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E-Journal №4(72)2026

"PROBLEMS of the REGIONAL ENERGETICS (https://doi.org/10.52254/1857-0070.2026.4-72)"

CONTENTS

1	Development and Operational Optimization of Green Hydrogen-Based Integrated Energy Complexes Authors: 1Balaji L., 1Balu P., 2Anbazhaghan N., 1Senthil Kumar M. 1Bharath Institute of Higher Education and Research (BIST), Chennai, Tamil Nadu, India 2V.R.S. College of Engineering and Technology, Arasur, Villupuram District, Tamil Nadu, India
	Abstract: The main objectives of this study were to develop and optimize a green hydrogen-based integrated energy complex for enhancing renewable energy utilization, reducing operating costs, and minimizing carbon emissions while addressing the challenges of renewable power intermittency, limited energy storage capability, grid instability, and multi-energy coordination. These objectives were achieved by formulating an integrated multi-energy optimization framework, developing mathematical models for renewable generation, hydrogen production, storage, and energy conversion, deter-mining the optimal sizing of system components, optimizing annual operational scheduling under electrical, hydrogen, and storage constraints using a mixed-integer linear programming model, validating the optimization results through a particle swarm optimization algorithm, and evaluating the techno-economic and environmental performance of different system configurations. The most important results show that the integrated battery and hydrogen storage configuration increased renew-able energy utilization from 28.6% to 71.4%, reduced the levelized cost of electricity from 0.181 to 0.061 USD/kWh, lowered total operating costs by approximately 42%, and decreased carbon dioxide emissions by more than 60%, while the levelized cost of hydrogen ranged from 3.15 to 5.85 USD/kg, with a base-case value of 4.35 USD/kg. The significance of the study lies in demonstrating that integrated battery and hydrogen storage combined with advanced optimization provides a scalable, economically competitive, and low-carbon solution for renewable-powered industrial energy systems while offering practical guidance for optimal capacity planning and operational scheduling.
	Keywords: green hydrogen, integrated energy complex, renewable energy integration, hydrogen storage, proton exchange membrane electrolyzer, techno-economic optimization. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.01
2	Diagnostics and Forecasting of Photovoltaic Module Degradation: Analysis of Problems and Research Directions Authors: 1Karpenko O., 2Zaslavskiy A., 1Sosnin K. 1Dnipro University of Technology Dnipro, Ukraine 2OBLIK Corporation
	Abstract: Abstract. The purpose of this paper is to systematize the current state of research on photovoltaic (PV) module degradation, analyse existing methods for its diagnosis and forecasting, and identify unresolved problems relevant to information-measurement and intelligent monitoring systems. These objectives were achieved through a structured review of publications from 2023 to 2026 covering degradation mechanisms, instrumental and data-driven diagnostic techniques, and physical, data-driven, and hybrid forecasting approaches, complemented by a comparative analysis of the methods presented in two summary tables and four generalizing diagrams. The most important results are as follows: a systematized classification of degradation mechanisms, including electrochemical corrosion, potential-induced degradation, delamination, microcracks, and technology-specific mecha-nisms in PERC, HJT, and perovskite tandem cells; a comparative characterization of diagnostic methods, showing that instrumental techniques (I–V tracing, infrared thermography, electroluminescence, and UAV-based inspection) provide high spatial accuracy but limited scalability, whereas data-driven methods (year-on-year analysis, performance loss rate estimation, and machine-learning-based trend models) can be scaled to large arrays but remain sensitive to data quality; and the identification of four unresolved scientific problems: separation of reversible and irreversible performance losses, automatic correction of erroneous retrospective data, quantitative real-time assessment of the degree of degradation, and forecasting of the remaining useful life (RUL) of PV modules. The significance of the obtained results lies in demonstrating that a hybrid prognostic model combined with training-sequence decimation, the k-FC method, and a reflexive learning approach, previously developed by the authors for PV power-plant monitoring, provides a coherent methodological basis for addressing all four problems without requiring additional diagnostic hardware.
