Piston Pressure Research Articles

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.

Study on wear characteristics of friction pair in high pressure and high-speed axial piston pump

Axial piston pump is the core component of electro-hydraulic control system. High-pressure and high-speed development of the axial piston pump can significantly improve the power density of the system, but it also causes a series of problems, such as the reduction of energy conversion efficiency, the enhancement of solid-liquid coupling, the intensification of vibration and noise, and the deterioration of service conditions of friction pairs, which poses a serious challenge to the service reliability of the axial piston pump. Therefore, the friction wear experiments of key friction pairs of axial piston pump are carried out in this paper to explore the influence of various factors on the friction wear performance and the wear mechanism of friction pairs under normal stress. And the results are expected to be used to find out the matching materials of friction pairs which is the key to improve the working efficiency and the service reliability of axial piston pump.

Extension of sound field reconstruction based on element radiation superposition method in a sparsity framework

Nearfield acoustic holography (NAH) is a powerful tool for realizing source identification and sound field reconstruction. The wave superposition (WS)-based NAH is appropriate for the spatially extended sources and does not require the complex numerical integrals. Equivalent source method (ESM), as a classical WS approach, is widely used due to its simplicity and efficiency. In the ESM, a virtual source surface is introduced, on which the virtual point sources are taken as the assumed sources, and an optimal retreat distance needs to be considered. A newly proposed WS-based approach, the element radiation superposition method (ERSM), uses piston surface source as the assumed source with no need to choose a virtual source surface. To satisfy the application conditions of piston pressure formula, the sizes of pistons are assumed to be as small as possible, which results in a large number of pistons and sampling points. In this paper, transfer matrix modes (TMMs), which are composed of the singular vectors of the vibro-acoustic transfer matrix, are used as the sparse basis of piston normal velocities. Then, the compressive ERSM based on TMMs is proposed. Compared with the conventional ERSM, the proposed method maintains a good pressure reconstruction when the number of sampling points and pistons are both reduced. Besides, the proposed method is compared with the compressive ESM in a mathematical sense. Both simulations and experiments for a rectangular plate demonstrate the advantage of the proposed method over the existing methods.

Parametric analysis on the critical oscillation point of a free piston Stirling engine with a nonlinear load

ABSTRACT In this study, a numerical model of a gamma-type free piston Stirling engine (γ-FPSE) with a nonlinear load is developed and verified experimentally. A dimensionless parameter δ is proposed to define the critical oscillation state of the FPSE. The influences of the average pressure, heating temperature, spring stiffness of displacer and power piston on the critical oscillation point are investigated. The results prove that when δ is equal to 1, the power that is generated by self-oscillation of nonlinear load equals the sum of power dissipated by linear damping of pistons, load, and the power dissipated by pressure drop of heater, regenerator and cooler, the FPSE reaches the state of critical oscillation. Besides, for the cases of critical oscillation, the ratio of displacement amplitudes χ decreases with average pressure and heating temperature, but does not change with spring stiffness of displacer and power piston. Increasing average pressure, heating temperature and power piston’s spring stiffness contribute to achieve oscillation. However, increasing displacer’s spring stiffness inhibits the oscillation, the maximum displacer’s spring stiffness that can ensure FPSE’s oscillation are identified. In addition, because of the influence of nonlinear load, the nonlinearity of power piston’s displacement amplitude is more evident than that of displacer.

Design of opposed piston 2-stroke internal combustion engine test platform

Opposed piston two-stroke engine, due to its characteristics of fast expansion, high power density and indicate efficiency, and dynamic balancing, attracts many researchers’ attention. In order to explore its combustion performance, a novel test platform consisting of a drive system and combustion control system is proposed in this paper. The drive system mainly contains a 75-kW induction motor, a synchronous gearbox, and two crankshaft mechanisms. The displacement of the piston and chamber pressure is acquired and used to control combustion parameters. Using this mechanical device, the rotary motion can be converted to the opposite movement of the two pistons precisely. All the designed functions of the platform are verified by the combustion experiments of an opposed-piston two-stroke prototype. Furthermore, the experimental data is used to verify a one-dimension simulation model to evaluate the combustion characteristics of the prototype.

