Piston-cylinder Unit Research Articles

Analysis of a High-Pressure Reciprocating Compressor Piston's 2D Simulation Utilizing Computational Fluid Dynamics

Reciprocating compressors represent the most renowned and extensively utilized compressors within the positive displacement category. A compressor that takes input gas at pressures above atmospheric and delivers it very high pressures (> 100 bar) is specifically called a booster pump. These pumps commonly consist of two or more piston-cylinder units in series, connected through check valves that determine the final delivery pressure, and they are instrumental in a range of applications centered around the storage and delivery of gases and fuels. Despite the availability of various booster pumps in the global market, literature offers limited insights into their design specifics. The design intricacies of a booster pump, tailored to operate at specified output pressure and mass flow rate, are contingent upon the interplay of coupled flow dynamics and heat transfer phenomena within the system. These phenomena include fluid flow dynamics through check valves, heat transfer across cylinder walls, and mechanical properties of pump materials, alongside cyclic operational parameters. To address this gap, we have embarked on an experimental-computational investigation aimed at elucidating the transport processes occurring in a single-cylinder booster pump. This work focuses on computational investigations concerning gas compression and the actuation of check valves in a single-cylinder reciprocating booster. Momentum and energy conservation equations were solved on a dynamic mesh platform through Ansys Fluent. Adiabatic conditions were employed, and the numerical solver was partially validated by comparison with thermodynamic theory for simulations conducted in a closed adiabatic cylinder. Calculations were then extended for an open cylinder with inlet and outlet check valves. Simulations indicate that forced cooling plays an important role for the longevity of sealing parts.

Determination of parameters generating the reference pressure in the primary level dynamic pressure measurement system based on the drop weight method

For some industries such as automotive, defence, aerospace, pharmaceutical manufacturing, dynamic pressure measurement is an important requirement. In a primary level dynamic pressure measurement system with a drop weight method, the dynamic pressure value is calculated using parameters such as the effective area value depending on the piston cylinder unit, the maximum acceleration value measured by a laser interferometer. On the other hand, the type of liquid used in the measuring head is another important factor affecting repeatability and providing ease of measurement. In this study, a new measurement head, piston and cylinders were designed, manufactured and the Taguchi method was used to accurately determine some parameters affecting the measurements in a dynamic primary pressure measurement system operating with the drop weight method. In the studies carried out, four pistons, four cylinders, four sampling frequency values and two liquid types were considered. By using the Taguchi method, the optimum parameters of the dynamic pressure measurement system with drop weight method were determined with only sixteen experiments instead of one hundred and twenty-eight.

Experimental Investigation of a Free-Form Honed Cylinder Liner for Heavy-Duty Engines

For future internal combustion engines, driven by regenerative fuels, efficiency is more important than ever. One approach to reduce the losses inside the piston cylinder unit (PCU) is to improve the alignment of the liner and the piston. Therefore, a cylinder liner with a free form was developed at the Institute of Technical Combustion (ITV) of the Leibniz University Hannover which compensates radial and linear deformations along the stroke. The layout is based on a FEM simulation. The liner was manufactured by the Institute of Production Engineering and Machine Tools (IFW) of Leibniz University of Hannover with a novel turn-milling process. The liner was investigated on the heavy-duty Floating-Liner engine of ITV with a displacement of 1991 ccm and a bore diameter of 130 mm. The experimental results show improvement in the friction losses over the whole engine map in the range of 9% and up to 17.3% compared to a serial liner. Sealing efficiency could be improved up to 28.8%, depending on the operational point. Overall, the investigation aims for lower fuel consumption which would in result fewer emissions.

