Piston-cylinder Assembly Research Articles

Effect of piston bowl shape on the in-cylinder flow characteristics of IC engines

Numerical simulation of the in-cylinder flow for internal combustion (IC) engine with different bowl shapes has been performed. The LES models are applied to a piston-cylinder assembly with a stationary valve and a harmonically moving piston. Gas motion inside the engine cylinder determines the thermal efficiency of an IC engine, and combustion chamber geometry affects the performance of the IC engine. Comparison of the flow characteristics inside the engine cylinder equipped with different piston geometries shows that the squish flow affects the turbulence generation process near the top dead center during compression stroke. The A-type combustion chamber with reentrant shape is shown to have higher radial velocity and turbulence intensity in the piston bowl compared with other types. Results of these simulations aid in the improved understanding of the effect of intake and compression process of piston geometry on the in-cylinder flow. The detailed flow characteristics inside the in-cylinder for different piston bowl shapes can offer basic guidelines to improve the combustion process.

Isotope fractionation of Li and K in silicate liquids by Soret diffusion

Laboratory experiments were used to determine the thermal (Soret) isotopic fractionation of lithium and potassium in a basalt melt, which adds elements with ionic charge +1 to the list of elements for which thermal isotopic fractionations in silicate liquids have been previously reported (i.e., Ca, Mg, Fe, Si, O, Sr, Hf, and U). The new experiments were run at a moderate pressure of about 1.5GPa in a piston cylinder apparatus in order to avoid gas bubbles once the sample was melted. The samples were displaced slightly below the hot spot of the piston cylinder assembly graphite furnace so that there would be a temperature difference of about 125°C across the samples while molten. The thermal isotopic fractionation factor Ω (per mil fractionation per 100°C per one atomic mass unit difference) was found to be 6.0 for lithium isotopes and 1.1 for potassium isotopes. The isotopic fractionation in both cases resulted in the heavy isotopes becoming enriched at the cold end. The expanded data set of thermal isotopic fractionation in silicate liquids is used to evaluate the degree to which recently proposed parameterizations are able to reproduce the experimental data.

Direct numerical simulation of multiple cycles in a valve/piston assembly

The dynamics and multiple-cycle evolution of the incompressible flow induced by a moving piston through the open valve of a motored piston-cylinder assembly was investigated using direct numerical simulation. A spectral element solver, adapted for moving geometries using an Arbitrary Lagrange/Eulerian formulation, was employed. Eight cycles were simulated and the ensemble- and azimuthally-averaged data were found to be in good agreement with experimentally determined means and fluctuations at all measured points and times. During the first half of the intake stroke the flow field is dominated by the dynamics of the incoming jet and the vortex rings it creates. With decreasing piston speed a large central ring becomes the dominant flow feature until the top dead center. The flow field at the end of the previous cycle is found to have a dominant effect on the jet breakup and the vortex ring dynamics below the valve and on the observed significant cyclic variations. Based on statistical averaging, the evolution of the turbulent flow field during the first half of the intake stroke is dominated by the jet breakup process leading to a strongly anisotropic behavior. In the second part of the intake stroke, the decrease of the incoming jet velocity results in a more isotropic behavior.

Estimation of parasitic losses in a proposed mesoscale resonant engine: Experiment and model

A resonant engine in which the piston-cylinder assembly is replaced by a flexible cavity is realized at the mesoscale using flexible metal bellows to demonstrate the feasibility of the concept. A four stroke motoring technique is developed and measurements are performed to determine parasitic losses. A non-linear lumped parameter model is developed to evaluate the engine performance. Experimentally, the heat transfer and friction effects are separated by varying the engine speed and operating frequency. The engine energy flow diagram showing the energy distribution among various parasitic elements reveals that the friction loss in the bellows is smaller than the sliding friction loss in a typical piston-cylinder assembly.

