Academic literature on the topic 'Coefficient d'asymétrie du cycle de charge'
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Journal articles on the topic "Coefficient d'asymétrie du cycle de charge"
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Madani, Seyed Saeed, Erik Schaltz, and Søren Knudsen Kær. "An Experimental Analysis of Entropic Coefficient of a Lithium Titanate Oxide Battery." Energies 12, no. 14 (July 12, 2019): 2685. http://dx.doi.org/10.3390/en12142685.
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In order to understand the thermal behaviour of a lithium-ion battery, the heat generation within the cell should be determined. The entropic heat coefficient is necessary to determine for the heat generation calculation. The entropic heat coefficient is one of the most important factors, which affects the magnitude of the reversible heat. The purpose of this research is to analyze and investigate the effect of different parameters on the entropic coefficient of lithium titanate oxide batteries. In this research, a lithium ion pouch cell was examined in both charging and discharging situations. The state of charge levels range was considered from 10% to 90%, and vice versa, in 10% increments. The temperature levels vary from 5 °C to 55 °C and the voltage levels vary from 1.5 V to 2.8 V. The effect of different parameters such as initial temperature, state of charge, thermal cycle, time duration for thermal cycles, and procedure prior to the thermal cycle on the entropic coefficient of lithium titanate oxide batteries were investigated. It was concluded that there is a strong influence of the battery cell state of charge on the entropic heat coefficient compared with other parameters.
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Ning, Jing Hong, and Sheng Chun Liu. "Performance Experiment of Natural Refrigerant Cascaded Refrigeration System." Advanced Materials Research 383-390 (November 2011): 846–51. http://dx.doi.org/10.4028/www.scientific.net/amr.383-390.846.
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In this paper, the performances of natural refrigerant R290/CO2 cascaded refrigeration system using R290 as high temperature cycle refrigerant and CO2 as low temperature cycle refrigerant were investigated experimentally. The test results show that both CO2 compressor and R290 compressor start up stably and present good running performance. The start-up power and start-up electric current of CO2 compressor are higher than that of R290 compressor. The COP (Coefficient of performance) of R290/CO2 cascaded system enhances with the increase of cooling water mass flow rate and the decrease of cooling water inlet temperature. The effect of CO2 refrigerant charge on the COP of cascaded system is obvious; however, the effect of R290 refrigerant charge on the COP of cascaded system is not obvious. Hence, the hermetic scroll type compressor is urgent to be developed and used in CO2 cycle for ensuring run safely and reliably, the value of cooling water mass flow rate and the cooling water inlet temperature must be selected reasonability for saving water resource and energy, as well as the charge amount must be determined by experiment for obtaining the optimum refrigerant charge.
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Xue, Qian, and Xijuan Chen. "Optimization of Planar Array Electrostatic Sensor for Metal Surface Defect Detection." Journal of Physics: Conference Series 2370, no. 1 (November 1, 2022): 012019. http://dx.doi.org/10.1088/1742-6596/2370/1/012019.
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Static electricity is usually generated in the damage area of the metal surface due to contact friction, and the charge distribution density can reflect the size, shape, and relative position of the damage area. Based on this, a planar array electrostatic sensor is designed to detect metal surface defect in this paper, and the shielding method, number of electrodes, electrode shape, and arrangement of the sensor are optimized taking account of the induced charge value, the uniformity of sensitivity and the image correlation coefficient. Different image reconstruction algorithms (e.g. Landweber algorithm, conjugate Gradient algorithm, Tikhonov regularization and primary dual interior point method) are utilized to evaluate the performance of the designed electrostatic sensor. The results demonstrated that the sensor with hexagonal electrode shape, integrated shielding, a new arrangement, a duty cycle of 80%, and a peripheral shielding electrode, has better image quality for all the tested damage models. When using the PDIPA algorithm for image reconstruction, the image correlation coefficient can exceed 0.9.
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Xingcai, Lu, Ji Libin, Ma Junjun, and Huang Zhen. "Experimental study on the cycle-by-cycle variations of homogeneous charge compression ignition combustion using primary reference fuels and their mixtures." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 221, no. 7 (July 1, 2007): 859–66. http://dx.doi.org/10.1243/09544070jauto481.
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In this paper, the combustion stabilities and cycle-by-cycle variations of homogeneous charge compression ignition (HCCI) combustion using neat n-heptane, PRF20, PRF40, PRF50, and PRF60 were investigated. In-cylinder pressures of 100 combustion cycles for each test fuel on a single-cylinder engine were recorded. Consequently, cycle-to-cycle variations of the main combustion parameters and performance parameters were analysed, and the interdependency between the combustion parameter and performance parameters were also evaluated. The results reveal that the cycle-by-cycle variations deteriorate with the increase of the research octane number (RON). Especially, the coefficient of variations (COVs) of all parameters increase substantially when the RON of test fuels exceeds 40. For a certain test fuel, the COVs of combustion parameters that were used to depict the combustion characteristics during the early stage of combustion are very small, the COVs of combustion parameters that were used to describe the combustion characteristics of the post stage of the combustion are the largest, and the COVs of the i.m.e.p. and Pmax maintain at a middle level. Furthermore, a better interdependency also exists between the ignition timing of the low temperature reaction (LTR) and high temperature reaction (HTR), between the maximum pressure rise rate and its corresponding crank angle, between the peak values of the heat release and its corresponding crank angle.
