The use of alternative fuels to generate mechanical and thermal energy in engines is a promising and sought-after technological area with its own unique advantages and characteristics. Consequently, enhancing the technical, economic, and environmental efficiency of gas engines fueled by propane-butane mixture and syngas through optimized operating cycle parameters (including valve timing, ignition timing angle, fuel mixture composition, and compression ratio) is a pressing imperative for scientific and energy sectors. The aim of the study was to investigate and compare the performance of an engine with different compression ratios running on a propane-butane mixture and laboratory syngas. The research’s primary originality lies in its joint study of syngas production technology and the evaluation of the efficiency of a mini power plant fueled by the resulting gas and conventional gas. This article presents a description of the experimental setup, data on measuring instruments, technical characteristics of the mini-power plant, the process for obtaining laboratory syngas, the properties of the gaseous fuels used, and experimental methods. Data on air and fuel consumption, as well as engine efficiency at different compression ratios when running on a propane-butane mixture and syngas, were obtained and analyzed. Converting an engine from a propane-butane mixture to syngas results in a reduction in power of almost 30% and efficiency by 13%–33%. Increasing the compression ratio by 0.9 units causes a rise in maximum efficiency from 0.177 to 0.235 for an engine running on a propane-butane mixture and an increase in maximum efficiency from 0.136 to 0.161 for a syngas engine. It has been confirmed that the compression ratio significantly impacts the technical and economic performance of an engine running on gaseous fuel. The obtained results can be used to modernize existing engines for operation on alternative fuels (syngas) and to design new mini-power plants with promising technical, economic, and environmental characteristics.

Additive manufacturing has become an important technology for turbomachinery blades because it enables lightweight components of high geometric complexity and allows the external shell and internal infill to be designed separately. However, published studies on blade internal structures remain fragmented because different works consider different cell types, materials, optimization formulations, and evaluation criteria, which complicates cross-study comparison. This review synthesizes 47 sources and classifies internal structures according to the method of geometric definition, distinguishing 2D parametric structures (class A1), 3D parametric strut-based and TPMS-based structures (class A2), free-topology structures obtained by topology optimization or generative design (class B), and hybrid structures combining parametric infill with free topology (class AB). Comparative analysis based on normalized data extracted from 17 studies is used to examine the effects of these structure classes on natural frequencies, stress state, thermal state, and fatigue life. The review is complemented by a structured study-by-study summary, which systematizes the studies used in the review discussion in terms of component type, material, additive-manufacturing process, internal-structure class, analysis method, investigated indicators, main results, and limitations. The available evidence indicates that class A1 structures are used mainly for mass reduction in narrow internal cavities, class B structures are especially effective for targeted material redistribution and often provide the largest increase in lower natural frequencies, whereas TPMS-based structures appear particularly promising for thermal-state-related applications. At the same time, fatigue life and manufacturing accuracy remain among the least studied and least experimentally validated characteristics.

The specific, technical, and economic indicators of an engine can be significantly increased by using a turbocharger. The relevance of this study is that enhancing the design and physical processes in the elements of a centrifugal compressor can result in improved efficiency and productivity of the turbocharger and engine. The study's objective was to create design strategies for upgrading the compressor outlet air duct to regulate the gas-dynamic and heat-exchange characteristics of the flow. The compressor outlet air duct of an automobile turbocharger served as the research object, and both the compressor and turbine wheels had a diameter of 61 mm. The scientific novelty of the article consists in the study of physical processes in the turbocharger outlet air duct (other authors' studies were aimed at the inlet channels) and the development of original designs of outlet air ducts. Two approaches were employed: one to stabilize the flow by using a honeycomb in the air duct and another to increase flow turbulence by applying dimples on the channel surface. The study covered the range of rotor speeds from 20,000 to 60,000 min(-1) (1.910(5) < Re < 3.310(5)). New experimental data on gas dynamics and heat transfer of flows for different air duct designs were obtained through tests on a laboratory bench and measuring equipment based on constant-temperature anemometers, a pressure sensor, thermocouples, tachometers, and an analog-to-digital converter. It has been shown that the use of a honeycomb in the air duct leads to a drop in air flow of up to 14 %, a decrease in turbulence number of up to 36 %, and an increase in the heat transfer coefficient of up to 21 % compared with the basic design. It was found that the application of dimples in the air duct causes a decrease in air flow of up to 8 %, an increase in the number of turbulences of up to 17 %, and an intensification of heat transfer of up to 25 %. Additionally, a simple examination was done to evaluate the impact of modernized air outlet ducts on the engine's efficiency and power.

