Piston Motion Research Articles

Impact of the JAZARI technology piston motion profile on the indicated thermal efficiency of a 4-cylinder diesel engine

As fuel economy and consumption become global concerns, engine developers strive to reduce fuel consumption. However, due to complexity and development challenges, only a few new engine technologies have been introduced recently. Nevertheless, the market demands more efficient engines, prompting a focus on new mechanisms. This study evaluates a theoretical 4-cylinder Compression Ignition (CI) diesel engine implementing the JAZARI mechanism, which alters piston speed near top dead center TDC claiming a faster combustion, reduced duration, and improved power output. The evaluation compares indicated thermal efficiency, torque, and fuel consumption using a 1-Dimensional simulation model based on the first law of thermodynamics., which then was calibrated using testing data obtained from an engine test cell dynamometer. Two load cases at 2500 RPM were examined, The simulation results indicate that when using the JAZARI mechanism compared with the calibrated conventional mechanism engine, an increase of 1% in thermal efficiency and 2.5% in indicated torque is seen with only reducing the injection duration and timing to fit the JAZARI mechanism piston motion profile, and when aiming for maximum indicated thermal efficiency it was increased by 1.2% and 3.1% in indicated torque, the final results case indicated that when using the JAZARI mechanism, the engine reached the same indicated torque of 295 N.m, with same indicated efficiency of 45.8% with a peak firing pressure of 155 bar, which is almost 30 bar less than the conventional mechanism case, meaning the ability to boost the JAZARI engine with less risk on the engine internals is an advantage.

Analysis on Lubrication Performance of Piston Ring-Cylinder Liner based on Numerical Simulation

This paper mainly studies the tribological performance of friction pairs and poor lubrication during piston movement. Based on the average Reynolds equation and comprehensively considering the variable viscosity and variable density characteristics of lubricating oil, a transient hydrodynamic lubrication model of the piston ring-cylinder liner friction pair is established. By solving the established lubrication model, the lubricating oil film thickness value, friction value and other parameters that can characterize the lubrication performance of the friction pair throughout the cycle are obtained, whilst revealing the surface roughness, lubricating oil viscosity and piston ring barrel surface height. And the influence mechanism of the friction performance of the friction pair is presented on the basis of the previous analysis. The research shows that improving the surface roughness of the piston ring will help to improve the lubrication, increasing the viscosity of lubricating oil will help to improve the lubricating performance of friction pairs and reduce the peak friction at the top dead centre of piston rings and improving the surface texture of the piston rings can reduce the oil film thickness and reduce the friction caused by fluid shear effect in the high-speed region.

Outlet Pressure and Flow Characteristics of a New Two-Dimensional Piston Pump with an Overlapped Distributor

This article presents the design of a two-dimensional (2D) piston pump flow-distribution port with an overlapped structure that reduces backflow in the pump chamber and pressure ripples at the pump outlet, thus minimizing vibration and noise caused by the high-frequency distribution process of a single two-dimensional (2D) piston pump. We describe the flow distribution structure and operation principle of the 2D pump, create a mathematical model of the pump chamber pressure by using the motion and flow continuity equations of the 2D piston, and use a Matlab program to compile and solve them. The influence of the flow distribution port overlap on the pump chamber pressure and the outlet flow rate was simulated. A prototype was designed and tested on a dynamic performance test bench. Our test bench results show that the flow distribution port overlap can reduce the pressure ripple at the pump outlet, which is consistent with the simulation results.

