Search Results (795)

Wear metal monitoring is an important component of lubricant condition monitoring but commonly relies on elemental techniques such as inductively coupled plasma optical emission spectroscopy (ICP-OES), which require dedicated laboratory infrastructure and sample preparation. This study evaluates whether Fourier-transform infrared (FT-IR) spectra of used engine oils can be combined with partial least squares (PLS) regression to provide a rapid screening estimate of iron (Fe) concentration. Used petrol and diesel engine oil samples were analyzed by FT-IR spectroscopy and ICP-OES. PLS models were developed using processed FT-IR spectra as predictor variables and ICP-OES-derived Fe concentrations as response variables. For petrol used oil samples, the optimized model employing 18 latent variables achieved a root mean squared error of 5.02 ppm and a coefficient of determination of 0.97 between measured and predicted Fe concentrations. Model loadings indicated contributions from spectral features associated with soot, oxidation, nitration, antioxidant (AO) depletion, and zinc dialkyldithiophosphate depletion. Combining petrol and diesel samples in a single model reduced predictive performance and increased uncertainty, indicating that their differing degradation pathways cannot be adequately represented by one common latent variable model. The approach does not directly measure Fe and is not intended to replace elemental analysis. Instead, it provides a rapid, low-cost screening tool for identifying samples with potentially elevated wear metal concentrations and prioritizing them for confirmatory analysis. Full article

The use of sugarcane molasses (SCM) as a sustainable stabilizing agent for geomaterials, particularly granular subbase soils, has recently attracted growing attention as an alternative to traditional stabilization methods employing cement, lime, or bitumen, which are often associated with high costs and environmental concerns. This study presents a mechanistic–experimental evaluation of SCM for stabilizing granular subbase materials at dosages of 2.5%, 5%, 7.5%, and 10% by weight of dry granular material. A comprehensive testing program was conducted, including compaction characteristics, California Bearing Ratio (CBR), resilient modulus (${\mathrm{M}}_{\mathrm{r}}$), permanent deformation under repeated loading, optical microscopy, and FTIR spectroscopy. In addition, multilayer elastic analysis using KENLAYER was performed to assess pavement structural performance in terms of critical strains and service life. The results showed that SCM significantly improved subbase performance within an optimum dosage range. The mixture containing 5% sugarcane molasses (5SCM) exhibited the highest overall performance, increasing CBR from approximately 26% to 34% and reducing accumulated permanent strain by approximately 45% compared with the control mixture. Optical microscopy and FTIR analyses supported the proposed stabilization mechanism, indicating improved particle contact at moderate SCM contents, whereas excessive SCM contents adversely affected performance due to lubrication and excessive particle-coating effects. Mechanistic analysis demonstrated that 5SCM improved pavement durability, increasing allowable load repetitions from 9.54 × 10⁵ to 1.14 × 10⁶ and extending pavement service life by approximately 20%. A durability–cost assessment further identified 5SCM as the most efficient dosage from both engineering and economic perspectives. Water immersion assessment indicated that SCM stabilization is suitable for pavement structures with effective drainage, whereas its application in continuously saturated or flood-prone environments is not recommended. Overall, SCM demonstrates strong potential as an environmentally sustainable stabilizer for granular subbase materials, with an optimum dosage of approximately 5% for enhancing both material performance and pavement durability. Full article

With the advancement of industrial IoT and artificial intelligence technologies, bearing maintenance is gradually evolving toward predictive maintenance. For large bearings, the internal grease must be replaced promptly once it has deteriorated. As the core lubrication component of such bearings, the suction and discharge device directly determines the efficiency of grease discharge and the operational stability of the bearing. To address the issue of insufficient intake capacity in existing units, this study employs the Herschel–Bulkley non-Newtonian fluid model to analyze intake characteristics and conduct multi-parameter co-optimization, revealing the underlying mechanisms by which vacuum level, grease temperature, and the chamfer structure of the grease inlet pipe influence suction performance. Based on the yield stress and shear thinning characteristics of the grease, the flow equation for the inlet section was derived, and the analytical and CFD results showed consistent trends. With the volumetric flow rate in the inlet section as the optimization objective, a multi-parameter co-optimization of the vacuum level, temperature, and chamfer radius was conducted through orthogonal experiments. The results show that under the optimal parameter combination, the inlet volumetric flow rate was significantly increased, and grease supply stability was markedly improved. The research findings provide a theoretical basis and engineering reference for the design optimization of the suction and discharge device for wind turbine bearings. Full article

