Spontaneous Ignition of Methane–Air Mixtures in a Wide Range of Pressures

The ignition delay in methane–air mixtures = 0.5) within the range of temperatures of 1200–1700 K and pressures of 3–450 atm behind reflected shock waves in a shock tube is measured on the basis of emission of the electronexcited OH radical (transition A²⁺ – X²) at the wavelength of 306.4 nm and on the basis of absorption corresponding to the component F₁ ⁽²⁾ (₃ = 1) F₂ ⁽²⁾ (₃ = 0) of the P(7) line of the ₃ mode of the CH₄ molecule at the wavelength of 3.3922 m. The measured ignition delays are compared with those calculated by the GRIMech 3.0 mechanism; good qualitative agreement of results is obtained in a wide range of pressures.     

Kinetic Mechanisms of Ignition of Isooctane–Air Mixtures

A kinetic scheme was developed to describe the autoignition of isooctane in air. The scheme includes 976 reactions and 126 species and adequately describes the process at both low and high initial temperatures of the mixture. The results of numerical modeling agree with experimental data on isooctane pyrolysis and autoignition delay of isooctane–air mixtures at initial pressures of 0.1–4.5 MPa, initial temperatures of 700–1300 K, and a fueltoair ratio of 0.5–2.0 with an accuracy not worse than 30%.     

Effect of the Molecular Structure on the Adsorption Properties of Cationic Surfactants at the Air–Water Interface

The surface activity and thermodynamic properties of adsorption at the air–water interface of two series of cationic surfactants based on isourea: the O-dodecyl-N,N′-diisopropylisourea hydrochloride, hydrobromide, and hydroiodide and the O-tridecafluorooctyl-N,N′-diisopropylisourea hydrochloride and hydrobromide were studied. The effect of structural parameters as the nature of the halide counter ion and the nature of the non-polar chain on the surface activity and thermodynamic properties of adsorption were investigated. The surface parameters, the maximum surface excess concentration (Γ _max), the minimum area per molecule (A _min) at the aqueous solution-air interface, effectiveness of surface tension reduction (π_CMC), and efficiency of surface tension reduction (pC ₂₀) were estimated. The standard Gibbs free energy of adsorption, (ΔG°_ads) change has been calculated at different temperatures.     

Ignition Delay Time for Hydrogen–Silane–Air Mixtures at Low Temperatures

A modified physicomathematical model of ignition of hydrogen–silane–air mixtures is applied to calculate the ignition delay time for these mixtures at low initial temperatures (300–900 K) and pressures (0.4–1 atm) of the mixture. It is shown that the diagram of the ignition delay time as a function of temperature contains a region of the so-called negative temperature coefficient. The influence of the pressure in the mixture and of the silane fraction on the length of this region is studied. It is found that an increase in both factors (silane concentration and pressure in the mixture) leads to an increase in the length of the negative temperature coefficient region.     

Analysis of Nitrogen‐Oxide Formation Mechanisms in Filtration Combustion of Methane–Air Mixtures

The kinetics of nitrogenoxide formation under conditions of filtration combustion of lean and rich methane–air mixtures is analyzed. Intense interphase heat exchange in the wave of filtration combustion of gases leads to a drastic decrease in the gas residence time in the hightemperature region and also to a decrease in the maximum temperatures in the reaction zone. As a result, the processes of filtration combustion of gases are characterized by reduced emission index of nitrogen oxides as compared to diffusion flames. Under these conditions, the thermal mechanism does not make any significant contribution to NO formation, and the dominating channels are the NNH channels for lean mixtures and the Fenimore mechanism for rich mixtures. Nitrogen oxides in lean mixtures are mainly represented by NO and N₂O, whereas nitrogencontaining components HCN and NH₃ are typical of rich mixtures. NO decomposition in rich mixtures occurs in afterburning reactions with participation of HCCO, CH₃, and CH₂ radicals.     

Continuous Detonation of Methane/Hydrogen–Air Mixtures in an Annular Cylindrical Combustor

Regimes of continuous detonation of methane/hydrogen–air mixtures in spin and opposing transverse detonation waves are obtained for the first time in a flow-type annular cylindrical combustor 503 mm in diameter. A two-component (methane/hydrogen) fuel with the H₂ mass fractions of 1/9 to 1/2 in the range of specific flow rates of the mixture from 64 to 1310 kg/(s ·m²) and the fuel-to-air equivalence ratio ? = 0.78–1.56 is considered. In methane/hydrogen–air mixtures with two compositions of the fuel (CH₄ + 8H₂ and CH₄ + 4H₂), one-wave and two-wave regimes of continuous spin detonation are obtained; the frequency of rotation of transverse detonation waves is 0.56–1.66 kHz at ? = 0.78–1.02. For the fuel compositions CH₄ + 2H₂ and CH4 + 1.5H2, continuous multifront detonation with two opposing transverse detonation waves rotating with the frequency of 0.86–1.34 kHz at ? = 1.0–1.23 is obtained. For the CH₄ + H₂ + air mixture, both combustion in the chamber and continuous spin detonation outside the combustor with transverse detonation waves rotating with the frequency of 1.01–1.1 kHz are observed. The lean limits of continuous detonation are obtained in terms of the specific flow rate of the mixture: 64, 100, 200, and 790 kg/(s · m²) for the fuel compositions CH₄ + 8H₂, CH₄ + 4H₂, CH₄ + 2H₂, and CH₄ + 1.5H₂, respectively, for the mass fraction of hydrogen in the methane/hydrogen fuel of ≈0.16. Violation of regularity of the continuous detonation wave structure and the wave velocity with a decrease in the fraction of hydrogen in the two-component fuel is detected.     