Multi-field coupling effect of injection on dynamics and thermodynamics of a linear combustion engine generator with slow compression and fast expansion

An asymmetric reciprocating engine (ARE) with slow compression and fast expansion is designed in this paper, which can improve combustion performance and energy conversion efficiency by optimizing piston motion. However, due to the particularity of piston motion, how to consider the multi-field coupling effect of injection position (IP) on dynamics and thermodynamics becomes a key issue. Therefore, this paper proposes a multi-dimensional coupled model including motion, gas exchange and combustion, and uses an iterative algorithm to solve the model. The results show that ARE has better gas exchange performance and higher acceleration near TDC than conventional engines because of its slow compression and fast expansion processes, which lead to its obvious advantages in gas organization and combustion heat release. Furthermore, increasing IP has a positive excitation effect on the operating frequency and the combustion performance of ARE because the changed motion results in a longer ignition delay and a better fuel atomization environment. However, increasing IP continuously will lead to weak turbulent motion, which will greatly reduce the combustion reaction rate. The results suggest that increasing the IP is beneficial to improve the thermal efficiency of ARE and reduce soot generation, but too large an IP is not supported.

Design of Long-Stroke ejector with Traveling Charge Structure

Generally, the independently designed charge is used in traditional ejectors, where the gunpowder is usually fixed at its end. For long-stroke ejectors, the energy from gunpowder combustion in the later period of piston movement is mostly used for structure expansion, and only a small part is converted to piston actuation. The energy for piston movement can only be improved by increasing the amount of gunpowder, which results in large instantaneous pressure in the combustion chamber, thus leading to a big impact on the system structure by the pyrotechnic products. To deal with this problem, a design method for the long-stroke ejector based on traveling charge structure is proposed. It integrates the charge structure with piston design to ensure that the energy from gunpowder combustion can fully act on the bottom of the piston during the whole combustion process, thus improving the proportion of energy from gunpowder combustion transformed to the piston’s kinetic energy and reducing the charge quantity, which will then lessen the impact of pyrotechnic products on the system structure and improve its reliability. It has been experimentally proven that when designing a long-stroke ejector, the energy utilization rate of gunpowder can be increased by about 1.5 times by adopting the traveling charge structure compared to the traditional charge structure.

Algorithmic linearization improves Syringe-based extrusion in elastic systems using Hydrogel-based materials

Accuracy and precision are essential in extrusion-based material handling such as three-dimensional (3D) bioprinting. However, the elasticity of components, backlash, variability of nozzle and cartridge shapes, etc. can lead to unpredictable printing results, which is further complicated by the wide range of rheologically diverse materials and complex sample designs.To address this issue, we present an algorithmic approach to compensate for the discrepancies between piston motion and material extrusion in syringe-based extrusion systems. This approach relies on cyclical, iterative optimization through rapid piston movements, which are adjusted based on extrusion analysis.In this work we establish a general theoretical framework for extrusion and link the rheological properties of prepared hydrogels with shear rates in a typical bioprinting process. The determined properties are compared with the success of the developed algorithm to modify machine instructions for precise material deposition of short, interrupted lines, as well as multi-layered scaffold structures.Overall, our approach provides a means of improving the accuracy and precision of complex extrusion-based bioprinting systems, without prior knowledge of set-up or material properties, making it highly versatile and suitable for a wide range of applications, particularly when the combined set-up and material properties are too complex for solely predictive approaches.

Experimental Analysis of the Discharge Valve Movement of the Oil-Free Linear Compressor in the Refrigeration System

In a linear compressor, the valve motion significantly affects the thermodynamic efficiency and the compressor’s reliability, especially in oil-free conditions. To better understand the dynamic behavior of the discharge valve, a real-time test bench was built. The piston movements and dynamic pressure in the cylinder were also observed to obtain the synchronizing characteristics among the reed valve motion, cylinder pressure, and piston motion. Observing the motion of the discharge valve visually, the discharge valve flutters due to the change in the form of the cylinder pressure, the delayed opening of the valve is caused by the inertia of the valve itself, and additional displacement fluctuations are present. This paper presents the dynamic behavior of the discharge valve under different discharge pressure/operating frequency/piston stroke/clearance length conditions. The results show that the valve flutters increase, the mean displacement of the valve increases, and the duration of the discharge increases when the discharge pressure decreases. When the operating frequency increases, the duration of the discharge decreases, while the mean displacement of the valve increases. For a high stroke or a low clearance length case, the duration of the discharge increases, while the valve flutters increase due to the pressure fluctuations in the cylinder. Through analyzing the synchronizing characteristic among the valve movements, piston movements, and cylinder pressure, it is shown that the phenomenon of the delayed opening valve is much worse for a low stroke or a high operating frequency case. In addition, the delayed closing of the valve appears for a high operating frequency case (75 Hz).

