Search Results (347)

Novel fiber-reinforced polysiloxane composites (FRPCs) using various fibers infiltrated with a high char yield polysiloxane resin were developed and tested under extreme aerothermal environments. Techneglas manufactures the preceramic polysiloxane resin. FRPCs using glass, silica, carbon, graphite, carbon/polybenzimidazole, alumina, and quartz fibers in different architectures were manufactured by the Koo Research Group. Characterization of thermal stability, flammability, ablation, thermophysical, and mechanical properties of these FRPCs was performed. Thermal stability properties of these FRPCs were characterized using thermogravimetric analysis, and flammability properties using microscale combustion calorimetry. Ablation properties using an oxy-acetylene test bed with advanced diagnostics were performed at several heat fluxes and exposure times. Recession rate, mass loss rate, front surface temperature, and back-face heat-soaked temperature are criteria to compare material performance. The microstructures of these pre- and post-tested FRPCs were investigated using scanning electron microscopy and micro-computed tomography. Thermophysical properties of these FRPCs in virgin and char states were characterized at elevated temperatures. Using these material properties and surface thermochemistry analysis, material response modeling was performed and validated with aerothermal test data. The composites’ tensile, compression, and flexural properties were conducted via ASTM standards. These FRPCs compared favorably with legacy phenolic-based ablatives under similar extreme aerothermal environments. Full article

The rapid expansion of Unmanned Aerial Vehicle (UAV) applications in both civilian and military sectors has intensified the demand for propulsion systems capable of delivering higher speed, increased endurance, and improved payload capacity. While battery-electric propulsion remains dominant for small UAV platforms, its limited energy density restricts operational range and mission flexibility. As a result, micro gas engines have emerged as a viable alternative for applications requiring high power-to-weight ratios and sustained high-speed operation. This review examines the fundamentals, scaling effects, and classification of micro gas turbine propulsion systems used in UAV applications, with emphasis on micro turbojets and related hybrid configurations. The paper discusses the thermodynamic principles governing micro gas engines and analyzes the aerodynamic, thermal, and combustion challenges associated with miniaturization, including low Reynolds number effects, tip leakage losses, thermal management limitations, and combustion instability. Furthermore, the study reviews the operational characteristics and mission suitability of different propulsion architectures for reconnaissance UAVs, high-speed UAVs, including reconnaissance and loitering platforms, target drones, and hybrid-electric aerial platforms. Recent developments involving additive manufacturing, advanced control systems, recuperated cycles, and hybrid-electric integration are also evaluated as enabling technologies for next-generation UAV propulsion. The findings demonstrate that although micro gas turbines continue to face important efficiency and manufacturing challenges at reduced scales, they remain essential for mission profiles that exceed the capabilities of purely electric propulsion systems. Full article

This work examines the performance, combustion, and emission characteristics of a diesel engine coated with a ceramic thermal barrier coating and fueled with emulsified Jatropha biodiesel blended with water and butanol. A low heat rejection (LHR) engine was prepared by depositing a 100 µm NiCrAlY bond coat and a 200 µm of 8YSZ ceramic top coat via air plasma spraying. B20W10Bu5, B20W10Bu10, and B20W10Bu15 ternary emulsions were successfully produced using ultrasonic homogenization. The experimental outcomes indicate that the ceramic-coated engine exhibited higher thermal efficiency than that of the conventional engine. The highest performance was achieved with B20W10Bu10 fuel, which resulted in a 7.4% increase in the brake thermal efficiency and a 7.8% decrease in the brake-specific fuel consumption relative to the results for the conventional coated diesel engine. Hydrocarbons, carbon monoxide, and smoke emissions decreased considerably due to the combined impacts of oxygenated fuel composition, micro-explosions, and thermal insulation capability. It can be seen from the discussion above that the utilization of a ceramic thermal barrier coating and the Jatropha-based ternary emulsion fuel, especially B20W10Bu10, shows great promise for enhancing engine performance while lowering exhaust emissions. Full article

