During the study of premixed NH3/CH4 fuel mixtures, flame separation into two reaction zones was observed upon flashback into a Bunsen burner. Stable combustion regimes were obtained, with a gap between the burner rim and the upper luminous region, the size of which depended on the mixture composition and the position of the combustion zone inside the burner. The work examines combustion regimes of NH3/CH4 mixtures with an ammonia content of 10–60% in the fuel blend. The equivalence ratio was varied in the range of 0.95–1.1. The Reynolds number was maintained in the range of 270–300, ensuring laminar flow conditions. At the burner exit, temperature and gas composition profiles were measured. Flame emission was recorded at the chemiluminescence bands of OH* (308 nm) and CH* (431 nm), and emission spectra were acquired both inside and outside the burner. Spectra in the range of 190–1080 nm were recorded. Spectral analysis revealed a band corresponding to NO2 emission in the upper part of the luminous region. It is most likely that nitrogen dioxide is formed through low-temperature reactions occurring when the combustion products mix with atmospheric air.

В работе изучалась тепловая динамика при натекании водородосодержащей струи на нагретую каталитическую поверхность. Исследовались режимы течения с числами Рейнольдса Re<2000, когда истечение в пространство происходит в ламинарном режиме, а на выходе из трубки реализуется установившееся течение Пуазейля.

This paper investigates the combustion characteristics of promising decarbonized fuel mixtures—methane/hydrogen (CH4/H2) and ammonia/hydrogen (NH3/H2)—with a focus on how they interact with external electric fields. The key findings are that these flames possess significant electrochemical properties, allowing for non-intrusive control over their stabilization, shape, and structure using relatively weak electric fields. The research combines experimental techniques like volt-ampere characteristic (VAC) measurement and advanced Hilbert visualization to analyze flame deformation, temperature distribution, and species concentration. Two orientations of the electric field were considered: transverse and longitudinal. For the transverse field, an assessment of the degree of flame deformation was made, indicating the preservation of the laminar combustion regime. In the longitudinal electric field, a change in the combustion stabilization mode was observed, which was detected through visualization and current-voltage characteristics (CVC).

A synthesis procedure for composite precursors of the composition yttrium-stabilized zirconia nanoparticles – 2,2,6,6-tetramethyl-3,5-heptandionato-hafnium(IV) is developed. The thermal behavior of the synthesized composites is studied by the complex thermal analysis up to 600 °C in a wide concentration range. Main components of thermolysis products are determined by the energy-dispersive X-ray (EDX) analysis. Features are revealed in TG curves for all compositions in the temperature range of 310-410 °C. From the IR, XPS, and EDX data it is found that the observed effects are due to low-temperature decomposition of a small part of the volatile metal-organic precursor irreversibly absorbed on the surface of nanoparticles. A hypothesis is put forward that irreversible adsorption is caused by Lewis acid centers on the surface of nanoparticles. The obtained information about the thermal properties of composite precursorscan facilitate the development of methods to control nanoparticle concentrations in the coating formed.

Разработан метод синтеза композитных прекурсоров состава «наночастицы оксида циркония, стабилизированного иттрием - 2,2,6,6- тетраметил-3,5-гептандионато-гафний (IV)». Методом комплексного термического анализа изучено термическое поведение синтезированных композитов до 600 °С в широком концентрационном интервале. Продукты термолиза проанализированы на основные компоненты методом энергодисперсионного анализа. Для всех составов на кривых ТГ выявлены особенности в интервале температур 310-410 °С. На основании данных ИК-спектроскопии, РФЭС и ЭДС установлено, что наблюдаемые эффекты связаны с низкотемпературным разложением небольшой части летучего металлоорганического прекурсора необратимо адсорбировавшегося на поверхности наночастиц. Высказана гипотеза, что необратимая адсорбция связана с кислотными Льюисовскими центрами на поверхности наночастиц. Полученная информация о термических свойствах композитных прекурсоров позволит разработать методы управления концентрацией наночастиц в формируемом покрытии.

В данной работе представлены результаты изучения влияния разбавления метана водородом на физико-химические и электрические характеристики пламени диффузионной струи СН4/Н2. Было обнаружено, что для смесей с молярной долей метана выше 40% величина протекающего тока линейно зависит от состава. Разбавление водородом при молярной доле метана в смеси менее 40% приводит к тому, что зависимость тока от состава становится нелинейной. В этом случае граница перехода от линейной зависимости к нелинейной не зависит от скорости потока и формы электрода. Результаты измерений хемолюминисценции радикала СН* выявили совершенно аналогичную зависимость свечения от объёмной доли водорода. Полученные результаты указывают на существование двух режимов, в которых возможно существенное различие в кинетических механизмах диффузионного горения смеси СН4/Н2.

An experimental study of a hydrogen-containing jet’s impact on a palladium-based catalyst in an air atmosphere was carried out. High-intensity temperature fluctuations on the catalyst surface are obtained in the case when large-scale vortex structures are contained in the jet. These superstructures have a longitudinal size of 20–30 initial jet diameters and a transverse size of about 3–4 diameters. To form such structures, it is necessary to use long, round tubes in the Reynolds number range of 2000–3000 as a source of the impinging jet when a laminar-turbulent transition occurs in the channel according to the intermittency scenario. This effect was obtained at a low hydrogen content in the mixture (XH2 = 3…15%) and a low initial temperature of the catalyst (180 °C). It is shown that the smallest temperature fluctuations are obtained for the laminar flow in the tube (<1.5%), and they are more significant (<4%) for the turbulent regime at low Reynolds numbers (Re < 6000). The greatest temperature fluctuations were obtained during the laminar-turbulent transition in the tube (up to 11%). Two important modes have been established: the first with maximum temperature fluctuations in the local region of the stagnation point, and the second with the greatest integral increase in temperature fluctuations over the entire area of the catalyst.