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Jeon, Min-Ju. "Experimental Analysis of the R744/R404A Cascade Refrigeration System with Internal Heat Exchanger. Part 1: Coefficient of Performance Characteristics." Energies 14, no. 18 (September 21, 2021): 6003. http://dx.doi.org/10.3390/en14186003.
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This study evaluates the performance of an R744/R404A cascade refrigeration system (CRS) with internal heat exchangers (IHE) in supermarkets. R744 is used as the refrigerant in a low-temperature cycle, and R404A is used as the refrigerant in a high-temperature cycle. In previous studies, there are many studies including theoretical performance analysis of the CRS. However, experimental studies on the CRS are lacking, and experimental research on the R744/R404A system with an IHE is scarce. Therefore, this study provides basic data for optimal refrigeration system design by experimentally evaluating the results of modifying various parameters. The operating parameters considered in this study include subcooling and superheating, condensing and evaporating temperature, cascade evaporation temperature, and IHE efficiency in the R744 low- and R404A high-temperature cycle. The main results are summarized as follows: (1) By applying the results of this study, energy efficiency is achieved by optimizing the overall coefficient of performance (COP) of the CRS, and the refrigerant charge of the R404A cycle is minimized and economic efficiency is also obtained, enabling operation and maintenance as an environment-friendly system. (2) When designing the CRS, finding the cascade evaporation temperature that has the optimum and maximum COP according to the refrigerant combination should be considered with the highest priority.
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Tong, Xiangling, Junyuan Zhong, Xinxin Hu, and Fan Zhang. "Preparation and Performance of Highly Stable Cathode Material Ag2V4O11 for Aqueous Zinc-Ion Battery." Crystals 13, no. 4 (March 27, 2023): 565. http://dx.doi.org/10.3390/cryst13040565.
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One of the hottest research topics at present is the construction of environmentally friendly and secure aqueous zinc-ion batteries (AZIBs) using an aqueous electrolyte instead of an organic electrolyte. As a result of their diverse structure, valence state, high theoretical specific capacity, and other benefits, vanadium-based materials, which are frequently employed as the cathode of AZIBs, have drawn the attention of many researchers. The low cycle stability of zinc ion batteries (ZIBs) is mostly caused by the disintegration of the vanadium-based cathode materials during continuous charge and discharge. In this work, using 3M Zn(CF3SO3)2 as the electrolyte and hydrothermally synthesized Ag2V4O11 as the cathode material, the high-rate performance and extended cycle life of ZIBs were evaluated. The effects of different hydrothermal temperatures on the microstructure, capacity, and cycle stability of the Ag2V4O11 cathode material were examined. The experimental results show that Ag2V4O11 exhibits a typical intercalation-displacement process when used as the cathode material. The multiplicative performance and cycle stability of the cathode material were significantly enhanced at a hydrothermal temperature of 180 °C. Ag2V4O11-180 has a high discharge specific capacity of 251.5 mAh·g−1 at a current density of 0.5 A·g−1 and a long cycle life (117.6 mAh·g−1 after 1000 cycles at a current density of 3 A·g−1). According to the electrochemical kinetic investigation, the cathode material has a high pseudocapacitive charge storage and Zn2+ diffusion coefficient. This is attributed to the large layer spacing and the Ag+ anchored interlayer structure.
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Bramlage, Silke, and Klaus-Jürgen Wolter. "Effects of Vapor Phase Soldering on the Properties of Piezoceramic Materials." Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2012, CICMT (September 1, 2012): 000603–5. http://dx.doi.org/10.4071/cicmt-2012-tha24.
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Eight different PZT (lead zirconate titanate) materials (Navy Type I and II) with Curie temperatures between 250 °C and 350 °C were subjected to a standard vapor phase soldering process with a peak temperature of 240 °C for three cycles. As indicators for the depolarization, the piezoelectric charge coefficient (d33) and the coupling coefficient (keff) were measured both before and after each heat treatment. Our studies demonstrate reductions in piezoelectric properties between 5% and 20%, depending on the Curie temperature of the corresponding material. The effects of the second and third cycle were minimal. The drop in performance, especially for materials with higher Curie temperatures, is moderate, and can be accounted for in the design of the device. Thus batch soldering processes become a viable alternative to selective soldering.