	Keywords: photovoltaic module degradation; diagnostics; forecasting; performance loss rate; remaining useful life; machine learning; k-FC method. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.02
3	Experimental Investigation of Ethanol–Nanoparticle Blended Gasoline on Performance and Emission Characteristics of a Spark-Ignition Engine Authors: Gundala S. P., Shaik F., Domakonda V. K. Vignan's Foundation for Science, Technology & Research, Vadlamudi, India
	Abstract: The main objective of this study was to evaluate how ethanol concentration and aluminium oxide nanoparticle addition influenced the performance and exhaust emissions of a spark-ignition engine. These objectives were achieved by experimentally testing commercial petrol, gasoline containing 10% or 20% ethanol by volume, and the corresponding blends containing 10 or 20 parts per million of aluminium oxide at five engine speeds from 1700 to 3300 revolutions per minute. Brake thermal efficiency, brake-specific fuel consumption, carbon monoxide, unburned hydrocarbons, nitrogen ox-ides and carbon dioxide were evaluated. The most important results are that the highest brake ther-mal efficiency was 36.93% for the 20% ethanol blend containing 20 parts per million of aluminium oxide at 2900 revolutions per minute. The lowest brake-specific fuel consumption was 0.24 kg/kWh for commercial petrol at 2900 and 3300 revolutions per minute and for the 10% ethanol blend containing 10 parts per million of aluminium oxide at 3300 revolutions per minute. The minimum car-bon monoxide concentration was 0.56%, the minimum unburned hydrocarbon concentration was 66 ppm, and the minimum nitrogen oxide concentration was 314 ppm, each under a different fuel and speed condition. The significance of the results lies in providing a controlled comparison of two ethanol concentrations and two nanoparticle dosages across the same operating range. Carbon dioxide emissions were higher for ethanol-containing blends than for commercial petrol and increased with engine speed. The findings show that responses depended on fuel formulation and engine speed, and no blend was best for every measured parameter.
	Keywords: SI engine, ethanol–gasoline blends, nanoparticles, performance; emissions. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.03
4	Influence of the Physicochemical Properties of Granulated Biofuel on Three-Dimensional Hydrodynamics, Heat Transfer, and Nitrogen Oxide Formation in Small- and Medium-Capacity Hot-Water Boilers Authors: Rachynskyi A.Yu., Baranyuk O.Yu., Tykhokhod V.A., Tkachenko S.S., Pikenin O.A. National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute” Ukraine, Kyiv
	Abstract: The aim of the study is to establish three-dimensional patterns of aerodynamics, heat and mass transfer, particle burnout kinetics, and CO and NOx emissions in the furnace volumes of 25 and 50 kW hot-water boilers firing six heterogeneous types of fuel pellets using CFD modeling in ANSYS Fluent. To achieve this aim, the following tasks were addressed: 3D polyhedral models of the boiler furnace chambers and gas ducts were developed with detailed representation of burner assemblies and staged air supply; the numerical framework (Euler-Lagrange DPM, Realizable k-ε, DO radiation, diffusion-kinetic char combustion, and detailed NOx chemistry) was verified against manufacturer data and adiabatic temperatures; velocity, turbulence (k), particle burnout, heat-flux (q), and NOx emission fields were investigated when changing from wood to agro-pellets and bottom sludge pel-lets. The most important results are the demonstration of flame stability (velocity variation ≤ 3.3%) at a fuel burnout degree of 94.0…99.2%, the identification of a 16.1% reduction in peak turbulence with a shift of maximum heat fluxes toward the inclined arch when firing agricultural biomass, the determination of a safe temperature window (1000…1150 °C) against slagging of heating surfaces, and the identification of reducing zones at the flame root (≤ 36 ppm NOx) suppressing fuel NOx when firing high-nitrogen feedstock (Nr ≤ 3.65%). The significance of the results lies in creating a computational and theoretical basis for operating-mode optimization and the safe conversion of seri-al pellet boilers to low-grade agricultural biomass and organic sludges.