Conical diffusers perform a variety of critical functions in final products (gas, hydraulic, and wind turbines, ejectors, gasifiers, combustion chambers, etc.). The purpose of this study was to experimentally study the flow distribution features in a vertical conical diffuser with different technical air supply methods to find directions for optimal movement organization. The vertical diffuser (apparatus) consisted of a conical section with an opening angle of 30° and a cylindrical section. The scientific results were obtained based on an experimental stand and the thermal imaging method. The article presents simplified equations of continuity and momentum balance for the system under consideration. Two methods of air supply to the diffuser were investigated: air supply through a single duct and air supply through 4 nozzles installed at different angles of 45°, 60°, and 70°. The experiments were carried out for stationary air movement with volumetric flow consumption through the system from 0.0018 m3/s to 0.006 m3/s. The Reynolds number for the air flow at the diffuser inlet ranged from 10,500 to 106,000. Significant differences in the flow structure for air supply to a diffuser through a single duct and nozzles were identified. The possibility of controlling the flow structure in a vertical diffuser by varying the inclination of the supply nozzles was demonstrated. Four characteristic patterns of air distribution in the diffuser were obtained: firstly, a pronounced central flow through the entire apparatus with a noticeable deviation of the flow to the right side; secondly, a local (from 30 to 75% of the apparatus height), central flow in the diffuser; thirdly, active air movement in the lower part of the diffuser with subsequent flow along the side walls of the apparatus; fourthly, multidirectional flow movement throughout the entire volume of the diffuser.

Industry and energy continue to require piston engines (PICE) at a high level worldwide. Therefore, science and technology must urgently work on improving the PICE working cycle. Improving the quality of the intake process of the working fluid into the cylinder is one of the most effective ways to improve the operational performance of PICE. The purpose of the study was to assess the impact of various cylinder head (CylH) designs on the gas-dynamic and heat-exchange qualities of air flows within an engine model's intake system. Three different CylH designs were studied: the basic configuration and upgraded cylinder heads with a square valve and a square valve port. These designs are innovative. Laboratory conditions were used to conduct the studies for stationary air flow. The experiments covered the range of Reynolds numbers from 8500 to 96,000. The intake system's gas dynamics and heat transfer were determined using the thermal anemometry method, which was based on constant-temperature hot-wire anemometers. It has been established that the use of upgraded CylHs causes an increase in the turbulence number of flow by an average of 13.5%. Additionally, it was found that the increase in the turbulence number of flow in the cylinder is about 19% when installing new CylH designs. It was shown that there was an increase in the heat transfer coefficient in the intake pipe by 10%-40% when installing modernized CylH designs in the intake system. The article focused on the problems of increasing the turbulence level and intensifying the heat transfer of stationary air flow in the intake system, specifically in PICEs. The study's findings are novel in the areas of applied gas dynamics and PICEs.

Experimental research into the boiling-up of a free jet of superheated water discharging through a short cylindrical nozzle with sharp inlet and outlet edges into the atmosphere has been carried out. The change in the shape of a liquid jet has been traced through changes in thermodynamic parameters (temperature, pressure) along the saturation line in both the visible range and the infrared spectrum. The flow shapes corresponding to various modes of boilingup have been identified. With thermal-imaging diagnostics, heterogeneities in the spray plume of a superheated liquid jet have been recorded and temperature distributions have been obtained in various sections of a boiling-up flow. The maximum temperature in the flare of a boiling-up jet has been determined at different distances from the short nozzle's exit edge.

