Piston Motion Research Articles

Dual-loop Segmented Piston Trajectory Control of Free Piston Linear Generator based on sliding mode control

Free piston linear generator (FPLG) can be applied as range extender for electrical vehicles to reduce greenhouse gas emissions attributed to its fuel flexibility and ultimate freedom of piston motion. However, FPLG still faces several challenges in control such as misfire and collision due to the eliminate of mechanical crankshaft. To fully utilize the potential of the ultimate freedom of piston motion, this paper presents a novel piston trajectory control strategy which employs the piston trajectory on the entire operation process of FPLG as the control objective. Considering disturbances and high coupling of FPLG, a sliding mode controller is employed to track reference piston trajectory. Additionally, a segmented control strategy is implemented to decouple the control of combustion pressure force and electromagnetic force. In order to ascertain the effectiveness of the proposed controller, a prototype of single-piston FPLG and a corresponding numerical model are constructed. The experimental and simulation results demonstrate the proposed controller shows fast response, precise tracking performance, and good robustness at various reference piston trajectories. Furthermore, the experimental results illustrate that the system can achieve cold start through the seamless transition between operation states and long-term stable operation by the controller.

Investigation of clearance leakage and piston offset of Joule-Thomson linear compressors at high pressure ratios

Linear compressors are renowned for oil-free operation, no crank mechanism and high efficiency, making them widely adopted in cryocoolers. Typically, high pressure ratio for linear compressor is desirable for Joule-Thomson type cryocoolers to reduce number of compression stage. However, a critical challenge to high pressure ratio is gas leakage across the radial clearance and associated the phenomenon of piston offset. This paper numerically investigated the effect of pressure ratio on clearance leakage and piston offset for a linear compressor. A comprehensive numerical model including a leakage sub-model and two control volumes (cylinder and body) was developed and validated against experimental data using nitrogen as working fluid. Real-time variations of the leakage, body pressure and piston offset were observed. The results show that the leakage due to piston movement is negligible, and the leakage due to pressure difference dominates overall clearance leakage. As the pressure ratio increases from 5 to 7, the body pressure rises by 17.9%, and the piston offset rises by 44.8%. Besides, the adiabatic efficiency decreases by 9.6%.

A Biomimetic Adhesive Disc for Robotic Adhesion Sliding Inspired by the Net-Winged Midge Larva.

Net-winged midge larvae (Blephariceridae) are known for their remarkable ability to adhere to and crawl on the slippery surfaces of rocks in fast-flowing and turbulent alpine streams, waterfalls, and rivers. This remarkable performance can be attributed to the larvae's powerful ventral suckers. In this article, we first develop a theoretical model of the piston-driven sucker that considers the lubricated state of the contact area. We then implement a piston-driven robotic sucker featuring a V-shaped notch to explore the adhesion-sliding mechanism. Each biomimetic larval sucker has the unique feature of an anterior-facing V-shaped notch on its soft disc rim; it slides along the shear direction while the entire disc surface maintains powerful adhesion on the benthic substrate, just like the biological counterpart. We found that this biomimetic sucker can reversibly transit between "high friction" (4.26 ± 0.34 kPa) and "low friction" (0.41 ± 0.02 kPa) states due to the piston movement, resulting in a frictional enhancement of up to 93.9%. We also elucidate the frictional anisotropy (forward/backward force ratio: 0.81) caused by the V-shaped notch. To demonstrate the robotic application of this adhesion-sliding mechanism, we designed an underwater crawling robot Adhesion Sliding Robot-1 (ASR-1) equipped with two biomimetic ventral suckers. This robot can successfully crawl on a variety of substrates such as curved surfaces, sidewalls, and overhangs and against turbulent water currents with a flow speed of 2.4 m/s. In addition, we implemented a fixed-wing aircraft Adhesion Sliding Robot-2 (ASR-2) featuring midge larva-inspired suckers, enabling transit from rapid water surface gliding to adhesion sliding in an aquatic environment. This adhesion-sliding mechanism inspired by net-winged midge larvae may pave the way for future robots with long-term observation, monitoring, and tracking capabilities in a wide variety of aerial and aquatic environments.

Effect of electromagnetic middle-ear implant simulating sites on the stapes spatial motion: A finite element analysis.