	Keywords: hot-water boiler, fuel pellets, agricultural biomass, bottom sludge, CFD modeling, discrete phase model (DPM), polyhedral mesh, heat-flux density, slagging, NOx emissions. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.04
5	Connecting Single-Phase Renewable Energy Sources to a 0.4 kV Three-Phase Line While Complying with Standardized Limits on Unbalance Factors Authors: Bosneaga V., Suslov V. Power Engineering Institute Chisinau, Republic of Moldova
	Abstract: The objective of this study is to develop the methodology and use it to investigate the feasibility of connecting single-phase renewable energy sources to a single 0.4 kV three-phase line while adhering to standardized limitations on unbalance factors. To achieve this goal the model of a three-phase low-voltage overhead cable line, built using MATLAB blocks, is proposed. The model enables calculations of the steady-state operating modes of a three-phase line consisting of five sections of arbitrary length with connection of phase loads and/or single-phase renewable energy sources at the end of each section. The novelty lies in the determination of phase voltage and current magnitudes at any connection points of loads and energy sources along the length of the line. Furthermore, unbalance factors for zero and inverse sequences are determined at the same points. The most important result is that the permissible injection values through a three-phase line, according to power quality requirements, decreases sufficiently with increasing line length due to the significant influence of its zero-sequence resistance. To estimate the permissible injection values from a power quality perspective, depending on the parameters and length of a three-phase line, in the presence of asymmetric loads and injections in different phases, a system calculation must be performed in each individual case. Therefore, it is not possible to develop simple general recommendations for maintaining the specified power quality.
	Keywords: resistance introduced by a three-phase distribution line, permissible single-phase injection value with asymmetric loads. DOI: https://doi.org.10.52254/1857-0070.2026.4-72.05
6	An Uncertainty-Aware Measurement and Verification Framework for Building Energy Savings Using Cross-Validated Regression and Symbolic Regression via Genetic Programming Authors: Hazem Hassan Ali Sayed Energy Management Department, Luminous Energy Solutions, Calgary, Canada Renewable Energy Department, New Cairo Technological University, Egypt
	Abstract: Quantifying energy savings from building retrofits is complicated by uncertainty in baseline model form, since agreement between two conventionally linear tools may simply reflect a shared assumption rather than genuine model adequacy. The main objective of this study is to develop and validate a general, uncertainty-aware measurement and verification (M&V) framework that resolves this ambiguity through three-way cross-validation, demonstrated via a lighting retrofit case study in a commercial building in London, Ontario, Canada. This objective was achieved by analyzing three years (2021–2023) of monthly electricity consumption alongside Cooling Degree Days (CDD) using linear regression aligned with IPMVP Option C, applying Cumulative Summation (CUSUM) analysis to track savings persistence, and cross-validating the baseline model across three independent methods: commercial M&V software (RETScreen Expert), custom numerical regression (MATLAB), and a structure-free evolutionary search (Symbolic Regression via Genetic Programming, GP) that imposes no predetermined functional form. The most important results are that all three methods converged on the same linear CDD-based baseline model (R² = 0.9762–0.9765, ΔR² ≤ 0.0003), confirming that this agreement reflects genuine model adequacy rather than shared linear bias. The case study yielded verified annual savings of 232.056 kWh (27.846.72 CAD; 23.57 tCO₂), with CUSUM confirming persistence, though the high fit obtained reflects this facility's specific consumption profile and is addressed as a limitation. The significance of the obtained results lies in demonstrating a replicable, uncertainty-quantified cross-validation methodology that practitioners can apply beyond the specific case examined.