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Dannoun, Elham M. A., Shujahadeen B. Aziz, Sozan N. Abdullah, Muaffaq M. Nofal, Khaled H. Mahmoud, Ary R. Murad, Ranjdar M. Abdullah, and Mohd F. Z. Kadir. "Characteristics of Plasticized Lithium Ion Conducting Green Polymer Blend Electrolytes Based on CS: Dextran with High Energy Density and Specific Capacitance." Polymers 13, no. 21 (October 20, 2021): 3613. http://dx.doi.org/10.3390/polym13213613.
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The solution cast process is used to set up chitosan: dextran-based plasticized solid polymer electrolyte with high specific capacitance (228.62 F/g) at the 1st cycle. Fourier-transform infrared spectroscopy (FTIR) pattern revealed the interaction between polymers and electrolyte components. At ambient temperature, the highest conductive plasticized system (CDLG–3) achieves a maximum conductivity of 4.16 × 10−4 S cm−1. Using both FTIR and electrical impedance spectroscopy (EIS) methods, the mobility, number density, and diffusion coefficient of ions are measured, and they are found to rise as the amount of glycerol increases. Ions are the primary charge carriers, according to transference number measurement (TNM). According to linear sweep voltammetry (LSV), the CDLG–3 system’s electrochemical stability window is 2.2 V. In the preparation of electrical double layer capacitor devices, the CDLG–3 system was used. There are no Faradaic peaks on the cyclic voltammetry (CV) curve, which is virtually rectangular. Beyond the 20th cycle, the power density, energy density, and specific capacitance values from the galvanostatic charge–discharge are practically constant at 480 W/Kg, 8 Wh/Kg, and 60 F g−1, for 180 cycles.
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Saldaña, G., José Ignacio San Martín, F. J. Asensio, Inmaculada Zamora, O. Oñederra, M. González-Pérez, and I. J. Oleagordía. "Cycle-Life Curves Determination and Modelling of Commercially Available Electric Vehicle Batteries." Renewable Energy and Power Quality Journal 19 (September 2021): 287–92. http://dx.doi.org/10.24084/repqj19.278.
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In recent decades, there has been a growing concern about the trend of global emissions, and in particular those of the transport sector. In this context, the electric vehicle is a promising technology, with some barriers still to be overcome. Among these deficiencies everything related to storage technology is found. In this sense, lithium-ion batteries are one of the options to be considered, although it is necessary to continuously monitor the state of health. Cycle life vs DoD curves are very useful for characterizing profitability in any application that considers battery storage, as well as life cycle optimization studies. Cycle life refers to the number of charge-discharge cycles that a battery can provide before performance decreases to an extent that it cannot perform the required functions (e.g., 80% compared to a fresh one in electromobility applications). In this paper, a model for calculating the Cycle Life vs DoD curves is proposed, applied to a commercially available electric vehicle, the Renault Zoe. Modelling results show R squared coefficient of determinations above 0.9890.
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Rahim, Ahmad Syahmi Abdul, Mohd Zieauddin Kufian, Abdul Kariem Mohd Arof, and Zurina Osman. "Variation of Li Diffusion Coefficient during Delithiation of Spinel LiNi0.5Mn1.5O4." Journal of Electrochemical Science and Technology 13, no. 1 (February 28, 2022): 128–37. http://dx.doi.org/10.33961/jecst.2021.00780.
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For this study, the sol gel method was used to synthesize the spinel LiNi0.5Mn1.5O4 (LNMO) electrode material. Structural, morphological, electrochemical, and kinetic aspects of the LNMO have been characterized. The synthesized LNMO was indexed with the Fd3̄m cubic space group. The excellent capacity retention indicates that the spinel framework of LNMO has the ability to withstand high rate charge-discharge throughout long cycle tests. The Li diffusion coefficient (DLi) changes non-monotonically across three orders of magnitude, from 10−9 to 10−12 cm2 s−1 determined from GITT method. The variation of DLi seemed to be related to three oxidation reactions that happened throughout the charging process. A small dip in DLi at the beginning stage of Li deintercalation is correlated with the oxidation of Mn3+ to Mn4+. While two pronounced DLi minima at 4.7 V and 4.75 V are due to the oxidation of Ni2+/Ni3+ and Ni3+/Ni4+ respectively. The depletion of DLi at the high voltage region is attributed to the occurrence of two successive phase transformation phenomena.
Dissertations / Theses on the topic "Coefficient d'asymétrie du cycle de charge"
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Didych, Iryna. "Estimation of structural integrity and lifetime of important structural elements." Electronic Thesis or Diss., Université Clermont Auvergne (2021-...), 2021. http://www.theses.fr/2021UCFAC116.