Numerical Assessment of Tribological Performance of Different Low Viscosity Engine Oils in a 4-Stroke CI Light-Duty ICE

<div class="section abstract"><div class="htmlview paragraph">Decreasing fuel consumption in Internal Combustion Engines (ICE) is a key target for engine developers in order to achieve the CO<sub>2</sub> emissions limits during a standard cycle. In this context, reduction of engine friction could help meet those targets. The use of Low Viscosity Engine Oils (LVEOs), which is currently one of the avenues to achieve such reductions, was studied in this manuscript through a validated numerical simulation model that predicts the friction of the engine’s piston-cylinder unit, journal bearings and camshaft. These frictional power losses were obtained for four different lubricant formulations which differ in their viscosity grades and design. Results showed a maximum friction variation of up to 6% depending on the engine operating condition, where the major reductions came from hydrodynamic-dominated components such as journal bearings, despite an increase in friction in boundary-dominated components such as the piston-ring assembly. Also, an evaluation of the potential fuel reduction that can be obtained by low viscosity oils during a WLTC approval cycle was performed. Overall, a fuel saving of 1% was obtained. In general terms, the majority of the engine map showed potential for mechanical loss reduction through LVEOs, that is, a better engine efficiency and consequently a decrease in the fuel consumption and CO<sub>2</sub> emitted to the atmosphere. The present work also exemplifies the trade-offs encountered when reducing the engine friction through LVEOs and highlights the need to co-engineer the hardware and lubricant in order to utilize the full friction reduction potential of LVEOs.</div></div>

2D flow model for calculating effective area of piston-cylinder units

A 2D flow model is described for calculation of the effective area (<em>A</em>) of pressure-measuring piston-cylinder units (PCU) based on their dimensional properties. With the 2D model, the uncertainty contribution associated with PCU's axial non-symmetry can be eliminated and the uncertainty of <em>A</em> can be reduced. The 2D model is applied to several primary PCUs operated in absolute and gauge pressure modes with different pressure-transmitting media. The benefit of the 2D model in dependence on PCU's geometrical perfectness is discussed.

Monte Carlo determination of the uncertainty of effective area and deformation coefficient for a piston cylinder unit

This paper describes the approach made to describe the uncertainty on the area at zero pressure ( A 0 ) and on the deformation coefficient of piston-cylinders used for pressure definition. We perform the Monte-Carlo simulation for an ordinary least squares (OLS) as well as for a weighted least squares (WLS) and a generalized least squares (GLS). We also introduce an innovative technique to improve the results obtained by WLS in order to get close to the quality obtained using GLS. We discuss the different situations that guides to the best choice between OLS, WLS and GLS.

Development of alumina-based porosity reference materials for the mercury porosimetry method

This paper presents the results of a study on the development of alumina-based porosity reference materials (RMs), which are intended for controlling the accuracy of the measurement results obtained using the mercury porosimetry method. These mercury porosimetry RMs are being developed in the Russian Federation for the first time and are primarily intended for verification / calibration and testing for type approval of mercury porosimeters. The study of metrological characteristics was conducted using a reference system, which is to be included in the GET 210-2014 State Primary Measurement Standard for units of specific gas adsorption, specific surface area, specific volume and pore size of solid substances and materials. This reference system was calibrated prior to conducting the study with the use of external reference pressure sensors of the 2nd order at 0.6 MPa and 400 MPa, as well as a laboratory balance (special accuracy class 1) having a maximum weighing limit of220 g. In the course of conducted research work, procedures for reproducing and estimating the uncertainty of porosity characteristics using the mercury porosimetry method were developed. When estimating the PM metrological characteristics, the standard uncertainty, associated with the characterisation and heterogeneity of the studied materials (PM candidates), was evaluated. The standard uncertainty due to instability was disregarded due to the high stability of the alumina matrix. According to the results of the conducted studies, four types of alumina-based porosity PM were developed. Their pore sizes are of about -lOnm; -2,000 nm; -9,000 nm; -60,000 nm. The RMs with pore sizes of -10 nm; -2,000 nm were intended for use in controlling the accuracy of mercury porosimeters operating at high pressures, while the RMs with pore sizes of -9,000 nm; -60,000 nm were for controlling the accuracy of mercury porosimeters operating at low pressures. The developed RMs are different from their foreign counterparts, which are produced by BAM (Germany) and NIST (USA) metrological institutes. The standard uncertainty due to characterisation of the RMs in question was estimated, not by the method of interlaboratory experiment, but by a full analysis of the constraint equations taking into account all sources of uncertainty included in the equations on the basis of the Guide to the Expression of Uncertainty in Measurement. The conducted studies allowed the RM certified values to be traceable at this stage to the GET 3-2008 State Primary Measurement Standard for the mass unit (kilogram), the GET 101-2011 State Primary Measurement Standard for the pressure unit in the field of absolute pressure in the range 1×10 –1 – 7×10 5 Pa, the GET 43-2013 State Primary Measurement Standard for the pressure unit in the range 10-1600 MPa and the effective area of the piston-cylinder unit of dead weight testers in the range 0.05-1 cm 2. In addition, a reference material having a large pore size of -60,000 nm, which currently has no analogues elsewhere in the world, was characterised.