This study numerically investigates the combustion characteristics of four catalytic micro-burners with different channel geometries: a straight-channel burner (Burner 1), a symmetric U-bend burner (Burner 2), and two asymmetric U-bend burners with either a wider inlet channel (Burner 3) or a wider recirculating channel (Burner 4). A steady-state, two-dimensional mathematical model accounting for gas-phase and catalytic reactions of propane on Pt/Al₂O₃ is employed. The results show that U-bend configurations significantly reduce the ignition equivalence ratio compared to the straight-channel design, with Burner 4 exhibiting the lowest value of 0.45. At an equivalence ratio of 0.85, Burner 4 achieves the highest maximum temperature and the most upstream flame location, attributed to enhanced heat recirculation and prolonged residence time in the wider recirculating channel. Temperature and propane mass fraction distributions reveal strong thermal coupling between the inlet and recirculating channels in asymmetric designs. The contribution of catalytic reactions to total heat release remains within a narrow range across the examined equivalence ratios for all U-bend burners, whereas Burner 1 shows a much higher catalytic contribution (~87%) due to suppressed gas-phase reactions. The U-bend geometries also exhibit lower heat loss ratios than the straight channel. The maximum wall temperature gradient increases with equivalence ratio, and the ranking among the three U-bend burners varies with operating conditions, indicating that geometry-specific thermal stress should be considered in practical design. Full article

Geometric asymmetry in recirculating micro-burners remains underexplored in catalytic micro-combustion research, despite its potential to significantly influence ignition behavior. This numerical study investigates the ignition and combustion characteristics of four micro-channel catalytic burners with distinct geometric configurations, aiming to evaluate the role of asymmetry on combustion behavior. Burner 1 is a straight-channel design without heat recirculation. Burners 2–4 are U-bend recirculating configurations: Burner 2 with symmetric channel sizes, Burner 3 with a wider inlet channel, and Burner 4 with a narrower inlet channel. A two-dimensional computational fluid dynamics model with a one-step global propane oxidation mechanism and catalytic wall reactions is employed. The results show that Burner 1 exhibits the highest ignition temperature (555 K) and shortest ignition delay (28.5 s) due to its low thermal mass. Among U-bend burners, Burner 4 achieves the lowest ignition temperature (530 K) and the highest steady-state combustion temperature (1726 K), owing to reduced recirculation velocity and enhanced thermal feedback. Burner 2 shows moderate performance, while Burner 3 gives the weakest combustion intensity among recirculating designs. The heterogeneous reaction contribution is highest in Burner 1 (69.3%) and lowest in Burners 2 and 3 (~55%). Asymmetric channel sizing, particularly a narrow catalytic channel combined with a wide recirculation channel (Burner 4), significantly improves ignition and combustion performance under cold-start conditions. Full article

The decarbonization of energy systems has intensified interest in hydrogen-enriched natural gas (H₂NG) as a transitional fuel for combined heat and power (CHP) units and micro-CHP systems. This review consolidates experimental and numerical studies that explore the energy, environmental, and techno-economic implications of H₂NG blends in CHP applications. Research conducted over the last decade highlights that enriching natural gas with hydrogen extends the flammability limits, enhances combustion stability, and reduces CO₂ and CO emissions, while maintaining or improving electrical efficiency. However, these benefits are accompanied by higher NO_x formation under stoichiometric conditions, which can be mitigated by operating under lean-burn regimes. The review further examines hybrid solutions that integrate electrolyzers, photovoltaic systems, and oxygen-enriched combustion to improve system flexibility and sustainability. The findings consistently show that moderate hydrogen fractions (5–20% vol.) provide optimal trade-offs between efficiency gains and emission control, supporting the role of H₂NG as an intermediate step toward fully hydrogen-powered CHP technologies. Technical challenges related to ignition control, thermal recovery efficiency, and infrastructure adaptation are also discussed, along with emerging strategies for techno-economic optimization. This comprehensive assessment contributes to understanding how hydrogen blending can accelerate the transition to low-carbon, distributed energy systems. Full article

