The pursuit of enhanced fuel efficiency has become increasingly critical amid growing concerns over energy scarcity and climate change. This review analyzes experimental techniques for evaluating the tribological performance of valve-train components in internal combustion engines. Key performance parameters including friction coefficient, frictional torque, surface roughness, roller slip, lubricant film thickness, follower rotation, and wear are systematically examined, with both qualitative and quantitative insights. Various valve-train configurations are assessed under diverse conditions, such as engine speed, load, temperature, valve-train type, lubricant oils, additives, and surface modifications. Experimental techniques include strain gauges, torque transducers, and piezoelectric sensors for friction measurement while wear assessment utilizes methods such as stylus profilometry, scanning electron microscopy (SEM)-based analysis, and radioactive tracer techniques. Advanced sensing technologies, including eddy current sensors, giant magneto-resistive (GMR) sensors, and optical sensors, are explored for follower rotation and roller slip measurement. The integration of artificial intelligence (AI) and machine learning (ML) algorithms for friction and wear analysis is also discussed, making a shift toward predictive, data-driven tribological assessments. However, research gaps persist, particularly in hybrid engine valve-train tribology under transient conditions like start-stop cycles and low-load operation. This review highlights the need for real-time monitoring systems, adaptive lubrication strategies, and predictive maintenance models to improve durability and fuel efficiency. Ultimately, this study can serve as a valuable resource for researchers and original equipment manufacturers (OEMs), offering essential insights into selecting appropriate techniques for evaluating tribological performance parameters. By refining evaluation methods, it supports advancements in fuel-efficient and high-performance internal combustion engine technologies.

The pursuit for fuel-efficient and durable engines has intensified the need to understand frictional losses in valvetrain systems operating mainly under boundary and mixed lubrication. This study introduces an advanced in-situ technique based on giant magneto-resistive (GMR) chip to directly measure independent tappet and shim rotation linked with friction measurement in a production engine head without altering its geometry. Complementary experiments were conducted on a reciprocating rig using real engine components to validate the findings. Tests with SAE 30 base oil and four friction modifiers namely MoDTC, Molyvan, Polymeric, and an Organic friction modifier (OFM) showed that MoDTC consistently delivered the lowest frictional torque but also suppressed tappet rotation, while the polymeric friction modifier yielded the highest tappet rotation with relatively modest friction reduction across all camshaft speeds and lubricant temperatures. The base oil produced the highest friction torque overall but minimal rotation, demonstrating the strong influence of tappet-bore resistance. Shim rotation was generally low but became significant at low camshaft speed and high lubricant temperature. The analysis revealed that nearly 10 % of cam-tappet friction contributes to tappet rotation, demonstrating that the equilibrium between cam-tappet and tappet-bore friction governs rotational dynamics. Reciprocating tribometer tests verified the friction reducing performance of MoDTC but showed a different ranking for the other modifiers due to the absence of rotational motion. This suggests that reciprocating sliding tribometers may not fully replicate real engine conditions. The results reveal that friction modifiers influence both tribological losses and the coupled rotational dynamics within the valvetrain.

This study investigates the influence of laser surface texturing (LST) on tribological performance by optimizing texture geometry, orientation, and density under varying lubrication regimes. AISI 5115 steel surfaces were textured with triangle, ellipse, and circle patterns at 5–20

Mobile robots are increasingly utilized in agriculture to automate labor-intensive tasks such as weeding, sowing, harvesting and soil analysis. Recently, agricultural robots have been developed to detect and remove weeds using mechanical tools or precise herbicide sprays. Mechanical weeding is inefficient over large fields, and herbicides harm the soil ecosystem. Laser weeding with mobile robots has emerged as a sustainable alternative in precision farming. In this paper, we present an autonomous weeding robot that uses controlled exposure to a low energy laser beam for weed removal. The proposed robot is six-wheeled with a novel double four-bar suspension for higher stability. The laser is guided towards the detected weeds by a three-dimensional linear actuation mechanism. Field tests have demonstrated the robot's capability to navigate agricultural terrains effectively by overcoming obstacles up to 15 cm in height. At an optimal speed of 42.5 cm/s, the robot achieves a weed detection rate of 86.2% and operating time of 87 seconds per meter. The laser actuation mechanism maintains a minimal mean positional error of 1.54 mm, combined with a high hit rate of 97%, ensuring effective and accurate weed removal. This combination of speed, accuracy, and efficiency highlights the robot's potential for significantly enhancing precision farming practices.

