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Project titleCritical conditions for fragmentation of heterogenous droplets of composite fuels with different sizes in a high-temperature gas environment

Research area 09 - ENGINEERING SCIENCES, 09-401 - Power systems that operate using organic fuel

Keywordsmulticomponent droplets, surrogates, composite propellants, fragmentation, puffing, micro-explosion, experiment, mathematical modeling, nucleation temperature, heating rates

Annotation
Environmental, economic, energy and geopolitical problems of the modern world motivate the development of alternative fuel technologies. In this regard, the scope of application of multi-fuel technologies is expanding. The main advantages of the latter are based on solving a group of tasks aimed at reducing the carbon footprint, depleting energy resources, and reducing waste from the raw materials sector. Composite fuels based on water, industrial waste, domestic sector, biomass, vegetable raw materials and water, as well as various surrogates with the replacement of expensive hydrocarbons, are considered to be a promising and affordable replacement for traditional energy resources for many countries. But the active use of such multi-fuel mixtures in real power plants and engines is constrained by certain difficulties in spraying in combustion chambers. It is required to obtain a finely dispersed fuel aerosol. Conventional spray systems require high pressures when handling multi-fuel formulations. The solution to this problem is the intensification of the fragmentation of fuel droplets directly in the combustion chamber. This is possible due to overheating of water in the composition of inhomogeneous droplets to a metastable state. To transfer the research results to promising surrogates and composite fuels containing both liquid and solid combustible components, it is necessary to determine the critical conditions for stable droplet fragmentation using dimensionless generalizing complexes. This problem has not yet been solved in the world. At Tomsk Polytechnic University, for two-liquid drops, the limiting temperatures of water overheating are established, sufficient for boiling and fragmentation. The limiting sizes of the parent drop are set, up to which it swells before fragmentation. These data are difficult to transfer to multifuel droplets without generalizing criteria. To obtain them, it is necessary to involve specialists from two partner organizations indicated in the application and to conduct an interdisciplinary study of the critical conditions for the fragmentation of different-sized droplets of composite fuels in a high-temperature gaseous medium. The specialists of the Institute of Thermal Physics of the Ural Branch of the Russian Academy of Sciences have experience in studying the initial conditions for the boiling up of complex systems using examples of different scales. Their knowledge is necessary to describe the detailed mechanism of boiling up and fragmentation of multifuel droplets at different heating rates. Samara University specialists have extensive experience in modeling the spraying and combustion of promising surrogates and traditional liquid fuels in the combustion chambers of aircraft and shipping installations. Project administrator Yanovsky L.S. is a famous specialist in fuel technology for aviation, land and marine engine applications. As a result of joint research, we have to describe in the form of dimensionless complexes and expressions the integral characteristics (decomposition delay times, mode, limiting temperatures, etc.) and critical conditions (overheating or heating rate, temperature and pressure drop, ratios of component concentrations, etc.) of boiling and fragmentation of different-sized droplets of composite fuels with initial sizes from the level of nano- to millimeters.

