Home – Home – Jornals – Combustion, Explosion and Shock Waves 2023 number 1

A kinetic model for the ignition and combustion of mixtures of propane and n-butane in the air has been developed. The model contains 348 reactions involving 72 species and includes both a high and low-temperature mechanism of propane and n-butane oxidation. The kinetic model was tested against experimental data on the ignition delay time and laminar flame speed. The model provides a good fit to experimental data on propane ignition and the laminar flame speed in propane-air mixtures, ignition of n-butane under different initial conditions (T₀ = 670 ÷ 1 550 K, ρ₀ = 1 ÷ 30 atm, φ = 0.3 ÷ 2.0), laminar flame speed in mixtures of n-butane with air at T₀ = 298 K, ρ₀ = 1 atm, and various stoichiometric ratios φ= 0.67 ÷ 1.5), as well as on the ignition of stoichiometric C₃H₈/C₄H₁₀/N₂/Ar mixtures with different relations C₃H₈/C₄H₁₀ at T ₀ = 710 ÷ 910 K and ρ₀ = 17.8 atm. The developed kinetic mechanism was used to perform a demonstration numerical simulation of combustion of propane-butane fuel in a homogeneous combustion chamber

This paper describes an experimental study of combustion initiation in a supersonic flow of a hydrogen-air mixture under the simultaneous action of focused pulse-periodic CO₂ laser radiation and an external electric field. Combustion in a supersonic jet is studied on the basis of data on the intrinsic glow of a flame at the radiation wavelengths of excited OH^* radicals. Mixture combustion initiation depends on the shape of electrodes and electrical signals. The flame that occupies the entire cross section of an air-fuel jet is observed only under the conditions of simultaneous action of laser radiation and an electric field. Thus, the combined use of optical and electrical discharges makes it possible to initiate combustion and stabilize the flame of a hydrogen-air mixture in a supersonic flow without mechanical stabilizers.

This paper presents a mathematical model of combustion of a coal dust particle-gas suspension in a methane-air mixture, which takes into account the inhomogeneity of temperature distribution in the particles. The particle-gas suspension state parameters are determined by the model of the dynamics of a two-phase two-velocity reacting gas-dispersed medium. The combustion of coal dust particles is simulated using a local mathematical model of a heterogeneous reaction on the particle surface and particle heating. A solution to local problems of coal dust particle combustion is used determine the heat release rate of the entire set of particles in the heterogeneous reaction of coal dust with oxygen and the heat exchange with gas. Dependences between the combustion front propagation velocity and the mass concentration of coal dust and the volumetric concentration of methane are determined. The estimated combustion front velocity in a methane-air mixture with no coal dust is in good agreement with experimental data. The comparison of calculating the flame velocity in a coal-methane-air mixture using two models (with and with no account for the inhomogeneity of the temperature distribution in the particles) is given. This comparison shows a significant difference in the values of the estimated combustion front velocity of rapidly burning gas-particle suspensions. For slowly burning particle-gas suspensions, this difference decreases. The developed model explains the shift of the maximum flame propagation velocity in the coal-methane-air mixture toward the excess of fuel in air.

Flame propagation over a thin film of various liquid fuels with an ignition point below the ambient temperature was experimentally studyied. The study was carried out on thin copper and thick glass substrates in media with different oxygen concentrations. It is shown that with an increase in the oxygen concentration, the flame speed increases faster than the normal speed of the corresponding homogeneous stoichiometric mixture. When the proportion of oxygen in the mixture with nitrogen changes from 0.21 (air) to 1, the flame speed range is 0.02 ÷ 2.4 m/s. At flame propagation speeds above 0.3 m/s, the condition of thermal thinness is not satisfied even for thin copper substrates. The flame speed ceases to depend on the properties of the substrate and the fuel layer thickness and becomes dependent only on the properties of the fuel. In this speed range, the flame propagation speed increases linearly with an increase in the thermal effect of a unit volume of a stoichiometric mixture of fuel vapor with oxidizer and decreases with an increase in the difference between the temperature T_st at which the stoichiometric composition is formed under equilibrium conditions and the ambient temperature T₀.