Influence of pressure distribution in the gap of piston-cylinder unit and properties of working fluid PES-3 on characteristics of high pressure piston-cylinder unit

A simulation of the use of PES-3 liquid in a high-pressure piston-cylinder units was performed, and the parameters of the piston-cylinder units were determined in the article. The equations of the mathematical model describing the pressure change in the gap between the piston and the cylinder are given. As a result of the calculations, the pressure distributions in the gap between the piston and the cylinder are determined at under piston pressures less than 1.6 GPa. The profiles of the gaps between the deformed piston and cylinder at different under piston pressures are calculated. The dependences of the speed of lowering the piston and the effective gap on the under piston pressure at different gaps of the undeformed piston-cylinder unit are obtained. The research results can be used in the design of piston cylinder units operating on PES-3 liquid in the pressure range of 0.01–1.6 GPa.

Fractional step method in problems of hydromechanical processes in piston-cylinder unit of axial piston swash plate hydraulic machines

Having analyzed the piston-cylinder unit kinematics, we obtained an equation for the clearance height in the piston-cylinder unit for the case of low speeds, the equation being the basis for Reynolds equation for the lubricant layer of the piston mechanism. By a numerical experiment using the fractional step method, we built a pressure field for two different cases of the piston mechanism kinematics, and compared the bearing capacity of the hydrodynamic force. It was revealed analytically and with the help of a numerical experiment that when the piston rolls in the edges of the guide bushing, the total hydrodynamic force significantly exceeds the force created when the piston slides in the bushing.

EVALUATION ON THE CONSISTENCY OF CALIBRATION RESULTS BETWEEN REFERENCE STANDARDS OF PNEUMATIC PRESSURE BALANCE BASED ON NON-FULL RANGE CALIBRATION

<p>To provide calibration services for pressure measuring devices, SNSU-BSN has several piston-cylinder standard that may traceable to different National Metrology Institute (NMIs). Non-full range calibration of pressure balance has been performed to evaluate the consistency of calibration results between those standard, especially for establishing self-traceability in the future. In this research, a piston-cylinder unit S/N 1926 with medium pressure range of 1750 kPa, was calibrated with low pressure range S/N 978 of 350 kPa and high pressure range S/N 1054 of 7000 kPa. The calibration was performed with cross-float method to evaluate the effective area of piston-cylinder at null pressure and reference temperature of 20⁰C (<em>A<sub>0,20</sub></em>) and distortion coefficient (λ) as the 1926 main parameters. The obtained value, respectively are (1.961 166 × 10<sup>-4</sup> ± 4.4 × 10<sup>-9</sup>) m<sup>2 </sup>and (-1.67 × 10<sup>-12</sup> ± 9.4 × 10<sup>-13</sup>) Pa<sup>-1 </sup>from 978 and (1.961166 × 10<sup>-4</sup> ± 5.1 × 10<sup>-9</sup>) m<sup>2</sup> and (-1.58 × 10<sup>-12</sup> ± 8.4 × 10<sup>-13</sup>) Pa<sup>-1 </sup>from 1054. The result of 1926 from both methods shows good conformity with Normalized Error (En) of 0.0007 and 0.069, respectively. Linearity of effective area changes to the pressure is very consistent in both low and high pressure range. Validation results by using PTB-Germany results, shows the relative different for <em>A<sub>0</sub></em> and <em>λ</em> obtained are less than 0,1 × 10<sup>-6</sup> and 6%,respectively. Therefore, the pneumatic pressure balance of SNSU-BSN is traceable, consistent with each other and capable for disseminating the pressure unit along all primary pressure standard owned with high agreement compared to those of other advance NMIs.</p>