The electromagnetic middle-ear implant (MEI) is a new type of hearing device for addressing sensorineural and mixed hearing loss. The hearing compensation effect of the MEI varies depending on the transducer stimulation sites. This paper investigates the impact of transducer stimulation sites on MEI performance by analyzing stapes spatial motion. Firstly, we constructed a human-ear finite element model based on micro-CT scanning and inverse molding techniques. This model was validated by comparing its predictions of stapes spatial motion and cochlear response with experimental data. Then, stimulation force was applied at four common sites: umbo, incus body, incus long process and stapes to simulate the electromagnetic transducer. Results show that at low and middle frequencies, stapes-stimulating and incus-long-process-stimulating produce similar spatial motion to normal hearing; at high frequencies, incus-body-stimulating produces similar results to normal hearing. The equivalent sound pressure level generated by the stapes piston motion is less sensitive to the stimulation direction than that deduced by the stapes rocking motion.

Mathematical analysis of the motion of a piston in a fluid with density dependent viscosity

We study a free boundary value problem modelling the motion of a piston in a viscous compressible fluid. The fluid is modelled by 1D compressible Navier–Stokes equations with possibly degenerate viscosity coefficient, and the motion of the piston is described by Newton’s second law. We show that the initial boundary value problem has a unique global in time solution, and we also determine the large time behaviour of the system. Finally, we show how our methodology may be adapted to the motion of several pistons.

Accelerating piston under isothermal condition

This article explores the motion of a frictionless piston within a cylindrical container that contains an ideal gas maintained under an isothermal condition. During expansion and compression, the gas exerts a force that accelerates the piston. This movement alters the gas pressure near the piston, referred to as dynamic pressure, which deviates from the equilibrium pressure. By investigating the linear and oscillatory motions of the piston, the effect of the dynamic pressure is shown to be dependent on the mass ratio of the gas to the piston. Moreover, work done by the gas is analysed, showing how the kinetic energy of the piston varies. The material covered in this article is appropriate for undergraduate mechanics and thermodynamics, offering insights into the concept of thermodynamic work.

Development of Methodologies and Software for Design, Simulation and Optimization of Oil Hydraulic Cylinders of Large Dimensions and Power

As part of the research carried out in the field of processing systems and the production process of oil-hydraulic cylinders of large dimensions and power, the specifics of fluid power transmission, in the functioning of hydropower facilities, were analyzed. The research also includes the optimization of the physical–mathematical model of non-stationary processes, which take place inside the chamber of a large hydrocylinder. In parallel with the definition of the optimization model, the work parameters that affect the process of fluid flow and piston movement were determined. The operating and technological construction parameters of the hydraulic cylinder, which most significantly affect the operation of the hydraulic cylinder, were defined, and the observed parameters were optimized, based on which a prototype with improved characteristics compared to existing solutions was realized.

Experimental study on the power generation characteristics of a free piston engine generator prototype with dual linear generator modules

The dual-piston dual-cylinder free piston engine generator (DD-FPEG) has garnered significant attention for its high thermal efficiency, power density, and suitability for various fuels. To improve performance and stability, this paper proposes a DD-FPEG prototype integrating dual linear generator (LG) modules. The structure and working process of the prototype is introduced, followed by testing its operating characteristics and power generation performance from the cold start to power generation process. When LG1 operates in motor mode, and LG2 operates in generation mode with no load, the motor thrust must exceed 126 N to ensure piston movement. As the motor thrust decreases from 221 N to 0 N and then switches to generation mode, the peak cylinder pressure, operating frequency, output voltage and power show a decreasing trend. The coefficients of variation for peak cylinder pressure position, top and bottom dead center positions are lower than that of peak cylinder pressure, and their values are below 3 %. When the load is 50 Ω, the prototype operates at about 31.2 Hz, with an average indicated power of 1422.8 W and a peak output power of about 1002.5 W. These results demonstrate that the proposed control strategy enables the designed prototype to achieve stable operation and smooth switching.

Stability Analysis of the Secondary Motion of a Textured Piston

Piston–cylinder pairs are very common in industrial mechanisms. While a piston is primarily designed for axial reciprocating motion, the occurrence of secondary motions—lateral and rotational—due to the small clearance between the piston and the cylinder may lead to frictional contact, energy loss, wear and an increase in unwanted leakage. This study focuses on mitigating the secondary motion of a ringless piston. The influence of a Rayleigh step bearing and partial surface texturing with numerous micro-dimples on the dynamic stability of the secondary motion is studied. A linear model was used to obtain the trajectory of the secondary motion and Floquet theory was applied to analyze the stability and draw stability maps. The influence of various texturing and step parameters, including the dimple area density and aspect ratio for partial texturing, as well as the length and depth of treatment for both partial texturing and step profiles, on the stability of the secondary motion was examined. The normalization method is presented, enabling the expansion of the results for various operating conditions and geometries. Conclusions and guidelines regarding the optimal parameters, in terms of a wider stability range and higher decay rate, are formulated.

