The benefits of surface textures on rolling and sliding tribological contacts have been an exciting field of study over the last three decades. Laser surface texturing (LST) is a comparatively newer texturing methodology that yields repeatable precise microtextures. A detailed overview of the available literature on the various works in this field is consolidated in this review. The main focus is on the effect of surface textures (with focus on laser ablation) for nonconformal contacts with elastohydrodynamic lubrication (EHL), as in rolling element bearings. A review of literature on textured contacts for the EHL regime, emphasizing its effect on friction, wear, rolling contact fatigue, vibration, texture geometry, and numerical simulation studies, is carried out with possibilities of future works. Basic details on LST processes and various parameters of the laser beam that determine the texture geometry are discussed. Being a field of continuing research, the review paper will aid in understanding the present developments and future directions in laser-based surface texturing for nonconformal tribological contacts.
Optimizing the bearing design is an essential step to maintain safe operation and extend the bearing life. Taguchi method is one of the powerful methods in this direction, which can be used to assess the geometrical design parameters under shaft deviation. Shaft deviation is unavoidable in the industrial applications of journal bearing. It results from installation and manufacturing errors, bearing deformation, asymmetric loading, and many other sources. This work investigates the use of three bearing profiles with a wide range of geometrical characteristics to minimize the deviation negative effects. These designs modified the inner bearing surface in a linear, parabolic, or cubic shape. A general 3D deviation representation is considered in the analysis where the deviations in the horizontal and vertical directions are taken into consideration. The analysis is performed for a finite-length journal bearing using the Taguchi method to determine the optimal design characteristics. This analysis is achieved in terms of the rotor critical speed and the film thickness of the lubricant. Furthermore, the system response to an impact load is analyzed. The finite difference method is used in the analysis to solve the governing equations of the hydrodynamic problem, and the 4th-order Range Kutta solution is considered to solve the motion equations of the rotor under the impact load. Results show that using the suggested designs enhances the system’s critical speed, elevates the thickness of the lubricant layer, and extends the safe operation limits under impact load. The parabolic profile gives the most effective outcome where the shaft trajectory under impact excitation is very close to the ideal journal-bearing case. The suggested design reduces the maximum pressure by 17.07%, increases the minimum film thickness by 175.04%, and increases the critical speed by 23.42%.
Automobile engines require lubrication to lessen the impact of friction due to the high levels of wear and frictional heat generated by the sliding parts. Wear and friction will cause engine parts to endure for less time, be less reliable, and require more maintenance. Diesel fuel can potentially be replaced with biodiesel among other fuels. Diesel engines have a serious problem with equipment that is lubricated by the fuel itself. This study’s goal is to assess the influence of bio-additives on the diesel fuel tribological behavior and energy balance during the car’s idle running, acceleration, constant speed, and braking. Lubricity issues with reformulated diesel and lubricity test procedures are explained. The relationship between tribology and bio-additives is also briefly illustrated. According to the literature, adding bio-additives to fuel boosts its lubricity. Biodiesel has long been considered an additive with excellent lubricant properties. Even in small amounts, adding biodiesel to diesel fuel can increase its lubricity without the need for conventional lubricity additives. This is especially true for diesel fuel with ultralow sulfur. Diesel fuel characteristics determine the precise blending percentage needed to provide the proper lubricity of maximum 520 μm testing wear scars with a high-frequency reciprocating rig (HFRR), although 2% biodiesel nearly invariably imparts adequate lubricity to biodiesel blends. Tall oil fatty acid (TOFA) was one of the bio-additives investigated by HFRR. When the additive concentration was raised from 0 to 500 g/g, the wear scar diameter (WSD) of nonadditive diesel fuel was lowered by 60.3%, from 630 to 250 μm, and the coefficient of friction (COF) was lowered by 95.7%, from 0.47 to 0.02.
This paper includes the laboratory and experimental methodology used to compare the effect of using mineral, semi-synthetic, and synthetic engine oil on the parts wear of a four-stroke gasoline internal composition engine (ICE). Three test platforms included three engines with identical, technical, and design specifications. They were operated under the same investment, ambient, and climatic conditions. The first engine was equipped with synthetic oil, the second with semi-synthetic oil, and the third with mineral engine oil. All of them had (SAE10W40 API: SL/CF). All test platforms were operated through three stages with variable loads for up to 1,500 operating hours (hr). Oil drain intervals (ODI) were every 100 operating hours. Used oil samples were taken to analyze the physical and chemical characteristics of viscosity, total base number TBN, flash point, metals wear Irion (Fe), copper (Cu), chromium (Cr), and wear index (WI) to investigate the effect of all oils on the wear of engine parts and by comparing the changes in wear. The used oil analysis (UOA) results were drawn that showed the superiority of the use of synthetic oil over semi-synthetic and mineral. It prolonged the technical engine’s lifetime.
Cavitation in hydro turbines causes component deterioration that requires continuous and costly maintenance in the hydroelectric power generation stations. The Tarbela Dam Hydel Project (TDHP) in Pakistan is facing a cavitation problem in the Francis Turbine components, such as the runner and draft tube. Simulation work has been performed to examine and quantify the cavitation rate as a function of the suction head (SH) and flow velocity (FV) by utilizing a homogeneous cavitation model. The result shows that pressure fluctuation is maximum for overcrowded conditions and minimum for rated load conditions. Moreover, a higher cavitation rate is found for the part and overcrowded conditions compared to the rated load condition. Additionally, the cavitation rate becomes 50% higher when the SH increases from 5.54 to 12.34 m. Moreover, SEM results have verified the CFD results that higher FV and SH enhance the cavitation rate. Furthermore, the numerical work is validated by simplified hydrofoil geometry. The computational fluid dynamics results presented a good arrangement with the experimental data.
