Piston Profile Research Articles

Thermal Analysis of Different Piston Head Profiles by using FEM

The objective of this research work is to optimize the stress variations at the top of the piston in real engine conditions. During this pressure analysis on the examined surface of the piston, the thermal behavior is examined. The operating gas pressure, temperature and piston material functions are used as investigation functions. The analyzes carried out showed that the upper part of the piston could be damaged or broken due to the temperature caused by the working conditions, as the replacement of damaged or non-functioning parts is very expensive and usually difficult to obtain. Concave and convex piston profile designed in Solid Work 2023, used to design the piston geometry and for FEM analysis to optimize the thermal behavior of the used ANSYS R23.0 piston. Aluminum alloy and gray cast iron material for piston construction. Stress and displacement are analyzed for the piston by applying pressure to it in the structural analysis. By observing the results of the analysis, we can decide whether the piston we are designing is safe or not under the applied load conditions. Heat flow and thermal temperature distribution are analyzed using piston surface temperatures in thermal analysis.

Active Stirling Thermocompressor: Modelling and effects of controlled displacer motion profile on work output

Recent work suggests that Stirling device performance can be improved using a decoupled, actively controlled displacer piston to directly shape the device’s thermodynamic behavior. In this paper, the authors validate the controlled displacer concept using a low-frequency thermocompressor platform whose displacer and power output mechanisms are not kinematically coupled. As a little-known class of Stirling devices whose work output is pneumatic rather than mechanical, the thermocompressor presents new challenges for modeling and experimental validation because few devices have actually been built and tested. The device presented here is currently the highest pressure experimental research platform of a Stirling thermocompressor known to the authors. A third-order dynamic model is derived using first principles and is validated against experimental results. The model contains parameters that are known and/or measurable and as such is not a “fitted” model. This first-principles model is used to explore the influence of different displacer motion profiles on the output of the thermocompressor. The model is able to incorporate an arbitrarily-specifiable displacer motion profile. Using a controlled displacer piston profile, we experimentally demonstrate 1.45X higher peak cycle power and 3.6X higher work output, compared to a traditional sinusoidal displacer motion. This model is appropriate for optimizing the control of the displacer motion with respect to desired thermocompressor power, efficiency, or other performance metrics for any general Stirling thermocompressor.

Shaping the Piston–Cylinder Interfaces of Axial Piston Machines for Running in the High-Pressure Regime with Water as the Hydraulic Fluid

Water’s low viscosity renders it a poor lubricant, but its green footprint, non-toxicity, inflammability, and low cost make it a desirable hydraulic fluid. Axial piston machines running on water are commercially available, but, especially the larger units, do not operate in the high-pressure regime ( ≥300 bar). The present work investigates micro surface shaping as a design solution for the critical piston–cylinder interfaces of these units, which are particularly hard-struck by the low viscosity of water in that the pistons are subject to a heavy side load, and these interfaces cannot be hydrostatically balanced. Through virtual prototyping, the effect of two surface shapes at a high-pressure operating condition is studied for the case of a 75 cc commercial unit: first, the concave bore profile, which gives the bore surfaces through which the pistons travel the lengthwise cross-section of a circular arc, and second, the barrel piston profile, which bestows this cross-section on the piston running surface instead. The design studies conducted show that, on account of the manner in which the pistons of these machines deform over the high-pressure stroke, the concave bore profile is most able to improve overall load support when its apex is in the middle of the guide length, or shifted toward the displacement chamber. Furthermore, the concave bore profile outperforms the barrel piston profile, largely because when the piston’s axial movement takes its apex into the displacement chamber, this surface shape is no longer able to enhance the piston-bore surface conformity at the end of the interface bordering the displacement chamber that is conducive to hydrodynamic pressure buildup in that region.