	Keywords: symbolic regression, genetic programming, cooling degree days, cumulative sum tracking, cross-platform validation, emission verification. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.06
7	Optimal Coordination of Directional Overcurrent Relays Using a Modified Red Deer Algorithm Authors: Almajali Ziyad, Al-Mbaideen Amneh, Al-Adaileh Fras Mutah University Karak, Jordan
	Abstract: Main objectives of the study have been formulated as the creation of the modified Red Deer Algorithm for optimal coordination of directional overcurrent relays in closed loop power systems, taking into account their total operating time under the coordination time interval constraints. These objectives were achieved by solving the following tasks: (1) obtaining an exact linear-programming solution for the time dial setting subproblem, replacing the heuristic sequential-update procedure used previously; (2) formulating a slack-penalized objective function to guarantee reliable convergence of the population-based search; (3) establishing an independent, non-circular criterion for breakpoint selection in looped coordination structures, applied to an eight-relay test network containing a six-relay ring and a mutually backed-up relay pair; and (4) performing a statistically grounded comparison with Particle Swarm Optimization under identical decision variables, objective function, and evaluation budget. The most important results are the following: the proposed algorithm converged to feasible solutions in every independent run, with a mean total operating time of 8.5244 s and a standard deviation of 0.0029 s over eight runs; there have been no constraint violations, confirmed for all six active relay pairs; the comparison algorithm also converged fully, and the difference between the best objective function values of the two algorithms was equal to 0.0002 s. The significance of the obtained results lies in demonstrating that the exact linear-programming evaluation combined with the slack-penalty and breakpoint concepts provides reliable, reproducible coordination for looped-network relay protection, achieving a 100% feasibility rate without requiring conservative or ad hoc penalty tuning.
	Keywords: coordination time interval, directional overcurrent relays, red deer algorithm, relay coordination, metaheuristic optimization, power system protection. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.07
8	Integration of ORC Turbines and Thermal Energy Storage Systems to Cover Peak Electricity Demand During the Summer Period in Distributed Energy Supply Systems Authors: Byk F.L., Myshkina L.S., Nasibova E.M. Novosibirsk State Technical University Novosibirsk, Russian Federation
	Abstract: The main objective of this study is to assess the effectiveness of Organic Rankine Cycle (ORC) turbines for recovering surplus thermal energy from cogeneration units during the non-heating season. To achieve this objective, the following tasks were addressed: municipal energy supply conditions in countries with extended summer periods were analyzed; international ORC experience was systematized by facility type, heat source, and power range; a conceptual scheme for integrating an ORC turbine with a thermal energy storage (TES) system was developed to smooth fluctuations in the waste-heat profile; and an analytical criterion for the techno-economic feasibility of ORC–TES systems at distributed generation facilities was derived, relating annual waste-heat availability to in-vestment payback. The most important results are as follows: TES integration increases the ORC turbine capacity factor by stabilizing the supplied heat flow while reducing required rated capacity; the generated electricity can cover peak summer air-conditioning loads without increasing equipment loading in the centralized power system; and criteria were formulated for preliminary screening of territories and industrial facilities suitable for such systems. The significance of the obtained results lies in developing a scientifically substantiated approach for converting seasonal waste-heat losses into additional electricity generation without increasing fuel consumption. Unlike previous studies, where thermal storage is mainly used to shift electrical or thermal load profiles, the proposed approach couples TES directly with an ORC turbine to convert otherwise unrecovered non-heating-season heat into electricity and introduces a quantitative payback criterion and a five-criteria procedure for facility selection.
	Keywords: Organic Rankine Cycle, non-heating season, waste heat, thermal energy storage, municipal energy supply, low-grade heat recovery, energy efficiency. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.08
9	Asynchronous Sensor Systems as the Next Generation of Urban Monitoring Systems for Resource Consumption, Air Pollution, and Meteorological Parameters Authors: 1Tirsu M.S., 2Surnov G.S., 2Surnov S.I., 2Bychkovskiy I.A., 2Zorin I.V., 2Surnov S.G. 1Institute of Power Engineering, Technical University of Moldova, Chisinau, Republic of Moldova 2Monitoring Technologies Laboratory LLC, Chisinau, Republic of Moldova
	Abstract: The aim of this study is to examine the feasibility of establishing urban monitoring systems to support the energy transition. To achieve this aim, the following tasks were addressed: analyzing the limitations of traditional synchronous Advanced Metering Infrastructure (AMI) systems; demonstrating the advantages of shifting to asynchronous systems—which utilize a unified technology and set of rules to collect granular data not only on resource consumption but also on weather conditions and indoor/outdoor air pollution, with adjustable granularity for each parameter; and identifying the initial step in deploying urban monitoring systems—the international ASMI pilot project—while outlining its goals, objectives, and expected outcomes. Key results include moving away from complex "smart meters" in favor of extremely simple, low-cost sensors; standardizing data transmission protocols across all monitored parameters; and reducing the costs associated with establishing and operating the monitoring system. The significance of these results lies in the fact that lower costs and enhanced data value pave the way for a new market—a market for urban resource consumption and environmental data—thereby attracting private-sector investment and laying the groundwork for future research involving artificial intelligence, the directions of which are outlined in the article.