A Comprehensive Review of the Free Piston Engine Generator and Its Control

Review A Comprehensive Review of the Free Piston Engine Generator and Its Control Patrick Brosnan 1, Guohong Tian 1, * , Umberto Montanaro 1, and Sam Cockerill 2 1 School of Mechanical Engineering Sciences, University of Surrey, Surrey GU2 7XH, UK 2 Libertine FPE Ltd., Sheffield S9 1DA, UK * Correspondence: g.tian@surrey.ac.uk; Tel.: +44-1483-300-800 Received: 2 February 2023 Accepted: 10 March 2023 Published: 23 March 2023 Abstract: The Free Piston Engine (FPE) is a unique machine with a higher thermal efficiency than its counterpart, the Conventional Reciprocating Piston Engine (CPE). The unique piston motion of the FPE is not constrained kinematically like the CPE with its connecting crankshaft and rotational inertial masses. Moreover, when directly coupled to the Linear Electric Machine (LEM) to harness electric energy production, the Free Piston Engine Generator’s (FPEG) characteristic motion, now being dynamically constrained, permits an extensive range of piston trajectory profiles to be exploited during operation. In addition, exploring varied piston trajectories during the development stages may be vital in reducing in-cylinder combustion emissions through strategies such as Low-Temperature Combustion (LTC) and Homogeneous Charge Compression Ignition (HCCI). This review paper will focus on the key motivations and drivers for continued FPEG development. It will also highlight and review its distinct advantages and challenges in being a viable solution as a future zero-carbon engine technology. Finally, FPE fundamentals, alongside its rich history, will be introduced, clearly presenting how academia and industry have described and controlled its intrinsic non-linear dynamics.

Large Displacement Detection Using Improved Lucas–Kanade Optical Flow

Displacement is critical when it comes to the evaluation of civil structures. Large displacement can be dangerous. There are many methods that can be used to monitor structural displacements, but every method has its benefits and limitations. Lucas-Kanade (LK) optical flow is recognized as a superior computer vision displacement tracking method, but it only applies to small displacement monitoring. An upgraded LK optical flow method is developed in this study and used to detect large displacement motions. One motion controlled by a multiple purpose testing system (MTS) and a free-falling experiment were designed to verify the developed method. The results provided by the upgraded LK optical flow method showed 97 percent accuracy when compared with the movement of the MTS piston. In order to capture the free-falling large displacement, the pyramid and warp optical flow methods are included in the upgraded LK optical flow method and compared with the results of template matching. The warping algorithm with the second derivative Sobel operator provides accurate displacements with 96% average accuracy.

An improved Closed-Circuit RO (CCRO) system: Design and cyclic simulation

A volume-varying stirred tank with a free-piston are placed in front of DuPont's Closed-Circuit RO (CCRO) system to achieve improved energetics. Valves are used to direct fluid flow and piston motion to enable cyclic operations consisting of CC filtration and flushing steps. Similar to CCRO, overall system recovery in the proposed system is controlled by the CC/flushing time ratio, and uninterrupted permeate production is possible if the flushing is done at high pressures. Spatiotemporal system-level models are developed and formulated as a set of coupled partial differential equations (PDEs) and ordinary differential equations (ODEs). Detailed numerical simulations and parametric studies are carried out to explore the flow and mass transfer characteristics and to compare its performance at the cyclic steady-state (CSS) with the original CCRO and the conventional steady-state RO.

