


Vol 16, No 3 (2023)
On the criteria of hydrogen self-ignition during its release from a high-pressure vessel
Abstract
The paper presents results of the numerical modeling of high-pressure hydrogen release into air followed by self-ignition. Two problem statements are studied: release through a slit from a tube or a vessel into the space with an obstacle and release through two separated slits. The modeling is performed in two-dimensional approach in Cartesian coordinates. In the framework of the first statement, the initial pressure of hydrogen and the distance to the obstacle are varied, the half-width of the slit is set equal to 1 mm. In the framework of the second statement, the size of slits and the distance between them are varied while the initial pressure of hydrogen is 350 atm. It is shown that the mentioned parameters of the problem determine regimes of hydrogen flow: with and without ignition. For the first statement, two regimes of flow with ignition are observed: before the jet reaches the obstacle and as a result of the reflection of the flow from it. The obtained results could be interesting for the elaboration of hydrogen safety systems.



Comparison of the effect of Н2О and СО2 additives on the conversion of methane into synthesis gas
Abstract
For the first time, detailed kinetic modeling of the behavior of undiluted mixtures of methane with oxygen with СО2 and Н2О additives was carried out taking into account the formation of microheterogeneous soot particles in the temperature range 1500–1800 K at a pressure of bar. The appearance of soot particles was observed for rich mixtures, starting with the equivalence ratio . At the lower limit of the studied temperature range K, a small amount of soot particles (less than 1 %(mass) of C atoms) is formed, and they do not have a significant effect on the other parameters of the reacting system. A noticeable effect of soot particles at K is observed for . This is most clearly manifested in the fact that the temperature profile of the process changes markedly. When water is added, two maxima are observed on it at times of the order of 0.01 and 0.1 s. In the case of CO2 additives, the second maximum is almost not pronounced. A complex temperature profile leads to the appearance of a second maximum concentration of hydroxyl OH radicals at s.



Oxidative pyrolysis of ethane under pulsed adiabatic compression
Abstract
The oxidative pyrolysis of ethane has been studied in a rapid compression machine with a free flied piston over a range of temperatures 1100–1450 K. In the initial mixtures with a constant ethane content of 2 %(vol.), the oxygen content varied from 0 to 1.05 %(vol.). The ranges of conversion degrees of ethane were 6%–86% and of oxygen 8%–97%. The main (ethylene, hydrogen, methane, and CO) and secondary reaction products were determined. The composition of the mixture of products qualitatively corresponds to the products of ethane pyrolysis previously studied in the adiabatic compression reactor. It is found that an increase in the O2/C2H6 ratio in the studied range leads to a monotonic decrease in the residual ethane content, an increase in the residual oxygen content, and an increase in the degree of conversion of both initial components. As the O2/C2H6 ratio increases, the yields of H2, CO, CH4, acetylene, 1,3-butadiene, and some other hydrocarbons increase. The value of ethylene yield passes through a maximum approximately at .



Fast deflagration-to-detonation transition in helical tubes
Abstract
When designing a new type of power plants operating on pulsed detonations of gaseous or liquid fuels, the concept of fast deflagration-to-detonation transition (FDDT) is used. According to the concept, the flame arising from a weak ignition source must accelerate so fast as to form an intense shock wave at a minimum distance from the ignition source so that the intensity of the shock wave is sufficient for fast shock-to-detonation transition due to some additional arrangements. Hence, the FDDT concept implies the use of special means for flame acceleration and shock wave amplification. In the present work, FDDT has been studied using a standard pulsed detonation tube (SDT) comprising a Shchelkin spiral and a helical tube section with ten coils as the means for flame acceleration and shock amplification (focusing) devices, respectively. To attain the FDDT at the shortest distances for fuels of essentially different detonability, the diameter of the SDT is taken close to the limiting diameter of detonation propagation for air mixtures of regular hydrocarbon fuels (50 mm). The experiments have been conducted with air mixtures of individual gaseous fuels (hydrogen, methane, propane, and ethylene) and binary fuel compositions (methane–hydrogen, propane–hydrogen, and ethylene–hydrogen) at normal pressure and temperature conditions. The use of the helical tube with ten coils is shown to considerably extend the fuel-lean concentration limits of detonation as compared to the straight tube and a tube with a helical section with two coils.



Pressure measurements in air shock waves from the aboveground explosion by isolated suspended gauges
Abstract
Various factors are discussed that affect the measurement of the parameters of air shock waves (ASW). A novel method for obtaining the parameters of ASW from explosions of condensed explosive charges elevated above the surface is considered. It is shown that the use of suspended sensors isolated from the seismic wave in the ground makes it possible to avoid factors that deform the results of pressure traces. The vertical fields of the ASW parameters in the plane of symmetry for explosions of aboveground spherical charges are obtained, clearly demonstrating the zone of increased parameters along the surface, corresponding to the reflected shock wave. The obtained results can be used both for a quick assessment of the impact of blast wave and to verify the numerical modeling of the explosion above the surface.