Final Report on EUROMET Project 881 / EURAMET.M.P-K7: High pressure comparisons between seven European National Laboratories Range 50 MPa to 500 MPa

An inter-comparison in the high oil pressure range was arranged in 2005 - 2007. The participating laboratories were CMI/Czech Republic, Metas/Switzerland, MIKES/Finland, NMi-VSL/The Netherlands, PTB/Germany, SMD/Belgium and SP/Sweden. CMI, Metas, NMi-VSL and PTB are pressure laboratories of the primary level, and the three others are traceable to LNE/France.The transfer standard was a Desgranges & Huot piston-cylinder unit with a nominal effective area of 1,96 mm2, mounted in a D&H 5316 balance body. The participants determined the effective area at ten nominal pressures from 50 MPa to 500 MPa in steps of 50 MPa. All the results were in a good agreement with the reference values, calculated as weighted means of the results from the four primary level laboratories. The results fully support the uncertainties claimed in the CMC tables of the participants.As the pressure distortion is the dominating source of uncertainty in this range, the claimed uncertainties were highest at 500 MPa, ranging from 5,6 · 10-5 of PTB to 1,2 · 10-4 of MIKES (expanded relative uncertainties, k = 2). Except for PTB, there were no big differences in the claimed uncertainties between the primary and the secondary level laboratories.Some of the participants underestimated the uncertainties when giving their results in terms of the effective area at null pressure S0 and the pressure distortion coefficient, λ. The uncertainties given by some others were unnecessarily high.The transfer standard was not as stable as expected, and the uncertainties of the reference values were to some extent increased by the observed drift.The comparison, registered as EUROMET Project #881, was started as an informal one between MIKES, Metas, NMi-VSL and CMI, and in the beginning the rules for EUROMET comparisons were not strictly followed.No links to other comparisons were made as the latest EUROMET key comparisons in the high pressure range were carried out more than twelve years ago. Linking will be made as soon as results from newer comparisons are available.Edited in 2018:The link between this comparison (EUROMET 881 / EURAMET.M.P.K7) and the key comparison CCM.P.K13 was calculated, and the original EUROMET 881 report (MIKES Publication J4/2007) was updated accordingly in 2018.KEY WORDS FOR SEARCHcomparison, pressure, effective area, piston cylinder, pressure balanceMain textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Characterization of gas pressure balances at LPM

This paper describes development of gas pressure scale up to 18 MPa using dimensional and cross-float experiments in Croatian national pressure laboratory (HMI/FSB-LPM). Practical pressure scale for gas as transmitting medium is realised using a group of six gas-operated-piston-cylinder assemblies and diving bell manometer. For more than 15 years, traceability of pressure measurements has been achieved through German national pressure laboratory PTB. Recently, Croatian national length laboratory (HMI/FSB-LPMD) improved their measurement capabilities and LPM started independent realization of traceability for gas pressure scale through dimensional measurements. The purpose of this work was to develop a method for direct determination of effective area using basic SI units, determine stability of piston cylinder units from 15 years of measurement data history, compare results from cross-float and dimensional method and to establish prerequisites for independent traceability chain in LPM. Dimensional measurements were performed for two gas-operated-piston-cylinder units with diameters of 35 mm and 8 mm and their effective areas were calculated with relative standard uncertainty of 18 and 35 ppm, respectively. A comparison of these results with cross-float experiments is given, showing good agreement. Finally, measurements, calculation method, results of effective area and other important metrological characteristics such as deformation coefficient and fall rate are presented for the entire group of six gas-operated-piston-cylinder assemblies.

