Search Results (27)

The mechanisms of in-service damage caused to the cylinder units of internal combustion engines (ICE) during their operation are analyzed. Long-term operation under harsh conditions, failure to comply with operating conditions, and breach of design and technology standards were found to be the major reasons for the initiation and propagation of in-service defects. The life of ICE cylinder liners is proposed to be extended by forming regular microreliefs. This represents a promising surface engineering strategy. Axial lines of the regular microrelief’s grooves were considered using analytical dependencies, which helped determine their coordinates and those of their equidistant. The authors simulated the pattern according to which the groove axes of type II regular microrelief could be aligned on the inner surface of the cylinder liner. To this end, a tool with three deforming elements was used. Technical means have been developed to implement this technology on the working surfaces of the liner–piston group’s mating parts. Full article

The damping groove structure of the port plate plays a crucial role in the pulsation suppression, vibration reduction, and noise optimization of the piston pump. Different damping groove structures have a significant impact on the flow distribution process during the normal operation of the port plate, affecting the pump outlet flow and pressure pulsations, which in turn influence the noise level of the piston pump. Therefore, the damping groove in the piston pump is one of the key structures influencing the pump’s pressure and cavitation behavior. To address the pressure shocks and oscillations caused by the distribution process in the piston pump, this study proposes a novel damping groove and performs CFD simulations on the non-damped groove. The analysis focuses on the pressure pulsation characteristics in the plunger chamber and the cavitation behavior of the pump. Additionally, an optimization analysis of the structural parameters of the new damping groove is conducted, which effectively reduces pressure shocks and cavitation in the swash plate axial piston pump. This study provides a theoretical foundation for improving the performance and lifespan of piston pumps. Full article

The objective of this study is to analyze the piston rebound energy storage characteristics of the nitrogen-hydraulic combined impact hammer and to investigate the manner in which the piston rebound energy is converted and utilized. The kinetic equation of the impact hammer system is established. A numerical calculation model is constructed based on AMEsim, which incorporates the piston, cylinders, reversing valve, accumulator, power source, drill rod, and impacted device. The performance experiment system is designed, the oil pressure experiment and the piston motion experiment are constructed, and the accuracy of the numerical calculation model is verified by comparing the numerical calculation results with the experimental results. This paper investigates the fundamental principles of the piston rebound energy storage and analyzes the relationship between the opening percentage of the reversing valve high-pressure port and the piston rebound energy storage at the outset of the rebound stage. Furthermore, the influence of the length of the piston middle section and the number of high-pressure grooves in the signal chamber on the piston rebound energy storage is investigated. Finally, the experimental comparison allows for an analysis of the influence of the piston rebound energy storage on the performance of the nitrogen-hydraulic combined impact hammer. Full article

With the marine industry’s demands for carbon reduction and increased reliability, the friction and wear performance of marine engines is becoming increasingly important. MAX phase materials show great potential in marine engine tribopair materials due to their unique microstructure and performance. The typical MAX phase material Ti₃AlC₂ was combined with MoDTC and added to the lubricant containing ZDDP additive for the tribopair composed of chromium-based ceramic composite coated steel (CKS) piston rings and cast iron cylinder liners under impact-sliding conditions. Compared to Ti₃AlC₂ alone, the friction coefficient and wear depth of the designed composite additive MoDTC/Ti₃AlC₂ were reduced by 36.9% and 41.4%, respectively. The worn surface lubricated with the Ti₃AlC₂/MoDTC composite additive showed fewer scratches with significantly less plastic deformation and clearer honing grooves. The multi-component tribofilm containing FeS, MoS₂, MoO₃, ZnO, TiO₂, Al2O₃, unoxidised particles, short-chain phosphates, and some ZnS was present on the worn cylinder liner surface. The synergistic effect of Ti₃AlC₂, MoDTC and ZDDP additives in the lubricant can isolate the mutual contact, generate a solid tribofilm and reduce the scratching. This can provide some guidance for the development of high-performance lubricant additives under impact-sliding conditions. Full article