This paper presents a novel, non-intrusive measurement technique to independently monitor the absolute rotation of the tappet and the relative rotation of a shim in a direct-acting valvetrain of a production engine. The system integrates ultra-compact giant magnetoresistive (GMR) sensors and custom slip rings, enabling real time monitoring without modifying engine geometry or lubrication conditions. Most existing studies on engine valvetrain friction lack the ability to capture the actual rotational behaviour of tappet and shim, assuming both components to function as a single unit. The proposed measurement technique overcomes this limitation, providing new insights into the distinct motion of these components under engine operating conditions. Tests were conducted at multiple camshaft speeds and oil temperatures using a multigrade lubricant. The results revealed that conventional friction measurements alone do not fully capture the dynamic behaviour of the valvetrain follower system. While friction increased with temperature, tappet rotation unexpectedly decreased. Independent shim measurements indicated that a significant portion of rotational motion was transferred to the shim under specific conditions. This behaviour, especially evident at intermediate oil temperatures, highlights the role of surface texture in promoting lateral motion and redistributing frictional energy. By isolating tappet and shim rotation, this measurement approach not only enhances the understanding of valvetrain friction mechanisms but also provides a pathway for optimizing component design and surface engineering to reduce friction and improve fuel economy in modern engines.

The study of tribological applications requires measuring various parameters, including RPMs, friction, and wear. The useful information is sometimes not readily available in a measurement and requires further postprocessing to extract that information. In this research, a production engine test rig has been developed to study a direct-acting valvetrain’s tribological performance for various operating conditions. The measurement of the drive torque is carried out by using a shaft-to-shaft torque transducer. The total drive torque is a combination of geometric torque and frictional torque. The geometric torque is not affected by changes in parameters such as surface modification or lubricant chemistry but the frictional torque changes. We need to extract the frictional torque from the total drive torque to study the effect of any parameter or operating condition change on friction. As variation in frictional torque helps the tribologists to compare the performance of different parameter changes. This paper explains the complete procedure of measuring the experimental frictional torque from drive torque data. In this study, the frictional torque variation between an untextured and a textured tappet shim is studied for a direct acting cam tappet contact of a real production engine.

This research investigated the tribological performance of phosphonium-based ionic liquid Tri hexyl tetra decyl-phosphonium bis (2, 4, 4-trimethylpentyl) phosphinate (IL) when used as an additive at a concentration of 1wt% to Cotton seed oil (CSO), Rattan Jot oil (RJO), Waste Cooking oil (WCO) and Polyalphaolefin (PAO) at different operating conditions. The results were compared with conventional PAO base oil. The tribological performance of all lubricants was studied using a Vertical Universal Testing Machine (MMW1A) and wear scar diameter were measured using an electronic microscope OLYMPUS DX-1000. The results indicated that the addition of ionic liquid further enhanced the tribological performance in terms of wear for all bio-lubricants except for waste cooking oil. However, the addition of ionic liquid does not have much effect on the tribological performance of PAO. Rattan Jot oil was found to have the best tribological properties with the addition of ionic liquid.

Reduced wear and friction are directly related to longer component service lives and increased energy efficiency. The mechanisms used to achieve this goal in mechanical systems include the study of lubricant chemistry, surface coating, and surface modification. Significant research has been conducted on friction reduction of valve trains of internal combustion engines using surface modifications such as coatings and surface texturing. Here, an experimental approach has been adopted to investigate the effect of micro surface texturing on Thermo-Elastohydrodynamically Lubricated cam/tappet contact in a direct-acting valve train. A commercial vehicle valve train has been instrumented to study the effect of varying surface texture area density on friction under realistic engine operating conditions. Fiber laser surface texturing has been used to microtexture three samples of tappet shims with texture densities of 5%, 8%, and 10%. The tests have been run at four engine speeds—300, 500, 700, and 900 RPM—and three temperatures—30 °C, 60 °C, and 90 °C. The experimental results show a significant friction reduction of up to 18.33% for textured shims at the temperature of 90 °C. The friction reduction performance of the 8% textured shim has been optimum for all RPMs at the higher temperatures.