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Ce travail a été réalisé sous co-tutelle entre l’Université Technique Nationale de Ternopil (Ukraine) et l’Université Clermont Auvergne, CNRS, SIGMA Clermont, l’Institut Pascal à Clermont-Ferrand (France). La thèse porte sur la solution d’une tâche scientifique réelle d’évaluer la résistance et la durabilité des éléments responsables des structures. L’objectif de l’étude est d’évaluer la résistance et la durabilité résiduelle des éléments structurels par des méthodes d’apprentissage automatique. La plupart des parties des machines et des composants des structures pendant l'exploitation sont influencés par des charges de nature différente. Ces forces sont soit directement attachées à l’élément, soit transmises par des éléments adjacents qui y sont reliés. Pour le fonctionnement normal des parties responsables des structures,chaque élément doit être d’une taille et d’une forme qui lui permettent de résister aux charges. En particulier, il doit être solide, pas avoir de déformation significative sous tension, rigide et conserver sa forme d’origine. La durée de vie estimée des machines et des structures peut être prédite à l’aide des diagrammes de la croissance des fissures de fatigue des matériaux. Dans la plupart des cas, les données expérimentales présentent certaines variations dont il faut tenir compte. L’expérimentation prend souvent beaucoup de temps et de ressources humaines. Par conséquent, il est conseillé d'apprendre à calculer la durabilité par des méthodes d'apprentissage automatique, en particulier les réseaux de neurones, les arbres renforcés, les forêts aléatoires, les machines à vecteurs de support et les k-plus proches voisinsThis work has been performed under co-tutelle supervision between Ternopil IvanPuluj National Technical University in Ternopil (Ukraine) and UniversityClermont Auvergne, CNRS, SIGMA Clermont, Institut Pascal in Clermont-Ferrand (France).This thesis solves the scientific task of responsible structural elements strength andlifetime evaluation. The aim of the thesis is to evaluate the strength and residuallifetime of structural elements by machine learning methods.Most parts of machines and structural elements while being in service are under theinfluence of loads of various nature. Such forces are applied either directly to theelement or transmitted through neighbor elements connected to it. For the normaloperation of the responsible structures parts, each element must have certain sizeand shape that will withstand the loads acting on it. In particular, it must haveappropriate strength properties, not deform significantly under the action ofstresses, be rigid, and preserve its original shape.The calculated residual lifetime of machines and structures can be predicted usingfatigue crack growth (FCG) diagrams. Often, the experimental data have a certainspread, which should be taken into account in their analysis. The experimentalmethod often takes a lot of time and human resources. Therefore, it is advisable tolearn how to calculate the residual lifetime using machine learning methods,particularly, neural networks, boosted trees, random forests, support-vectormachines and the method of k–nearest neighbors
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Bigot, Jérôme. "Étude du refroidissement diphasique d'une pile à combustible de traction automobile." Université Joseph Fourier (Grenoble ; 1971-2015), 2005. http://www.theses.fr/2005GRE10225.
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Cette étude s'inscrit dans le cadre du refroidissement des piles à combustible de traction automobile. La solution étudiée au cours de ce travail est le recours à écoulement en ébullition dans des mini-canaux situés à l'intérieur de la pile. Pour améliorer les connaissances encore disparates dans la bibliographie, deux bancs d'essais ont été construits. Le premier est constitué d'un seul mini-canal de section carré de 1 mm de côté pour se familiarise avec les techniques de mesure de pression et de température dans des petites dimensions et identifier les régimes d'ébullition prédominants. Le deuxième mesure les pertes de pression et le coefficient d'échange thermique dans des plaques constituées de plusieurs canaux en parallèle de section rectangulaire de 2,6 mm par 0,5 mm de côté. Les mesures obtenues montrent qu'en monophasique les résultats connus sur le facteur de frottement et le nombre de Nusselt pour des canaux conventionnels continuent de s'appliquer. En diphasique, le modèle homogène et celui de Mishima [1996] prédire les mesures de pertes de pression par frottement avec un écart moyen respectif de 29 et 15%. Pour le coefficient d'échange thermique, les corrélations utilisées donnent de bons résultats pour le calcul de la valeur moyenne mais échouent pour prédire les variations locales. Une représentation de ce coefficient en fonction de la vitesse apparente est proposée. Elle améliore les prédictions sur nos mesures ainsi que sur le titre critique d'apparition de l'assèchement pour notre dispositif expérimental et celui d'Agostini [2002]This study lies within the scope of the fuel cell cooling for automobile traction. The solution studied during this work is the recourse to boiling flow in mini-channels located inside the pile. To improve still disparate knowledge in the bibliography, two experimental set-ups have been elaborated. First consists of only one square mini-channel of 1 mm on side to investigate the measurement techniques of pressure and temperature in small dimensions and to identify the prevalent two-phase flow pattern. The second gives pressure drop and heat transfer coefficient measurements in rectangular multi-channels configurations with a section of 2,6 mm by 0,5 mm on side. These measurements show that the results known on the factor of friction and the number of Nusselt for conventional channels in single phase flow continue to apply. In two phase flow, the homogeneous and Mishima [1996] models are able to predict measurements of frictional pressure drop with a respective average deviation of 29 and 15%. For the heat transfer coefficient, the correlations used give good results for the calculation of the average value but fail to predict the local variations. A representation of this coefficient according to superficial velocity has been proposed. It improves the predictions to our measurements and to the critical quality of the dry-out onset for our experimental set-up and that of Agostini [2002]
Book chapters on the topic "Coefficient d'asymétrie du cycle de charge"
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Thakur, Vaishali, and Ekta Sharma. "Application of Carbonaceous Quantum dots in Energy Storage." In Carbonaceous Quantum Dots: Synthesis And Applications, 178–91. BENTHAM SCIENCE PUBLISHERS, 2023. http://dx.doi.org/10.2174/9789815136265123010012.