Recent progress in high pressure metrology in Europe

Five European national metrology institutes in collaboration with a university, a research institute and five industrial companies are working on a joint research project within a framework of the European Metrology Research Programme aimed at development of 1.6 GPa primary and 1.5 GPa transfer pressure standards. Two primary pressure standards were realised as pressure-measuring multipliers, each consisting of a low pressure and a high pressure (HP) piston-cylinder assembly (PCA). A special design of the HP PCAs was developed in which a tungsten carbide cylinder is supported by two thermally shrunk steel sleeves and, additionally, by jacket pressure applied to the outside of the outer sleeve. Stress-strain finite element analysis (FEA) was performed to predict behaviour of the multipliers and a pressure generation system. With FEA, the pressure distortion coefficient was determined, taking into account irregularities of the piston-cylinder gap. Transfer pressure standards up to 1.5 GPa are developed on the basis of modern 1.5 GPa pressure transducers. This project shall solve a discrepancy between the growing needs of the industry demanding precise traceable calibrations of the high pressure transducers and the absence of adequate primary standards for pressures higher than 1 GPa in the European Union today.

Studies on compaction behavior of composite flours during uniaxial compression process of pasta making

The mechanical compaction behavior of composite flours during simulated direct compression process of pasta making was studied using a uniaxial compression test. Composite flours (decorticated minor millet flour viz., foxtail millet, little millet and kodo millet with refined wheat flour), blend in the ratio of 30:70, 40:60, 50:50 at 9 and 37% moisture contents (db) were subjected for compaction studies through instrumental (piston-cylinder assembly, D:H, 60:65 mm) measures with known applied pressure range (0 - 1477 kPa) and manual tapping procedures. The range of initial bulk density, critical bulk density, tap density and compressibility index for foxtail millet, little millet and kodo millet composite flours at 9 and 37% moisture content (db) were determined as 505 - 438 and 618 - 548 kg m−3, 1224 - 999 and 1539 - 1119 kg m−3, 778 - 658 and 733 - 649 kg m−3 and 39.34 - 3.22 and 38.29 - 10.07%, respectively. Data were analyzed statistically for its significance with different moisture levels and composite flour ratio. Pressure-density relationship for composite flours were established and validated with Peleg's equation (R2 >0.948) to evaluate the compaction behavior of composite flour during pasta making

Numerical Simulation of Instantaneous Heat Transfer in Reciprocating Internal Combustion Engines

This study provides a detailed instantaneous heat transfer solution in a cylinder during a motored cycle. The piston-cylinder assembly is modeled by a two-dimensional cavity with a sinusoidal moving wall. A high order differential algorithm is used to solve the unsteady compressible Navier-Stokes equations. The order of differencing is raised progressively from the walls toward the center of the cylinder, enabling oscillation free and accurate calculation on a very coarse grid. The numerical fluxes are integrated based on the dual-time stepping of the preconditioned matrix with a third-order Runge-Kutta scheme. The absolute pressure is determined by enforcing the global mass conservation for each grid. The predicted results of the absolute pressure, temperature, and velocity components of the fluid inside the cylinder at any instant during the start-up and the periodically stable periods are compared well with the results given in the literature.

Process Conditions Governing Mechanical Expression of Shea Butter from Crushed Shea Kernel under Uni-Axial Compression

Mechanical expression of shea butter from shea kernel (Vitelaria paradoxa) was studied using a 43factorial experiment under a Randomized Complete Block Design. The mechanical expression rig comprised an instrumented pistoncylinder assembly in conjunction with a Universal Testing Machine (UTM). Shea butter was mechanically expressed through the perforated base of the press cage cylinder when crushed shea kernel was subjected to uniaxial compressive loading by the UTM. The process conditions were heating temperatures of 50, 70, 90 and 110 °C; applied pressures of 1.5, 2.9, 5.8 and 8.8 MPa and loading speeds of 2.50, 5.00, 7.50 and 10.00 mm min-1. Heating of the crushed shea kernel samples prior to shea butter extraction was achieved by a temperaturecontrolled band heater enfolding the press cage cylinder. Results showed that a maximum oil yield of 35.10 %, a maximum oil recovery efficiency of 58.50 % and a minimum process loss of 2.83 % were obtained at a heating temperature of about 70 °C, an applied pressure of about 8.8 MPa and a loading speed of about 2.50 mm min-1.