Evaluation of the concentration of suspended particles in underground subway stations in Tehran and its comparison with ambient concentrations

Subway lines are responsible for 20% of the total passenger traffic in Tehran. Particulate matter is one of the most important major pollutants in subway stations and increasing their concentration leads to numerous health consequences for passengers and subway employees. This study aims to investigate the concentration of PM10 and PM2.5 in four underground metro stations and compare them with the concentration of these particles in the open air. Seasonal sampling (April 2018 - April 2019) of particulate matters was conducted in the middle months of all four seasons for one week in the middle months of each season at peak traffic times from 8am to 12am, at three locations (entrance, middle, and exit in each station) and also at outside ambient of each station. The results are then compared with the relevant standards. The main sources of suspended particulate matter in the underground subway stations were due to passenger traffic, train piston pressure, floor cleaning, maintenance operations, wheel-rail wear and braking, and the performance of the ventilation system in the subway station. The results of the monitoring measurements in this study showed that the annual average concentrations of PM10 and PM2.5 in the four underground subway stations were 68 μg/m3 and 47 μg/m3 and in the outdoor ambient around these stations were 42 and 29 μg/m3, respectively. Also, this study showed that in the four underground subway stations, the annual average concentrations of PM10 and PM2.5 were 1.5-1.7 times higher than those in the outdoor ambient, respectively.

Adaptive slip engagement control of a wet clutch in vehicle powertrain based on transmitted torque estimation

In the slip engagement of a wet clutch, the solenoid current-to-actuator piston pressure model (CPM) and the piston pressure-to-clutch transmitted torque model (PTM) are utilized for the clutch torque control. However, the CPM is changed depending on the amount of hysteresis, which is influenced by the hydraulic fluid temperature, and the PTM is changed due to the variation of the clutch friction coefficient and the touch point. Thus, the CPM and PTM should be adapted using the measurement information of the solenoid current and piston pressure for precise control of the clutch torque. In this study, an adaptive control method of the clutch torque in the slip engagement of a wet clutch is proposed which. The purpose of this study is to propose a clutch torque control method that does not use a piston pressure sensor when controlling the clutch torque of a wet clutch, so the suggested method does not require measurement of the piston pressure. In the method, the adaptation of the target piston pressure-to-clutch torque model (TPTM) is performed instead of the adaptation of the CPM and PTM, and the clutch torque is controlled using the compensated TPTM and nominal CPM instead of the compensated CPM and PTM. The proposed control method is verified experimentally by applying it to the slip engagement control of an engine clutch equipped in a production parallel hybrid vehicle.

Simultaneous integration of supercritical fluid extraction and mechanical cold pressing for the extraction from Baru seed

Supercritical fluid extraction (SFE) assisted by cold pressing (SFEAP) was previously reported in the literature for oleaginous raw materials to improve the SFE process, but it suffers from operational disadvantages due to its sequential, instead of simultaneous, extraction operations. Therefore, this study aimed to address this issue by simultaneous integrating of SFE and mechanical cold pressing. This new extraction unit, which is called sCO2 + MCP, was successfully examined for the extraction of oil from Baru seed (BS) under the extraction pressure from 10 to 30 MPa and piston pressure from 10 to 30 MPa. The highest extraction yield (25.1% w/w) obtained by a combination of piston pressure of 15 MPa and an extraction pressure of 10 MPa. The main advantage of the sCO2 + MCP unit over SFE and SFEAP units is significantly reducing extraction pressure from 35 MPa to 10 MPa.