Improving the specific, technical, economic, and environmental characteristics of piston engines (ICE) operating on alternative gaseous fuels is a pressing task for the energy and mechanical engineering industries. The aim of the study was to optimize the parameters of the ICE working cycle after replacing the base fuel (propane-butane blend) with syngas from wood sawdust to improve its technical and economic performance based on mathematical modeling. The modeling results were verified through experimental studies (differences for key parameters did not exceed 4.0%). The object of the study was an electric generator based on a single-cylinder spark ignition engine with a power of 1 kW. The article describes the main approaches to creating a mathematical model of the engine working cycle, a test bench for modeling verification, physicochemical properties of the base fuel (propane-butane blend), and laboratory syngas. It was shown that replacing the fuel from a propane-butane blend to laboratory syngas caused a decrease in engine efficiency to 33% (the efficiency of the base ICE was 0.179 vs. the efficiency of 0.119 for the converted ICE for the 0.59 kW power mode). Engine efficiency was chosen as the key criterion for optimizing the working cycle. As a result of optimization, the efficiency of the converted syngas engine was 6.1% higher than that of the base engine running on the propane-butane blend, and the power drop did not exceed 8.0%. Thus, careful fine-tuning of the working cycle parameters allows increasing the technical and economic characteristics of the syngas engine to the level of ICEs running on traditional types of fuel.

RELEVANCE of the study is determined by the fact that vertical conical diffusers are used as auxiliary devices in many technical applications in various industries (chemical industry, power engineering, technological devices, etc.).THE PURPOSE. The influence of the method (design) of air supply, the cross-sectional shape of the supply channels and nozzle tubes on the gas-dynamic structure of the flow in a vertical diffuser for different flow characteristics was assessed.METHODS. The structure (distribution) of the flow inside a vertical diffuser for supplying air using different designs of supply channels was studied on an experimental bench. Based on the thermal imaging method, the flow structure in a vertical diffuser was studied. In this study, two methods of supplying air to a vertical diffuser were studied: supplying air through one straight channel from the bottom and nozzle supplying air through four tubes. The channels and nozzles had cross sections in the shape of a circle, square and triangle. Accordingly, the influence of six air supply designs into a vertical diffuser and their influence on the gas-dynamic flow structure were studied.RESULTS. The experiments were carried out under stationary air flow conditions in the diffuser for air flow rates from 0.015 to 0.06 m3/s. The Reynolds number for the air flow at the outlet of the supply channel was in the range from 42500 to 150000. Thermograms of the flow structure in a vertical diffuser were obtained for different methods of air supply for different flow characteristics.CONCLUSION. Features of the flow structure in a vertical diffuser with traditional air supply from below through one channel consist in the formation of a pronounced central air flow along the vertical axis of the diffuser when using all channel configurations. In this case, the cross-sectional shape of the supply channel has a significant impact on the flow structure in the conical diffuser. Features of the flow structure in a vertical diffuser with nozzle air supply through four tubes are the absence of stagnant zones and a central air flow along the axis. At the same time, the use of square and triangular nozzle tubes leads to a more uniform distribution of air flow throughout the entire volume of the vertical diffuser.