Spray ignition is widely encountered in energy and power engineering and is an important characteristic in combustor operation and design. Droplet ignition is an important part of spray ignition. Most present studies of droplet and spray ignition use numerical simulation, which sometimes cannot explicitly indicate the mechanism of ignition and is inconvenient for engineering applications. This paper reports experimental and analytical studies on ignition of a single droplet and spray under different flow conditions. Analytical results based on a one-dimensional model are compared with experimental results. The results reveal that the droplet ignition temperature decreases with an increase in the droplet size and increases with an increase in the relative gas velocity. The temperature of kerosene spray ignition by propane combustion products increases with an increase in the excess air and decreases with an increase in the droplet size. The obtained research results are useful for liquid-fueled combustor design and operation.

The thermal decomposition of bis-R-substituted gem-dinitroethyl-N-nitramines in diphenyl ether solution was studied by a manometric method in combination with mass spectrometry and photoelectric colorimetry. The reaction proceeds according to the first order equation and is not complicated by chain and heterogeneous processes. The rate-determining step of the process is the homolysis of the C-NO₂ bond in the gem-dinitro group. The kinetic parameters of the rate-determining step were determined. The influence of the structure on the reactivity of the investigated compounds was analyzed. Linear relationships were found between the rate constant, the activation energy of thermal decomposition, and the steric constants of the α-substituent of the reaction center.

Phase composition of thermal explosion products in compacts made of Ti-C-Al powder mixtures with an equiatomic ratio of titanium and carbon (soot) and with an aluminum content of 10 ÷ 40 % (wt.) is studied. The compacts are heated at a rate of 40 ± 5 °C /min in an argon atmosphere. Self-ignition temperature of all compositions was close to the melting point of aluminum (660 °C). Peak temperatures and the maximum rate at which temperature elevation becomes higher as the aluminum powder content in the mixtures increases. Synthesis products contain titanium carbide and Al₃Ti titanium trialuminide, whose ratio depends on the aluminum content in the mixture. Pretreatment of reaction mixtures in a planetary mill flattens aluminum particles, thereby preventing the formation of a melt. The spreading of a melt over the titanium surface with subsequent reaction diffusion and the formation of Al₃Ti increases the temperature in compacts made of nonactivated mixtures.

This paper describes experimental studies and a mathematical model of mechanical activation and high-temperature synthesis during the Nb-2Si combustion. The model is constructed in the macroscopic approximation. Synthesis regimes are determined depending on the duration of joint mechanical activation of the reagents. The kinetic parameters of pulverization of the initial powder mixture and the mechanochemical synthesis of the reaction product are obtained on the basis of experimental data by the inverse problem method.

Alloys based on the Ti-Al-Mn ternary system are among the most important in the development of doped titanium alloys for various purposes. In this work, an alloy made of 42.9 % of Ti, 24.3 % of Al, and 32.8 % of Mn (by wt.) is obtained via self-propagating high-temperature synthesis (SHS) during a thermal explosion. X-ray diffraction analysis shows that the final synthesis product containsa cubic TiMn_0.32Al_2.68 phase, a hexagonal TiMn_0.755Al_1.246 phase, and a binary Mn₃Al₂ phase. The porosity of synthesized samples is rather high ≈41 %), and they contain many pores (up to 300 ÷ 400 μm). Phase formation may be due to the fact that the maximum temperature reached during the combustion of this system in the SHS process is insufficient for complete interaction with the formation of a Mn₂Ti intermetallic phase and the dissolution of aluminum Al in it with the formation of a solid solution (Mn, Al)₂Ti. This promotes the formation of intermediate intermetallic phases, which can be in equilibrium with the liquid phase up to a melting point of titanium.