Coupling Vibration Analytical Model and Vibration Suppression of Linear Motor Driven Free Piston Stirling Cryocoolers

Linear motors are widely utilized in free-piston Stirling cryocoolers (FPSCs) due to their high efficiency, high reliability, and low noise. The reciprocating motion of the compression piston and the expansion displacer in a FPSC will inevitably lead to the vibration output. Most researches only focused on the vibration of a single moving component, and few studies discussed about the coupling vibration of linear compressor and expander. In this paper, the vibration of a linear motor-driven Stirling cryocooler is studied through theoretical analysis and experiments. A passive absorber is designed to suppress the vibration output from the linear compressor and expander simultaneously. The dynamic model of the Stirling cryocooler system is established, and the network transfer function between the input voltage and the system displacement of the linear motor is derived. The influences of these linear motor parameters of thrust constant, resistance and inductance, and working condition of charged pressure, is investigated in detail, on the system's vibration output. The experimental results are presented to evaluate the validity of the proposed model.

Performance of large-diameter pneumatic down-the-hole (DTH) hammers: A focus on influences of the hammer structure

Pneumatic down-the-hole (DTH) hammer has been extensively used in air drillings through hard and ultra-hard geological formations. Numerical modeling can offer close observation on the working behaviors by visualizing internal pressure status as well as provide reliable performance predictions for large-diameter DTH hammers to which conventional empirical and experimental approaches cannot be applied. In this study, CFD simulations coupled with dynamic meshing are utilized to simulate the air flow and piston movement inside the large-diameter DTH hammers. The numerical modeling scheme is verified against a theoretical model published in literature. Effects of structural parameters on hammer performance, including piston mass, piston upper-end diameter, piston groove diameter, and lengths of intake and exhaust stroke in both front and rear chambers, are analyzed in detail by virtue of sets of numerical simulations. The simulations suggest that changing the intake stroke of front chamber has a negligible influence on hammer performance while increasing the piston groove would lower all the four indicators of hammer performance, including impact energy, impact frequency, maximum stroke, and air consumption rate. Changing the other structural parameters demonstrates mixed effects on the performance indicators. Based on the numerical simulations, a large GQ-400 DTH hammer has been designed for reduced air consumption rate and tested in a field drilling practice. The air drilling test with the designed hammer provided a penetration rate 1.7 times faster than that of conventional mud drilling.

Heat transfer and flow characteristics of intermittent oscillating flow in tube

Motions of piston and displacer in ideal Stirling cycle is non-sinusoidal and rise-dwell-fall-dwell. However, heat transfer and flow characteristics of present oscillating flow are based on sinusoidal motions. In this work, heat transfer and flow characteristics of intermittent oscillating flow with intermittent ratio = 1 in tube were numerically studied. The model was firstly validated based on literature's empirical equations for sinusoidal oscillating flow. Then, heat transfer and flow characteristics of intermittent and sinusoidal oscillating flows were simulated and compared. The simulation results showed that the total heat transfer coefficient and pressure drop in intermittent oscillating flow were 14.6% lower and 0.83% higher respectively compared to those in sinusoidal oscillating flow. The curves of pressure drop were nearly the same in sinusoidal and intermittent oscillating flows with removal of stagnation periods. Besides, velocity distributions in two oscillating flows were also investigated. The simulation results showed that the “velocity loop” in two oscillating flows occurred at the same time and the changing amplitudes of wall's velocity over central axis's velocity in “velocity loop” were nearly the same.

Motion of a Piston Separating Magnetic and Non-Magnetic Fluids in a Magnetic Field

The pumping of non-magnetic fluid by a dosing pump that is based on a magnetic fluid with an immersed body made of a magnetizable material is studied theoretically and experimentally. The process of fluid pumping in an applied vertical uniform magnetic field is investigated. The time dependences of the rise of the piston between the magnetic and non-magnetic fluids are calculated and measured in constant and stepwise magnetic fields. A good agreement between theory and experiment is obtained. The dependence of the rise time of the piston on the magnitude of the constant magnetic field is calculated. The motion of piston is theoretically investigated after the magnetic field is switched off.