Introduction/Objectives: Temporomandibular joint osteoarthritis (TMJOA) causes pain, mandibular dysfunction, fibrocartilage degradation, and synovial inflammation. Current therapies are mainly palliative and limited by rapid intra-articular clearance and insufficient disease-modifying effects. This review summarizes injectable hydrogels for TMJOA as regenerative scaffolds, drug delivery systems, joint lubricants, and mechanical buffers. Methods: Relevant studies were identified from PubMed/MEDLINE, Web of Science and Google Scholar using terms related to TMJOA, injectable hydrogels, intra-articular delivery, tissue engineering, cartilage repair, lubrication, viscosupplementation and mechanical buffering. Studies were selected if they addressed hydrogel design, biological function, mechanical performance, biosafety or translational evaluation. Results: Injectable hydrogels have been investigated mainly as bioactive regenerative scaffolds and acellular functional biomaterials. Bioactive systems may regulate inflammation and oxidative stress, deliver cells, exosomes, drugs or growth factors, and support fibrocartilage repair. Acellular systems primarily aim to improve intra-articular retention, lubrication, viscoelastic adaptation and mechanical buffering. However, current evidence remains largely preclinical, with limited validation of long-term residence, degradation behavior, TMJ-specific mechanical performance, repeat dosing, biosafety and functional outcomes. Conclusions: Injectable hydrogels represent promising multifunctional platforms for TMJOA treatment. Cell-, exosome-, and growth factor-loaded systems show regenerative potential but face manufacturing, safety, regulatory, and long-term validation challenges. Acellular multifunctional hydrogels may be more feasible for near-term translation. Clinical Significance: Injectable hydrogels may provide minimally invasive, locally sustained treatment for TMJOA by integrating symptom control, microenvironment modulation, and mechanical adaptation. Full article

The escalating global accumulation of plastic waste (PW) poses a critical obstacle to environmental sustainability, necessitating the development of viable valorization strategies. Pyrolysis process offers a thermo-chemical conversion pathway capable of transforming waste plastics into a potentially functional liquid product. This work presents a systematic and comprehensive investigation of the physicochemical, wettability, thermal stability, rheological, and tribological properties of pyrolysis oil (i.e., pyro-oil) derived from virgin linear low-density polyethylene (LLDPE) pellets to mimic the behavior of common polymers in such thermo-chemical conversion processes. Pyro-oil was produced under controlled slow pyrolysis conditions in a fixed-bed reactor at 700 °C, and its properties were benchmarked against tire-derived pyro-oil and a commercial engine oil. Chemical and structural characterization was conducted via Fourier transform infrared spectroscopy (FTIR), wavelength dispersive X-ray fluorescence (WDXRF), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). Wettability was evaluated through temperature-dependent contact angle measurements, and thermal stability was assessed by thermogravimetric analysis (TGA). Rheological profiling of the plastic pyro-oil was investigated using a rheometer apparatus at different temperatures. Lastly, the tribological properties of plastic pyro-oils at various temperatures were examined using a tribometer instrument in a ball-on-disk configuration. Results demonstrate that plastic-derived pyro-oil exhibits a hydrocarbon-dominant chemical composition similar to that of tire pyro-oil and engine oil. Its absolute viscosity is nearly similar to that of the tire pyro-oil and is lower than that of engine oil across different temperatures. Tribological testing revealed that the plastic pyro-oil results in lower friction at elevated temperatures compared to both tire pyro-oil and commercial engine oil. However, the thermal examinations showed that plastic pyro-oil has lower thermal stability than tire pyro-oil and engine oil. Overall, these findings indicate that plastic pyro-oil holds promise as a functional lubricant for low-load and moderate-temperature industrial applications, positioning PW pyrolysis as a viable contributor to circular economy strategies in the lubricants sector. Full article

