Том 55, № 2 (2019)

The present paper describes the development of two reduced kinetic schemes suitable for multidimensional turbulent flame simulations in high-temperature oxidation of methane. Formal reduction of the USC Mech II C1-C4 detailed kinetic model by using the directed relations graph mechanism results in a 31-species derivative scheme for lean to near-stoichiometric conditions. To deduce a still shorter, simpler, and less stiff kinetic model, further species elimination is based on combined sensitivity and chemical time scale information to arrive at a 22-species scheme. The kinetic rates of lumped reactions are here expressed as simple Arrhenius rates, avoiding nonlinear algebraic combinations of excluded elementary steps or species. The accuracy is maintained by tuning pre-exponential constants in the global Arrhenius rate expressions and computing a range of target data. A more compact, quasi-global 14-species scheme is subsequently formulated by modeling fuel decomposition to a methyl radical pool, followed by CH₃ oxidation with O and OH toward CH₂ and CO, and retaining a full CO/H₂/O₂ subset. The C2-chain with recombination of CH₃ into C₂H₆ and production of C₂H₂ is also represented in both schemes. Equilibrium 0D and 1D propagating premixed flames and axisymmetric co-flowing lifted laminar jet flames are computed through an iterative validation process. Accompanying computations with the USC Mech II mechanism, as well as available experimental results, are exploited for optimization. The comparisons demonstrate that the derived schemes ensure satisfactory agreement with data over the investigated parameter space.

A negative erosive effect arises in the simulation of combustion due to a generated turbulent motion in the gasification zone of a solid energy material. A thermal energy in the gasification zone comprises the heat of chemical sources in it and the heat coming up to the gasification surface from the flame zone in a gaseous phase. Some of this energy returns to the gaseous phase in the form of the mechanical energy of turbulent motion, and this turbulence cools down the gasification zone. This model is used to explain the weakening of the negative erosive effect, observed in the experiments, with increasing pressure and decreasing initial temperature.

The burning rate and combustion limits of tapes rolled from titanium-boron mixtures were determined as a function of the concentration of boron. The combustion of single tapes near the lower limit is unsteady and has a two-zone structure across the width of the tapes, due to the difference in burning and cooling rates between the edges of the tapes and its middle. With increasing boron concentration in the mixture, the combustion becomes steady-state and the front becomes more even. Maximum burning rate of the tapes is achieved at a boron concentration of 21-25% in the mixture.

We have studied the effect of preload and the time delay in pressure application to the product of high-temperature synthesis by thermal explosion of a stoichiometric powder mixture on the grain size in the synthesized Ni₃Al compound, on the nature of its fracture, strength, and ductility.

In this study, millimeter-sized magnesium particles are ignited using a CO₂ laser. The flame structure, particle temperature, heat release region, and spectral information of the burning magnesium particle are determined. The experimental results show that the developing process of the particle temperature can be divided into five stages: gradually rising stage, steady stage, sharply rising stage, high-temperature stage, and descent stage. Through a series of ignition experiments, the ignition temperature of a magnesium particle ≈3 mm in air is estimated to be 900–940 K. During steady combustion, the maximum diameters of the flame and of the heat release region are found to be greater than the particle diameter approximately by a factor of 1.9 and 3–3.5, respectively. The experimental results also suggest that the combustion of magnesium in air should be controlled by vapor diffusion from the particle surface.

Physicomathematical modeling of interaction of detonation waves in silane/hydrogen composite mixtures with clouds of inert micro- and nanoparticles ranging from 10 nm to 100 µm is performed. The normalized detonation velocity is calculated as a function of the volume concentration of particles. It is found that the efficiency of detonation suppression increases only as the particle diameter decreases to 1 µm. The influence of the thermodynamic parameters of particles on the detonation suppression efficiency is identified. The concentration limits of detonation are determined. It is demonstrated that a certain equilibrium asymptotic level of the concentration limits of detonation is reached as the particle diameter decreases below 1 µm. An approximation of the concentration limits of detonation is obtained in the form of an analytical dependence of the limiting volume concentration of particles on their diameter and fuel concentration in a composite two-fuel mixture of silane, hydrogen, and air.