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Carbon quantum dots (CQDs) are a type of carbon nanomaterial that has lately received attention as a potential replacement for standard semiconductor quantum dots (QDs). CQDs feature a quasi-spherical structure and amorphous to nanocrystalline carbon cores with diameters of 10-20 nm. Based on the carbon core, CQDs are further classified as graphene quantum dots (GQDs), carbon nanodots (CNDs), and polymer dots (PDs). CQDs exhibit unique electrical and optical properties due to their bigger edge effects and quantum confinement; better than graphene oxide nanosheets, they can also be easily split into electrons and holes due to their high dielectric constant and extinction coefficient. CQDs are crucial in the sector of energy storage and transformation because CQDs offer the advantageous properties of low toxicity, environmental friendliness, low cost, photostability, favourable charge transfer with increased electronic conductivity, and comparably simple synthesis processes. Due to their superior crystal structure and surface properties, CQD nanocomposites often helped to shorten charge transfer paths and maintain electrode material cycle stability. CQDs provide cost-effective and environmentally friendly nanocomposites used for supplying high energy density and stable electrodes for energy storage applications. This chapter provides a summary of the role that CQDs play in energy transmit technologies, including solar cells, supercapacitors, lithium-ion batteries, and hydrogen and oxygen evolution reactions.
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"Performance of Adsorptive Heat Storage Devices for Heat Supply." In Technology Development for Adsorptive Heat Energy Converters, 124–73. IGI Global, 2021. http://dx.doi.org/10.4018/978-1-7998-4432-7.ch005.
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The chapter is focused on modelling of performance of adsorptive heat storage devices and estimation of performance of heat storage devices. Two groups of models of adsorptive heat storage units suggested previous researchers are analyzed. The first one is focused on predicting the heat energy storage density, it being based on Dubinin-Polanyi theory. The second one is devoted to analyzing the kinetic of adsorption processes and performance of the adsorber or adsorptive-desorptive reactor filled with traditional adsorbent or salt which forms crystalline hydrates. The key drawback of both groups of models concerns with considering only one stage of exploitation of adsorptive heat storage device in spite of its operating in two-stage mode, that is, alternating discharge (adsorption) and charge (regeneration). It inhibits estimation of efficiency of adsorptive heat storage device basing on full operating cycle and its involving in heat supply system. Two algorithms for estimation of operating parameters are proposed by authors for closed-type and open-type heat storage devices. The algorithm for calculation of operating parameters of closed type adsorptive heat storage device is proposed: calculation of the mass transfer coefficient, adsorption, useful heat, that is, heat of adsorption, determination of the heat input, it being calculated as heat inputs for heating the adsorbent, device housing, water in the tank, evaporation of water in the tank, heating of the adsorbed water and desorption. Then efficiency factor is calculated. The operating characteristics of a closed-type heat energy storage device were studied when the composite adsorbent ‘silica gel – sodium sulphate' used. The effect of the humid airflow velocity on the efficiency factor is taken into account by introducing a coefficient equal to the value of the adsorption. An increase in the efficiency coefficient was stated when the velocity and relative humidity of the airflow. It is shown that the humid air flow temperature practically does not affect its value. Having been used the suggested algorithm, the optimal operating characteristics of an adsorptive heat storage device of a closed type based on a composite adsorbent ‘silica gel – sodium sulphate' for a private house heating system are revealed to be humid air velocities of 0.6 – 0.8 m/s and relative humidity 40 – 60%. When these operational data applied, the efficiency coefficient is shown to reach the maximum values (about 55%). Algorithm of calculation of operating parameter of open-type heat storage device includes computation of mass transfer coefficient, adsorption, useful heat (heat of adsorption), heat input for heating the adsorbent, device casing, water in the humidifier, evaporation of water, heating the adsorbed water, desorption, and calculating efficiency coefficient. Performance of open-type heat storage device based on the composite adsorbent ‘silica gel – sodium sulphate' is estimated. The optimal operating conditions of the heat accumulating device which allow operating with maximal magnitudes of efficiency coefficients 53 – 57% are stated to be humid airflow speed of 0.6 – 0.8 m/s and relative humidity of 40 – 60%. Correlation between efficiency factors obtained by experiments and calculated with suggested algorithm is confirmed. The possibility of reducing the power consumption when heat storage devices applied in 2,4 – 90 times versus decentralized heating systems on basis of solid fuel boiler, gas boiler and electric boiler is stated when open-type sorptive heat storage device used. Results of the study can be used to develop adsorptive storage devices in decentralized heat supply and ventilation systems and adsorption units for utilization of low-temperature waste heat.