Metrological Characterization of Non-Rotating Low-Pressure Piston-Cylinder Unit System

A Low-pressure non-rotating new piston gauge covers the range of gauge and absolute pressure from less than 1 Pa to 15 kPa in gas media [1]. The instrument operates on the piston gauge principle. However, the force resulting from pressure on the piston is measured by a force balanced load cell rather than a balanced system against masses subjected to the acceleration due to gravity. For this reason, the measuring portion is designated a force balanced piston gauge (FPG) [1]. While pressure measurement range of a conventional pressure balance can start from around 5 kPa, as the FPG can measure pressure starting from a few pascal. Calibration or determination of the effective area of FPG system can be done using a conventional pressure balance reference instrument gauge in gauge and absolute modes. This paper describes the metrological characterization of a low-pressure non-rotating piston-cylinder unit both in absolute and gauges pressure modes, in the range of 1 Pa to 15 kPa by direct comparison method.

Research on High Efficiency Operation Method of Linear Generator Engine

In this paper, a novel generator engine designed to achieve high efficiency, which we call an internal combustion engine with linear generator (ICELG), is proposed and its feasibility and validity are demonstrated using a simulator. Unlike conventional crank-type engines, the ICELG employs a linear motor, which is directly connected to the piston-cylinder unit, instead of a crank mechanism, thus eliminating the motional constraints. This allows the stroke to be changed in mid-operation. The simulator is based on a model of the DC motor and consists of the motor model, which combines the actuator and generator, the engine model, which computes the state changes in the cylinder, and the charge/discharge model, which computes the energy charge and discharge. The ICELG’s feasibility is evaluated by determining the energy losses and charge in the respective models. It is possible to extract a greater amount of energy in the combustion stroke by lengthening the stroke. Losses can be reduced during the intake and exhaust strokes by operating at low speed in order to prevent drastic pressure changes in the cylinder. During the compression stroke, the inertial energy is stored when the pressure in the cylinder is still low, and then subsequently released as inertial force beyond the position from which it can complete the combustion stroke, as a result of which the motor resistance loss is reduced. It was found that the ICELG achieves higher efficiency than conventional generator engines when operated in this manner.

On the Measurement and Modeling of High-Pressure Flows in Poppet Valves Under Steady-State and Transient Conditions

Flow coefficients of intake valves and port combinations were determined experimentally for a compressed nitrogen engine under steady-state and dynamic flow conditions for inlet pressures up to 3.2 MPa. Variable valve timing was combined with an indexed parked piston cylinder unit for testing valve flows at different cylinder volumes while maintaining realistic in-cylinder transient pressure profiles by simply using a fixed area outlet orifice. A one-dimensional modeling approach describing three-dimensional valve flow characteristics has been developed by the use of variable flow coefficients that take into account the propagation of flow jets and their boundaries as a function of downstream/upstream pressure ratios. The results obtained for the dynamic flow cases were compared with steady-state results for the cylinder to inlet port pressure ratios ranges from 0.18 to 0.83. The deviation of flow coefficients for both cases is discussed using pulsatile flow theory. The key findings include the followings: (1) for a given valve lift, the steady-state flow coefficients fall by up to 21% with increasing cylinder/manifold pressure ratios within the measured range given above and (2) transient flow coefficients deviated from those measured for the steady-state flow as the valve lift increases beyond a critical value of approximately 0.5 mm. The deviation can be due to the insufficient time of the development of steady-state boundary layers, which can be quantified by the instantaneous Womersley number defined by using the transient hydraulic diameter. We show that it is possible to predict deviations of the transient valve flow from the steady-state measurements alone.