Quality Assuring a Ring Vortex Flow Phantom in Real-Time

Introduction: The ring vortex phantom is a novel, cost-effective prototype which generates complex and well-characterised reference flows in the form of the ring vortex. Although its reproducibility has been demonstrated, with ring speeds routinely behaving within 10% tolerances at speeds of approximately 10 - 70 cm/s, a form of real-time QA of the device at the time of imaging is needed to confirm correct function on demand in any environment. Methods: The technology described here achieves real-time QA, comprising a linear encoder, laser-photodiode array, and Doppler probe, measuring piston motion, ring speed and intra-ring velocity respectively. This instrumentation does not interfere with imaging system QA, but allows QA to be performed on both the ring vortex and the device in real-time. Results: The encoder reports the reliability of the piston velocity profile, whilst ring speed is measured by laser behaviour. Incorporation of a calibrated Doppler probe offers a consistency check that confirms behaviour of the central axial flow. For purposes of gold-standard measurement, all elements can be related to previous Laser PIV acquisitions with the same device settings. Conclusion: Consequently, ring vortex production within tolerances is confirmed by this instrumentation, delivering accurate QA in real-time. This implementation offers a phantom QA procedure that exceeds anything seen in the literature, providing the technology to enhance quantitative assessment of flow imaging modalities.

Parametric Analysis of Gas Leakage in the Piston–Cylinder Clearance of Reciprocating Compressors

Gas leakage is one of the main sources of inefficiencies in low-capacity reciprocating compressors, undermining the compressor performance by reducing the mass flow rate and increasing the energy consumption. In reciprocating compressors, leakage in the piston–cylinder clearance is driven by the piston motion and pressure difference between the compression chamber and the internal environment of the shell. This paper reports a parametric numerical analysis of leakage in the piston–cylinder clearance of a low-capacity reciprocating compressor. A simulation model based on the Reynolds equation is applied throughout the compression cycle to assess the effect of the compressor operating conditions, clearance geometry, piston velocity and piston secondary motion on the leakage and compressor performance. A 3D CFD model is also developed to validate the Reynolds leakage model and to evaluate the effect of the piston secondary motion on leakage, assuming the piston is fixed with predetermined eccentricities. The results show that the compressibility effects are very relevant to estimate the gas leakage. The simulations also revealed that leakage is more detrimental to the compressor performance when it is operating in low back-pressure conditions. Additionally, the piston secondary motion can intensify the gas leakage in the piston–cylinder clearance by up to 90%. On the other hand, the piston velocity only plays a minor role in assessing the leakage.

Detection of physiological control inputs preload and afterload from intrinsic pump parameters in total artificial heart.

In the total artificial heart (TAH), the inputs to the physiological control unit, preload, and afterload, are detected from intrinsic pump parameters (e.g., motor current). Within this study, their detection techniques are developed, and their reliability in pre- and afterload prediction is mapped for a broad range of cardiovascular system states. We used ReinHeart TAH which is a fully implantable TAH with a plunger coil drive that is alternately emptying the left and right chambers. From the coil currents we first derived a force generated by the piston with respect to its position and then analyzed its pattern to detect (1) preload-chamber filling, found as piston position at begin ejection and (2) afterload-mean outflow pressures, determined as linearly calibrated average piston force during ejection. TAH is then integrated into a mock loop circulation (MLC) which is set to 135 different steady operating points varying in chamber filling (0%-100%, five steps), mean outflow pressures (system circulation: 60-90-120 mm Hg, pulmonary circulation: 15-30-45 mm Hg), and heart cycle duration (171-600 ms in seven non-equidistant steps). The detected preload and afterload are compared to MLC set values, and the errors are mapped. Respectively for the left and right chambers, the preload was detectable in 134 and 118 operating points and the mean error was ±3% and ±2%. The afterload was detectable in 135 and 87 operating points and the mean error was 37% and 30% respectively for left and right circulation. The operational points that are further away from homeostatic equilibrium values generally yielded larger errors. The largest errors were observed for right circulation at long cycle duration, low afterload, and low filling. The study yields reliable preload estimation in a broad range of physiological states, particularly for left circulation. Detection of afterload needs further improvements. The study revealed a need for piston movement optimization within the ReinHeart TAH during the early phase of systole.