Expected results
The main expected results of the project for research team: 1. Experimental combined methods have been developed for measuring temperature distributions in multicomponent droplets before micro-explosion using modern optical methods Planar Laser Induced Fluorescence, Shadow Photography, Laser Induced Phosphorescence, 2ColorLIF. 2. The optimal conditions for micro-explosion of multicomponent droplets are determined with an emphasis on the development of advanced gas-vapor-droplet technologies. 3. The conditions for controlling the critical temperatures of multicomponent droplets before micro-explosion are established. 4. An information database has been created with information on the critical conditions of micro-explosion of multicomponent droplets. 5. Physical and mathematical models of micro-explosion of multicomponent droplets are developed taking into account the parameters varied in experiments and refined criteria for fragmentation according to the limiting temperatures of droplets. 6. Generalized dimensionless criteria are formulated in the form of expressions, ratios, dependencies and formulas that take into account the influence of all the studied processes, transformations, factors and effects. 7. Recommendations have been developed for the practical use of research results in the educational process, as well as for the development of science, engineering and technology. This will include methodological materials for the preparation of masters of engineering and technology and postgraduate students in the areas of "Mechanics of liquid, gas and plasma", "Thermal physics and theoretical heat engineering", "Industrial thermal power engineering", "Chemical physics, combustion and explosion", "Thermal, electric rocket engines and power plants of aircraft. 8. Articles published in international journals Q1. The results were tested at leading international conferences. A collective monograph with the results of the project was published by the publishing house of the Siberian Branch of the Russian Academy of Sciences. The main expected results of the partner - the Institute of Thermal Physics of the Ural Branch of the Russian Academy of Sciences: 1. Development of the method of controlled pulse heating of the probe, aimed at a detailed study of the initial stage of boiling by separating the electrical signal caused by the phase transition (its precursor), with a sub-microsecond resolution and microimaging the nucleation process; 2. Experimental and theoretical description of the effect of water microadditives on the temperature of achievable overheating Т* and the intensity of boiling up δТ* of hydrocarbon fuel components; 3. Measurement of the dependence of the temperature of achievable overheating of hydrocarbon fuel components on pressure at three heating rates (10^5, 10^6, 10^7 K/s); generalization of the data obtained in coordinates reduced to the parameters of the liquid-vapor critical point (Tc and pc); 4. Determination of dependences T*, Tc, body transfer coefficient α on concentration and reduced pressure; 5. Determination of the dependence of the boiling delay time for hydrocarbon fuel components; 6. Generalization of dependence of boiling intensity δТ*; elucidation of the factors of intensification of boiling up during pulsed heating; 7. Modelling of dependences Т*(с) and α(с); verification of models taking into account the results of impulse experiments and data on the thermophysical properties of the solution obtained by the second partner (Samara University); 8. Construction of an extended phase diagram of the studied binary systems, including approximations for the mechanical spinodal and the liquid-vapor critical curve; 9. Generalization of results; theoretical description of the initial stage of the boiling up of solutions, taking into account their thermal instability. The main expected results of the partner - Samara University: 1. Method for determining the physicochemical properties of multicomponent mixed fuels containing both traditional hydrocarbon components and promising components from biofeedstock (alcohols, oils and their derivatives). 2. Surrogates of promising types of fuels, which differ from the existing ones in the presence of components from biofeedstock. 3. Technique for numerical modeling of heating and evaporation of droplets of promising fuels containing both traditional hydrocarbon components and components from biofeedstock. 4. Patterns of heating, evaporation and explosion of both individual droplets and a group of droplets of promising fuels for conditions typical of engines for various purposes. (temperature range 300-1000 K, pressure range 1-50 atm). The synergistic effect of the interdisciplinary approach is that by applying a group of methods from the theory of combustion, phase transformations, fluid mechanics, gas and plasma, it will be possible to describe a complex set of processes, factors and effects that precede the fragmentation of multifuel droplets at different heating rates. It is due to the interdisciplinary approach that one can look at the complex phenomena of puffing and micro-explosion from the plane of different theories and form a single and more complex one. Scientific and social significance of the results on a global scale: The planned results of the presented project will be ahead of the world level of research, since the critical values of the temperatures of multi-fuel compositions in a wide range of heating rates have not yet been established. The studies will be performed using panoramic optical methods (Planar Laser Induced Fluorescence, Shadow Photography, Laser Induced Phosphorescence, 2ColorLIF), color and monochrome high-speed (up to 100,000 frames per second) video cameras, specialized software systems Tema Automotive, Davis, Actual Flow, and also own image processing algorithms in Matlab and Mathematica. The results of such studies in the world have not yet been published, judging by international journals (Physics of Fluids, Atomization and Sprays, Mechanica, Experimental Thermal and Fluid Science, International Journal of Multiphase Flow, International Journal of Heat and Fluid Flow, International Journal of Thermal Science, International Journal of Heat and Mass Transfer), included in the 1st quartile of Web of Science. Possibility of practical use of the expected results of the project: The obtained experimental and theoretical results will be the scientific basis for the development and modernization of promising high-temperature gas-vapor-droplet applications, as well as the development and improvement of existing ones. These include fuel technologies, namely combustion devices, engines for water, land and aviation transport (the use of new fuels based on water and a combustible component to jointly improve environmental, energy and economic performance).