The high- and low-pressure switching of the axial piston pump is realized by the structure of the valve plate, and the buffer-groove structure on the valve plate is very important to reduce the pressure shock and flow fluctuation. In order to optimize the structural parameters of the buffer tank of the piston pump, the influence of the triangular-groove structure on the outlet pressure–flow characteristics was analyzed, and the low-pulsation buffer-groove structure was designed. First, the relationship between the structure of the triangular buffer tank and the output pressure and flow characteristics of the pump was analyzed theoretically. The Computational Fluid Dynamics (CFD) method was used to calculate the pressure and flow characteristics of the whole pump flow field of the triangular-groove structure, and the influence of the buffer-groove structure parameters on the outlet flow pulsation characteristics was studied. The multi-objective optimization algorithm was used to optimize the structure parameters of the buffer tank, and the optimized structure significantly reduced the outlet pressure–flow pulsation of the piston pump. The results show that, after optimization, the width angle of the front and rear triangular groove is 82.3°, the depth angle is 12.7°, the optimized pressure pulsation rate is 0.3%, and the optimized flow pulsation rate is 13.7%. Full article

In a hydraulic system, a micro variable pump is required to be high pressure and high speed, and this work presents a new type of 2D bivariable pump structure in which the worm gear and worm mechanism are used to rotate the cylinder block to change the flow distribution state of the cylinder window and the piston groove to change the displacement of the 2D pump. The flow–pressure mathematical model of the 2D variable pump is established to analyze the relationship between pump displacement and the pump cylinder rotation angle and the effects of variable displacement on pump pressure characteristics, flow characteristics, and volume efficiency in Matlab. During the experiment, we tested the change in the corresponding pump output flow when the cylinder rotation angle is 0~12°, which verifies the correctness of the variable calculation model. The experimental results indicate that the volume efficiency and mechanical efficiency of the single-piston 2D pump are reduced to different degrees after variable displacement, the volume efficiency is reduced by approximately 3% at most, and the mechanical efficiency is reduced by approximately 5% at most. Full article

The Three-Piece Oil Control Ring (TPOCR) is becoming a viable option for heavy duty gas and hydrogen engines due to the low particle concentration in these engines. Although direct oil leakage from the gap is not likely to happen with the misalignment of the upper and lower rail gaps, there exist other less-apparent oil leaking mechanisms through the TPOCR. This work is targeted at understanding the oil leakage’s source and destination through the rail and liner interfaces across the whole cycle. The 2D Laser Induced Fluorescence technique was applied on an optical engine to study the oil transport behavior. Combined with a TPOCR model for dynamics and lubrication, the mechanisms that cause rail twist and oil scraping by the upper rail were analyzed. It was found that the symmetrical rail can scrape the oil up in the up-strokes. The scraped oil first accumulates in the clearance between the upper rail and groove, as well as at the upper corner of the rail Outer Diameter before being transferred to both the third land and liner when the piston changes direction at Top Dead Center. Rails with an asymmetrical profile can reduce or enhance these effects depending the orientation of the rails. This study provides findings that could help design the engine to better control Lubricate Oil Consumption and properly lubricate the Top Dead Center’s dry region at the same time. Full article

Internal combustion engines, during their operation, subject the piston to high-temperature and high-pressure conditions, requiring it to endure intense, continuous reciprocating motion. This strenuous process leads to significant wear and tear. Among the engine’s crucial components, the piston ring plays a pivotal role but is particularly susceptible to wear. Therefore, extensive research has been devoted to investigating the wear of piston rings, a critical sealing component within internal combustion engines. To address the high cost of existing coating methods, which hinders widespread application, we propose a bionic design approach inspired by groove structures observed on earthworm bodies, aimed at enhancing the wear resistance of piston rings. Bionic piston rings featuring optimally designed groove structures inspired by the earthworm’s anatomy were designed. These rings exhibited varying groove depths (1 mm, 2 mm, and 3 mm), groove widths (0.1 mm, 0.3 mm, and 0.5 mm), and groove spacings (0.1 mm, 0.2 mm, and 0.3 mm). We conducted thermal–structural coupling analyses on both standard piston rings and these bionic counterparts. The results revealed that the maximum stress was concentrated at the first piston ring, precisely at the opposing region of the end gap. Thus, the initial piston ring endured the primary frictional losses. Moreover, a comparison of stress levels between bionic rings and the standard ring revealed that the bionic groove structure substantially reduced stress and minimized stress concentration, thus enhancing wear resistance. Groove width had the most notable influence on wear performance, followed by groove depth and groove spacing. Optimal wear resistance was achieved when the groove depth was 3 mm, groove width was 0.1 mm, and groove spacing was 0.1 mm. Subsequently, we constructed a piston ring friction test bench to validate the wear resistance of the most effective piston ring. The results indicated that the wear resistance of the bionic piston ring exceeded that of the standard piston ring by up to 19.627%. Therefore, incorporating a bionic groove structure within the piston ring can effectively reduce surface friction and enhance wear resistance. This, in turn, can enhance the operational lifespan of internal combustion engines under favorable working conditions. Full article