Exploring the Effects of Piston Bowl Geometry and Injector Included Angle on Dual-Fuel and Single-Fuel RCCI

Abstract Reactivity control compression ignition (RCCI) is a low-temperature combustion technique that has been proposed to meet the current demand for high thermal efficiency and low engine-out emissions. However, its requirement of two separate fuel systems (i.e., a low-reactivity fuel system and a high-reactivity fuel system) has been one of its major challenges in the last decade. This leads to the single-fuel RCCI concept, where the secondary fuel (reformates of diesel) is generated from the primary fuel (diesel) through catalytic partial oxidation reformation. Following the in-depth analysis of the reformate fuel (reformates of diesel) and its benefit as the low-reactivity fuel with diesel, the effects of the start of injection (SOI) timing of diesel and the energy-based blend ratio were also studied in detail. In this study, the effects of piston profile and the injector included angles were experimentally examined using both conventional fuel pairs (gasoline—diesel and natural gas—diesel) and reformate RCCI. A validated computational fluid dynamics (CFD) model was also used for a better understanding of the experimental trends. Comparing a reentrant bowl piston with a shallow bowl piston at a constant compression ratio and SOI, the latter showed better thermal efficiency, regardless of the fuel combination, due to its 10% lower surface area for the heat transfer. Comparing the 150-degree included angle and 60-degree included angle on the shallow bowl piston, the latter showed better combustion efficiency, regardless of the fuel combination, due to its earlier combustion phasing (at constant SOI timing). The effect was particularly prominent on reformate RCCI because of its incredibly high diluent concentration, which retards the combustion further for the 150-deg injector. Later, using convergecfd, seven different injector included angles were studied at a constant SOI. With the change in injector included angle, the region of the cylinder targeted by the fuel spray varies significantly, and it was found to have a significant impact on the combustion efficiency and the engine-out emissions. As the injector included angle changed from 60-deg to 150-deg, the combustion efficiency increased by 15% and the CO, NOx, and HC emissions decreased by 96%, 70%, and 86%, respectively.

Practical profile tracking for a hydraulic press using sliding mode controller

Electro Hydraulic Servo Systems (EHSS) offer fast response in different industrial aspects such as heavy machines, cranes and robots. To obtain a precise piston profile and to achieve the designed speed, a Sliding Mode Controller (SMC) for the duration of piston extension and retraction is presented in this paper. The novelty lies in the development of a practical profile connecting the system supply pressure dynamics to the duration of piston extension and retraction. Based on the curve fitting technique, a quadratic profile is designed for a practical hydraulic press. The Sliding Mode Controller is employed to achieve repeatable tracking of the profile generated with guaranteed soft seating velocity, thereby increasing the lifetime of the hydraulic press. The performance of the proposed controller is compared with the baseline Proportional Integral Derivative (PID) controller with square wave as well as exponential wave tracking tests in simulation and experimentation which confirm the effectiveness of the proposed control scheme.

Redesign of a Piston for a Diesel Combustion Engine to Use Biodiesel Blends.

Biofuels represent an energy option to mitigate polluting gases. However, technical problems must be solved, one of them is to improve the combustion process. In this study, the geometry of a piston head for a diesel engine was redesigned. The objective was to improve the combustion process and reduce polluting emissions using biodiesel blends as the fuel. The methodology used was the mechanical engineering design process. A commercial piston (base piston) was selected as a reference model to assess the piston head’s redesign. Changes were applied to the profile of the piston head based on previous research and a new model was obtained. Both models were evaluated and analyzed using the finite element method, where the most relevant physical conditions were temperature and pressure. Numerical simulations in the base piston and the new piston redesign proposal presented similar behaviors and results. However, with the proposed piston, it was possible to reduce the effort and the material. The proposed piston profile presents adequate results and behaviors. In future, we suggest continuing conducting simulations and experimental tests to assess its performance.

Modification and discussion of the Green-Ampt model for an evolving wetting profile

ABSTRACT The Green-Ampt (GA) model has been widely used to evaluate soil water infiltration. While a simple piston profile is commonly used, the wetting profile of a soil changes during infiltration and a quarter-ellipse has been found to better describe its evolution. This study aims to improve the GA model and discuss the model parameters when the quarter-ellipse profile is utilized. The soil column is divided into three zones: saturated, transient and dry. The variable γ is introduced to express the ratio of the saturated zone depth to the wetting front depth. A modified GA model is derived via mathematical methods, but an exact solution is difficult to obtain. Therefore, a simplified (SGA) model is developed via a segmented method. Compared with the measured results, the SGA model is more accurate than the traditional model. Finally, the model parameters are discussed and a value of γ = 0.5 is recommended.