The gas-dynamic and heat-exchange behaviours of air flows in gas-dynamic systems have a significant impact on the efficiency and environmental performance of most technical equipment (heat engines, power plants, heat exchangers, etc.). Therefore, it is a relevant task to obtain reliable experimental data and physical laws on the influence of cross-sectional shape and initial turbulence intensity on gas dynamics and the level of heat transfer. In this study, data were experimentally obtained on the instantaneous values of the local velocity and local heat transfer coefficients of stationary air flows in straight pipes with circular, square, and triangular cross-sections at different initial values of the turbulence intensity. The measurements were carried out with a constant temperature hot-wire anemometer, thermocouples, and pressure sensors. Based on the research results, data on the turbulence intensity and averaged local heat transfer along the length of pipes with different cross-sections were summarised. It has been established that turbulence intensity in a square pipe is up to 40% higher than in a round channel; in a triangular channel, on the contrary, it is up to 28% lower. After the air flow's initial turbulence, the relaxation of the flow in square and triangular pipes occurs faster than in a round channel. It is found that the initial intensity of turbulence leads to an increase in the averaged local heat transfer, which is typical of all investigated pipe configurations and initial conditions.

Conical diffusers are widely used in technical devices (gasifiers, turbines, combustion chambers) and technological processes (ejectors, mixers, renewable energy). The perfection of flow gas dynamics in a conical diffuser affects the intensity of heat and mass transfer processes, the quality of mixing/separation of working media and the flow characteristics of technical devices. These parameters largely determine the efficiency and productivity of the final product. This article presents an analysis of experimental data on the gas-dynamic characteristics of stationary air flows in a vertical, conical, flat diffuser under different initial boundary conditions. An experimental setup was created, measuring instruments were selected, and an automated data collection system was developed. Basic data on the gas dynamics of air flows were obtained using the thermal anemometry method. Experimental data on instantaneous values of air flow velocity in a diffuser for initial velocities from 0.4 m/s to 2.22 m/s are presented. These data were the basis for calculating and obtaining velocity fields and turbulence intensity fields of the air flow in a vertical diffuser. It is shown that the value of the initial flow velocity at the diffuser inlet has a significant effect on the gas-dynamic characteristics. In addition, a spectral analysis of the change in air flow velocity both by height and along the diffuser axis was performed. The obtained data may be useful for refining engineering calculations, verifying mathematical models, searching for technical solutions and deepening knowledge about the features of gas dynamics of air flows in vertical diffusers.

Data are presented on the gas-dynamical structure of flow in the cylinder when it is filled through poppet valves with heads in the form of a circle and a square. The studies were carried out on a laboratory setup simulating a piston internal combustion engine. The air flow through the gas-dynamical system of the engine was carried out in a stationary mode with an initial speed of 8 to 41 m/s. Thermograms of the flow structure were obtained for two control sections of this system using the thermal imaging method. It has been established that the configuration of the cylinder valve head exerts a significant impact on the structure in it and that in a cylinder with a round valve there are pronounced stagnant zones. It has been shown that the use of valves with a square head ensures more uniform filling of the cylinder with air throughout its entire volume compared to a traditional round valve. The data obtained can be useful for refining mathematical models of the process of cylinder filling and for developing new methods of modernizing valve assemblies of piston machines.

Heat engines based on reciprocating machines remain in demand as energy converters in a variety of industries around the world. The aim of the study was to evaluate the gas-dynamic, consumable and heat exchange characteristics of non-stationary air flows in a supply system with transverse profiling of valve channels based on experimental studies. Valve channels with cross sections in the form of a circle, square and triangle were used to control the consumable and heat exchange characteristics of the flows in the supply system of the reciprocating-engine model. The article presents data on changes in local velocity, volumetric airflow and instantaneous heat transfer coefficient of non-stationary airflow in supply systems with different valve channel designs. A spectral analysis of the pulsations of the local heat transfer coefficient was also performed. The Nusselt number was calculated for the studied supply systems. The figured valve channels lead to an increase in the volumetric airflow through the supply system up to 32% compared with the basic configuration. The use of a square valve channel leads to suppression of heat transfer (drop is about 15 %) compared to the basic supply system, and the use of a triangular valve channel causes an intensification of heat transfer (growth is about 17.5%). The obtained data can be useful for refining mathematical models, adjusting machine learning algorithms, and improving design methods for supply systems of reciprocating machines to improve their technical, economic, and environmental characteristics.