With advantages of high efficiency and low cost, DTH hammer drilling has been highly applied in various drilling projects. When drilling in unconsolidated formations, it is prone to drilling accidents such as drilling tools sticking or burying. Thus, a bidirectional pneumatic DTH hammer is designed to drill boreholes using forward impact and release sticking drilling tools using backward impact. With a floating gas distribution mechanism, impact strokes of the DTH hammer piston can be changed when flat keys are in a different position of the key grooves on the gas distribution shaft. In drilling mode, the piston has a larger impact stroke and can impact the anvil at high speeds to drive the bit breaking rocks. When drilling tools become stuck, by changing to a smaller impact stroke, the piston can impact backward on the gas distribution valve to break rocks above the DTH hammer so sticking drilling tools can be released. According to the structure and working principle of the bidirectional pneumatic DTH hammer, a physical model based on the pneumatic transmission circuit is established; then, a simulation model is built with pneumatic transmission module components in software of SimulationX 4.1 student version. Piston velocities, displacements, and impact energy are analyzed, with main factors including piston mass, total weight of the DTH hammer, compressed air pressure, and backward impact stroke being considered. Analysis results show that working characteristics of the DTH hammer are fairly affected by piston mass and compressed air pressure. Based on the changing laws of the impact frequency, peak of impact velocity, and impact energy, a piston mass of 18 kg, total weight of 125 kg, gas source pressure of 2.2 MPa, and lifting distance of 60 mm for backward impact were recommended. To verify the performance of the bidirectional pneumatic DTH hammer, field experiments were carried out in the gravel stratums. The bidirectional DTH hammer was in good working condition and the maximum drilling rate can reach up to 1.5 m/min. By lifting the DTH hammer away from the bottom of the borehole and pumping compressed air, the DTH hammer piston could achieve a high frequency backward impact. There are no drilling tools’ sticking or burying accidents in the drilling experiments. The bidirectional pneumatic DTH hammer can effectively drill boreholes in loose formations and deal with drilling tools’ sticking or burying accidents. Full article

This paper proposes a CFD methodology for the simulation of the slipper’s dynamics of a swash-plate axial piston unit under actual operating conditions. The study considers a typical slipper design, including a vented groove at the swash-plate interface. The dynamic fluid–body interaction (DFBI) model is exploited to find the instantaneous position of the slipper, while the morphing approach is adopted to cope with the corresponding mesh distortion. A modular approach is adopted to ensure high-quality mesh on the entire slipper surface and sliding interfaces provide the fluid dynamic connection between neighboring regions. The external forces acting on the slipper are included by means of user-defined lookup tables with the simulation estimating the lift force induced by fluid compression. Moreover, the force produced by the metal-to-metal contact between the slipper and the swash plate is modeled through a specific tool of the software. The pressure signal over an entire revolution of the pump is taken as an input of the simulation and a variable time step is used to manage the high-pressure gradients occurring in the regions of inner and outer dead points of the piston. The weakly compressible characteristic of the fluid is considered by a specific pressure-dependent density approach, and the two-equation eddy-viscosity k-ω SST (shear stress transport) model is used to assess the turbulent behavior of the flow. Furthermore, the transitional model predicts the onset of transition, thus solving different equations depending on whether the flow enters a laminar or turbulent regime. In conclusion, the proposed methodology investigates the motion of the slipper in response to several external forces acting on the component. The numerical results are discussed in terms of variable clearance height, pressure distribution within the gap, and lift forces acting on the slipper under specific pump operations. Full article

The article describes a multi-grid algorithm for integrating the Reynolds equation for hydrodynamic pressures in the lubricating film of a heavy-loaded journal bearing. This equation is the basic one in solving the tasks of designing friction units of piston- and rotary machines. Lubrication sources of various configurations in the form of grooves and holes located on the friction surfaces were taken into account. The version of the multi-grid algorithm developed by the authors is based on Brandt’s work. At each level of grids, not only the convergence of the solution is controlled, but also the rate of convergence. The pressure equation was approximated by finite differences using the control volume method and passed to a system of algebraic equations, which were solved by the Seidel method. Bessel formulas were used as the interpolation operator. The function for taking into account the non-Newtonian properties of the lubricant is based on the power law. Comparison of the developed algorithm with other versions showed high efficiency. The use of multi-grid algorithms makes it possible to perform multi-variant calculations of the dynamics of heavily loaded bearings. As a result of the calculations, the characteristics of the connecting rod bearing of the heat engine, as well as the multilayer bearing of the turbocharger, are presented. Full article