Development And Application Of A New Visualization Technique Using Photochromism For Transport Process Of Lubricating Oil Around The Engine Piston

A new visualization technique using photochromism for the movement of oil film was developed and applied to an optical gasoline engine. A photochromic dye was dissolved in the oil and an arbitrary position of the oil film was illuminated by UV laser light, which makes a marker in the oil film via a photochromic reaction. The lifetime of color change by photochromism is relatively long and therefore, by tracking the movement of a marker makes it possible to visualize the movement of oil film directly. The color density was quantified based on the absorbance calculated from images taken before and after coloring in two wavelengths. Through the experimental and theoretical considerations, it was confirmed that the calculated absorbance is effective in reducing a noise originated by the color, the shape of the piston surface, the temporal variation of oil film thickness and the illuminating light intensity distribution. Furthermore, the value of the absorbance is in a very good linear relationship with the oil film thickness. This technique was applied to an optical gasoline engine and confirmed the availability of this technique. In the top land of piston surface, the oil film between the piston and cylinder liner was separated and the majority of the oil is at the piston surface and moved with the piston motion. The oil film thickness on the cylinder liner was very thin. On the contrary, at the piston skirt region, a wider region of the oil film is connected between the linear and the piston skirt. However, there are regions where the oil film between the liner and the skirt is separated by cavitation and the majority of the oil film is on the piston skirt. The change of the flow direction by the operating condition, i.e., the throttle condition, was able to clearly visualize, though the movement of oil film on the piston surface was very slow in normal case. The relatively fast complexed flow for opposite direction was also able to visualize by this technique.

A study on water resonance between double baffle under oblique waves

This work investigates the interactions between oblique waves and a partially immersed double baffle. An analytical solution to this problem, based on the linear potential flow theory, has been found by utilizing the eigenfunction matching method. The resonance issues between the double baffle under the action of oblique waves is primarily investigated using this model, considering various relative widths, 2B/L (2B is the distance between the two baffles, L is the wave length), and the relative submergence, kD (k is the wavenumber, D is the submergence of the baffles). When resonance occurs, the transmission coefficient will rapidly increase to 1. By analyzing the relationship between the transmission coefficient and the relative width 2B/L, it is found that there are different resonance points and modes. The resonance points and modes depend on the submergence of baffles kD. This study provides a formula for calculating the resonance points. For a normal incident wave, when kD is below 1.0, the 1st-order resonance occurs in the small 2B/L region, resulting in a piston motion. High-order modes exhibit different forms, with standing waves occurring for kD ≥ 0.8, progressive waves for kD ≤ 0.48, and resonant modes ranging between standing and progressive waves for 0.48 <kD < 0.8. The effects of the incident angle on the resonance point and mode under oblique waves have also been investigated. The incident angle wave affects the interval between the two neighboring resonance points, which increases to 1/cosα times of the normal incidence for an angle of α. The resonance motion under oblique waves is nearly identical to that under the normal incident waves in the transverse plane. The difference is that there is a progressive wave in the longitudinal plane under the action of oblique waves.

Performance enhancement of a vortex ring thruster by adopting the Coanda effect

A vortex ring thruster (VRT) is a propulsion device in which a piston pushes fluid and thrusts it in reaction. As the fluid inside a VRT is moving, the boundary layer near the wall at the edge of the exit surface of a VRT separates and rolls up into a vortex ring. In this paper, we performed performance analysis on a regular VRT and a VRT enhanced by the Coanda effect (hereafter referred to as a CoVoRT) on axisymmetric geometry. A CoVoRT consists of two jets: a primary jet and a Coanda jet. The primary jet has a relatively large volume flow rate compared to the Coanda jet, and the Coanda jet attracts the surrounding fluid by flowing along the curved surface at a relatively small flow rate. The present study evaluates the propulsion performance in two ways using SNUFOAM. This software was developed based on OpenFOAM, which is an open-source computational fluid dynamics (CFD) toolkit and specialized for naval hydrodynamics. The first one quantifies the propulsion performance by calculating the ratio of energy input and energy output generated by two jets during a stroke of the piston motion. The second one is to observe the evolution and pinch-off process of a vortex ring with formation time, which is a non-dimensional time scale. The comparison of propulsion performance was conducted with changes in the curvature of the Coanda jet, changes in the length of the Coanda jet exit, and changes in the Coanda jet velocity and piston stroke ratio. For quantitative evaluation of propulsion performance, the propulsion performance evaluation index (PPEI) was introduced. The results showed that the PPEI of a CoVoRT was improved by about 50% compared to that of a VRT, and it was confirmed that the dynamic characteristics of a CoVoRT’s vortex ring were superior to those of a VRT in terms of propulsion performance.