This paper presents an analysis of approaches to ensuring the performance of a ramjet combustor using an unconventional method of measuring the axial force in testing a liquid-fuel combustor model under flight conditions simulated by a fired heater. The thrust and drag of the combustor model were measured in fire tests on an attached air duct using an axial force meter. Thrust is a parameter that characterizes the energy potential of any engine. In the conventional method, lengthy multi-parameter studies and calculations of performance are required to get an idea of the thrust and economic characteristics of a heat engine. The new method allows one to determine the effect of any parameter or structural element on the physical process in a combustor in units of the thrust force and evaluate the change in any parameter by the thrust level directly in fire tests. Using the proposed thrust measurement system at an initial stage of testing, one can clarify the direction of the search for the organization of the workflow and reduce the amount of intermediate calculations, saving a huge amount of time and money. This, combined with measurements of static pressure along the length of the combustor, allows a guaranteed prediction of the direction of search for improving the workflow efficiency. The ways to improve the workflow efficiency in a ramjet combustor using a thrust meter to evaluate the overall engine performance under conditions of limited technical and methodical possibilities in fire tests of the combustor are discussed.

Three-dimensional numerical simulation of a detonation wave propagating in a circular tube filled with a gas suspension of aluminum particles in oxygen is performed with the use of the HyCFS-R code developed by the authors for modeling on hybrid computational systems. The regime of propagation with a single-head spin is reproduced. It is shown that combustion occurs in a certain localized front zone rotating during front propagation, which is typical for spin detonation in both purely gaseous mixtures and heterogeneous media. Data on the basic parameters of detonation wave propagation in a gas suspension of aluminum particles in the spin detonation mode are obtained. Comparisons with theoretical predictions and with numerical and experimental results of other researchers are performed.

Industrial micron-size hexahydro-1,3,5-trinitro-1,3,5-triazine (m-RDX) has been widely used in RDX-based polymer-bonded explosives (PBX). However, m-RDX results in poor mechanical properties and adhesive properties of RDX-based PBX m-RDX-PBX). Nano-RDX (n-RDX) has a small particle size and a large specific surface area, which provides a larger contact area with the polymer system. Thus, the porosity and compressive properties of PBX are improved if n-RDX is used in RDX-based PBX (RDX-PBX). In this study, m-RDX and n-RDX are used in RDX-PBX. The microstructure, component content, compressive properties, sensitivity properties, and detonation properties of RDX-PBX are investigated. The results show that n-RDX can make RDX-PBX more compact than m-RDX. The strain of n-RDX-based PBX (n-RDX-PBX) is increased by 39.7 % as compared to that of m-RDX-PBX. Meanwhile, the content of each component in n-RDX-PBX is consistent with that of the formula. The sensitivity of n-RDX-PBX is lower as compared to that of m-RDX-PBX, whereas the detonation velocity, detonation pressure, and detonation heat of n-RDX-PBX are equivalent to those of m-RDX-PBX.

Explosives are often exposed to war environments at different temperatures. The shock initiation characteristics of explosives are related to their properties and the ambient temperature in which they are located. In the present work, the parameters of the Ignition and Growth model of the LX-04 explosive at different temperatures are determined, based on the shock initiation experiments at different temperatures. Furthermore, the impact sensitivity simulation of LX-04 at initial temperatures of 25, 60, 100, 150, and 170 °C is carried out, and the critical impact velocity at these initial temperatures is found to be 325, 280, 233, 201, and 194 m/s, respectively. Based on the present simulation data, a new model for the relationship between the critical impact velocity and initial temperature is proposed. In addition, the initial temperature of the explosive has an important effect on the detonation performance: the higher the initial temperature, the higher the impact sensitivity of LX-04, and the higher the peak temperature of detonation.

Experimental data on the electrical resistance of aluminum under shock compression are analyzed. The electrical resistance of two types of aluminum foil located in dielectrics with different shock impedances is measured by the electrical contact method. The resultant dependences of the electrical resistance of aluminum on the shock wave pressure are monotonically increasing functions of pressure. However, the dependence of the specific electrical resistance of aluminum on the shock wave pressure can be monotonic (foil in Plexiglas) or nonmonotonic (foil in fluoroplastic). In the latter cased, the specific electrical resistance first slightly decreases with an increase in pressure and then increases. This behavior can be explained by the competing effects of compression and temperature heating on the specific electrical resistance. Due to shock compression of metal foil in the dielectric with a smaller shock impedance (Plexiglas), the measured electrical resistance is greater than that in the dielectric with a greater shock impedance (fluoroplastic). This result is caused by the greater temperature heating of metal foil in Plexiglas. The reasons for the qualitative difference in the behavior of the specific electrical resistance of metal under static and dynamic compression are discussed.