Annotation of the results obtained in 2023
In accordance with the work plan, all expected results were obtained. In particular: 1. Three experimental stands were created to study the mechanisms of fragmentation of binary compositions with different compositions with fixation in the heating region and in free fall without the use of holders. The stands differ in heating conditions in terms of temperatures, heat flows, gas-air pressure, and the duration of recording key characteristics of physical and chemical processes until the conditions for droplet fragmentation and ignition are achieved. On the created stands it is possible to conduct experiments with different-sized initial drops (from 100 microns to 5 mm) and their quantity in the range from a single to 100 drops at a time. The stands provide dosing and mixing systems for conducting experiments with unmixed two-liquid drops, prepared emulsions and suspensions. 2. Methods have been developed for studying physicochemical processes during the decomposition of droplets of binary compositions with varying key properties over wide ranges to study their separate influence on the decomposition criteria. During the first year, the methods were tested for research with compositions containing the following components: water, ethers, fats, acids, kerosene, gasoline, diesel fuel, rapeseed oil, kerosene surrogates, decane, dodecane, heptane. The methods are developed to record critical heat flows, temperature and pressure of the external environment, sizes, concentration, temperature and velocity fields of initial droplets, the degree of overheating of the interfluid boundary, the number, sizes and component composition of secondary fragments, their surface areas and occupied volume in the aerosol cloud. Techniques based on a combination of optical methods were used, in particular, Planar Laser Induced Fluorescence, Laser Induced Phosphorescence, Particle Image Velocimetry, Interferometric Particle Imagine and Shadow Photography. Author's codes have been developed for automatic processing of videograms of experiments when recording the size, quantity and component composition of initial and secondary drops in the recording area. Methods have been developed to control the composition of flue gases and soot particles (size, shape, surface structure) during the combustion of fragmenting two-liquid droplets. 3. Experimental studies were carried out for binary compositions with varying the temperature of the gas medium, the initial sizes of droplets, the concentration of liquids and recording decomposition modes, fragmentation delay time, the number and sizes of secondary fragments. The size distributions of daughter droplets with water and flammable liquid in the composition of secondary fragments formed during a micro-explosion and puffing of two-liquid droplets have been established. Significant differences in the component composition of secondary fragments for different heat supply mechanisms were identified. The measurements performed using the Laser Induced Fluorescence method made it possible to substantiate the different degrees of grinding of water and the combustible component. The greatest efficiency, from the point of view of secondary grinding, was shown by the scheme with heating of two-liquid droplets in a flame. The relationships between the luminosity of droplets and the concentration of the combustible component at different temperatures of the gaseous medium were determined. Using these dependencies, the content of the flammable component in the composition of the droplets was determined. The conditions for the sequential occurrence of three modes of deformation of the surface of a two-liquid drop under intense heating have been identified: the nucleation and growth of a bubble inside the drop, swelling and micro-explosion. Curves were plotted for the dependence of the droplet decay delay on the displacement of the water core from the center of the droplet, and the limits of this displacement were determined for various compositions and heating conditions. Mechanisms have been determined to control the characteristics of droplet decay, based on providing droplets with ready-made evaporation centers and maintaining a certain temperature regime. The influence of the mass concentration of solid particles from 0% to 60% on the delay time of the disintegration of droplets of coal-water suspension has been established, which will contribute to the intensification of dispersion in fuel combustion plants. Functional connections between the recorded characteristics of micro-explosive fragmentation of droplets and the properties of liquids in their composition, supplied heat flows, heating patterns and placement of droplets in a gas-air environment are identified. A database was created with the initial process parameters and integral fragmentation characteristics. The differences in the decay delay times of the initial drops based on decane, dodecane, heptane, kerosene surrogate, diesel fuel, rapeseed oil and other components were determined. It is substantiated that the times of complete evaporation of these components and water are significantly different. Rapeseed oil and diesel fuel seem to be the most inert. Their fragmentation and evaporation can be accelerated by fragmentation due to the addition of microdroplets of water. By replacing water in the initial droplets with acids, esters, fats, oils, alcohols and other components, it was possible to prove that the main mode of fragmentation in this case is puffing. However, with a certain combination of initial parameters, an intense micro-explosion can be achieved. It has been shown that when temperatures exceed 900 K, the differences in the decay times of droplets with different component compositions do not exceed 6%. When comparing the modes and characteristics of fragmentation of unmixed binary droplets, emulsions and suspensions, it was found that the earlier the triggering volume of water is formed in the form of a nucleus, the faster fragmentation occurs. If microdroplets of water are distributed in the initial drop, then their coalescence is required with the formation of enlarged nuclei, which act as centers for the nucleation of bubbles. Bubbles of air and other gases, solid particles act as centers of vaporization in the initial drops. In their presence, overheating of the initial drop to a metastable state occurs faster. It is substantiated that the delay times of micro-explosive fragmentation of droplets of flammable liquids due to the addition of water to their composition are from several times to tens of times less than the times of complete evaporation of homogeneous drops. 4. The results of generalization of the obtained data are presented using known criteria that describe the joint influence of a group of properties and effects. The main dimensionless criteria (Kutateladze and Bond numbers, relative pressure drop, etc.) are identified for assessing the limiting conditions for micro-explosive crushing of two-component water-fuel droplets, taking into account three determining mechanisms for the occurrence of a micro-explosion: overheating of the internal interface between the components, internal vapor pressure, increase in volume due to the steam bubble. Based on the experimental data obtained, estimates were made of the ranges of values of three dimensionless criteria characterizing the conditions of micro-explosive disintegration of two-component drops. Similar values of dimensionless criteria were obtained for heating different model compositions under similar physical conditions (Ku=60-200, ΔP=1.09-1.35, Bo=1.2-2.6). A dimensionless criterion for micro-explosive decomposition of ME is obtained, based on the degree of overheating of the interface in a two-component drop and including the minimum number of variables determined on the basis of dimensional analysis. The results of the experiments made it possible to substantiate the exponential nature of the dependence of the delay time of the micro-explosive disintegration of two-liquid drops on the heating temperature. Using the obtained experimental functions of the form τd(Ta) and the Arrhenius equation for the rate of heating of droplets to micro-explosion conditions, the inverse problem of finding the values of the pre-exponential factor A and the activation energy Ea was solved. These parameters characterize the kinetics of droplet heating for stable micro-explosive disintegration. When generalizing the obtained experimental data, the expression for the pre-exponential factor takes into account the joint influence of the set of input parameters, in particular, the size and component composition of the initial drop. 5. Physical and mathematical models have been created to calculate the critical conditions of micro-explosive disintegration and its consequences. Three models have been developed based on the following criteria: overheating of the interfluid boundary to the metastable state of water; reaching the size of the initial drop 2-3 times larger than the initial one due to the growth of steam bubbles; reaching the thickness of the flammable liquid film around the vapor bubble of a critical size corresponding to its decay. For the first time, the effects of the nonsphericity of the initial drops and the intensification of convection in them were taken into account. A hydrodynamic model has been developed to predict the consequences of micro-explosive fragmentation of liquid droplets, based on the use of the VOF method. The influence on the recorded characteristics of a set of input parameters was studied: the size and component composition of the initial drop, its nonsphericity, the presence of several triggering nuclei in the drop, their different locations relative to the center and shell, the properties of liquids in the composition of the initial drop. A model has been developed to take into account the micro-explosive fragmentation of droplets in the composition of jets, sprays and aerosols. Certificates of state registration of computer programs with copyright calculation codes have been received. 6. Mathematical modeling of the heating and evaporation of droplets of promising fuels containing both traditional hydrocarbon components and components from bio-raw materials was carried out. Functional connections between output characteristics and input parameters, dimensional and dimensionless dependencies, ratios, regime maps, temperature fields, concentrations, speeds, size distributions and composition of secondary fragments and other numerical modeling data have been established for conditions that correspond to energy and propulsion systems operating on liquid fuels of different compositions. 7. The most rational conditions for the application of the effects of micro-explosive fragmentation of two-liquid initial fuel droplets in propulsion and power plants with different productivity have been established. It is substantiated that these effects, as a stage of secondary grinding of fuel droplets, will improve the integral characteristics of fuel combustion by optimizing the ratio of fuel and air consumption, temperature and heat flows in the combustion chamber, the concentration of oxidizer and flue gases. 8. Research results are published in highly rated peer-reviewed international and national journals. 2 articles were published in journals of the 1st quartile of Web of Science (Physics of Fluids, Energiest), 2 articles (prepared by partners from Ural Oransk Academy of Sciences and Samara State University) were accepted for publication in the journals of the SB RAS “Physics of Combustion and Explosion” and “Applied Mechanics and Technical Physics” (references from editions are attached to the report). 9. The research results were tested at 15 leading all-Russian and international conferences.