Sliding Mode Analysis of a Counterbalance Valve Induced Instability in an Electrohydraulic Drive

Abstract This paper analyzes the dynamic effects of an electrohydraulic drive that uses a counterbalance valve for rod volume compensation. It shows that local stability analysis is not sufficient in this particular case to get general statements of the system's chattering properties. A reduced-order switched system is proposed to gain deeper insights in system dynamics with saturation effects such as the end-stop of a valve poppet and solutions are compared numerically to the full-system dynamics which incorporates pressure built-up, piston, and valve dynamics as well as motor dynamics. It is shown that in cases of, e.g., fast valves with small cracking pressures undesirable chattering of the full system exists which can be easily understood in terms of the reduced-order system in form of sliding mode solutions. The paper also describes under which conditions such sliding modes exist, how they behave, and how they can be interpreted in terms of the full system.

Prediction of the working conditions for the pulse tube cooler based on artificial neural network model

An artificial neural network (ANN) model is proposed to predict the working conditions for the pulse tube cooler (PTC) in this paper. Using this model, the piston stroke and pressure amplitude of a given PTC can be accurately predicted by measured input electric parameters and working conditions of the cold finger. Then it could be decided whether the PTC still operates in the safe status with an allowable piston stroke and pressure amplitude when the cooling temperature and heat load have been changed. The ANN model is based on machine learning, by which the best mapping of the inputs and the outputs can be obtained automatically. Some methods to optimize the ANN model have been presented as well in this paper, including data normalization, setting appropriate activation functions and optimizing ANN structure. A quantity of experimental data is adopted for ANN training and testing. As seen, the ANN model would make a satisfactory prediction of piston stroke and pressure amplitude in a short time instead of massive experiments.

An Investigation on the Techniques used in Force Calibration using Deadweights and Pressure Piston Gauge

This paper presents two mechanisms for load cell calibrations. The first technique was to use deadweight to generate the required reference load (Applied load). The second method was to use a pressure piston gauge to generate the required calibration force. In both mechanisms, the setup and procedures are described. For verification the results of these methods were compared with international metrology institute calibration results. It was found that deadweight method is the most accurate and the piston gauge is the most realistic at high force values.

Nitrogen solubility in basaltic silicate melt - Implications for degassing processes

The distribution of nitrogen between the different terrestrial reservoirs (core-mantle-atmosphere) and how this may have changed since the earliest planetary stages is uncertain. In particular, the primordial degassing processes of the magma ocean and its role in the formation of the atmosphere remains to be quantified. Since no geological samples can capture this early degassing process, we need to go through the thermodynamic modeling of the nitrogen solubility in silicate melt. We hence performed experiments on basaltic samples at fluid saturation in the C-H-O-N system, using an Internally Heated Pressure Vessel (IHPV) and Piston Cylinder (PC) in the pressure range 0.8 kbar to 10 kbar, temperature between 1200 and 1300 °C, and a wide range of fO2 conditions from IW + 4.9 to IW-4.7 (IW standing for the Iron-Wustite redox buffer). The nitrogen concentration in the quenched silicate melts at fluid saturation was analysed by secondary ion mass spectrometry (SIMS), and the speciation of the dissolved C-O-H species was determined by Fourier transform infrared spectroscopy (FTIR). We identified two nitrogen species in the silicate melt: N2 dominating at fO2 > IW and N3− at lower fO2. Using these data and a database constraining nitrogen concentration at fluid saturation from 1 bar to 10 kbar pressure, we calibrated a solubility law for nitrogen in basalts defining its P-T-fO2 dependences. This model expands the model of Libourel et al. (2003) to high pressure and higher C-O-H activities. It can be used to investigate the nitrogen degassing processes for different pressure, temperature and fO2 conditions relevant to planetary accretion and modern volcanism.

Investigation of engagement characteristics of a multi-disc wet friction clutch

A kinematic coupling model of the rotation-axial engagement process of friction elements is established based on the oil film dynamic pressure lubrication and an elastic contact model of the asperities. The engagement characteristics of the multi-disc wet friction clutch are analyzed. The equation for the transmission torque of the clutch is derived by considering the axial movement of the friction elements and the surface morphology of the friction pairs. The influences of the piston pressure and the number of friction pairs on the speed and transmission torque of the clutch during engagement are analyzed considering the viscous torque and the contact torque. Finally, the effects of engagement pressure on the torque and engagement time of the clutch are verified.