Conference papers on the topic "Coefficient d'asymétrie du cycle de charge"
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Gardiner, David P., W. Stuart Neill, and Wallace L. Chippior. "Real-Time Monitoring of Combustion Instability in a Homogeneous Charge Compression Ignition (HCCI) Engine Using Cycle-by-Cycle Exhaust Temperature Measurements." In ASME 2012 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/icef2012-92191.
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This paper describes an experimental study concerning the feasibility of monitoring the combustion instability levels of an HCCI engine based upon cycle-by-cycle exhaust temperature measurements. The test engine was a single cylinder, four-stroke, variable compression ratio Cooperative Fuel Research (CFR) engine coupled to an eddy current dynamometer. A rugged exhaust temperature sensor equipped with special signal processing circuitry was installed near the engine exhaust port. Reference measurements were provided by a laboratory grade, water-cooled cylinder pressure transducer. The cylinder pressure measurements were used to calculate the Coefficient of Variation of Indicated Mean Effective Pressure (COV of IMEP) for each operating condition tested. Experiments with the HCCI engine confirmed that cycle-by-cycle variations in exhaust temperature were present, and were of sufficient magnitude to be captured for processing as high fidelity signal waveforms. There was a good correlation between the variability of the exhaust temperature signal and the COV of IMEP throughout the operating range that was evaluated. The correlation was particularly strong at the low levels of COV of IMEP (2–3%), where production engines would typically operate. A real-time combustion instability signal was obtained from cycle-by-cycle exhaust temperature measurements, and used to provide feedback to the fuel injection control system. Closed loop operation of the HCCI engine was achieved in which the engine was operated as lean as possible while maintaining the COV level at or near 2.5%.
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Juttu, S., S. S. Thipse, Praveen Mishra, N. B. Dhande, N. V. Marathe, and M. K. Gajendra Babu. "Experimental Investigations of Cycle-to-Cycle and Cylinder-to-Cylinder Variation of PCCI Combustion With High Injection Pressures." In ASME 2010 Internal Combustion Engine Division Fall Technical Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/icef2010-35021.
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Recently HCCI combustion concept has gained the attention of industry and academia due to its potential to reduce NOx and PM emissions simultaneously from diesel engines. The HCCI concept also called as Partially-Premixed Charge Compression Ignition (PCCI) when heavy fuel like diesel is used as fuel. To achieve homogeneous mixture of diesel+air+residual gases, high injection pressures are required with fine atomization. The cycle-to-cycle and cylinder-to-cylinder variations in rail pressure and EGR ratio caused to variations in engine performance. In this study combustion stabilities and cycle-to-cycle variations of diesel engine operated in PCCI combustion mode were investigated at different fuel injection pressures on a 4-cylinder, 4-stroke diesel engine. The experiments were conducted with 500bar, 1000bar, 1500bar and 1800bar injection pressures at low load (IMEP = 2bar) and 50% load (IMEP = 8.5bar) at 2500 and 3000 rpm. No EGR was used at low load condition and 50% EGR was used at 50% load at all injection pressures. In-cylinder pressures of 100 cycles were recorded for each test conditions running with PCCI mode. Consequently, cycle-to-cycle variations of the maximum Rate of Heat Release (ROHRmax), maximum Total Heat Release (THRmax), IMEP and Pmax were analyzed and evaluated using Coefficient of Variation (COV) of each parameter. The significant difference in COV from cylinder-to-cylinder was observed at higher injection pressures. With high injection pressures, wide range of cycle-to-cycle variations were observed in engines operated in PCCI combustion mode limiting the injection pressure and operating range of engine. The results show that the injection pressure need to be optimized with respect to load to control the PCCI combustion at constant EGR ratio to minimize the cycle-to-cycle variations and also extend the operating range of PCCI mode.
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See, Y., M. Wang, J. Bohbot, and O. Colin. "Validation of Species-Based Extended Coherent Flamelet Model in a Large Eddy Simulation of a Homogeneous Charge Spark Ignition Engine." In ASME 2020 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/icef2020-2942.