Friction loss in an internal combustion engine largely depends on elastohydrodynamic lubrication. The piston compression ring is a contributor to such parasitic losses in the piston subsystem. The complex elastodynamics of the ring are responsible for the transient and regime-altering film that affects the elastohydrodynamic lubrication of the ring liner contact conjunction. The current paper will discuss the ring radial, lateral deformation, and axial twist, and its effect on the film profile of the compression ring and its subsequent effect on tribological characteristics like elastohydrodynamic pressure, friction, and lubricant. A finite difference technique is used to solve the elastohydrodynamic issue of elastodynamic piston compression by introducing the elastodynamically influenced film thickness into the lubrication model. The results show that consideration of the elastodynamics predicts a 23.53% reduction in friction power loss in the power stroke due to the elastodynamic ring compared to the rigid ring. The elastodynamic effect improves the lubricant oil flow into the conjunction. A finite element simulation predicts a von-Mises stress of 0.414 N/mm², and a maximum deformation of 0.513 µm at the core and coating interface is observed at the ring–ring groove contact. The sustainability of EHL in this case largely depends on the ring–liner elastodynamics. Full article

The effect of cylinder liners on engine performance is substantial. Typically, the cylinder surfaces were plateau honed. However, recently additional dimples or grooves were created on them. This work discusses the tribological impacts of textured cylinder liner surfaces based on a review of the literature. The results of the experimental research obtained using test rigs and fired engines were critically reviewed. In addition, the results of the modeling are shown. Circular oil pockets and grooves perpendicular to the sliding direction of piston rings of small depths were typically used. Surface texturing of the cylinder liners governs lubrication between the cylinder liner and the piston ring by an increase in oil film thickness near the reversal points leading to reductions in friction force and wear and in the fired engine to a decrease in fuel consumption and to an increase in power or torque. The correct texturing pattern ensures a decrease in the oil consumption, blow-by, and emissions of the internal combustion engine compared to plateau-honed surfaces. Considerations of future challenges are also addressed. The volume of lubricant reservoir in surface topography, called oil capacity, should be a substantial parameter characterizing textured surfaces. Full article

During the present study, a double groove texture was designed on the surface of a piston ring to improve the sealing performance between the piston ring and cylinder liner. The experimental design method was used to fabricate the test plan according to the groove width, depth, and spacing. By using the thermal–structural coupling analysis method, the finite element analysis of the standard piston ring and the textured piston ring was carried out to simulate the deformation state of the cylinder liner system of the piston ring group during the working stroke. The piston rings with different parameters designed by the test scheme were manufactured by wire electrical discharge machining, and the self-made experiment device carried out the sealing test. The results showed that the groove texture could improve the sealing performance of the piston ring, and the analyzed results demonstrated that the groove texture had little effect on the maximum deformation of the piston ring. Still, it could significantly reduce the minimum deformation of the piston ring group. A piston ring with groove texture would improve the sealing performance and reduce the deformation during the work stroke. During the test, the average deformation of the No.7 piston ring group, with a groove depth of 1 mm, a groove width of 0.5 mm, and a groove spacing of 0.1 mm, was the smallest, about 29.6% lower than that of the standard piston ring group. The sealing performance of the No.7 piston ring group was the best, and the reduction rate of the top gas leakage rate was 52.18%. During the present study, the sealing performance of the piston ring was improved by designing the grooved structure on the piston ring surface, thereby improving the fuel economy and power performance of the engine. The present study could provide a reference for the engineering field to design a piston ring with high sealing performance. Full article

Tribological interactions between the piston groove and ring in combustion engines have a significant influence on mechanical friction losses. Based on the analysis of the distribution of forces acting on the piston, the conditions for the friction tests were selected. The research was carried out on composites reinforced with silicon carbide (SiC_p), glassy carbon (GC_p), and a hybrid mixture of particles (SiC_p + GC_p). Tribological tests were carried out under extremely unfavorable dry sliding conditions using a pin-on-block tester. The friction of coefficient and wear values of the matrix alloy, composites, and iron were compared. Profilometry was used to perform quantitative and qualitative analyses of the wear tracks formed on the tested surfaces. The effect of the presence of reinforcing particles on the geometry of working surfaces was also evaluated. The obtained results show that AlSi12CuNiMg/SiC_p and AlSi12CuNiMg/SiC_p + GC_p composites provided satisfactory effects towards stabilizing the friction coefficient and reducing the wear of tested tribological couples. This may provide a new solution dedicated to an important system, which is the piston groove/piston ring in diesel engines. Full article