Dependence of the Characteristics of a High-Pressure Piston Pair on the Properties of PES-3 Working Fluid and the Pressure Distribution in the Piston-Cylinder Gap

The use of the liquid PES-3 in a high-pressure piston pair is modeled and the parameters of the piston pair are determined. Equations are derived for a mathematical model describing the variation of the pressure in the gap between the piston and cylinder. The distribution of the pressure in the gap between the piston and cylinder is calculated for piston pressures below 1.6 GPa. The profiles of the gaps between a deformed piston and the cylinder are calculated for different piston pressures and the dependences of the piston downstroke velocity and gap efficiency on the piston pressure are calculated for different gaps of the undeformed piston pair. The results of this study can be used for the design of piston pairs operating in PES-3 fluid at pressures ranging from 0.01–1.6 GPa.

Suitability of low‐field nuclear magnetic resonance (LF‐NMR) combining with back propagation artificial neural network (BP‐ANN) to predict printability of polysaccharide hydrogels 3D printing

SummaryThe water state of polysaccharide hydrogel is closely related to its rheological properties, which is the critical parameter determining the printability of 3D printing. Low‐field nuclear magnetic resonance (LF‐NMR) results showed that T23 (free water) values of polysaccharide hydrogels gradually decreased with increasing concentration, while the viscosity values exhibited a opposite trend. As concentration increased, the printed objects gradually changed from the fluid, which cannot form a shape, to a stable shape and then to a hydrogel of low fluidity that cannot print normally. Hydrogels became hard to extrude smoothly at the piston pressure higher than 428716 Pa. Back propagation artificial neural network (BP‐ANN) nonlinear models established by taking the fingerprint LF‐NMR signal as input variables yielded good predicting ability of the piston pressure values (R2adj = 0.982) and printing scores (R2adj = 0.988). The BP‐ANN model based on LF‐NMR might be a promising approach to quickly predict the 3D printability of polysaccharide hydrogels.

Study on the reasonable tilt angle of ventilation shafts in Xidianwan Tunnel, China

The “asthma effect” of shaft natural ventilation is common, which makes the actual air exchange volume impossible to be quantified and the pollutant concentration along the tunnel unable to be analyzed. In order to improve the ventilation effect of the ventilation shaft and realize the steady air flow in the air well, the reasonable tilt angle of the ventilation shaft is studied. Firstly, the numerical simulation software FLUENT is used to establish a tunnel model of a certain traffic volume based on dynamic grid technology, and to analyze the relationship between the shaft tilt angle and the air flow state, including intake and exhaust air volume, and air flow direction. Secondly, model experiments are carried out to verify the numerical simulation results, in which jet fan thrust pressure is substituted for traffic piston pressure. The result shows that the natural ventilation state with the proposed direction can be realized on condition that the shaft tilt angle is around 15 degrees. That means to discharge polluted air from one group of ventilation shafts and suck in fresh air from the other group of ventilation shafts. At the same time, by dividing the tunnel rationally, the calculation formula of pollutant concentration of the cross section along the tunnel under the condition of different diverging amounts caused by the change of tilt angle of the ventilation shafts is derived, which provides guidance and reference for determining whether the air quality in the tunnel meets the requirements of relevant specifications.