Reduction in friction ensures fuel economy, control on emissions and durability of components in internal combustion engines. A modern gasoline internal combustion engine was instrumented to determine the friction values at the cam–roller interface considering the effects of surface treatment and engine operating state. A series of tests under different operating speeds and lubricant inlet temperatures were undertaken using both an original surface roller and a Wonder Process Craft (WPC) surface-treated engine roller. The results clearly revealed a substantial reduction in friction magnitude for the WPC surface-treated engine roller in comparison to the original roller while operating under similar conditions, indicating their strong potential for employment in engines. An increase in friction with the rise in temperature was also observed for both types of rollers, whereas increased lubricant entraining velocity due to higher operating speed had the opposite impact. A considerable reduction in frictional drive torque ranging from 8% to 28% was observed by employing the WPC-treated roller in comparison to original/untreated roller at various operating conditions, which signifies the strong potential for employment of WPC surface treatment in the roller/follower valve train engines.

https://www.elsevier.com/about/policies/article-withdrawal). This article has been retracted at the authors' request and approved by the Editor in Chief. In this article, authors proposed and analyzed novel fractional order controllers (original contribution of the authors) for UAVs swarm formation and for the numerical validations, a simulation test bench (originally designed by the same group of authors) was utilized. The test bench that was published in another article by the same group of authors (https://www.mdpi.com/1424-8220/21/7/2401), was not properly cited in the current article. As such the authors deem it necessary to have their article withdrawn in the current form. The authors apologize to the scientific community for any inconveniences or challenges resulting from the publication and withdrawal of this article.

This article has been retracted at the authors' request and approved by the Editor in Chief. In this article, authors proposed and analyzed novel fractional order controllers (original contribution of the authors) for UAVs swarm formation and for the numerical validations, a simulation test bench (originally designed by the same group of authors) was utilized. The test bench that was published in another article by the same group of authors (https://www.mdpi.com/1424-8220/21/7/2401), was not properly cited in the current article. As such the authors deem it necessary to have their article withdrawn in the current form. The authors apologize to the scientific community for any inconveniences or challenges resulting from the publication and withdrawal of this article. (C) 2023 Production and hosting by Elsevier Ltd. on behalf of Chinese Society of Aeronautics and Astronautics. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

This research was conducted through the experimentation on the High-Speed Diesel (HSD) Engine to determine the accuracy of the widely used classical empirical models (Eichelberg, Woschni, and Hohenberg) for the estimation of in-cylinder Gas-to-Wall Spatially Averaged Instantaneous Convective Heat Transfer Coefficient (HTC) at part-load conditions with retrofitted Out-Cylinder Water Injection (OWI) System. Absence of the availability of any accuracy determination methodology for HTC estimation models in water injected diesel engines has led to the development of this novel analytical methodology. For this research, in-cylinder pressure was experimentally measured at varying injected water mass flow rates in air intake manifold of the engine. Obtained data was then used for the analysis of multiple thermodynamic parameters, i.e. HTC, Heat Loss to Cylinder Walls (HLCW) and Engine Aggregate Heat Release (EAHR) to study the combustion behaviour of the engine. The Efficiency of Combustion (EOC) was estimated through the proposed comparison method between the Fuel Aggregate Heat Release (FAHR) and EAHR value calculated from each model separately for different Water Injection Rates (WIR). The Degree of Accuracy (DOA) of each HTC model was determined by the EOC value. It was proposed that larger the EOC value, more accurate will be the HTC model. So, through decision-making in developed algorithm, Woschni model appeared as the most accurate model for the determination of HTC for HSD Engine retrofitted with OWI due to its obtained 84% EOC value in comparison with the normal standard of 98% EOC for diesel engines without water injection systems.

The terahertz (THz) region has much appeal for differentiating between hydrate systems and for physically characterizing pharmaceutical drug materials. The present study employs THz absorption spectroscopy to investigate the effect of heating on dehydration and hydration in α-lactose monohydrate. Distinctive THz absorption spectra were observed following various heating durations. The THz absorption spectra for α-lactose monohydrate and anhydrous α-lactose exhibit clear differences. Pure α-lactose monohydrate displays clear absorption peaks at 0.53, 1.05, 1.11, 1.33, and 1.56 THz. The complete dehydration of α-lactose monohydrate takes only 15 mins at 145°C (418 K). Moreover, the THz refractive index of α-lactose monohydrate decreases during dehydration. The dehydration of α-lactose monohydrate was also studied using Beer–Lambert law to compare THz absorption spectra as functions of the heating time. The absorption coefficient spectra recorded at 0.53 and 1.35 THz for α-lactose monohydrate after different dehydration times vary linearly with the remaining water content.