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Abstract The Species-Based Extended Coherent Flamelet Model (SB-ECFM) was developed and previously validated for 3D Reynolds-Averaged Navier-Stokes (RANS) modeling of a spark-ignited gasoline direct injection engine. In this work, we seek to extend the SB-ECFM model to the large eddy simulation (LES) framework and validate the model in a homogeneous charge spark-ignited engine. In the SB-ECFM, which is a recently developed improvement of the ECFM, the progress variable is defined as a function of real species instead of tracer species. This adjustment alleviates discrepancies that may arise when the numerical treatment of real species is different than that of the tracer species. Furthermore, the species-based formulation also allows for the use of second-order numeric, which can be necessary in LES cases. The transparent combustion chamber (TCC) engine is the configuration used here for validating the SB-ECFM. It has been extensively characterized with detailed experimental measurements and the data are widely available for model benchmarking. Moreover, several of the boundary conditions leading to the engine are also measured experimentally. These measurements are used in the corresponding computational setup of LES calculations with SB-ECFM. Since the engine is spark ignited, the Imposed Stretch Spark Ignition Model (ISSIM) is utilized to model this physical process. The mesh for the current study is based on a configuration that has been validated in a previous LES study of the corresponding motored setup of the TCC engine. However, this mesh was constructed without considering the additional cells needed to sufficiently resolve the flame for the fired case. Thus, it is enhanced with value-based Adaptive Mesh Refinement (AMR) on the progress variable to better capture the flame front in the fired case. As one facet of model validation, the ensemble average of the measured cylinder pressure is compared against the LES/SB-ECFM prediction. Secondly, the predicted cycle-to-cycle variation by LES is compared with the variation measured in the experimental setup. To this end, the LES computation is required to span a sufficient number of engine cycles to provide statistical convergence to evaluate the coefficient of variation (COV) in peak cylinder pressure. Due to the higher computational cost of LES, the runtime required to compute a sufficient number of engine cycles sequentially can be intractable. The concurrent perturbation method (CPM) is deployed in this study to obtain the required number of cycles in a reasonable time frame. Lastly, previous numerical and experimental analyses of the TCC engine have shown that the flow dynamics at the time of ignition is correlated with the cycle-to-cycle variability. Hence, similar analysis is performed on the current simulation results to determine if this correlation effect is well-captured by the current modeling approach.
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Fu, Xue-Qing, Yan Zhang, Zhanming Ding, Anbang Zhuang, Wei Zhu, Linlin Hou, Jianghua cheng, and Shuyong Zhang. "Numerical Study on High-Load Performance of a Two-Stage Boosted Poppet-Valved Two-stroke Diesel Engine." In WCX SAE World Congress Experience. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2023. http://dx.doi.org/10.4271/2023-01-0443.
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<div class="section abstract"><div class="htmlview paragraph">Two-stroke cycle is one of the most effective methods to increase the torque and power output of a four-stroke engine due to the doubled firing frequency compared to four-stroke cycle at the same engine speed. As the two-stroke cycle lacks separate intake and exhaust strokes, the positive pressure difference between intake and exhaust ports is required to drive fresh charge into the cylinder, and is affected by intake port structures due to the different amounts of short-circuited fresh charge during scavenging process. To evaluate the effects of intake port structures on the high-load performance of a boosted poppet-valved two-stroke diesel engine, one-dimensional gas dynamic model and three-dimensional computational fluid dynamics model were established and used to predict the high-load performance of the boosted two-stroke diesel engine with top-entry intake ports, inclined side-entry intake ports, and side-entry intake ports, respectively. The results show that the engine with inclined side-entry intake ports has a much higher scavenging quality coefficient than the engine with other intake port structures. The maximum brake power of the 4.1 L four-cylinder two-stroke diesel engine equipped with a two-stage serial boosting system with a turbocharger and a downstream supercharger can reach 1.4 times that of a 5.1 L four-cylinder four-stroke diesel engine in the cases of top-entry and inclined side-entry intake ports, while that of the two-stroke engine with side-entry intake ports can only reach 1.2 times that of the four-stroke engine due to more power consumed by the supercharger resulted by large amount of short-circuited fresh charge. When the brake power of two-stroke engine is equal to 1.2 times that of the four-stroke engine, the intake pressure and mass flow rate of fresh charge are obviously decreased about 37.3% and 39.3% when intake port structure is changed from side-entry intake ports to inclined side-entry intake ports.</div></div>
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Dalkilic¸, Ahmet Selim, and Somchai Wongwises. "Comparison of Various Alternative Refrigerants for Vapour Compression Refrigeration Systems." In ASME/JSME 2011 8th Thermal Engineering Joint Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajtec2011-44267.
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Single-stage vapour compression refrigeration system was compared with an actual vapour compression cycle, single-stage process with internal heat exchanger, and a two-stage process with economiser using the refrigerants of HCFC-22, CFC-502 and their alternatives such as HFC-134a, HFC-32, HFC-152a, HFC-404A, HFC-407C, HFC-507, HFC-410A. A theoretical performance study on a cascade refrigeration system was performed using two refrigeration cycles connected through the heat exchanger in the middle working as the evaporator for the high pressurized cycle and condenser for the low pressurized cycle. Other performance study was performed using a two-stage cascade refrigeration system having low and high pressure compressors connected through the mixing chamber in the middle. The condensation temperatures were between 30 and 50 °C, evaporation temperatures were between −50 °C and 5 °C and heat exchanger and economiser temperatures were kept as constant for the comparisons. Some of the alternative refrigerants’ coefficients of performance values are found to be higher than their base traditional pure refrigerants. The effects of the main parameters of performance analysis such as refrigerant type, degree of subcooling, and superheating on the performance coefficient, refrigerant charge rate and volumetric refrigeration capacity are investigated for various operating conditions as case studies.