Study on the effect of piston skirt profile on the vibration behavior of non-road high pressure common rail diesel engine

The piston secondary motion is the most predominant excitation source for the mechanical vibration of diesel engine, which is directly affected by the piston profile. The effects of piston skirt profile on the dynamic behavior of piston and the vibration characteristics of engine block is studied synthetically by the method of a combination of experimental test and numerical simulation. The temperature distribution of the piston top surface under rated working condition is tested by a hardness plug, which is used as the boundary condition to carry out the thermodynamic simulation of diesel engine working process, to obtain the hot profile of the piston. Then, the dynamics model of piston assemblies are formally established, and the skirt profiles of different bump positions of the piston skirt are optimally designed. Based on the above analysis, a comprehensive study on the influence of bump position on the piston dynamic behavior is carried out. Then, applying the modal testing method for the engine block and crankshaft to establish the elastic multi-body dynamics model of diesel engine and load the piston slapping force at different bump positions, the vibration response of the surface structure under the action of different piston slapping forces is also studied. The results show that the mechanical vibration of engine block will become more severe with the hiking up of bump position at the piston skirt. Also, the vibration behavior of the engine block in the middle and high frequency section is very sensitive to the bump position of the piston skirt, especially in the frequency range of 1600 Hz–3150 Hz. In addition, vibration noise performance can be significantly improved by adjusting the bump position of piston skirt downwards. Particularly, the vibration noise performance can be best achieved when the bump position of piston skirt is 5 mm.

Kinematics of an Articulated Connecting Rod and Its Effect on Simulated Compression Pressures and Port Timings

This study discusses the motion of the articulated connecting rod of an integral-engine compressor and the effect of the kinematics on in-cylinder pressure and port timings. A piston position modeling technique based on kinematics and engine geometry is proposed in order to improve the accuracy of simulated in-cylinder compression pressures. Many integral-engine compressors operate with an articulated connecting rod. For this type of engine-driven compressor, two power pistons share a crank throw with the compressor. The hinge pins that attach the power piston connecting rods to the crank are offset, causing the piston locations for each cylinder to be out of phase with each other. This causes top dead center (TDC) to occur at different crank angles, alters the geometric compression ratio, and also changes the port timings for each cylinder. In this study, the equations of motion for the pistons of the four possible compressor/piston configurations of a Cooper-Bessemer GMW are developed. With the piston profiles, the intake and exhaust port timings were determined and compared to those of a slider-crank mechanism. The piston profile was then inputted into GT-POWER, an engine modeling software developed by Gamma Technologies, in order to obtain an accurate simulation match to the experimental in-cylinder pressure data collected from a Cooper-Bessemer GMWH-10C. Assuming the piston motion of an engine with an articulated connecting rod is similar to a slider-crank mechanism can create a difference in port timings. The hinge pin offset creates asymmetrical motion about 180°aTDC, causing the port timings to also be asymmetrical about this location. The largest differences are shown in the intake port opening of about 10 deg and a difference in exhaust port opening of about 7 deg when comparing the motion of the correct configuration to the motion of a slider-crank mechanism. It is shown that properly calculating the piston motion profiles according to the crank articulation and engine geometry provides a good method of simulating in-cylinder pressure data during the compression stroke.

Transient tribo-dynamics analysis and friction loss evaluation of piston during cold- and warm-start of a SI engine

Fuel economy improvement of the Internal Combustion (IC) engine is prompted by the broad promulgation of more stringent vehicle emission regulations. Friction loss during the engine start-up is a longstanding issue because of the high frictional dissipation under cold-start and the heavy wear within warm-start. This study presents a numerical cycle-by-cycle investigation into the piston tribo-dynamics characteristics and friction loss during the Spark Ignition (SI) engine cold- and warm-start based on a coupled piston tribo-dynamics model system. The model system consists of the piston skirt-liner mixed lubrication model and the piston-rod-crank mechanism multibody dynamics model. Thermal distortion of the piston and the liner, and the lubricant viscosity-temperature property are accurately incorporated into the corresponding engine start-up conditions. Analyses and comparisons between the cold- and warm-start are carried out in terms of tribology and dynamics. Results show that frictional energy dissipated by the cold-start is 72% higher than the warm-start, which primarily due to viscous shearing of lubricant oil. At low engine speed, the tight clearance under warm-start results in a lower level of slap noise excitation than under cold-start. It is also found that the low oil viscosity of warm-start leads to a high risk of catastrophic scuffing and seizure failure near the FTDC of the first ignition cycle. In the light of the above analysis, a piston profile optimization scheme is proposed and its influence on piston scuffing resistance and energy efficiency enhancement is assessed. The evaluations indicate that almost half of friction consumption can be reduced for the engine warm-start if the thermal intricacies are properly factored in the piston design.