The possibility of processing small-view hilbertograms by the Gershberg-Papulis method to restore the refractive index of phase objects is discussed. The method consists in iterative transitions from estimating a function in the Fourier plane to estimating it in a coordinate space with an adjustment using a priori information. The spectrum of the function is determined on the entire frequency plane as an iterative process result Numerical simulation of the refractive index reconstruction for various test functions was performed using the Gershberg-Papulis method using Radon data known for four angles. Experimental studies on the Hilbert diagnostics example of reacting media (flames) in a high-speed shooting mode (up to 2000 frames per second) were performed using a four-angle tomographic complex implemented on the basis of an upgraded IAB-463M shadow device.

The possibility of processing small-view hilbertograms by the Gerchberg–Papoulis method to restore the spatial distribution of the refractive index was studied. The method consists in iterative transitions from the function estimates in the frequency and coordinate spaces with correction based on a priori information. Numerical modeling of the refractive index reconstruction for various test functions by the Gerchberg–Papoulis method using the Radon data, known for four angles, has been carried out. Using a four-angle tomographic complex implemented on the basis of a modified IAB-463M shadow device, experimental studies were carried out by the example of optical Hilbert diagnostics of reacting media in a high-speed shooting mode (up to 2000 frames per second).

Hilbert-optics and signal conversion methods form the basis for modern information and measurement technologies. The Hilbert transform in the frequency space is physically reduced to a certain phase transformation of the Fourier spectrum of the signal in a wide frequency band. The article discusses the possibility of Hilbert tomography using the example of studying the isothermal flow of a freon-22 jet. An optical system based on the IAB-463M modernized wide-aperture shadow device has been developed. This system makes it possible to perform four-angle diagnostics of the studied phase object using probing light beams. The beams orientation is defined at angles of 0, π/2, π/4 and 3π/4 to the optical axis of the shadow device. This makes it possible to simultaneously register all four tomographic projections in the form of Hilbert images in separate sections of the CCD-matrix of the high-speed camera. The use of the iterative Gershberg-Papulis scheme for finding the parameters of the medium under study based on Hilbert tomography data is further proposed. This algorithm for reconstructing a function from its Radon data obtained by a limited number of projections consists in iterative transitions from estimating the function in the Fourier plane to its estimate in the spatial domain, corrected based on a priori information. The spectrum of the restored function is determined on the entire frequency plane as a result of an iterative process, which makes it possible to determine the values of the required function.

Thermal barrier coatings protect alloys (for example, in turbine blades) from extreme temperatures. There is a pressing need to find better materials than currently used yttria-stabilized zirconia (i.e. materials with better thermal stability, lower thermal conductivity, higher thermal expansion coefficient matching that of the alloy). Here we explore gehlenite (Ca2Al2SiO7) for possible application as a material for thermal barrier coatings. We found that gehlenite can indeed be used in next-generation thermal barrier coatings, as a top coat on a thin layer of yttria-stabilized zirconia.

The aim of this work is to adapt the methods of optical Hilbert diagnostics for the visualization and study of inverse diffusion H2/O2 flame. The diagnostic complex is implemented on the basis of the IAB-451 device with modified optical filtering. Visualization of phase perturbations induced by the studied medium in a probing multiwave light field is performed via polychromatic Hilbert and Foucault-Hilbert transformations in combination with registration and RGB-per-pixel processing of the dynamic structure of the images. From solution to the inverse problem of Hilbert optics using a physically justified initial approximation of the problem under consideration, the temperature field of the flame is reconstructed and the value of the H2, H2O, O2 and N2 concentrations may be restored.

Today, many technologies for the deposition of various functional coatings using volatile compounds are united under the general name chemical vapor deposition processes from the gas phase (CDV, MOCVD, ALD, CVI, PECVD, etc [...]

An experimental study of spatially localized very large-scale motion superstructures, propagating in a jet of carbon dioxide at low Reynolds numbers, was carried out. A hot-wire anemometer and a high-speed 2D PIV with a frequency of 7 kHz were used as measuring instruments. Such a puff-type superstructure in a jet with a longitudinal dimension of up to 20–30 nozzle diameters are initially formed in the jet source—a long tube in a laminar-turbulent transition mode (without artificial disturbances). It is shown that this regime with intermittency in time, when part of the time flow is laminar and the other part of time is turbulent, exists both at the exit from the nozzle and in the near field of the jet. Thus, the structural stability of such turbulent superstructures in the near field of the jet was found. Despite the large longitudinal scale, these formations have a transverse dimension of the order of several nozzle diameters. These structures have a complex internal topology, that is, superstructures are a conglomeration of vortices of different sizes from macroscale to microscale. Using the example of diffusion combustion of methane in air, it is demonstrated that in reacting jets, the existence of such large localized perturbations is a powerful physical mechanism for a global change in the flame topology. At the same time, the presence of a cascade of vortices of different sizes in the puff composition can lead to fractal deformation of the flame front.