Functional pixels: a pathway towards true holographic displays using today's display technology.

Today's 3D dynamic holographic display techniques suffer from severe limitations due to an available number of pixels that is several orders of magnitude lower than required by conventional approaches. We introduce a solution to this problem by introducing the concept of functional pixels. This concept is based on pixels that individually spatially modulate the amplitude and phase of incident light with a polynomial function, rather than just a constant phase or amplitude. We show that even in the simple case of a linear modulation of the phase, the pixel count can be drastically reduced up to 3 orders of magnitude while preserving most of the image details. This scheme can be easily implemented with already existing technology, such as micro mirror arrays that provide tip, tilt and piston movement. Even though the individual pixels need to be technologically more advanced, the comparably small number of such pixels required to form a display may pave the way towards true holographic dynamic 3D displays.

Effects of Piston motion on the power generated by Stirling cycle machines

This paper uses a simple model to estimate the power output of Stirling engine when giving the pistons a continuous motion with a prescribed pattern, fixed frequency, and a variable phase shift for different operational temperature ratios. Two continuous motions patterns, sinusoidal and modified sinusoidal, have been examined against the discontinuous motion of the ideal cycle. The power produced from engines having continuously moving pistons is lower than the power produced from the ideal cycle. The power ratio decreases as the temperature ratio increases. the highest produced power with a temperature ratio of 1.5, is 97% of the ideal cycle and it occurs at a phase-shift of 81o. Operating at ±10o off the highest power phase shift condition reduces the output power by 5-7%. For modified sinusoidal motion, the highest output power is 88% when the phase shift is 55o. Operating at ±10o off the maximum power phase shift condition reduces the output power by 2%. Moreover, at the highest output phase shift condition, the power output ratio drops from 97% to 93%, for sinusoidal motion as the cycle temperature ratio changes from 1.5 to 3. For modified sinusoidal motion, the output power drops from 88% to 78% at the highest phase shift condition.

Development of adjustable fluid damper device for the bridges subjected to traffic loads

In this research, an Adjustable Bypass Fluid Damper (ABFD) is developed by utilizing a pair of external fluid flow pipes and flow control valves. The flow control valves control the flow pressure of the fluid passing through bypass pipes and adjusted the function of the fluid damper to limit the displacement of the structure within the allowable range. Therefore, the function of the fluid damper device is adjustable according to the displacement of the structure.The ABFD device is developed through implementing an adjustable valve in bypass pipes that able to change and adjust the flow and pressure of the oil inside the viscous damper during movement of piston under applied vibrations and control the resultant damping and resistance force of the damper device. Therefore, through the new proposed design, the action of viscous damper has been changed from passive control device to an adjustable system which is capable to function as an device with different capacities and also able to change the response from a damping device to a restrainer system. The analytical model of the proposed ABFD device is developed and the performance of the device has been formulated according to the control valve position. Then the finite volume model of the moving fluid inside the device has been developed and the function of the device was evaluated through Computational Fluid Dynamics analysis.In the next step, the prototype of ABFD has been fabricated and experimental tests have been conducted using a dynamic actuator to evaluate the performance of the device in various control valve conditions.The numerical analysis and experimental test results for the ABFD prototype revealed that the developed device is capable of developing a wide range of damping levels and there is a desirable agreement between numerical predictions and experimental results.Thereafter, to examine the effect of the application of the ABFD device in the bridge structures, the proposed ABFD device was implemented in the 19/5 California overcrossing bridge. The considered bridge equipped with an ABFD device is modeled using the finite element method and it’s subjected to the passing vehicle loadings. The results showed that the bridge's response is dramatically improved with the implementation of the six ABFD dampers and the peak displacement of the structure reduces by 35 percent while the control valves are half-open.