The development of low-emission and reliable propulsion systems is essential for extending the operational capability of unmanned aerial vehicles (UAVs). Although aviation decarbonization is widely recognized as an important objective, it must be considered within the broader context of limited renewable-energy availability. Recent system-level analyses of transportation decarbonization have shown that the allocation of renewable electricity and sustainable fuels should prioritize sectors where direct electrification is most efficient, while hard-to-electrify sectors require alternative pathways. Aviation is one of the most difficult transport sectors to electrify because of strict energy-density requirements, especially for long-endurance airborne platforms. Therefore, sustainable liquid fuels and hybrid propulsion systems should not be considered universal replacements for electrification, but rather complementary solutions for applications where batteries alone cannot provide the required endurance, payload capacity or operational flexibility. In this context, the present study focuses on alcohol–kerosene blends for hybrid UAV power systems, where liquid-fuel energy density and partial emission reduction remain relevant engineering requirements. This work provides one of the first systematic experimental evaluations of ethanol–, butanol– and octanol–kerosene blends in a micro-turboprop engine operating as part of a hybrid UAV power-generation architecture. Unlike previous studies focused mainly on micro-turbojet thrust response, the present work evaluates the coupled influence of alcohol chain length and blending ratio on exhaust gas temperature, gaseous emissions, electrical output and operational stability under multi-load conditions representative of UAV operation. Jet-A and nine alcohol–kerosene blends containing 10%, 20% and 30% ethanol, butanol or octanol by volume were tested over four operating regimes, from idle to 2500 W electrical load. The results show that ethanol blends provided the strongest CO reduction, with E30 reducing CO by 24.9% relative to Jet-A under R3, while E10 offered the most balanced behavior across the full operating range. Higher ethanol fractions improved CO suppression but introduced NOx and low-load stability penalties. Octanol blends, particularly O20, exhibited the most kerosene-like and stable response, supporting reliable power delivery with reduced operational variability. Butanol blends showed intermediate behavior without providing a dominant advantage. A multi-criteria evaluation combining emissions, EGT behavior, relative performance, operational stability and cost identified E10 as the best overall compromise for hybrid UAV use. The study demonstrates that alcohol chain length produces nonlinear system-level effects in hybrid micro-turboprop architectures and provides an experimental basis for fuel selection in low-emission UAV power systems. Full article

With the increasing demands on energy efficiency and dynamic stability of modern combustion engines (e.g., TDI systems), conventional powder metallurgy materials are reaching their limits in terms of fatigue life and surface integrity. This scientific problem has led to the need to develop hybrid metal matrix (MMC) systems that use in situ hard phase formation. This study presents a comparative analysis of two real industrial components representing hybrid systems with a uniquely high content of titanium and vanadium (>1% by weight). The Ni-Mo-Ti system and the high-carbon C-Cu-Ti system were compared. The samples were processed by steam oxidation and plasma nitriding at 200 °C after sintering. The experimental methodology included chemical analysis on the Bruker Q2 ION 2 instrument, 10-point EDX analysis (Phenom), measurement of the apparent hardness of HV10 and dynamic ball-on-disc tribological tests at a load of 5.00 N supplemented by 3D profilometry. The results showed that the Ni-Mo-Ti system achieves higher hardness at functional edges (256 HV10) and three times higher resistance to deep penetration (11.46 μm vs. 34.67 μm) compared to the C-Cu-Ti system. Topographic analysis confirmed the positive role of porosity as a micro-reservoir for abrasion particles (negative Ssk). The study confirms that the nickel–molybdenum matrix ensures more efficient fixation of in situ generated TiC carbides, thus providing higher functional stability for automotive applications, which was verified by the non-destructive vibroacoustic diagnostics of Polytec PSV-500. Full article

This paper presents a numerical comparative study on the ignition characteristics of straight-channel and U-bend micro catalytic combustors, with particular focus on the role of inlet velocity. A two-dimensional computational fluid dynamics model with coupled gas-phase and surface catalytic reaction kinetics for propane combustion is developed using a fluid simulation program ANSYS Fluent. The catalyst coating (Pt/Al₂O₃) is modeled as a zero-thickness reaction surface, and the U-bend design features an uncoated recirculating channel to ensure identical catalyst loading between the two configurations. Simulations are conducted over an inlet velocity range of 0.25–8 m/s. Key ignition and combustion metrics including ignition temperature, ignition time, maximum combustion temperature, heterogeneous reaction contribution, and thermal/species field distributions are systematically compared. Results reveal a crossover in relative performance depending on flow regime. At low velocities (≤2 m/s), the straight-channel combustor exhibits lower ignition temperatures; at high velocities (≥4 m/s), the U-bend design achieves superior ignition performance with lower ignition temperatures (e.g., 526 K vs. 555 K at 8 m/s) and higher combustion temperatures (1726 K vs. 1474 K at 8 m/s). However, the straight-channel combustor consistently yields shorter ignition times across all velocities (25.9–108.6 s) compared to the U-bend (52.6–145.2 s). The heterogeneous reaction contribution decreases with increasing inlet velocity for both designs, with the straight-channel maintaining higher values than the U-bend. The U-bend achieves higher maximum temperatures due to enhanced heat recirculation, particularly at high flow rates. The findings suggest that the U-bend configuration is advantageous for high-flow-rate applications requiring low ignition temperatures and high combustion temperatures, whereas the straight-channel design is preferable for rapid cold-start scenarios. Full article