Flexible graphite packing rings are widely employed in high-temperature and high-pressure valve sealing systems owing to their intrinsic lubricity and thermal stability, yet their service reliability is often compromised by low mechanical strength, pronounced creep, and unstable tribological behavior under extreme conditions. Here, we present an interface-engineered strategy to enhance the service performance of graphite packing rings via reinforcement with surface-functionalized PAN-based carbon fibers (PAN-CFs; carbonized fibers derived from polyacrylonitrile precursors). Through controlled oxidative modification of carbon fibers combined with high-temperature graphite expansion, a three-dimensional reinforced graphite network with uniform fiber dispersion was constructed. The influence of PAN-based carbon fiber (PAN-CF) content (0–7 wt%) on compressive strength, thermal stability, friction behavior, and long-term durability was systematically evaluated. An optimal performance was achieved at 5 wt% PAN-CF, featuring a ~58% increase in compressive strength, a stable friction coefficient of 0.15–0.18, and enhanced creep resistance, while retaining over 78% of the initial strength after 1000 h of sustained loading. Microstructural and complementary structural analyses suggest that these improvements are associated with interfacial mechanical anchoring, fiber embedding, and load-transfer reinforcement enabled by fiber surface functionalization and the expanded graphite architecture. This work offers a practical material-level approach to improving the long-term reliability of graphite-based sealing components in demanding industrial environments. Full article

Improving motor efficiency by reducing frictional losses in the journal bearings used in many rotating machines is critical for advancing sustainable mechanical systems, especially automobiles. This study investigates the application of microbubbles, which are known to reduce frictional drag in fluids. The incorporation of microbubbles into lubricants offers an environmentally friendly friction-reduction method that avoids chemical additives. In this work, microbubbles were generated within lubricating oil and applied to a journal bearing. Experimental measurements of friction torque during shaft rotation demonstrated that lubricating oil containing microbubbles yielded lower torque than oil without microbubbles. These results indicate that microbubbles effectively reduce friction in journal bearings. Furthermore, a transparent quartz glass bearing and acrylic shaft were used to directly observe the dynamics of microbubbles flowing within the journal bearing clearance to elucidate the underlying frictional torque reduction mechanism. Full article

Tribology is a growing field concerning reductions in the environmental footprint of tribological systems while increasing their operational efficiency by minimizing friction, wear and lubrication in an environmentally conscious manner. This review aims to discuss in detail sustainable lubrication strategies, with particular emphasis on surface modification and coating-based strategies for advanced tribological applications. The surface engineering techniques covered in this study are critically reviewed with regard to their ability to improve wear resistance, reduce friction and increase the durability of components, such as laser surface texturing (LST), nitriding, plasma treatment and advanced coating technologies such as DLC-, TiN-, CrN- and PVD-based coatings. Another key focus is on the synergy of sustainable lubricants and engineered surface coatings. The tribochemical compatibility of eco-friendly lubricants, bio-lubricants, ionic liquids and advanced coated surfaces is explained in detail, because they are essential for the formation of stable tribofilms, lubricant retention, reductions in surface degradation, and the minimization of tribological losses. They are an important component of environmental footprint, energy consumption and the thermal stability and service life of tribological components. Recent developments in coating-assisted green tribology, sustainable tribochemistry and circular sustainability concepts of the design of tribological systems are also included in the review. In addition, the review briefly outlines the use of Life Cycle Assessment (LCA) as a potential tool for the future evaluation of the environmental sustainability of tribological systems. The proposed expanded set of Green Tribology principles offers useful guidance for the implementation of tribology-based solutions toward more sustainable engineering systems and responsible resource utilization. Full article

The present study investigates the physicochemical degradation and wear metal evolution of low-viscosity SAE 0W-20 engine oil during the first service interval of a modern gasoline internal combustion engine. Two oil samples were analyzed: fresh lubricant and used oil collected after approximately 13,000 km of vehicle operation. The analysis included determination of kinematic viscosity at 100 °C (ASTM D445), total base number (ASTM D2896), FT-IR spectroscopic indicators of chemical degradation (ASTM E2412), and elemental analysis of wear and additive metals using ICP-OES (ASTM D5185). The results show a viscosity reduction from 8.5 to 7.01 mm²/s and a decrease in the alkalinity reserve to 3.7 mgKOH/g, indicating progressive lubricant aging. FT-IR analysis revealed moderate oxidation, nitration, and sulfation processes, while elemental analysis identified Cu, Fe, and Al as the dominant wear metals. The observed changes correspond primarily to normal oil aging and engine running-in processes. The results demonstrate the effectiveness of combined oil analysis techniques for monitoring lubricant degradation and early engine wear. Full article