Large-eddy Simulation of Motored Flow in a Two-valve Piston Engine: POD Analysis and Cycle-to-cycle Variations

Large-eddy simulation (LES) has been performed for a single-cylinder, two-valve, four-stroke-cycle piston engine through 70 consecutive motored cycles. Initial comparisons of ensemble-averaged velocity fields have been made between LES and experiment, and proper orthogonal decomposition (POD) has been used to analyze the complex in-cylinder turbulent flows. Convergence of POD modes has been quantified, several POD variants have been explored, and sensitivity of results to analyzing different subsets of engine cycles has been studied. In general, it has been found that conclusions that were drawn earlier from POD analysis of a simplified non-compressing piston-cylinder assembly with a fixed valve carry over to the much more complex flow in this motored four-stroke-cycle engine. For the cases that have been examined, the first POD mode essentially corresponds to the ensemble-averaged mean velocity. The number of engine cycles required to extract converged POD modes increases with mode number, and varies with phase (piston position). There is little change in the lower-order phase-invariant POD modes when as few as 24 phases per cycle (30° between samples) are used, and complex 3-D time-dependent in-cylinder velocity fields through full engine cycles can be reconstructed using a relatively small number of POD modes. Quantification of cycle-to-cycle variations and insight into in-cylinder flow dynamics can be extracted through analysis of phase-invariant POD modes and coefficients.

Large-eddy simulations of turbulent flows in internal combustion engines

Large-eddy simulations (LES) of turbulent spray combustion in internal combustion engines are conducted with a new hybrid Eulerian–Lagrangian methodology. In this methodology, the Eulerian filtered compressible gas equations are solved in a generalized curvilinear coordinate system with high-order finite difference schemes for the turbulent velocity and pressure. However, turbulent mixing and combustion are simulated with the two-phase compressible scalar filtered mass density function (FMDF) and Lagrangian spray models. The LES/FMDF model is used for simulation of in-cylinder turbulent flow and spray mixing and combustion in three flow configurations: (1) a poppet valve in a sudden expansion, (2) a simple piston–cylinder assembly with a stationary valve, and (3) a realistic single-cylinder, direct-injection spark–ignition (DISI) engine. The flow statistics predicted by the LES model are shown to compare well with the available experimental data for (1) and (2). The computed in-cylinder flow for the third configuration shows significant cycle-to-cycle variations. The flow in the DISI engine is also highly inhomogeneous and turbulent during the intake stroke, but becomes much more homogeneous and less turbulent in the compression stroke. Simulations of spray, mixing and combustion in the DISI engine indicate the applicability of the LES/FMDF model to internal combustion engines and other complex combustion systems.

Final report on APMP.M.P-S4: Results of the bilateral supplementary comparison onpressure measurements in the range (60 to 350) kPa of gauge pressure in gas media

The bilateral supplementary comparison APMP.M.P-S4 on pressure measurements in the range (60 to 350) kPa of gauge pressure in gas media was organized by National Institute of Metrology of Thailand, NIMT, as the pilot laboratory, comparing with Physikalisch-Technische Bundesanstalt of Germany, PTB. The objective of this comparison is to check equivalence of gas pressure standards between NIMT and PTB. The period of measurement covered November to December 2012. NIMT provided a transfer standard, which was a WC–WC piston–cylinder assembly (PCA) with a nominal effective area of 10 cm2 manufactured by Fluke Corporation, DHI. The measurements were performed at pressures (60, 100, 150, 200, 250, 300 and 350) kPa. The NIMT laboratory standard used was a pressure balance with a PCA of 10 cm2 manufactured by DHI and identified by serial number 0693. The PTB laboratory standard used was a pressure balance with a PCA of 10 cm2 manufactured by Desgranges et Huot (DH) and identified by serial number 288. The results of this comparison show that the relative difference of the effective area values obtained by NIMT and PTB is not larger than 4.3 ppm, which corresponds to En = 0.26. Therefore, it confirms that the gas pressure standards maintained by the two institutes, NIMT and PTB, in the pressure range (60 to 350) kPa in gauge mode are equivalent under their uncertainties claimed. The result of this comparison is essential to support the calibration and measurement capabilities (CMC) of NIMT in this pressure range.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 the APMP, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Modeling and Characterization of Reed Canary Grass Pellet Formation Phenomenon

The behaviour of pelletized reed canary grass (RCG) with selected feedstock and process parameters was studied for variation in springback characteristics based on axial changes after the compaction process. Experiments were carried out using a uniaxial single piston cylinder assembly with a proportional integral derivative temperature controller which was built in house for research purposes. A Multiple linear regression analysis based on moisture, temperature, pressure, hold time and their interaction terms was carried out to predict the length of pellets under compression in the die and excellent correlation were obtained. A finite difference method with over relaxation technique was successfully adopted to analyse the pressure and density distributions of biomass under compressive load. The compact geometry and friction between particles and die wall had effects on the pressure and density distributions in the compacted biomass. RCG pellets with lowest expansion were subjected to axial and diametrical compression tests. Bonding and failure analysis were carried out using scanning electron microscope which showed uneven breakage and interparticle voids.