This study provides an empirical assessment of greenhouse gas emissions and the environmental performance of hybrid vehicles in the European Union. The analysis integrates a macro-level examination of nitrous oxide (N₂O) emission trends in EU Member States for road and pipeline transport with a micro-level econometric investigation of emissions generated by the internal combustion engines of hybrid vehicles. The empirical analysis is based on a large sample of hybrid vehicles of different brands and variants, including 1350 observations used to examine the relationship between CO₂ emissions and fuel consumption per 100 km, and 123 observations to analyze nitrogen oxides (NO_x) emissions. CO₂ is assessed as the principal greenhouse gas emitted during vehicle operation, while NO_x (NO and NO₂) is examined as a major regulated atmospheric pollutant relevant to environmental performance. A bibliometric analysis of NO_x-related publications further highlights increasing scientific attention to this pollutant, supporting the relevance of the current study. Results reveal significant heterogeneity across hybrid vehicle models in terms of fuel consumption and NO_x emissions, indicating that environmental performance is strongly influenced by technological design and operational characteristics. Robust multiple regression models (R² = 0.84 for vehicle with low CO₂ emissions, 0.82 for high CO₂ emissions and R² = 0.72 for NO_x emissions) revealed significant correlations between pollutant emissions and fuel consumption, providing valuable tools for predicting emissions and informing environmental policies and hybrid vehicle design. Overall, the findings indicate that hybrid vehicles can contribute to improved environmental performance and lower greenhouse gas emissions relative to conventional vehicles, while their effectiveness depends on model specific characteristics and broader sectoral emission dynamics in the EU. These insights provide evidence for policymakers and industry stakeholders to support the transition toward cleaner vehicle technologies and align climate neutrality targets in the European Union. Full article

The transition toward sustainable aviation fuels for unmanned aerial vehicle propulsion requires alternative fuel blends that reduce emissions while maintaining stable power generation. This study investigates the combustion performance, electrical output, emission behavior, and near-field pollutant dispersion of butanol–kerosene blends in a hybrid micro-turboprop propulsion platform representative of UAV applications. Conventional kerosene and three butanol–kerosene blends, containing 10%, 20%, and 30% butanol by volume, were tested under four operating regimes ranging from idle to approximately 2.5 kW electrical load. Exhaust gas temperature, CO, NO, NOx, SO₂, electrical power output, throttle response, and pollutant dispersion behavior were evaluated experimentally, while polynomial regression was applied to quantify throttle–power relationships. The results show that the 20% butanol blend provided the most favorable overall performance. Relative to conventional kerosene, B20 achieved approximately 4.8% higher electrical power output at equivalent throttle settings, reduced fuel demand by nearly 3.9%, and decreased the throttle requirement for 2 kW electrical output by almost 5%. In terms of emissions, B20 reduced CO formation across low and intermediate operating regimes while maintaining moderate NOx levels and stable exhaust gas temperature behavior. Increasing butanol content also improved plume homogenization: the anisotropy index decreased from 2.41 for B10 to 1.96 for B20 and 1.58 for B30, while high-concentration plume regions were reduced by up to 31%. However, B30 introduced stronger evaporative cooling, ignition delay effects, and reduced mid-load responsiveness. Overall, moderate butanol blending, particularly B20, represents the most balanced solution for reducing the environmental footprint of hybrid UAV micro-turboprop propulsion without significant performance penalties. Full article

To investigate the micro-scale combustion characteristics of composite propellants, a two-dimensional BDP micro-scale model for ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/HTPB) was developed. Numerical simulations were conducted to evaluate how AP particle size and mass fraction influence the diffusion behavior, flame structure, and gas-phase temperature distribution. The results indicate that increasing the AP particle size significantly enhances the overall diffusion characteristics, which gradually become the dominant factor in the combustion process. Specifically, the flame exhibits more pronounced diffusion features, and the temperature distribution near the burning surface becomes increasingly non-uniform. Furthermore, as AP particle size increases, each gaseous component demonstrates greater diffusion tendencies, requiring a thicker mixing layer to achieve complete homogenization. Regarding the AP mass fraction, its increase strengthens the thermal feedback from the gas phase to the solid phase, leading to a slight rise in the burning surface temperature. While the diffusion characteristics of AP-derived macromolecules remain relatively stable, the concentration of residual oxygen increases with higher AP mass fractions. Full article