Sapphire crystal, owing to its high hardness, chemical inertness, thermal stability, optical transparency, and superior dielectric strength, as well as resistance to scratching, abrasion, friction, and wear, is widely utilized in a broad range of engineering applications. Slicing is the most critical step in sapphire industry processing, as it largely dictates the final surface quality and morphology. Conventional wire sawing methods often lead to undesirable surface defects, while ultrasonic-assisted diamond wire sawing (UADWS) offers potential advantages through enhanced abrasive self-sharpening, micro-hammering, and improved lubricant penetration. However, its influence on sapphire slicing remains insufficiently studied. This study investigates the effects of UADWS parameters—ultrasonic amplitude, horn application position, feed speed, and wire speed—on the surface quality of sapphire crystals. Both single-factor and orthogonal five-level experiments were designed, taking wire and feed speed within industrial parameter ranges. Surface roughness (Ra) and waviness peak–valley (PV) difference were used as evaluation indices, and range and variance analyses were performed. In addition, power regression models were developed to predict Ra and PV under varying conditions. The surface morphology results from single-factor experiments reveal that increasing feed speed and wire speed reduces the effectiveness of ultrasonic assistance, while application horn position exerts only a minor influence. Overall, orthogonal analysis confirmed that the relative influence of process parameters on surface quality follows the order: feed speed > wire speed > amplitude > application horn position. These findings establish a foundation for optimizing the sawing and ultrasonic parameters of UADWS to enhance sapphire surface quality, reduce downstream processing requirements, and clarify the importance of controlling feed speed and wire speed. Full article

When predicting cavitation erosion risk in practical engineering bearings, traditional vapor cavitation models neglect the effect of dissolved air in the lubricant and fail to account for its precipitation and dynamic evolution in local low-pressure regions, leading to deviations in the prediction of cavitation extent, intensity, and distribution. Taking the main bearing of a certain type of diesel engine as the research object, a coupled cavitation model combining the Schnerr–Sauer vapor cavitation model and a Henry’s law-based gas dissolution model is established. Together with large eddy simulation (LES), the accuracy of the numerical model is verified by constructing a visualization experimental platform. Numerical analysis is then carried out to investigate the effect of dissolved air in the lubricant on the cavitating flow field of the bearing oil film under initial conditions ranging from undersaturated to saturated states (air mass concentration of 0–0.4 g/L). The results show that as the mass concentration increases, the amount of air precipitation in the near-wall region gradually increases and extends downstream. When the mass concentration reaches 0.1 g/L, the precipitated air mass reaches 50% of the vapor cavitation mass, significantly expanding the cavitation range. In the critical mass concentration range of 0.24–0.28 g/L, intense air precipitation occurs inside the oil hole and covers the entire region. Through the synergistic effects of inhibiting high-speed jets, altering the local pressure field, and competing for cavitation nuclei, the precipitated air significantly suppresses the development of near-wall vapor cavitation, and the vapor cavitation mass decreases by 83.1% at saturation. In summary, within the practical mass concentration range, the presence of dissolved air significantly enhances the gas phase intensity near the bearing bush surface and expands the cavitation range, thereby exacerbating the risk of cavitation erosion damage in this region, while having little effect on the oil supply performance of the oil hole. Full article

The use of aluminium alloys in internal combustion engines is an effective strategy for increasing energy efficiency, reducing component mass, and lowering harmful gas emissions. This paper analyses different types of Al–Si alloys (hypoeutectic, eutectic, and hypereutectic) in the context of their use in the production of engine blocks, pistons, and cylinder liners. Special attention is given to the tribological challenges of using aluminium, such as increased wear and lower strength compared to traditional materials such as cast iron. Modern methods for improving wear resistance are discussed, including alloying, the application of solid lubricants and protective coatings (Ni–SiC, Al₂O₃, MoS₂, etc.), and advanced surface engineering technologies such as PTWA, HVOF, and laser alloying techniques. This paper also presents practical examples of industrial applications, highlighting their essential role in the development of lightweight, high–performance internal combustion engines. This review highlights that the combination of optimized alloy composition and advanced surface engineering technologies represents the most effective approach for enhancing the durability and tribological performance of lightweight engine components. Full article