Establishment of a force balanced piston gauge for very low gauge and absolute pressure measurements at NPL, India

National Physical Laboratory, the National Metrology Institute (NMI) of India is maintaining Primary standards of pressure that cover several decades of pressure, starting from 3.0E-06 Pa to 1.0 GPa. Among which a recent addition is a Force Balanced Piston Gauge, the non-rotating piston type, having better resolution and zero stability compared to any other primary pressure standards commercially available in the range 1.0 Pa to 15.0 kPa (abs and gauge). The characterization of this FPG is done against Ultrasonic Interferometer Manometer (UIM), the National Primary pressure standard, working in the range 1.0 Pa to 130.0 kPa (abs and diff) and Air Piston Gauge (APG), a Transfer Pressure Standard, working in the range 6.5 kPa to 360 kPa (abs and gauge), in their overlapping pressure regions covering both absolute and gauge pressures. As NPL being one of the signatories to the CIPM MRA, the Calibration and Measurement Capabilities (CMC) of both the reference standards (UIM & APG), are Peer reviewed and notified in the Key Comparison Data Base (KCDB) of BIPM. The estimated mean effective area of the Piston Cylinder assembly of this FPG against UIM (980.457 mm2) and APG (980.463 mm2) are well within 4 ppm and 10 ppm agreement respectively, with the manufacturer's reported value (980.453 mm2). The expanded uncertainty of this FPG, Q(0.012 Pa, 0.0025% of reading), evaluated against UIM as reference standard, is well within the reported value of the manufacturer, Q(0.008 Pa, 0.003% of reading) at k = 2. The results of the characterization along with experimental setup & measurement conditions (for gauge and absolute pressure measurements), uncertainty budget preparation and evaluation of measurement uncertainty are discussed in detail in this paper.

Tolerance design of mechanical assembly using NSGA II and finite element analysis

The technological and financial limitations in the manufacturing process are the reason for non-achievability of nominal dimension. Therefore, tolerance allocation is of significant importance for assembly. Conventional tolerance allocation methods are limited by an assumption that all parts are rigid. Every mechanical assembly consists of at least one or more flexible parts which undergo significant deformation due to inertia effect. Finite element analysis is used to determine the deformation of components in an assembly. Therefore, integration of statistical tolerance design with finite element analysis will guarantee that the optimal tolerance values of various components of the assembly obtained as end product of the tolerance design will remain within tolerance variation. Then the product can function as intended under a wide range of operating conditions for the duration of its life. In this paper, tolerance design of a piston cylinder assembly is done to demonstrate the proposed methodology.

Selective Assembly for Components with Multiple Characteristics

Considering the limitation and production costs, the selective assembly is often used to enhance the precision of assembly of complex products. This paper presents an imporved grouping method based on MOPSO( Multi-Objective Particle Swarm Optimization) for selective assembly with multiple characteristics. The properties and quality criteria of selective assembly of components with multi-quality characteristics were analyzed to establish a mathematical model. The objective function of this model is to minimize the clearance variation in selective assembly. Fitness sharing strategy and dynamic archiving strategy are introduced to improve the solving performance of MOPSO. The method is applied to the optimization in a piston-cylinder selective assembly problem. The results show that the presented method can effectively reduce the clearance variation of of the product assembly

Establishment of High Pressure Pneumatic Standard up to 40 MPa at NPLI

The current paper describes the successful establishment of high pressure pneumatic secondary standard for the realization of national pneumatic pressure scale up to 40 MPa from the previously existing 12 MPa. The traceability as well as the uncertainty in measurement was established through a continuous chain of measurements from very low pressures starting with the ultrasonic interferometer manometer and successive extension in overlapping pressure ranges. For this purpose a piston cylinder assembly designated as NPLI-40, with a pressure range of 0.2–40 MPa was coupled to a mechanical gas booster through a high gas pressure controller. We have experimentally estimated the zero pressure effective area of piston as well as the distortion coefficient which is traceable to the international system of unit SI. The CMC for the same is now on the BIPM website. The results obtained are discussed in detail.

