Vol 14, No 2 (2021)

The article comments on the results of research on the ignition of combustible gas by a heated body. In the classic work by Ya. B. Zel’dovich, using a steady ignition model, the main properties of the process were identified and the ignition criterion was obtained. Subsequent research mainly followed the path of numerical simulation using unsteady ignition models. The question remains open as to whether the ignition criterion obtained from the steady model can be applied to reproduce the experimental data. In the present article, the experiments, described in the S. Kumagai’s book, on the ignition of a propane–air mixture by a heated cylindrical wire were calculated using the criterion derived on the basis of the Zel’dovich’s steady model. But the experimental points fell on different curves corresponding to different wire diameters. Using the idea of stability theory that the appearance of an inflection point at the temperature profile results to ignition, the authors obtained a new criterion which correlates very well with the experimental data and enables one to get the parameters of the chemical reaction of ignition. The present authors believe that the criterion based on the inflection point will be useful for solving new problems of ignition and revise some old solutions.

The experimental method for evaluating the detonability of fuel–air mixtures (FAMs) based on measuring the run-up distance and time of deflagration-to-detonation transition (DDT) in a pulsed detonation tube (DT) was used to study the DDT in FAMs based on the blended ethylene–hydrogen fuel with a volume fraction of hydrogen ranging from 0 to 1 at the same thermodynamic and gasdynamic conditions. Based on the available data on combustion and self-ignition of such a blended fuel, it was expected that with an increase in the volume fraction of hydrogen, the DDT run-up distance and time should monotonically decrease and the corresponding dependences should be close to linear. Contrary to expectations, the obtained dependences turned out to be nonlinear. The analysis of the results suggests that the observed dependences are a manifestation of the physicochemical properties of the FAMs under study. Changes in the design of the flame acceleration section in the DT do not affect much the nature of the obtained dependences: they remain nonlinear.

Based on the analysis of the structure of a quasi-stationary mathematical model of the working cycle of a piston engine cycle, the algorithm and method of calculation of working processes in diesel engines with gas turbine charging at nonuniform alternating inlets to the cylinders with fresh charge are presented. It is shown that the efficiency of joint operation of the engine and turbocharger is greatly influenced by the nature of fluctuations during the working cycle of air flow and boost pressure which determine the efficiency of the compressor and the entire power plant. For the coordination of their operation, an approximate calculation using a certain algorithm is proposed. After selecting the turbocharger and charge air cooler, the boost parameters are adjusted to the technical data of the selected turbochargers and the final initial data for the calculation of the engine boost system are drawn up. At further calculation, the flow coefficients in the inlet and exhaust pipelines are corrected which ensures with the accepted relative error coincidence of the specified and calculated average values of pressures and weight of the working body leaving and entering the cylinder. In this case, the fuel injection advance angle, the duration of the ignition delay of the fuel–air mixture, and other parameters are adjusted. The proposed dependence is used to calculate the characteristics of heat release and the rate of heat release in the engine with compression ignition. The latter is not monotonous, since it causes the presence of two maxima of speed: at explosive and diffusion combustion of fuel.

An experimental study of combustion of magnesium powder with liquid water and with gelatinous water was carried out. The limits of combustion wave propagation and the velocity of combustion wave in cylindrical charges 10 and 30 mm in diameter were determined, which can reach 3.3 mm/s in mixture with water and 4.5 mm/s in mixture with water thickened with hydrogel at mixture density in charges within 0.6–0.98 g/cm³. A new way of intensification of combustion is proposed that allows increasing the amount of water by 10%–18% compared to the combustion of homogeneous mixtures in the charge, in which complete combustion of magnesium is possible without a combustion promoter. It is shown that the degree of chemical conversion of magnesium into reaction products exceeded 85% in almost all experiments. These studies can be useful in creating promising hydrojet and hydrogen-generating charges.

One of the criteria for the development of high-energy processes is the large specific surface area of the solid component of composites. Therefore, the maximum preservation of its nanostructured skeleton when separating the porous layer from the monocrystal substrate is relevant. Based on the analysis of the quality of the porous layer under various methods and modes of its formation, two methods were selected that provide simple and effective separation of the porous structure from the monocrystal. For composites based on mounds of porous silicon (pSi) fragments (MPSF), three series of experiments were carried out with fragments of porous layers of different age (formed within the previously established time limits before composites creation) with registration of combustion dynamics, temperatures and combustion spectra, as well as intensity of disturbances in the atmosphere forming during combustion of MPSF-composites. Four combustion modes of MPSF-composites were established: smoldering, frontal, aerosol, and frontal-aerosol. The ignition induction times were determined: from 1 to 50 μs, pressure pulses in the atmosphere at a distance of 260 mm from the ignition site — up to 1.6 bar (with a mass of composites up to 0.4 g). Combustion velocities of MPSF-composites and their dependences on the coefficient of stoichiometry and humidity of sodium perchlorate monohydrate are established.

Based on the method of double-difference, the enthalpy of formation of radicals of naphth-1-yl and naphth-2-yl ($405.0\pm 2.0$ kJ/mol) has been calculated. As objects of study, data on the enthalpies of formation of naphthalene derivatives were used and as the reference values, the phenyl radical and benzene derivatives have been applied. The obtained data on the enthalpies of formation of radicals of naphth-1-yl and naphth-2-yl were applied to adjust the existing enthalpies of formation of naphthalene derivatives in the gas phase. For 1- and 2-nitronafthalines, the same value was obtained equal to 133 kJ/mol. The literature data were $111.2\pm 5.3$ and $145.0\pm 1.9$ kJ/mol for 1-nitronaftaline and 129.8 kJ/mol for 2-nitronaftaline (calculation). The data obtained allowed calculating the dissociation of bonds $D(C-N{O}_2)$ in 1- and 2-nitronaftaline which was $306\pm 2.0$ kJ/mol and close to the energy of this bond in benzene ($305.4\pm 1.3$ kJ/mol). To determine the identity of bonds in naphthalene and benzene, a joint calculation of C–N and C–C bonds in naphthalene and benzene from the enthalpy of atomization of these compounds was performed. The energies of bonds are obtained identical, i. e., the values are the same which means that the energies of the rearrangement of radicals naphth-1-yl and naphth-2-yl are equal to 0 kJ/mol.