	Keywords: asynchronous sensor monitoring system, ASMI, data granularity, monitored parameter sensors, resource consumption, energy transition, urban data market. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.09
10	Development of a Control System for the Tennessee Eastman Control Problem that Eliminates Excessive Variability in Control Actions Authors: Stopakevych A. О., Stopakevych О. A., Odesa Polytechnic National University Odesa, Ukraine
	Abstract: The Tennessee-Eastman Process (TEP) model has served as a globally recognized standard for evaluating advanced control methods for unstable technological processes for over 20 years. Research data published in leading scientific journals are used to evaluate modern control algorithms and are accumulated in a dedicated repository. Analysis shows that the problem of eliminating unwanted oscillations in control actions caused by measurement noise and sensor discreteness, without reducing robustness and cost-effectiveness, remains unresolved. To achieve this goal, the following tasks were solved: a multi-faceted analysis of the physical, dynamic, and economic characteristics of the process was performed, based on which a hierarchical control structure with decentralized PI controllers was synthesized; advanced filtering methods have been developed and implemented, including discrete Kalman filters with constant-rate models for reconstructing continuous concentration signals, second-order setpoint filters in cascaded loops, and Smith predictors for delay compensation. Cross-coupling compensation and pressure stabilization schemes using additional control channels have been proposed. The most important results include the virtually complete suppression of high-frequency noise from level, flow, and concentration sensors without introducing critical phase delays; the elimination of excessive oscillations in valves and pumps, which radically reduces their mechanical wear; and the successful compensation of typical process disturbances while maintaining process operability. The significance of the obtained results lies in the fact that the proposed approach demonstrates for the first time the possibility of integrating observers and filters into a classical circuit architecture for controlling an unstable chemical engineering process. This enables high-quality control to be achieved and the average cost of production to be reduced, while avoiding the "black box" disadvantages inherent in multivariable MPC-class systems and ensuring practical applicability in industrial settings.
	Keywords: automatic control system, technologically unstable process, Tennessee Eastman control problem, measurement noise, hierarchical control structure, Kalman filter, Smith predictor, cross-links. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.10
11	Development and Simulation of Operating Modes of a Hybrid PV-T System for Integrated Energy Supply of Urban Residential Buildings Authors: Zaitsev D., Golub I., Tirsu M., Caloshin D., Staikov N. Technical University of Moldova, Institute of Power Engineering, Chisinau, Republic of Moldova
	Abstract: The aim of this work is to assess the technical and economic efficiency of using hybrid photovoltaic-thermal (PV-T) panels in the energy supply system of an urban residential complex in the Republic of Moldova, to improve energy efficiency and relieve centralized energy supply networks. This aim is achieved by developing a mathematical model of PV-T system integration into urban infrastructure in Simulink MATLAB, selecting and justifying the main equipment (PV-T panels, inverters, heat pumps, energy storage), simulating characteristic operating modes, and a comparative techno-economic analysis of the existing and proposed supply strategies. The proposed hybrid system uses solar energy to simultaneously generate electricity, provide domestic hot water and support space heating in a multi-apartment complex. The most important result is the substantiation of the technical feasibility and economic viability of integrating PV-T panels into urban buildings, reducing grid energy use during peak load with an acceptable payback period. The significance of the results lies in a comprehensive method for assessing the efficiency of hybrid solar systems under regional conditions. The study showed that PV-T panels not only increase solar energy conversion efficiency through effective cooling of the photovoltaic cells, but also relieve transformer capacity and reduce losses in distribution networks. The results can support regional programmes for renewable energy in the housing and utilities sector of the Republic of Moldova, the design of autonomous and hybrid energy supply systems for social facilities, and further research on optimizing distributed generation within an urban Smart Grid.
