Том 17, № 3 (2024)

The efficiency of steam addition is studied in relation to the problem of reducing nitrogen and carbon oxide emissions for low-power atmospheric burners using the example of gaseous fuel combustion. Thermal and environmental characteristics of gaseous fuel combustion are experimentally determined when it is supplied to the base of a high-speed jet of superheated steam as a method of low-emission combustion. During the experiment, the completeness of fuel combustion, gas analysis of exhaust gases, and average temperature along the flame symmetry axis are measured. The results demonstrate that the supply of superheated steam can significantly reduce the concentration of harmful substances in combustion products (NOx and CO by 1.6 and 1.8 times) compared to blowing heated air, while maintaining high completeness of fuel combustion due to the reaction of hydrocarbon fuel with steam.

The paper experimentally determines the conditions for mild detonation initiation in a vertical semiconfined flat layer of stoichiometric ethylene–oxygen mixture of finite thickness. Pointwise ignition of the layer is performed by a single spark gap or two spatially separated spark gaps. Mild detonation initiation means deflagration-to-detonation transition (DDT). The flame and detonation propagation process is recorded by high-speed black-and-white and color video cameras. Mixture ignition by a single spark gap shows that the probability of DDT monotonically increases from 0 to 1 with the height of the combustible mixture layer. There is always the critical height of the layer, at which this probability has an intermediate value between 0 and 1. In the experiments, the critical height of the layer was 80–100 mm. Simultaneous ignition of the mixture by two spark gaps can lead to both deceleration and acceleration of DDT. Comparison of black-and-white and color images of the DDT process shows that the shapes of the flame front and detonation wave are similar in both cases but the color image allows obtaining additional information on the flame temperature. However, the black-and-white image with a large dynamic range better displays the structure of the flame front and detonation wave. The obtained results can be used in developing the procedures for safe and reliable starting of continuous-detonation engines, which require careful control of the time of filling the engine combustor with fuel and oxidizer as well as the ignition time of the explosive mixture.

Numerical simulation is used to study the differences and specific features of the propagation of heterogeneous detonation waves in a vertical channel filled by air suspensions of droplets of n-hexadecane and iso-octane — flammable liquids with very different vapor pressure under normal conditions. The difference in vapor pressure exerts a strong effect on the conditions for the existence of heterogeneous detonation in the suspensions. Thus, heterogeneous detonation in air suspensions of iso-octane droplets can be initiated in a channel without taking special measures. However, for the initiation of heterogeneous detonation in air suspensions of n-hexadecane droplets, there is a need in significant liquid prevaporization. For example, for the air suspension of stoichiometric composition, a degree of liquid prevaporization must exceed a certain critical value (about 40%). When the degree of liquid prevaporization is lower than this critical value, the chemical energy release behind the lead shock wave does not ensure the self-sustaining character of reaction wave propagation. When passing through the critical value of the degree of liquid prevaporization, there is a drastic change in the energy release mode in the propagating reaction wave: the energy release starts from the volumetric (kinetically controlled) self-ignition of the vapor–air mixture behind the lead shock wave accompanied with a significant increase in temperature, which accelerates subsequent processes of mixture formation and (diffusion controlled) energy release. At a subcritical value of the degree of liquid prevaporization, this starting period is weakly manifested.

The effect of 11-diethylferrocene (DEF) individually and in combination with carbon black (CB) and carbon nanotubes (CNT) on the combustion of a model sample based on an inactive binder 12.2% polyvinyl butyral, plasticized with 15.8% dibutyl phthalate and 70% ammonium perchlorate containing 1.4% teflone-4 and 0.6% technological additives was studied. Propellants samples were manufactured using rolling and through-pressing. Burning rate was determined in a constant pressure device in a nitrogen atmosphere on armored checkers with a diameter of 6 mm and a height of 15 mm. The structure and elemental composition of the combustion surface of the quenched samples are investigated. It was shown that when samples with a catalyst and CNT are burned, a frame is formed on the combustion surface on which a significant accumulation of the catalyst particles, CNT, and teflone occurs. Thus, combustion catalysis occurs by the same mechanism as for double-based propellants and various explosives containing nitrogroups, i. e., the mechanism of catalysis of energetic materials is uniform.

Paste propellant propulsion is a possible alternative to the commonly used liquid and solid propellant propulsion. However, information on the burning process of pasty condensed systems remains very limited. The paper presents the results of experimental study of the burning process of pasty condensed systems at varying their composition. The study deals with determining the parameters of the burning rate law and the characteristics of the agglomeration process. The description of the research methodology is provided. Paste compositions have been identified that provide control of the burning process of pasty propellants which includes changing the law of burning rate and agglomeration characteristics. A significant role of the intermediate structure — skeleton layer — in the burning process of the system under consideration has been established. The obtained data made it possible to reveal a general physical mechanism of the burning process of pasty propellants.

A method for estimating the transparency for the radiation of an iron–aluminum thermite of moderate gravimetric density is proposed. The transparency of such compounds is caused by their porosity. It is assumed that the patterns of light reflection from the outer surface of the sample are similar to those in the pores. The experimentally known dependence between the reflection coefficient and density for model compositions (coarse) ammonium perchlorate + (fine) aluminum (∼ 25%) and the transmission dependence of content of aluminum found for compositions with a small amount of aluminum (∼ 0,2%) but pressed to the maximum density have been used. It is shown that in the first case, starting with a relative density of Δρ ≥ 0,3, the reflection coefficient does not increase with the density of the observed composition. In the second case, the dependence is linear. To determine the transmission coefficient of a porous composition with a large amount of aluminum, it is necessary to set a conditional concentration of Al. This value is calculated based on the assumption that the fine Al powder, due to the adhesion of individual particles, consists of separate agglomerates containing 8–10 particles. After that, according to the linear dependence in the second case, the transmission coefficient has been found. So, for an iron–aluminum termite, the transmission parameter k is 10³–10⁴ сm⁻¹ that agrees with the data given in the literature.