Optimization of fire-resistant and fire-thermal protective properties of intumescent composites using mathematical experimental planning
Abstract
Using the method of mathematical planning of the experiment, the formulation of a foaming polymer composite material based on an ethylene-vinyl acetate thermoplastic binder was optimized. To determine the dependence of the combustibility characteristics (maximum temperature increment and weight loss) of the composite on the content of components in its gas-coke-forming system, a regression model of a full factorial experiment was used using the completed matrix of the orthogonal central-composition plan (OCCP) of the two-factor model of the 2nd order experiment. By adjusting the composition of the gas-coke-forming system, consisting of ammonium phosphate, amine, and carbonate mineral, a slow-burning material with improved thermal insulation ability was obtained. For the studied composition, it was found that the one of the factors causing a decrease in combustibility and an increase in the fire resistance limit (up to 104 min) is the formation of a foamed mechanically strong coke-like structure, stable in a wide temperature range (300–800 C).



To the problem of hearth combustion on the surface of double-base propellant
Abstract
The paper presents an approximate model for determining the shape of the formed hot spot on the surface of burning gunpowder at different pressures of gas medium. It was found that with increasing pressure, the geometric dimensions of the hot spot decrease. The burning hearth appears in extinguishment or in nonstationary mode. Apparently, if the dimensions of the hot spot along the surface of the powder and along its height are connected by an “elliptical” connection then its geometric shape is the closest to the experimental shape.



Combustion transfer through inert barriers in high-porosity nanotermites
Abstract
The paper presents the results of an experimental study using high-speed video recording of the combustion propagation through inert barriers in Al/CuO nanothermites placed in closed shells (tubes) made of quartz glass. Viscose and air gaps were used as inert barriers. When the luminous front (which the present authors associate with the burning rate) passes through the barrier made of viscose, its propagation velocity drops noticeably but after it enters the nanothermite, its propagation velocity recovers to the original value. As for the air gaps, when the luminous front expands into the air, its speed increases by a factor of 2–3, then the normal mode of propagation is established. The presence of air gaps in a tube with a thermite mixture makes it possible to significantly reduce the mass of this mixture with a slight decrease in the average burning rate compared to a completely filled tube of the same length.



Combustion mechanism of perchlorates of methyl ammonium derivatives
Abstract
Possible reasons for the unusual dependences of the burning rates on the pressure of onium salts of perchloric acid with methylamines are considered. It is shown that combustion of perchlorates of methyl ammonium derivatives is formed from the competition of precesses in the gas and condensed phases. In the implementation of the gas-phase combustion mechanism, very large evaporation enthalpies of salts play a huge role in the stability of salt combustion. The process of salt evaporation also affects the condensed-phase mechanism through high dissociation (surface) temperatures.



Dicyanomethyl and ditetrazomethyl derivatives of bisfurazanopiperazine as potential solid fuel dispersants for gas generator engines
Abstract
New energy-intensive compounds 4,8-dicyanomethyl-4H,8H-difurazano[3,4-b:3',4'-e]piperazine (DCMFP) and 4,8-ditrazolomethyl-4H,8H-difurazano[3,4-b:3',4'-e]piperazine (DTMFP) have been synthesized for the first time. The synthesis of these compounds is described. Both compounds were studied as possible dispersants of solid fuels for gas generator engines, their densities, enthalpies of combustion and formation, sensitivity to impact and friction were determined (for DCMFP, the sensitivity is very low, at the level of TNT; for DTMFP, at the level of HMX), the ballistic efficiency of solid fuels was estimated based on DCMFP and DTMFP (against 7-amino-7 -difurazano[3,4-b:3',4'-f]furoxano[3'',4''-d]azepine, Az(O)NH2 the first wins 4%, the second loses ). A comparison was also made with a number of other dispersants developed over the past few years. Preliminary testing of DCMFP and DTMFP for thermal stability was carried out by DTA in a nonisothermal mode, it was shown that these components are very stable, the so-called temperature of the beginning of intensive decomposition is 312 and 270°C, respectively.



Effect of self-fluidization of reaction medium and its application to the combustion synthesis of Ni–Al intermetallics
Abstract
The paper studies the mechanism of self-propagating high-temperature synthesis in powder mixtures of . Using CaCO makes it possible to form a fluidized state of the reaction mixture in the preheat zone of the combustion wave and synthesize highly permeable intermetallic alloys. The mechanism was studied using high-speed imaging, dynamic temperature measurements, and reaction quenching. It was found that highly mobile microdroplets of reacting Ni and Al melts (~0,1-0,2 mm in diameter) participate in the structural transformation of the reaction medium in the combustion wave zone. A wide range of capillary processes accompanies the synthesis: ( ) formation of droplets in the process of reaction coalescence of melts; ( ) intake of melting powder by moving droplets; ( ) wrapping a rolling droplet with a thin layer of newly-formed melt; and ( ) thermocapillary drift of droplets in a fluidizing powder medium. The effect of self-fluidization of the reaction mixture on the structure of the synthesized alloys has been discussed.



Enthalpy of formation of the trinitromethyl group
Abstract
The enthalpies of combustion and enthalpies of formation of three trinitromethyl derivatives of 1,3,5-triazine were determined by the calorimetric method. The data obtained can be used for calculating the energy capabilities of related compounds by the method of replacing functional groups. The thermochemical characteristics of trinitromethyl groups from 1,3,5-triazine derivatives are compared with the corresponding properties of these groups in azoles and nitroalkanes.