Heat machines based on reciprocating-engines remain in demand in various fields of engineering and technology. Therefore, further research is needed to improve the efficiency, reliability, and environmental friendliness of engines. The thermomechanical improvement of non-stationary processes in outlet systems is an appropriate way to improve engine performance. The purpose of this research is to obtain and analyse the gas-dynamic and heat transfer characteristics of pulsating gas flows in an outlet system with ducts of various designs, using a laboratory model to simulate the outlet process in an engine. Thermal anemometry is used to receive data on the instant velocity values and local heat transfer coefficient of unsteady flows in ducts. The article examines two designs of outlet ducts, namely cylindrical (basic) and conical (with a taper of 0.0225) ducts. Spectral analysis of velocity, pressure and heat transfer coefficient pulsations, assessment of turbulence intensity, and calculation of flow characteristics of pulsating flows were performed to obtain detailed information on gas dynamics in the outlet system. The use of a conical duct (in comparison with a cylindrical one) leads to a slight increase in the turbulence intensity by up to 12 %, a decrease in the heat transfer coefficient by 15-20 %, and a change in volumetric gas flow within +/- 7.5 %. Thus, the use of a conical duct will lead to the stabilisation of the flow in the outlet system, improved cleaning of the cylinder from outlet gases, a reduction in thermal stress, and a slight growth in the specific power of engines.

Improving the process of cleaning the cylinder from exhaust gases has a significant impact on the operational and environmental performance of a piston engine. The purpose of the work was to assess the influence of the exhaust pipeline design on the gas dynamics and heat transfer of a stationary flow in the cylinder and exhaust system. The article obtained data on the flow structure in the cylinder and exhaust pipelines with different cross-sectional shapes. Additionally, the values of the turbulence number and heat transfer coefficient in the profiled exhaust pipelines were determined. Cross sections in the form of a circle (base), square and equilateral triangle were used. The thermal imaging method and the thermal anemometry method were used to determine the gas-dynamic and heat transfer characteristics of stationary flows. The studies were carried out on full-scale experimental stands. It has been established that the cross-sectional shape of the exhaust pipeline has virtually no effect on the flow structure in the cylinder. Differences in flow patterns in exhaust pipes with different cross-sections for different air flow rates through the system were shown. It was revealed that there was a decrease in the flow turbulence number in the exhaust system for profiled pipelines by an average of 25

Piston machines are used in distributed generation, are in demand as auxiliary energy sources in hybrid systems and are indispensable devices in compressor technology. The purpose of this article is to develop a method for improving the quality of the cylinder filling process based on an experimental study of the gas dynamics and heat transfer of stationary and pulsating flows in an intake system with profiled channels in a piston machine's cylinder head. Experiments were carried out on full-scale models of piston machines with thermal anemometry and thermal imaging. The article examines three cross-sectional shapes for the intake port in the cylinder head: circle (basic design), square and triangle. It is established that profiled channels in a piston machine's intake system have a significant impact on the gas-dynamic, flow and heat-exchange characteristics of both stationary and pulsating air flows. It is shown that the use of profiled channels leads to a more uniform distribution of air flow throughout the entire cylinder volume and a significant reduction in stagnation zones, which should lead to a reduction in specific fuel consumption. It is established that air flow through an intake system with square and triangular ducts increases up to 30 % compared to the basic system, which should lead to an increase in power. It is found that the use of square and triangular channels leads to an increase in the flow turbulence intensity by 3... 30 % and an increase in the heat transfer coefficient to 25 % in a piston machine's intake system. On the practical side, the installation of a cylinder head with profiled channels should improve the technical, economic and environmental characteristics of piston machines.