Publications

1. D. V. Antonov, S. Tonini, G. E. Cossali, V. V. Dolgikh, P. A. Strizhak, S. S. Sazhin Droplet heating and evaporation: A new approach to the modeling of the processes Physics of Fluids, 35, 073311 (year - 2023) https://doi.org/10.1063/5.0158661

2. Igolnikov A.A., Rutin S.B., Skripov P.V. Отклик системы твердая поверхность - расслаивающийся раствор при мощном локальном тепловом воздействии. Методология эксперимента Прикладная механика и техническая физика, - (year - 2024)

3. Tsapenkov K.D., Kuraeva Yu.G., Sidorova E.I., Shtyrlov A.E., Zubrilin I.A. Обзор математических моделей расчета физико-химических свойств оксигенированного углеводородного топлива Физика горения и взрыва, - (year - 2024)

4. Dmitrii V. Antonov, Roman M. Fedorenko, Leonid S. Yanovskiy, Pavel A. Strizhak Physical and Mathematical Models of Micro-Explosions: Achievements and Directions of Improvement Energies, 16(16), 6034 (year - 2023) https://doi.org/10.3390/en16166034

5. - Определение времени испарения капель биотоплива -, 2023680006 (year - )

6. - Определение времени задержки микро-взрывного распада неоднородных капель -, 2023681326 (year - )

7. - Определение количества и размеров вторичных фрагментов неоднородных капель после фрагментации -, 2023681499 (year - )