In recent times, multiple Unmanned Aerial Vehicles (UAVs) are being widely utilized in several areas of applications such as agriculture, surveillance, disaster management, search and rescue operations. Degree of robustness of applied control schemes determines how accurate a swarm of UAVs accomplish group tasks. Formation and trajectory tracking controllers are required for the swarm of multiple UAVs. Factors like external environmental effects, parametric uncertainties and wind gusts make the controller design process as a challenging task. This article proposes fractional order formation and trajectory tacking controllers for multiple quad-rotors using Super Twisting Sliding Mode Control (STSMC) technique. To compensate the effects of the disturbances due to parametric uncertainties and wind gusts, Lyapunov function based adaptive controllers are formulated. Moreover, Lyapunov theorem is used to guarantee the stability of the proposed controllers. Three types of controllers, namely fixed gain STSMC and fractional order Adaptive Super Twisting Sliding Mode Control (ASTSMC) methods are tested for the swarm of UAVs by performing the numerical simulations in MATLAB/Simulink environment. From the presented results, it is verified that in presence of wind disturbances and parametric uncertainties, the proposed fractional order ASTSMC technique showed improved robustness as compared to the fixed gain STSMC and integer order ASTSMC.

Series of water tunnel experiments are performed to study the improvement in energy harvesting by vortex-induced vibrations. Inverted C-shape cylinders with different cut angles are placed in the uniform fluid flow and electrical energy is harvested using the undulating behavior of the piezo-flag in the downstream vortices. Experimental results demonstrate different flapping modes like poorly and optimal coupling with the wake flow. It is also showed that the streamwise gap and flow speed have a significant impact on the amplitude and flapping frequency, which results in the variation of the energy output of piezo-flag. The results indicate that the highest gain in output power is 66% for an inverted C-shape cylinder with a 120° cut angle compared to a circular cylinder performance. For each cylinder and flow velocity, it is also observed that there exists a critical streamwise gap for which vortex shedding does not produce any energy using piezo-flag due to poor coupling with wake flow. The results show that there is no significant difference in the performance of circular and 60° inverted C-shape cylinders regarding energy harvesting. However, changing the shape and cut angle leads to a remarkable increase in the flapping amplitude and its growth rate along with the dominant frequency. Particle Image Velocimetry (PIV) experimentation also endorses the results as wake dynamics is in good agreement with the energy efficiency improvement. Therefore, a 120° cut angle configuration holds a vivid preeminence over a circular cylinder as the kinetic source of a fluid energy harvester. The present study contributes effectively to harvesting energy from impinging vortices by tuning the streamwise gap, flow velocity, and cut angle of the inverted C-shape cylinder.

Leader follower formation of unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs) has found numerous applications such as surveillance of critical infrastructure, industrial automation and disaster management emergency. For completion of high precision group tasks, the choice of appropriate control mechanism is of utmost importance. In presence of environmental effects,external disturbances and parametric uncertainties in the UAVs and UGV models, the controller design process is a challenging task. In order to address the aforementioned problems and to ensure minimum tracking errors and fast convergence of the states, this article proposes an adaptive robust formation and trajectory tracking control scheme for a leader follower formation of UAVs and UGV using Non-Singular Terminal Super Twisting Sliding Mode Control Method.Adaptive compensators are derived based on Lyapunov function method and stability of the proposed controllers is guaranteed. Two variants of the control schemes namely Adaptive Super Twisting SMC (AST-SMC) and Adaptive Non-Singular Terminal Super Twisting SMC (ANSTS-SMC) are tested using numerical simulations performed in MATLAB/Simulink. From the results presented, and with the proposed ANSTS-SMC control scheme, the measured [X Y] tracking errors for leader, follower1 and follower2 UAVs are [0 0.01]m,[0.01 0.02]m and [0.01, 0.02]m respectively, While with the AST-SMC method the peak [X Y] tracking errors for leader, follower 1 and follower2 UAVs are [0.05 0.05]m,[0.1 0.2]m and [0.05 0.1]m respectively. The proposed leader follower formation can be effectively used to monitor solar/PV panels and cables in large solar parks.

Skid-steered vehicles (SSV) are gaining huge importance in the market due to their applications like construction, agricultural work, material handling etc. The accuracy of performing such tasks require a robust control algorithm. The design of such controller is very challenging task due to external disturbances caused by wheel-ground interaction and aerodynamic effects. This paper proposes robust fractional and integral order fuzzy sliding mode controllers (FSMC, FFSMC) for a skid-steered vehicles with varying coefficient of friction and a displaced center of gravity (CG). FFSMC controller reduces the outcome of forces generated as a result of ground tire interaction during skidding and friction variations. The proposed controllers are implemented for a four-wheel SSV under high-speed turning motion. A simulation environment is constructed by implementing the SSV dynamics with wheel-road model and the performance of the proposed algorithms is tested. The simulation test is conducted for a Pioneer-3AT (P-3AT) robot SSV vehicle with displaced CG and variable coefficient of tires friction. Simulation results demonstrate the efficiency of the proposed FFSMC algorithm in term of reduced state errors and minimum chattering. The proposed controller compensates the effect of different responses of the wheels generated as a result of variable CG. The chattering phenomenon generated by conventional SMCs is also minimized by fuzzy tuning approach.