Effect of piston profile on performance and emission characteristics of a GDI engine with split injection strategy – A CFD study

Gasoline direct injection (GDI) engines have gained popularity in the recent times because of lower fuel consumption and exhaust emissions. But in these engines, the mixture preparation plays an important role which affects combustion, performance and emission characteristics. The mixture preparation in turn depends mainly upon combustion chamber geometry. Therefore, in this study, an attempt has been made to understand the effect of piston profile on the performance and emission characteristics in a GDI engine. The analysis is carried out on a four-stroke wall guided GDI engine using computational fluid dynamics (CFD). The spray breakup model used is validated with the available experimental results from the literature to the extent possible. The analysis is carried out for four piston profiles viz., offset pentroof with offset bowl (OPOB), flat piston with offset bowl (FPOB), offset pentroof with offset scoop (OPOS) and inclined piston with offset bowl (IPOB) fitted in an engine equipped with a six-hole injector with the split injection ratio of 30:70. All the CFD simulations are carried out at the engine speed of 2000 rev/min., with the overall equivalence ratio of about 0.65±0.05. The performance and emission characteristics of the engine are compared while using the above piston profiles. It is found that, the OPOB piston is preferred compared to that of the other pistons because it has better in-cylinder flow, IMEP and lower HC emissions compared to that of other pistons.

Research on MCVE piston machining and process parameter optimization

A piston is an important part of an engine. Its shape is designed into middle-convex and varying ellipse (MCVE) to adapt to the complex working environment. The main requirements of MCVE piston machining are high frequency response, small range tool motion, and high precision. In this article, an MCVE data model is established for the piston profile design, and the turning principle and control procedure are discussed to develop a fast tool servo (FTS) system for piston turning. In the end, back propagation neural network (BPNN) and genetic algorithm (GA) are combined to optimize the process parameters in the MCVE piston machining, which includes general turning parameters and special MCVE turning parameters. Through the experiments and BPNN-GA optimization, the ellipticity error (E) and surface roughness (Ra) of all pistons met the design requirements. According to verification experiments, the optimization results of E and Ra are 3.04 and 1.204 μm, respectively, and their relative errors are 10.13 and 4.27%, respectively. It has been proved that the MCVE data model and the control design of FTS are feasible and can effectively produce MCVE piston; the BPNN-GA optimization method is obviously effective and can improve processing effect and machining efficiency.

1202 油圧機器に用いられるピストンの弾性変形による摩擦特性への影響(GS4-5 材料力学・計算力学)

1202 油圧機器に用いられるピストンの弾性変形による摩擦特性への影響(GS4-5 材料力学・計算力学)

Effect of closed-loop controlled resonance based mechanism to start free piston engine generator: Simulation and test results

Two general methods to start the engine are investigated by the linear electric machine operating as a linear motor and identified one for a specific FPEG prototype configuration. Based on that, a novel method to start the engine by mechanical resonance is proposed. Both simulation and test results are presented, and the numerical model is successfully validated. The results show that with a fixed motor force of 110N, within 0.5s, the maximum in-cylinder pressure could reach 13bar, indicating that the engine is ready for ignition. Further investigation on the engine performance with the closed-loop control strategy is carried out. The results demonstrate that it is feasible to start the FPEG with mechanical resonance with a closed-loop controlled electric linear machine that applies a proper constant motor force in the direction of the natural bouncing motion. With different starting motor force, the top dead centre (TDC) value for both cylinder is different during the first few running cycles, but the difference reduces and tends to be zero during the stable resonance state. There is not any significant difference observed on the engine frequency and piston profile during combustion process.

