simulations employed coupled Eulerian-Lagrangian solvers, advanced material models, and embedded gauge points to capture detonation physics, jet formation, and structural response over microsecond timescales. Case B demonstrated significant improvement in debris reduction, while Case C achieved a clean single-plane cut with no debris. The final configuration was realized and tested experimentally using a flat plate test article. The results closely matched simulation predictions, showing precise separation, intact fasteners, and no flying fragments, thus confirming the effectiveness of the hydrocode-optimized design. This work highlights the potential of hydrocode simulations to guide cost-effective, time-efficient, and experimentally validated design of FLSC-based stage separation systems. The insights gained offer practical pathways for the development of next-generation separation mechanisms in space and missile applications, where precision and safety are paramount.