Diesel particulate filters (DPF) are typically used for particle filtration in vehicle exhausts after a treatment system. The monolith inside a DPF is a symmetrical column structure, frequently an axisymmetric cylinder structure where filtration and regeneration occur. Due to the complex structure before the symmetric monolith, the internal particle distribution is not uniform, which leads to an uneven temperature change when regeneration occurs. During thermal regeneration, the temperature field inside a DPF is affected by the particle load, exhaust temperature and exhaust flow. The relationship between the temperature gradient and velocity vector is also a key factor influencing regeneration performance. Based on the particle-loading test method, a bench for thermal distribution testing during regeneration was built. Via experiments and simulations, the temperature field in an axisymmetric monolith during particle combustion given an uneven particle distribution was analyzed. Through field synergy analysis of the temperature and velocity fields in the monolith, the influence of connection cones with different structures on heat transfer enhancement was studied. The results indicated that compared with a monolith with a conventional linear cone, the radial temperature gradient is 1.1 °C/mm lower, the area of enhanced regeneration is larger, and the regeneration rate is improved in the monolith with a streamlined cone.

The environmental concerns associated with artificially formulated engine oils have forced a shift towards bio-based lubricants. The deposition of hard coatings on engine components and migrating to environmentally friendly green lubricants can help in this regard. Chemically modified forms of vegetable oils, with better low-temperature characteristics and enhanced thermo-oxidative stability, are suitable substitutes to conventional lubricant base oils. The research presented in this manuscript was undertaken to experimentally investigate the wear and friction performance of a possible future generation of an environmentally friendly bio-based lubricant as a potential replacement for conventional engine lubricants. In order to quantify the tribological benefits which can be gained by the deposition of DLC coatings, (an (a-C:H) hydrogenated DLC coating and an (a-C:H:W) tungsten-doped DLC coating) were applied on the cam/tappet interface of a direct acting valve train assembly of an internal combustion engine. The tribological correlation between DLC-coated engine components, lubricant base oils and lubricant additives have been thoroughly investigated in this study using actual engine operating conditions. Two additive-free base oils (polyalphaolefines (PAO) and chemically-modified palm oil (TMP)) and two multi-additive-containing lubricants were used in this investigation. Real-time drive torque was measured to determine the friction force, detailed post-test analysis was performed, which involved the use of a specialized jig to measure camlobe wear. An optical profilometer was used to measure the wear on the tappet, high-resolution scanning electron microscopy was employed to study the wear mechanism and energy-dispersive X-ray spectroscopy was performed on the tested samples to qualitatively access the degradation of the coating. When using additive-free TMP, a low friction coefficient was observed for the cam/tappet interface. The presence of additives further improved the friction characteristics of TMP, resulting in reduced average friction torque values. A tremendous enhancement in wear performance was recorded with a-C:H-coated parts and the coating was able to withstand the test conditions with little or no delamination.

Recently, formation flying of multiple unmanned aerial vehicles (UAVs) found numerous applications in various areas such as surveillance, industrial automation and disaster management. The accuracy and reliability for performing group tasks by multiple UAVs is highly dependent on the applied control strategy. The formation and trajectories of multiple UAVs are governed by two separate controllers, namely formation and trajectory tracking controllers respectively. In presence of environmental effects, disturbances due to wind and parametric uncertainties, the controller design process is a challenging task. This article proposes a robust adaptive formation and trajectory tacking control of multiple quad-rotor UAVs using super twisting sliding mode control method. In the proposed design, Lyapunov function-based adaptive disturbance estimators are used to compensate for the effects of external disturbances and parametric uncertainties. The stability of the proposed controllers is guaranteed using Lyapunov theorems. Two variants of the control schemes, namely fixed gain super twisting SMC (STSMC) and adaptive super twisting SMC (ASTSMC) are tested using numerical simulations performed in MATLAB/Simulink. From the results presented, it is verified that in presence of disturbances, the proposed ASTSMC controller exhibits enhanced robustness as compared to the fixed gain STSMC.