	Keywords: renewable energy sources, solar energy, photovoltaic-thermal (PV-T) modules, hybrid energy supply systems. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.11
12	Improving the Efficiency of the Ammonia–Hydrogen Power Plant for an Autonomous Refrigerated Railway Car Authors: Kim K.K., Monastyrsky D.Ya. Emperor Alexander I St. Petersburg State Transport University Saint Petersburg, Russian Federation
	Abstract: The objective of the study was to determine the feasibility of improving the energy efficiency and environmental performance of autonomous refrigerated transport by replacing the conventional diesel–generator set with an ammonia–hydrogen power plant. The relevance of the work is conditioned by the need to decarbonize and improve the reliability of autonomous refrigerated transport while ensuring the quality preservation of perishable products by partially or completely replacing air (oxygen) in the cargo compartment of the car with an inert gas (nitrogen). The use of liquid ammonia as a chemical carrier of hydrogen within the rolling stock was substantiated, and a coupled model was described for the joint operation of a catalytic cracking reactor, a hydrogen internal combustion engine with an electric generator, a heat-recovery system, and a nitrogen utilization unit. The material and heat balances of the power plant were compiled, and its operating and mass-and-size limits of applicability were determined. The conditions for thermal autonomy of the catalytic ammonia decomposition process via exhaust gas heat recovery and the afterburning of residual combustible components were established, ensuring a significant reduction of the required on-board ammonia reserve compared with the non-recovery scheme. The material balance regularities of ammonia dissociation were determined, substantiating the complete in-system utilization of the associated nitrogen flow. The obtained results confirm the possibility of replacing the diesel–generator set with an ammonia–hydrogen power plant without reducing the useful carrying capacity of the car at an operational cargo density of 0.3–0.4 t/m3.
	Keywords: hydrogen, ammonia, decarbonization, catalytic cracking, autonomous refrigerated railcar, ammonia-hydrogen power unit. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.12
13	Research into the Influence of the Laws of Changing the Stator Supply Frequency on the Electromechanical Processes of an Asynchronous Motor During Controlled Starting Authors: Spodoba M.O., Spodoba О.O., Kovalchuk S.I. National University of Life and Environmental Sciences of Ukraine, Kyiv, Ukraine
	Abstract: The aim of the work is to obtain graphical dependences of the electromechanical response of an asynchronous motor during controlled start-up using frequency control, to analyze the influence of the laws of changing the stator supply frequency on the dynamic characteristics of the electric drive of the mechanical mixer of a biogas reactor, under conditions of quadratic growth of the resistance moment and increased starting torque. To achieve the objective, the following tasks were carried out: a mathematical model of the electromagnetic processes in an asynchronous motor was synthesized; frequency-dependent reactance functions were applied; the equations of motion were numerically integrated using the Runge-Kutta method; and a model of the load torque for a mixer operating in a viscous medium was developed. The working hypothesis posits that applying exponential and S-shaped laws for stator frequency regulation will minimize the motor's energy consumption during startup. The most significant results are the graphical dependencies of the electrodynamic parameters of the asynchronous motor driving the biogas reactor mixer; these dependencies were constructed using exponential and S-shaped functions for the variation of the stator winding supply frequency, based on a mathematical model presented in the study. The significance of the results lies in the ability to analyze the dynamics of asynchronous motors (currents, rotational speed, electromagnetic torque) under various stator control laws. An S-shaped profile for the stator frequency variation of the mixer's asynchronous motor reduces starting energy consumption by an average of 45.3% compared to an exponential profile.