The accessory gearbox of an aero-engine operates under high-speed and heavy-load conditions, where insufficient lubrication may lead to oil-film failure, increased frictional losses, and reduced transmission reliability. Therefore, understanding oil-jet injection and tooth surface oil-film spreading characteristics is essential for improving lubrication performance. In this study, a three-dimensional geometric model incorporating the meshing region and oil nozzles was established based on a typical accessory gear pair. The model employs the VOF multiphase flow approach and the standard k-ε turbulence model, coupled with dynamic mesh techniques to accurately capture the transient interactions between gear rotation and oil–air two-phase flow. Numerical simulations reveal the dynamic evolution of oil injection, impingement on the tooth surface, oil-film spreading, and transport into the meshing zone, while the effects of injection velocity and nozzle length on lubrication performance are quantitatively analyzed. Results indicate that an injection velocity of 45–55 m/s yields optimal oil-film coverage and uniformity, and a nozzle length of h = 30 mm minimizes jet energy decay and airflow interference, achieving uniform oil filling in the meshing zone. The optimal lubrication performance for accessory gears is obtained at an injection velocity of 45–55 m/s and a nozzle length of 30 mm. This study provides a reference for the design optimization of accessory gear lubrication systems. Full article

Bubble-assisted drag reduction is a promising strategy for improving the energy efficiency of underwater bodies, but its effectiveness depends not only on air injection but also on the ability of the body geometry to retain bubbles close to the surface. Drawing inspiration from the air retention and bubble release mechanisms of penguin plumage, this study examines whether a simplified penguin-inspired geometry can enhance bubble coverage compared to a conventional axisymmetric body. Prototypes featuring a penguin-inspired shape and a torpedo shape, each equipped with an air diffuser and injection holes, were designed and evaluated in a dedicated towing tank. At low air pressure, the penguin-inspired body demonstrated a 31.5% reduction in drag coefficient compared to the condition without bubbles. In contrast, the torpedo-shaped body did not exhibit a reduction in drag coefficient under identical air-injection conditions. Both geometries showed diminished performance at higher pressures, likely due to bubble growth, coalescence, and decreased near-wall retention. These findings indicate that the effectiveness of bubble-assisted drag reduction is highly dependent on body geometry and that bioinspired body morphology may play a critical role in sustaining a layer rich in air bubbles near the surface. This study offers a preliminary experimental assessment of penguin-inspired air lubrication and identifies bubble size, air-flow control, and quantification of surface coverage as key areas for future research. Full article

Piston engines are the core power units of large unmanned aerial vehicles (UAVs), and the characteristics of their thermal-fluid working processes directly affect the power performance and operational reliability of UAVs. To address the difficulty of simultaneously ensuring simulation accuracy and computational efficiency in conventional piston engine models, a lightweight simulation method for the thermal-fluid modeling of piston engines is proposed. A Rotax 915 piston engine for large UAVs was selected as the target engine. A one-dimensional thermal-fluid working process model was first established in GT-Power, and a Kriging surrogate model was then constructed to develop a lightweight simulation framework, enabling the fast and accurate prediction of key engine response parameters. The proposed framework enables the rapid prediction of engine performance, propeller load, and lubrication responses under UAV mission-related operating conditions. The surrogate model delivered favorable prediction accuracy against the GT-Power model (R² > 0.95, MAPE < 5%); flight data verification (excluding cold start) presented a MAPE of 11% and 27% for exhaust gas temperature and lubricating oil pressure, respectively. The proposed lightweight model was validated against actual UAV flight data, and the results show that it can effectively capture the variation trends of exhaust gas temperature and lubricating oil pressure. Further simulation results indicate that with increasing altitude, engine power decreases whereas brake specific fuel consumption (BSFC) increases. With increasing engine speed, engine power increases, BSFC decreases, and lubricating oil pressure declines. Under different flight phases, the takeoff phase shows the highest engine power and BSFC, the cruise phase corresponds to the maximum propeller torque and thrust, and the descent phase exhibits the lowest overall load level. The results provide a useful basis for performance evaluation, condition monitoring, and digital-twin-oriented modeling of piston engines for large UAVs. Full article