A new prototype system for automated suppression of disc brake squeal

This paper presents a new prototype system capable of automated disc brake squeal suppression using a method of varying the leading and trailing piston pressures in a multi-piston opposed brake caliper. The new system consists of a novel modular four-piston brake caliper, a two-channel brake actuation system and an advanced control system that is capable of varying the leading/trailing pressure ratio (LTPR) when squeal is detected. The amended LTPR results in movement of the centre of pressure (CoP) position at the pad/disc interface, which leads to new dynamic parameters of the brake system and thereby to different squeal propensity. Moreover, the control system maintains the overall brake torque at a constant value, so the variation of the LTPR on the brake performance is minimised. Experiments using the current disc brake setup showed that by varying the LTPR, thereby changing the CoP position, the squeal occurrence can be successfully controlled. Large leading or trailing offsets typically lead to a quieter brake. Tests demonstrating operation of the proposed squeal control system in an automatic mode reduced the squeal occurrence significantly for a given duty cycle.

Pressure induced superconductivity in a CeRhSi3 single crystal—the high pressure study

Pressure induced superconductivity in non-centrosymmetric CeRhSi3 and CeIrSi3 compounds has attracted significant attention of the scientific community since its discovery 15 years ago. Up-to-date, all reported experimental results were obtained employing the hybrid-cylinder piston pressure cells with a maximum reachable pressure of 3 GPa. Present study focuses on the superconducting state at higher, so far unreported, pressures using the Bridgman anvil cell and a CeRhSi3 single crystal synthesized by the Sn-true-flux method. The initial increase of superconducting critical temperature from 0.4 K at 1.1 GPa to 1.1 K at 2.4 GPa is followed by a gradual suppression of superconducting state upon increasing the pressure above 3.0 GPa, forming a typical dome. The pressure induced superconductivity is expected to be completely suppressed in the pressure region between 4.5 and 5.0 GPa. Temperature dependence of electrical resistivity in constant magnetic fields and high pressures, as well as the magnetoresistance measurements, reveal a large critical field, exceeding 19 T at 0.6 K and 2.4 GPa, sharply decreasing receding the superconductivity dome. The previously reported T–p and H–T phase diagrams are completed by our high-pressure data and discussed in the frame of previous results.

Pressure media for high pressure experiments, Daphne Oil 7000 series

ABSTRACT Characterization of a new pressure medium Daphne Oil 7575 using a set of three manganin coils, a superconducting temperature of lead and the response of two perpendicular strain-gages down to low temperatures is presented. A complementary study of Daphne Oil 7474 and Daphne Oil 7373 employing identical methods is included as well. Temperature dependence of the solidification point of Daphne Oil 7575 follows the behavior of its predecessor, Daphne Oil 7474, shifted to slightly higher pressure by about 0.2 GPa. Both Daphne Oil 7474 and Daphne Oil 7575 exhibit larger pressure decrease – between the pressure at room temperature and that at low temperature – than Daphne Oil 7373. On the other hand the solidification pressure of the two media is more than 1 GPa higher than for their ancestor, making them more suitable for experiments in frequently used piston pressure cells with nominal pressure of about 3 GPa.

AlSi10Mg alloy infiltration into porous SiC structures manufactured by sponge replication

An AlSi10Mg aluminium casting alloy is infiltrated into porous silicon carbide (SIC) structures, and the microstructural, mechanical and physical properties of aluminium composites are investigated. Silicon carbide porous structures were formed by the polymeric template sponge replica method. Reticulated and open-pore polyurethane sponges with 45, 60 and 80 pores per inch were used for the polymeric replica application. The high-pressure die casting method was preferred to infiltrate the liquid aluminium alloy into porous ceramic structures. An AlSi10Mg aluminium casting alloy was used as the matrix alloy for the manufacturing of aluminium matrix composites. Molten aluminium alloy was pushed into the mould cavity for 5 s with 8 atm piston pressure. Microstructural, mechanical and physical properties of aluminium composites were examined, and the analyses of energy-dispersive spectrometry, X-ray diffraction and scanning electron microscopy and tensile test were performed for this. The experimental density of the non-reinforced sample was obtained as 2.62 g cm−3, while the composites were changed between 2.71 and 2.72 g cm−3 according to the pore structure. The highest tensile strength value was determined in aluminium composites with a pore density of 80 ppi reinforcement element with a value of 160 MPa.