	Keywords: controlled start, frequency control, asynchronous electric motor, modeling, electrodynamic parameters. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.13
14	Numerical Investigation of In-Cylinder Cold Flow Characteristics Using Dynamic Mesh in a Compression Ignition Engine Authors: Bambhania M.P.1*, Jani D.M.1, Jani D.S.2 1The Maharaja Sayajirao University of Baroda, Faculty of Technology and Engineering, Mechanical Engineering Department, Vadodara, India 2Gyanmanjari Institute of Technology, Mechanical Engineering Department Bhavnagar, India
	Abstract: The main objectives of the study are to characterize the transient cold flow structures in the cylinder of a compression ignition engine, to quantify how piston motion changes these structures relative to a fixed geometry, and to determine the pressure and temperature histories of the motored cycle as a baseline for subsequent combustion modeling. These objectives were achieved by building a two-dimensional computational model of a single-cylinder production engine with a bore of 95 mm, a stroke of 110 mm and a compression ratio of 15.5 (the effective volume ratio of the planar model is 12), and by solving the unsteady compressible conservation equations with a pressure-based solver and the standard k–epsilon turbulence model; piston motion was represented by a layering and spring-smoothing moving-mesh technique, and three cases were simulated: intake with fixed geometry, intake and exhaust with a moving piston, and motored compression and expansion. The most important results are that the fixed-geometry intake produced a single dominant toroidal vortex, whereas the moving piston produced one dominant clockwise vortex with two smaller counter-rotating vortices and a markedly asymmetric flow, that the exhaust stroke left residual vortical structures in the cylinder, and that motored compression reached a peak gauge pressure of 3.18 MPa and a peak temperature of 808.6 K near top dead centre, accompanied by organized tumble and recirculation zones. The significance of the obtained results lies in showing that neglecting piston motion misrepresents the in-cylinder vortex structure, and in providing a mesh-independent motored baseline on which fuel injection, combustion and emission models can be built.
	Keywords: moving mesh; layering; piston kinematics; tumble; toroidal vortex; motored cycle; turbulence modeling; pressure–volume diagram. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.14
15	Development of a Method for Formulating a Decision Function in Automated Navigation Control Systems under Energy Resource Constraints Authors: 1Sotnikov A.М., 2Tiurina V.Yu., 3Lukyanova V.A., 4Petrov K. E., 5Kobzev I.V., 6Bespalko O.V. 1,6Kharkiv National Air Force University (KNAFU), Kharkiv, Ukraine 2National Defence University of Ukraine: Kyiv, Ukraine 3V. N. Karazin Kharkiv National University, Kharkiv, Ukraine 4Kharkiv National University of Radio Electronics, Kharkiv, Ukraine 5Simon Kuznets Kharkiv National University of Economics, Kharkiv, Ukraine
	Abstract: This article develops a robust method for formulating a decision function in automatic optoelectronic navigation systems to ensure operational accuracy and stability under highly distorted current images. This is achieved through the sequential application of the polynomial fractional Fourier transform, the log-polar Mellin transform, and a two-stage Tikhonov regularization scheme. For the first time, an image formation method is proposed based on the spatial-frequency separation of the signal-noise mixture and dynamic motion blur compensation within the integral transform operators. The method automatically searches for optimal fractional-order parameters by minimizing the Rényi spectral entropy. A scale-invariant model strictly distinguishes between intra-frame blurring compensation in the fractional frequency domain and inter-frame carrier altitude variation elimination within the Mellin operator. Analytical expressions for the optimal Tikhonov regularization parameters are derived and evaluated in real time via Hansen's L-curve curvature maximization without computationally expensive matrix inversions. This mathematical approach ensures strict decision function unimodality verified by the Sylvester criterion under extreme signal-to-noise ratios (down to –15 dB) without reliable landmarks or landmarks availability. Numerical simulations in Python using real-world aerial imagery under angular heading evolutions within ± 15° confirmed a reduction in the root-mean-square error (RMSE) of ground-based coordinate localization by more than a factor of 20 compared to classical spatial correlation algorithms, achieving a framing processing time of 12–25 ms on an ARM architecture. The scientific novelty lies in substantiating a new fifth-generation navigation system concept, wherein noise spectrum and destructive dynamic blur separation occurs strictly at the spatial-frequency level.