For electric vehicles, accurate real-time estimation of the road friction coefficient is critical for maintaining stability, as the millisecond-level response of electric motors and the integration of regenerative braking demand higher perception fidelity than traditional internal combustion vehicles. This paper proposes a methodological framework for road friction estimation specifically designed for intelligent E-Chassis based on micro-signal features of intelligent tires and deep learning. An intelligent tire system, integrated with tri-axial accelerometers and strain gauges, was installed on the front-left wheel of a test vehicle to capture raw dynamic signals during transitions from cement to snow-covered surfaces across a velocity gradient of 10–50 km/h. The Savitzky–Golay convolutional smoothing algorithm was applied to reconstruct the high-frequency raw signals, enabling the extraction of a five-dimensional feature vector comprising vehicle velocity, peak strain, contact patch width, peak-to-peak acceleration, and signal standard deviation. The study revealed a natural filtering effect originating from the porous elastic properties of snow, resulting in a 60–70% reduction in signal standard deviation compared to cement, accompanied by a cliff-like feature collapse at the moment of snow entry. A BP neural network model with a 5-7-1 architecture achieved an identification accuracy of 96.2% on the test set, facilitating a rapid real-time prediction of the friction coefficient transitioning from 0.75 to 0.23. Unlike traditional methods, the proposed approach does not rely on high slip ratios and can complete identification within the first physical rotation cycle. This provides a robust physical criterion for the torque vectoring and regenerative braking stability of intelligent electric vehicles in extreme environments. Full article

To solve the problems of poor fuel atomization effect, low combustion efficiency, and uneven temperature distribution of the evaporator tube of a certain micro turbojet engine, a structural optimization design method based on a genetic algorithm is proposed. Taking the inner diameter of the evaporator tube, the diameter of the nozzle hole, the number of nozzle holes as design variables, the fuel atomization particle size (d₅₀), combustion efficiency (η), and maximum wall temperature (T_max) as optimization objectives, a multi-objective optimization mathematical model is established. The iterative optimization is carried out through the selection, crossover, and mutation operations of the genetic algorithm, and the optimization effect is verified by combining CFD (Computational Fluid Dynamics) numerical simulation. The results show that when the inner diameter of the evaporator tube is 2.6 mm, the diameter of the nozzle hole is 0.8 mm and the number of nozzle holes is eight, the fuel atomization particle size of the evaporator tube is reduced by 18.3%, the combustion efficiency is increased by 7.6%, and the maximum wall temperature is decreased by 12.4%, which significantly improves the working performance of the evaporator tube and provides an effective reference for the optimization design of key components of micro turbojet engines. Full article

The growing importance of renewable energy sources and the implementation of circular economy principles highlight the need for the rational management of biomass combustion by-products. The aim of this study was to assess the chemical composition of ash produced through the combustion of various biomass fractions from four varieties of common hazel (Corylus avellana L.) in the context of its potential for secondary use. The analysis covered the shells, husks, leaves, and shoots of the following varieties: Kataloński, Olbrzymi z Halle, Olga, and Webba Cenny. Combustion was carried out under laboratory conditions at a temperature of 550 °C, and the content of macro- and micro-element oxides (P₂O₅, K₂O, CaO, SO₃, Cl, SiO₂, MnO, Fe₂O₃, NiO, CuO) and potentially toxic elements (ZnO, TiO₂, Cr₂O₃) was determined using the EDXRF method. The results showed significant variation in the chemical composition of the ash depending on the biomass fraction and variety. The highest P₂O₅ content was found in the leaves of the Kataloński variety (5.02), whilst the highest K₂O concentration was found in the husk of the Olga variety (47.33%). The maximum CaO content was found in the leaves of the Webba Cenny variety (32.60). The leaf and husk fractions were characterised by the highest content of nutrients of fertilising importance, whilst the shells exhibited the lowest values for most macronutrients. The content of potentially toxic elements was low. The results obtained indicate that the selective utilisation of specific fractions of hazel biomass can increase the efficiency of mineral recovery whilst maintaining environmental safety, in line with the principles of the circular economy. Full article