Uncertainty Modelling of the Reference Pressure Generating with OIML and ASTM Weights in Pressure Balances

A pressure balance is a combined with a piston-cylinder unit and a system for the application of a vertical load on the piston. Pressure balances are primary measuring systems those measure pressure in terms of force per unit area. Reference pressure can be generated by a pressure balance. There are many parameters to calculate reference pressure, such as piston’s area, linear deformation of piston and cylinder, measuring temperature, mass, local gravity, surface tension of measuring liquid… All of these parameters have got measurement uncertainty, effects of these uncertainty components must be added to the uncertainty budget of reference pressure. In this study, the uncertainty model function of reference pressure is derived. And the uncertainty model function is rearranged. If the masses of pressure balance are calibrated according to the OIML R-111 or ASTM E-617 guides, the uncertainty model function that is given in the study can be used directly to calculate uncertainty of reference pressure.

A theoretical and experimental study of the deformation of the piston-cylinder unit of a metrological pressure balance

Pressure balance is a measuring system widely used in metrology as a reference standard. The common procedure is to estimate the pressure from an analytical formula involving a set of phenomenological parameters. These parameters are determined experimentally by calibration tests of the balance. In particular, the piston-cylinder deformation is taking into account by the use of a global distortion coefficient and by the use of an effective area of the piston. In order to analyze the possible influence of local deformation on the pressure estimation, a Finite Element (FE) model has been developed using OpenCavok FE code. For a given position of the piston in the cylinder chamber, for a given initial gap between of the cylinder and the chamber, a coupled fluid-structure calculation is carried out. From the local fields, mean values are calculated from which the effective area of the piston-cylinder unit. The analysis is conducted for several engagement lengths of the piston in the chamber and for several loads. The first results obtained show that the local deformation play a role and that FE models could help for precise calculation of the measured pressure.

Measurement of pressures up to 7 MPa applying pressure balances for dielectric-constant gas thermometry

For the determination of the Boltzmann constant by dielectric-constant gas thermometry, the uncertainty of pressure measurements in helium up to 7 MPa has been decreased compared with previous achievements (Sabuga 2011 PTB-Mitt. 121 247–55). This was possible by performing comprehensive cross-float experiments with a system of six special pressure balances and the synchronization of their effective areas. It is now possible to measure a helium pressure of 7 MPa with a relative standard uncertainty of 1.0 ppm applying a 2 cm2 piston-cylinder unit, the calibration of which is traceable to the SI base units.

Final report on key comparison EURAMET.M.P-K13 in the range 50 MPa to 500 MPa of hydraulic gauge pressure

The regional key comparison EURAMET.M.P-K13 for pressure measurements in liquid media from 50 MPa to 500 MPa was piloted by the TÜBİTAK UME Pressure Group Laboratories, Turkey. The transfer standard was a DH-Budenberg pressure balance with a free deformation piston-cylinder unit of 2 mm2 nominal effective area. Six laboratories from the EURAMET region, namely PTB, INRIM, SMU, IMT, NPL and UME, and two laboratories from the AFRIMETS region, NIS and NMISA participated in this comparison. Participant laboratories and countries are given in the bottom of the page.PTB participated in this comparison to provide a link to corresponding 500 MPa CCM key comparison CCM.P-K13.The results of all participants excepting NMISA and NPL were found to be consistent with the reference value of the actual comparison and of CCM.P-K13 within their claimed uncertainties (k = 2), at all pressures. Compared in pairs all laboratories with exception of NPL and NMISA demonstrate their agreement with each other within the expanded uncertainties (k = 2) at all pressures. The results are therefore considered to be satisfactory.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Effects of pelletization conditions on breaking strength and dimensional stability of Douglas fir pellet

The compression behavior of Douglas fir ground particles using a heated piston–cylinder unit was investigated. A complete randomized design (CRD) of experiment with three factors (die temperature, applied pressure and relaxation time), three levels and five replicates were studied. From the analysis of variance (ANOVA) with α=0.05, all of the three pelletization factors were significant parameters to the maximum breaking strength and the relaxed pellet density. The significant factors to the initial pellet density of pellets were the die temperature and the applied pressure. Three out of five compaction models of Walker, Jones, Kawakita and Ludde were well described to the compression behavior of Douglas fir ground particles with R2 values between 0.90 and 0.99. The optimum processing condition to produce the best quality of Douglas fir pellets was 100°C die temperature, 126MPa applied pressure and 30s relaxation time.