	Keywords: spectral-energy representation of current images, polynomial fractional Fourier transform, Mellin transform, Tikhonov regularization, unimodal decision function, dynamic image blurring, informative features, fifth-generation navigation system. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.15
16	Optimum Melting Temperature and Latent-Heat Contribution of a PCM Layer in Multilayer Walls for Mediterranean, Semi-Arid and Hot Desert Climates Authors: 1Belkacem N., 2Missoum M., 1Benciamma S. 1Universitatea Hassiba Benbouali din Chlef, Chlef, Algeria 2Universitea din Tipaza, Chlef, Algeria
	Abstract: The main objectives of the paper are to determine, for three climatic zones (Mediterranean coast, semi-arid High Plateau and hot desert), the optimum melting temperature of a PCM layer in a wall for each position and orientation, and, as a new contribution, to separate the benefit of the latent heat from that of the added layer. These objectives were achieved with an enthalpy model validated against the Stefan solution (within 0.2 %): eight PCMs were compared under a constant load, RT-27 was retained among the three best (melting at 28 °C, above the initial wall temperature), and its melting temperature was varied from 18 to 44 °C in a periodic regime on a typical and a heat-wave day for one site per zone. The most important results are that RT-27 between the bricks lowered the maximum internal surface temperature from 31.5 to 25.8 °C and the daily heat gain by 88 %, that the latent heat accounted for only 0.1 to 0.5 °C (20 % of the reduction, median), and that the optimum melting temperature between the bricks was 28 to 30 °C (walls) and 32 °C (roof) on the coast and the High Plateau, and 32 to 35 °C and 38 °C in the Sahara. The significance of these results lies in showing that most of the benefit comes from the added layer, and that choosing the melting temperature of the zone instead of RT-27 gains up to 0.5 °C and keeps the PCM active in the desert.
	Keywords: phase change material (PCM), heat transfer, numerical simulation, multilayer wall. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.16
17	Optimization of Operational Performance Indicators of a Power Plant with a Gas-Liquid Fuel Supply System. Part I Authors: Lysenko R. D., Ryaboshapka V. B. Vinnytsia National Agrarian University Vinnytsia, Ukraine
	Abstract: The main objectives of this study were to determine the maximum replacement of conventional diesel fuel with liquefied petroleum gas in a production diesel engine operating in dual-fuel mode, with diesel providing pilot ignition and gas serving as the primary fuel, ensure stable operation across all load and speed conditions, and assess the influence of pilot and gaseous fuel quantities on engine performance. These objectives were achieved by analysing diesel conversion methods, gas supply control and existing mathematical models, developing diesel and dual-fuel cycle models based on the Wiebe function with a variable combustion shape parameter, and computationally investigating how the fuel substitution coefficient affects heat release, cylinder pressure and temperature. The most important results include identification of differences in combustion and heat release between diesel and dual-fuel cycles, including lower calculated pressure and higher temperature in dual-fuel operation under the adopted modelling conditions, and determination of relationships describing changes in the combustion shape parameter, heat release fraction and rate, cylinder pressure and temperature as diesel fuel is replaced by liquefied petroleum gas in a naturally aspirated engine. The significance of the results lies in establishing analytical relationships between combustion characteristics, liquid and gaseous fuel quantities supplied per cycle and engine cycle parameters, providing a basis for model refinement, development of gas supply and pilot fuel quantity control systems and algorithms, and assessment of fuel and energy efficiency over the investigated operating range.
	Keywords: dual-fuel engine; liquefied petroleum gas; external mixture formation; pilot injection; heat release; fuel efficiency; energy efficiency. DOI: https://doi.org/10.52254/1857-0070.2026.4-72.17