The Influence of Complex Piston Movement on the Output Flow Rate of a Hingeless Bent-Axis Axial Piston Pump

The Influence of Complex Piston Movement on the Output Flow Rate of a Hingeless Bent-Axis Axial Piston Pump

Investigation of the minimum filling amount of ionic liquid in the multi-stage ionic liquid compressor

Ionic liquid compressors are the ideal solution for hydrogen refueling stations, and multi-stage compression is an inevitable choice for achieving high-pressure refueling, such as 90 MPa level. However, the initial filling amount of the ionic liquid in the compression chamber is lacking basis as the characteristics of gas-liquid two-phase flow during the reciprocating movement of the liquid piston are not understood. This study numerically investigates the variation characteristics of the gas-liquid interface in the compression chambers under different structural and operating parameters of a five-stage ionic liquid compressor. Based on the fluctuation feature of the phase interface, the minimum liquid piston heights in each stage that ensure effective sealing for the compression chamber with different stroke-to-diameter ratios (r) are determined. Finally, the mathematical relationship for calculating the minimum ionic liquid filling amount related to structural parameter r and suction pressure is established, which provides guidance for the design of the ionic liquid compressor.

Piston structure design and finite element analysis

The working characteristics of internal combustion engines rely on the explosive combustion of fuel in the combustion chamber to drive the piston movement. This working characteristic causes the main component of the combustion chamber, the piston, to bear high thermal and mechanical loads. It has very high requirements for design, manufacturing, and material selection. The working condition of the piston will affect its safety and stability. Therefore, the finite element analysis for the piston is particularly important. Thus, this article first establishes the piston model and divides it into grids in ANSYS, adds boundary conditions, and conducts analysis. The piston thermal analysis mainly includes thermal stress and deformation analysis under thermal load. The piston’s maximal thermal stress is 170.23 MPa and the deformation of thermal expansion is 0.61585 mm. The mechanical stress and deformation analysis under mechanical load are carried out. The maximal stress is 164.91 MPa and the maximal deformation caused by the mechanical stress is 0.24916 mm. Finally, the coupling analysis of thermal and mechanical stress is conducted. The maximal stress is 251.74 MPa, which is located at the outskirt margin of the piston pinhole. The maximal deformation is 0.60779 mm. The simulation analysis results indicate that the method proposed in this article provides a way to design the structure of similar automotive components such as pistons.

Effect of internal flow of Venturi-type power generation device on piston movement

ABSTRACT In the development and utilisation of hydraulic resources, high head and low flow hydraulic resources have not been fully utilised. To develop hydronic resources with low flow at high heads, this work designs a Venturi-type power generation device and studies the internal flow of the device by combining experiments and numerical simulations. The results indicate that the diameter ratio of the leading and branch pipes in the device significantly impacts pressure loss, and the diameter ratio at the throat is close, resulting in a significant pressure loss and an impact on the internal flow of the primary pipe. When the flow rate ratio of the leading and branch pipes is more than 4.03%, the piston can complete the reciprocating stroke, and the completion time decreases with the flow rate increase. When the flow rate ratio of the primary and branch pipes reaches 5.27%, the completion time approaches its limit. When the flow rate of the Venturi primary pipe is greater than 30 m3/h, the device begins to experience local cavitation, and noticeable noise appears at the diffusion tube.