Constant pressure hydraulic energy storage through a variable area piston hydraulic accumulator

Hydraulic accumulators are used in a variety of applications to minimize the pressure variation in hydraulic circuits and to store energy. Conventional hydraulic accumulators suffer from two major limitations, the hydraulic system pressure varies with the quantity of energy stored and the energy density is significantly lower than other energy domains. In this paper, a novel hydraulic accumulator is presented that uses a piston with an area that varies with stroke to maintain a constant hydraulic system pressure while the gas pressure changes. The variable area piston is sealed with a fabric reinforced rolling diaphragm. In this work, the piston radius profile is developed as a function of the piston displacement and then transformed into a function of the axial contact location between the piston and the diaphragm. The piston profile was solved numerically for a variety of conditions using both transformation methods to illustrate the geometric design trade-offs. Using a variable area gas piston with a fixed cylinder area, the maximum gas volume ratio was 1.8:1. An analysis of the energy density revealed that the constant pressure accumulator provides a 16% improvement in energy density over a conventional accumulator at a volume ratio of 2.71:1 and also exceeds the maximum energy density of a conventional accumulator at the lower volume ratio of 1.8:1. This new promising technology maintains a constant hydraulic system pressure independent of the quantity of energy stored, easing system control and allowing other circuit components to be downsized to meet the same power requirements, while also increases the energy storage density.

Analysis of Piston Slap Induced Noise and Vibration of Internal Combustion Engine (Effect of Piston Profile and Pin Offset)

This paper presents the analytical method to evaluate the impact force and engine noise induced by piston slap considering the detailed piston profile and dynamic characteristics of the piston. This method was applied to examine the effect of the piston profile and piston pin offset on the piston slap impact force and its induced engine noise. Present numerical method showed that increasing the upper clearance of the piston skirt enlarged the higher frequency components of the piston impact force and engine noise and this was verified by the experimental results. The analysis revealed that piston movement at the vicinity of the combustion top dead center was governed by the friction moment around the piston pin and the additional piston pin offset moment induced by combustion pressure could cancel this friction moment and reduce the piston impact force if the piston pin was offset to the major thrust side. This analytical results was confirmed by the measured results of actual diesel engine.

DESIGN OF IRONLESS LOUDSPEAKERS WITH FERROFLUID SEALS: ANALYTICAL STUDY BASED ON THE COULOMBIAN MODEL

This paper presents an analytical method based on the coulombian model of a magnet for studying a ferrofluid seal in ironless electrodynamic loudspeakers. Such an approach differs from the ones generally used for studying such geometries because the ferrofluid used is submitted to a magnetic field greater than 1 T which saturates the ferrofluid. Consequently, its shape and its mechanical properties depend mainly on the magnetic field produced by the permanent magnets that constitute the ironless structure. The motor is constituted of outer stacked ring permanent magnets and the inner moving part is a piston. In addition, one ferrofluid seal is used for centering the moving part and ensuring the airtightness between the loudspeaker faces. The ferrofluid seal also exerts a pull back force on the moving piston. It is noted that this force depends on the lateral shape of the moving piston. Therefore, the piston profile is analytically studied in this paper. A peculiar attention is given to profiles that ensure the axial pull back force to be proportional to the piston displacement. Furthermore, a geometrical method is presented to design the shape of the ferrofluid seal according to the chosen piston profile. It can be noted that such a profile is elliptical in this study. Then, the magnetic energy of the ferrofluid seal is determined with the analytical expression of the magnetic energy density. Such an expression allows us to calculate the axial force created by the ferrofluid seal for a given profile.

ピストンスラップによるエンジン振動・騒音の研究 : ピストン形状やピンオフセットの影響

ピストンスラップによるエンジン振動・騒音の研究 : ピストン形状やピンオフセットの影響

309 ピストンスラップによるエンジン放射音 : ピストンオフセットの影響

This paper presents the analytical method to evaluate the impact force and engine noise induced by piston slap considering the detailed piston profile. This method is applied to examine the effect of the piston profile on piston slap impact force and frequency spectrum related to the engine noise. The tendency of the piston pin offset to abate the piston slap is compared with the measured one to confirm the availability of this method. And it is pointed out that piston movement in the vicinity of the combustion top dead center is governed by the friction moment around the piston pin and the additional piston pin offset moment induced by combustion pressure.

Research on the on-line measuring system for the middle-convex and varying ellipse piston skirt

The middle-convex and varying ellipse piston is th e key component of an internal-combustion engine. In general,the piston is mac hined by non-circular section CNC lathe,but the measuring of piston profile is manipulated by off-line. Because the off-line measuring reference is differen t from the machining reference,the measurement result is diverse from the act ual dimension. A new method to measure the middle-convex and varying ellipse p iston profile, which is known as on-line measuring, is presented. By using thi s kind of method,the high measurement accuracy can be gained,as well as meeting the production requirement.