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

This report describes a CCM key comparison of hydraulic pressure standards of seven National Metrology Institutes, listed in the chronological order of their measurements, that was carried out in the period from December 2008 to March 2010 in order to determine their degrees of equivalence in the range 50 MPa to 500 MPa of gauge pressure. The pilot laboratory was PTB. The primary pressure standards were pressure balances of different design equipped with piston–cylinder assemblies operated in free-deformation, controlled-clearance or re-entrant operation mode. The transfer standard was a piston–cylinder assembly in a pressure balance. The pressure-dependent effective areas of the transfer standard at specified pressures were reported by the participants and led to the reference values calculated as medians. Results of all participants excepting NIM agree with the reference values and with each other within the expanded uncertainties calculated with a coverage factor 2, most of them even within their standard uncertainties. In addition, the results were analysed in terms of the zero pressure effective area and the pressure distortion coefficient. Also for them agreement within expanded uncertainties (k = 2) is observed. The results of the comparison demonstrate equivalence of the laboratory standards and of the Calibration and Measurement Capabilities currently presented in the BIPM key comparison database.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 the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Results of hydraulic pressure comparison in the range from 25 MPa to 200 MPa between NIS-Egypt and NIST-USA

The results of an informal pressure comparison between the National Institute of Standards and Technology (NIST), USA, and the National Institute of Standards (NIS), Egypt, are presented. The comparison was aimed to determine degree of equivalence between NIST and NIS in the pressure range from 25 MPa to 200 MPa at a reference temperature of 20 °C. The comparison used a transfer standard (TS) which was a piston-cylinder assembly (PCA) having nominal effective area of 4.9 mm2. The results of the comparison show good agreement between the laboratory results within their claimed standard (k=1) uncertainties.

Measurement of the elastic constants of pressure balance materials using resonance ultrasound spectroscopy

To minimise the uncertainty in pressure measured with a pressure balance its pressure distortion coefficient should be determined with a sufficiently low uncertainty. The elastic constants of piston–cylinder assembly (PCA) materials are used in the calculation of the pressure distortion coefficient and thus are one of the uncertainty sources. In this work, the resonant ultrasound spectroscopy (RUS) is applied to determine the elastic constants of PCAs’ tungsten carbide (WC) materials. A validation of the RUS technique has been carried out by measurements on rectangular parallelepiped and cylindrical samples of fused quartz, steel D22S (30CrNiMo8) and a well-known WC material. The WC materials which are used in new 7MPa absolute pressure balances aimed at a redetermination of the Boltzmann constant have been studied. The measurements demonstrate RUS to be suitable for determining the Young modulus (E) and the Poisson ratio (μ) with standard uncertainties as low as 0.03% and 0.05%, respectively. They show variations in E and μ of up to 4% and 2%, respectively, for different batches of nominally the same material. In a few cases, even for samples cut out of the same WC piece, material inhomogeneities have been observed in both RUS and the density measurements with variations in E and μ of up to 0.8% and 0.5%, respectively.

Determination of the Boltzmann constant by dielectric-constant gas thermometry

Within an international project directed to the new definition of the base unit kelvin, the Boltzmann constant k has been determined by dielectric-constant gas thermometry at PTB. In the pressure range from about 1 MPa to 7 MPa, 11 helium isotherms have been measured at the triple point of water (TPW) by applying a new special experimental setup consisting of a large-volume thermostat, a vacuum-isolated measuring system, stainless-steel 10 pF cylindrical capacitors, an autotransformer ratio capacitance bridge, a high-purity gas-handling system including a mass spectrometer, and traceably calibrated special pressure balances with piston–cylinder assemblies having effective areas of 2 cm2. The value of k has been deduced from the linear, ideal-gas term of an appropriate virial expansion fitted to the combined isotherms. A detailed uncertainty budget has been established by performing Monte Carlo simulations. The main uncertainty components result from the measurement of pressure and capacitance as well as the influence of the effective compressibility of the measuring capacitor and impurities contained in the helium gas. The combination of the results obtained at the TPW (kTPW = 1.380 654 × 10−23 J K−1, relative standard uncertainty 9.2 parts per million) with data measured earlier at low temperatures (21 K to 27 K, kLT = 1.380 657 × 10−23 J K−1, 15.9 parts per million) has yielded a value of k = 1.380 655 × 10−23 J K−1 with uncertainty of 7.9 parts per million.