DESIGN AND ANALYSIS OF CONNECTING ROD USING ANSYS

Connecting Rod is an important component of an internal combustion engine. It serves as an intermediate link between the piston and the crankshaft. It converts the reciprocating motion of piston into rotary motion of crankshaft. It is responsible for transferring power from piston to crankshaft and from there on to the transmission.The most commonly used materials in the production of Connecting Rod are Steel (for production of engines), Aluminium (ability to absorb high impact at the expense of durability, light in weight), or Titanium (combination of strength and lightness at the expense of affordability).The Objective of this project is to Design and Analyse Connecting Rod using different materials. A parametric model of Connecting Rod is modelled using CATIA V5 Software and Analysis is carried out using ANSYS 14.0 Software. Different materials taken into consideration are 42CrMo4, Al7075-T651, Al6061-1.5%SiC-1.5%B4C, Al7068.Performance parameters like Von-misses stress, Deformation and Factor of safety are analysed using ANSYS. From our work, it was observed that Al7068 has more Stiffness, less Stress and less Weight. Keywords:Al7075-T651,Al6061-1.5%SiC-1.5%B4C, Al7068, Aluminium, Connecting Rod

Experimental and simulation study on oscillating flow and heat transfer characteristics of the cooling gallery in steel pistons

To characterize the oscillating flow and heat transfer characteristics of the cooling gallery inside a steel piston, a visual experimental platform was designed and constructed. Based on experimental results, simulation models of the cooling gallery under calibration conditions were established, and the oscillating flow and heat transfer characteristics of different oil injection strategies were studied. The results show that adjusting the nozzle diameter has a more significant impact on the fluid charge ratio (FCR) of the cooling gallery compared to the injection pressure. During the reciprocating motion of the steel piston inside the cylinder, the gallery has the largest heat transfer coefficient (HTC) on the Top wall at the top dead center (TDC) and the largest value on the Bottom wall at the bottom dead center (BDC). The average HTC of the Top wall is always the largest, followed by the Bottom wall, the In wall, and the Out wall being the smallest. Compared to the original design, the average HTC of the Top, Bottom, Out, and In walls can be increased by a maximum of 4.39 %, 3.96 %, 8.01 %, and 11.80 %, respectively.

Experimental and simulation investigation on the impact performance of pneumatic hammer under varied drilling conditions

It is of great significance to reveal the influence on the output performance of pneumatic hammers under different drilling condition parameters to improve their impact efficiency used in drilling applications. In this study, Computational fluid dynamics (CFD) wisth dynamic mesh method was utilized to simulate dynamic airflow and piston movement within the hammer. User-Defined Functions (UDFs) are modified to introduce friction and varying well deviation angles. Meanwhile, a test bench of pneumatic hammer performance is designed and built to record real-time data on the piston displacement and chamber pressure within the hammer, validating the simulation results. The results show that the simulated and experimental data exhibit similar values and trends, with a maximum error of 10.92% for the impact velocity, 9.5% for the impact frequency, 8.36% for the maximum piston displacement, and 10.81% for the pressure drop, respectively. In addition, the piston motion mechanism was analyzed and the effects of well deviation angle, mass-flow rate, backpressure, restitution coefficient, and friction coefficient on the hammer's performance were investigated in detail. The results indicate that the mass-flow rate and restitution coefficient have a positive effect on increasing the piston's impact velocity and impact frequency, as well as pressure drop. In the context of directional drilling, the hammer's impact energy varies with the well deviation angle. At lower values of the friction coefficient, a clear positive correlation emerges between impact energy and deviation angle. Conversely, at larger values of the friction coefficient, a distinct biphasic behavior is observed, with the impact energy first decreasing before subsequently increasing. Furthermore, the backpressure, and friction coefficient adversely affect the hammer performance, with the backpressure being the dominant factor.

Study of hydrogen injection strategy on fuel mixing characteristics of a free-piston engine

The formation of the gas mixture in the cylinder has a significant effect on the combustion and emission of the engine. The main difference between a conventional engine and a free piston engine is that the piston movement mode is different. Therefore, a new coupled iterative method is adopted in this paper to study the injection position and duration of hydrogen fuel in a free piston engine where diesel fuels hydrogen, and reveal its influence on gas mixing and combustion in the cylinder of a free piston engine. The results show that it is suitable to spray hydrogen 55 mm from TDC. At this time, the mass fraction of H2 in the cylinder is relatively uniform, the cumulative heat release is about 620 J, and the pressure and temperature are relatively low, which are 7.2 MPa and 1529 K respectively. The duration of hydrogen injection is 0.4 ms, at this time, the mixing degree in the cylinder and the gas flow speed are better, although there is a little shortage of unburned equivalent ratio, but this has little impact on the overall, and the final cumulative heat release reaches 655 J.