Effect of Radiant Heat Transfer on the Minimum Spark–Ignition Energy of Gas Suspensions

A mathematical model of spark ignition of a gas suspension is constructed on the basis of a two–temperature thermal diffusion model of gas–suspension combustion and the radiant heat transfer is modeled in a diffusion approximation. The dependences of the minimum ignition energy on the parameters which describe the disperse phase and the domain of the disperse–phase parameters in which the radiant heat transfer affects greatly the minimum spark–ignition energy is determined by solving the problem numerically. The analytical formula that was obtained for determination of the critical spark–ignition energy of the gas suspension and that takes into account the radiant heat transfer in the gas suspension gives values different from numerical results by not more than 30% in a broad range of determining parameters of the problem. The theoretically obtained values of the minimum spark–ignition energy of a gas suspension of coal dust agree satisfactorily with experimental data.     

Simulation of Ignition and Combustion of a Homogeneous Methane–Air Mixture under Local Thermal and Photochemical Impacts

Combustion, Explosion, and Shock Waves - Ignition and combustion of a homogeneous stoichiometric methane–air mixture under simultaneous local thermal and photochemical impacts, resulting in...     

Effect of the Fuel Type on the Characteristics of Air‐Breathing Engines

Experimental studies of airbreathing engines operating on gaseous and liquid fuels are analyzed. It is shown that, for flight conditions with a Mach number 5 at the ground level, the results on operation and thrust–economic characteristics, which were obtained for hydrogenpowered engines, may be used directly in development of the ducts of hypersonic airbreathing engines operating on liquid organoborn fuels.     

Effect of Diffusion of Coal Pyrolysis Products on the Ignition Characteristics and Conditions of Coal–Water Fuel Droplets

This paper presents a theoretical study of the thermal preparation and ignition of a coal–water fuel droplet under intense radiative-convective heating with diffusion of gaseous pyrolysis products of the solid fuel into the ambient gaseous medium. It has been found that gaseous pyrolysis products are ignited at a distance from the heating surface approximately equal to the radius of the droplet, after which the coke of the main fuel layer is ignited. The time between the ignition of volatiles and the coke residue is less than 0.5 s. Comparison of the ignition delays obtained by mathematical modeling and experimentally has shown satisfactory agreement between theoretical and experimental values.     

Numerical Simulation of Spark Ignition of a Coal Dust–Air Mixture

This paper describes the development of a physico-mathematical model of spark ignition of a coal dust–air mixture, which is based on a two-phase two-speed model of reacting gas-dispersion medium. There are the results of numerical solution on the problem of spark ignition of a coal dust–air mixture with allowance for its movement caused by gas expansion during heating. The relationships between the minimal energy of spark ignition of a coal dust–air mixture and the mass concentration and particle size of coal dust are obtained. The particle size increases along with the minimal energy of spark ignition. There is mass concentration of coal dust particles with which the energy of spark ignition is minimal. The comparison of the results of calculations of the minimal energy of spark ignition of coal dust with known experimental data yields their satisfactory agreement.     

Effect of Metal Additives on Performance of Low-Carbon Magnesia-Carbon Materials

In this paper,both oxidation and corrosion resistance of low-carbon magnesia-carbon materials containing 4.0wt% graphite with metallic Al and Mg-Al alloy powders as antioxidants were investigated.Meanwhile,the microstructures of samples corroded by slag were observed with optical microscope as well.The test results revealed the properties of oxidation and corrosion resistance of low-carbon magnesia-carbon materials could be improved obviously by adding metal Al powder and Mg-Al alloy powder.The rule of improving oxidation resistance was illegibility when metal Al powder and Mg-Al alloy powder were added together.It was harmful to corrosion resistance by mixed adding metal Al powder and Mg-Al alloy powder into the materials,at the same time,the corrosion resistance would decreased with the increasing of Mg-Al alloy content.The corrosion resistance of samples with 0.5wt% or 3.0wt% Mg-Al alloy was better. The oxidation resistance and corrosion resistance of materials with metal Al or Mg-Al alloy respectively were better than that with mixed metal Al and Mg-Al alloy. As a result, Mg-Al alloy was more suitable for low-carbon composite materials than metal Al as additives.     

Ignition of β‐Azidoethanol Droplets in Air

The behavior of a droplet of azidoethanol, a liquid explosive, in heated air was studied. It was shown that droplet ignition is a gasphase process limited by heat release due to the vaporphase oxidation of azidoethanol. An increase in the ambient temperature with distance from the ignition limit eads to enhancement of the role of the thermal decomposition of azidoethanol molecules. In the range of ambient temperatures of 560–620 K, the droplet ignition is determined by the kinetics of the parallel reactions — the gasphase oxidation and thermal decomposition of azidoethanol.     