Vertical conical diffusers are used in power engineering, chemical industry, technological processes, and other industries. The efficiency of many machines and pieces of equipment is determined by the gas-dynamic and heat-exchange perfection of processes in diffusers. This study assesses the influence of the air supply method on flow structure in a diffuser. The studies were carried out on a test bench with thermal imaging for air flow rates ranging from 0.018 to 0.057 m3/s (42,500 < Re < 150,000). Two designs were examined: (1) a conventional air supply through one channel from below and (2) a nozzle air supply through four tubes at an angle of 45° to the vertical axis. In addition, the influence of the cross-sectional shape of the supply channels of both designs was studied. It is established that the use of a conventional air supply through one channel leads to the generation of a pronounced central flow along the vertical axis (all configurations of the supply channel) and the creation of stagnant zones in the corners of the diffuser (round and triangular channels; the use of a square supply channel causes the most uniform air distribution throughout the entire volume of the diffuser (while maintaining the central flow). It is found that with nozzle air supply, there are no stagnant zones in the corners and intense air movement generation in the centre of the diffuser (round and triangular tubes) can be observed; the use of square nozzle tubes causes intense flow movement at the base of the diffuser, which quickly collapses upstream, uniformly filling the entire volume of the diffuser’s cylindrical part. The presented data can be useful for designing various machines and pieces of equipment with vertical conical diffusers.

The thermal and mechanical perfection of the processes in the gas exchange system during the filling and emptying of the cylinder makes it possible to increase the productivity and efficiency of reciprocating machines for various purposes. The study was designed to obtain experimental data on the local heat transfer of pulsating flows in the intake and outlet pipelines of a piston engine model, their analysis, and mathematical description. The scientific novelty of the study is as follows: (1) the patterns of change in the local heat transfer coefficients of pulsating gas flows in the inlet and outlet pipelines for the piston engine model were obtained for the first time; (2) a mathematical description of the experimental data on local and average heat transfer in the inlet and outlet pipelines is proposed. The physical features of the change in the rate of heat transfer in the intake and exhaust systems for a full engine cycle are discussed. A spectral analysis of the harmonic functions of the change in the local heat-transfer coefficient in gas exchange systems is performed. A set of mathematical dependencies of changes in the local and average heat-transfer coefficients of flows in the inlet and outlet pipelines on operation factors are presented. These data can be used to assess the quality of filling and cleaning the cylinder, determining thermal stresses in the details of gas exchange systems, developing devices for using exhaust gas energy, creating engine control systems, and so on. Moreover, the results obtained can be used to adjust (and test) mathematical models, as well as refine engineering methods for calculating gas exchange processes in reciprocating machines for various purposes.

The article is devoted to the gas-dynamic improvement of processes in the cylinder of an internal combustion engine by using profiled channels in the intake tract. Based on experimental studies of the gas dynamics of stationary air flows, thermograms of distribution of the gas flow inside the cylinder for the intake tract with channels having cross sections in the form of a circle, square and triangle for various initial velocities were obtained. The flow structure inside the cylinder was studied using the method of thermal survey, the average air flow velocity was determined using the method of thermal anemometry. It is established that the use of profiled channels in the intake tract leads to a significant change in the flow structure inside the cylinder, improving uniformity of distribution of the velocity field and reducing stagnant zones, and in the future it will increase the specific power of the internal combustion engine, reduce specific fuel consumption and the amount of harmful substances in the exhaust gases.

Comparison of experimental research results of gas dynamics and instantaneous local heat transfer in the intake pipes for piston internal combustion engines (ICE) without and with supercharging are presented in the article. Studies were conducted on full-scale experimental setups in terms of gas dynamic nonstationarity, which is characteristic of piston engines. It has been established that the turbocharger installation in a gas-air system of piston internal combustion engine leads to significant differences in the patterns of change in gas-dynamic and heat transfer characteristics of flows. These data can be used in a modernization of piston engines due to installation of a turbocharger or in a development of gas-air systems for piston ICE with supercharging.