Fire and Explosion Risks of Glycol-Based Vapor–Air Mixtures

@Abstraction limits of flame propagation are determined for 13 glycols, as well as their enthalpy of formation and enthalpy of combustion. These characteristics depend on the number of carbon atoms in the glycol molecule. The combustion parameters are calculated for vapor–air mixtures of glycols and monoatomic alcohols, in the case where P = 1 atm and V = const. The adiabatic combustion temperature of mixtures of limiting and stoichiometric composition does not depend on the number of hydroxyl groups in the alcohol molecule. The explosive pressure of glycol is slightly higher than for monoatomic alcohols.     

Effect of Sintering Additives on the Nitridation and Densification Behavior of Si—SiC Composite

Most of the thermo-mechanical properties of reaction bonded silicon nitride,including a second phase such as SiC depend on the final denstiy and the grain boundary glass phase of the sintered material .Thus it is necessary to know the sintering aid system most effective for the Si0-SiC compostie system ,Sintering experiments carried out using different combinations of sintering aids has indicated that two combinations,i.e.,(a) yttria with alumina and (b) yttia with aluminium nitride are effective sintering aid systems for the reation bonded Si-SiC composites.Adensity of 98.5% theoretical was obtained with yttria and aluminium nitride system.     

Effect of ZrO2 Additives on the Thermal Shock Resistance of MgO—MA Refractory

The additirn of three kins ZrO2-bearing additives into MgO-MA refractory could all increase the latter‘s C.C.S.and the thermal shock resistance,XRD,polarizing microscope and electron probe analysis were used to analyze the mechanism to improve the thermal shock resistance of the material.The mechanism is that ZrO added into the material improves the microstructure,introduces asppropriate micro cracks into matrix ,enhances the matrix,and therefore increases the thermal shock resistance of ther refractory.     

Effect of the Location of the Detonation Initiation Point and the Position of the Air–Fuel Cloud on Explosion‐Field Parameters

The effect of the location of the initiation point on explosionfield parameters is studied numerically using as an example the detonation of a stoichiometric mixture of propane with air. The shape of the cloud of the mixture (toroid) and the ratio of its dimensions in calculations are typical of the volumes of air–fuel mixtures formed in accidents. The effect of the initiation point location within the cloud cross section was studied with variation in the position of the lower edge of the cloud above the underlying surface.     

Additives effect on the multiferroic behaviour of BiFeO3–PbTiO3

The use of additives as a sintering aid for promoting densification is well-known in processing structural ceramics. In leaky ferroelectric ceramics (e.g., BiFeO₃-based systems), additives are also used to reduce the leakage current, improve the poling efficiency and the piezoelectric response of a material. A less investigated aspect is how additives affect the multiferroic (ferroelectric and magnetic) features of BiFeO₃-based ceramics. In this work, we report a systematic study of the effect of different additives viz, MnO₂, CuO, K₂CO₃ and KMnO₄ on the microstructural, electromechanical, and magnetic properties of Dy-modified BiFeO₃–PbTiO₃. We found that all the additives help in the precipitation of the ferrimagnetic dysprosium iron garnet phase. The additives containing potassium (K) tend to suppress the grain size. We found that the best combination of ferroelectric and ferromagnetic behaviour was found in a mixture of additives.     

Effect of Self-Assemblies on the Dynamics of the Briggs–Rauscher Reaction

The study involves the dynamic evolution of the Briggs–Rauscher (BR) reaction in the presence of various surfactants—SDS (sodium dodecyl sulphate) as anionic, CTAB (cetyl trimethylammonium bromide) as cationic and TritonX‐100 [4‐(1,1,3,3‐(tetramethylbutyl) phenyl polyethylene glycol] as a neutral one in single as well as mixed mode conditions (SDS + TX‐100 and CTAB + TX‐100). The reaction has been monitored potentiometrically at 30 °C under CSTR conditions. These surfactants affect the reaction dynamics to an extent which depends on the nature and concentration of the surfactant and the formation of their self‐assemblies. The experimental findings indicate that the oscillatory behavior of the BR reaction in the presence of surfactants is due to the efficacy of organized surfactant assemblies to selectively distribute the key species involved in the reaction, and their interaction with the counter ions in cases of ionic micelles. The study reveals that the evolution of oscillatory behavior is a characteristic feature of the surfactant.     

Effect of the processing on the production of cordierite–mullite composite

In this study, effect of process on the production of cordierite–mullite composite was studied. For this reason two different processing methods were used in the production of cordierite–mullite composites. In first process, in situ cordierite–mullite composites were produced from cordierite and mullite layers which were formed by using aqueous tape casting method. In second one, composite was produced by addition of pre-produced mullite powders (in different weight percents, 0–30) into cordierite starting powders. The results show that the addition of pre-sintered mullite powders to the cordierite slip has more effect on densification behavior and mechanical properties of composites than layered production method.