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Zhou, Rongliang, Juan Catano, Tiejun Zhang, John T. Wen, Greg J. Michna, Yoav Peles, and Michael K. Jensen. "The Steady-State Modeling and Analysis of a Two-Loop Cooling System for High Heat Flux Removal." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11500.
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Steady-state modeling and analysis of a two-loop cooling system for high heat flux removal applications are studied. The system structure proposed consists of a primary pumped loop and a vapor compression cycle (VCC) as the secondary loop to which the pumped loop rejects heat. The pumped loop consists of evaporator, condenser, pump, and bladder liquid accumulator. The pumped loop evaporator has direct contact with the heat generating device and CHF must be higher than the imposed heat fluxes to prevent device burnout. The bladder liquid accumulator adjusts the pumped loop pressure level and, hence, the subcooling of the refrigerant to avoid pump cavitation and to achieve high critical heat flux (CHF) in the pumped loop evaporator. The vapor compression cycle of the two-loop cooling system consists of evaporator, liquid accumulator, compressor, condenser and electronic expansion valve. It is coupled with the pumped loop through a fluid-to-fluid heat exchanger that serves as both the vapor compression cycle evaporator and the pumped loop condenser. The liquid accumulator of the vapor compression cycle regulates the cycle active refrigerant charge and provides saturated vapor to the compressor at steady state. The heat exchangers are modeled with the mass, momentum, and energy balance equations. Due to the projected incorporation of microchannels in the pumped loop to enhance the heat transfer in heat sinks, the momentum equation, rarely seen in previous refrigeration system modeling efforts, is included to capture the expected significant microchannel pressure drop witnessed in previous experimental investigations. Electronic expansion valve, compressor, pump, and liquid accumulators are modeled as static components due to their much faster dynamics compared with heat exchangers. The steady-state model can be used for static system design that includes determining the total refrigerant charge in the vapor compression cycle and the pumped loop to accommodate the varying heat load, sizing of various components, and parametric studies to optimize the operating conditions for a given heat load. The effect of pumped loop pressure level, heat exchangers geometries, pumped loop refrigerant selection, and placement of the pump (upstream or downstream of the evaporator) are studied. The two-loop cooling system structure shows both improved coefficient of performance (COP) and CHF overthe single loop vapor compression cycle investigated earlier by authors for high heat flux removal.
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Baratta, Mirko, Stefano d’Ambrosio, Ezio Spessa, and Alberto Vassallo. "Analysis of Cyclic Variability in a Bi-Fuel Engine by Means of a ‘Cycle-Resolved’ Diagnostic Technique." In ASME 2005 Internal Combustion Engine Division Fall Technical Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/icef2005-1214.
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The paper investigates cyclic variability in a fast-burn engine running on both gasoline or CNG by applying a new diagnostic technique based on a quasi-dimensional multizone model. Two different procedures were proposed for the ‘cycle-resolved’ calibration of the heat transfer correlation in the multizone model. The first procedure relates the cycle-resolved unreleased energy of the charge at the end of the flame propagation to the combustion efficiency determined from the average exhaust gas composition. The second procedure evaluates the coefficient in the heat transfer correlation through the application of the overall energy balance to the ensemble-cycle combustion and keeps them unchanged for all cycles. Both methods gave similar results, though the second procedure showed to be more physically consistent and in better agreement with the experimental results reported in the literature. The experimental matrix covered different engine speeds (n = 2000–4600 rpm), loads (bmep = 200–790 kPa), relative air-fuel ratios (RAFR = 0.80–1.60) and spark advances (SA ranging from 8 deg retard to 2 deg advance from MBT), for both CNG and gasoline operations, 100 consecutive in-cylinder pressure cycles were analyzed for each point in the test matrix and the sensitivity to cyclic variability of pressure, burn-rate and flame front position related parameters was analyzed. Main results showed that maximum pressure derivative, delay from SA of detected combustion start, NO exhaust concentration and maximum burning speed were the most sensitive parameters to cyclic variability. Strong correlations were found to hold between PFP and burned-gas temperature peak value, as well as between peak values of HRR and burning speed. On the contrary, some seemingly reasonable correlations were not assessed: for example, delay from SA of detected combustion start is related neither with PFP value nor with combustion duration. Finally, the results from mean cycle and cycle-resolved calculations were compared. Though they were usually in good agreement, in the case of NO emission and combustion interval calculation. cycle-resolved approach results in improved accuracy.
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Zhou, Rongliang, Juan Catano, Tiejun Zhang, John T. Wen, Greg Michna, Yoav Peles, and Michael K. Jensen. "The Steady-State Modeling and Static System Design of a Refrigeration System for High Heat Flux Removal." In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-69074.
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This paper investigates the steady-state modeling and static system design of a refrigeration system for high heat flux removal of high power electronics system. The refrigeration cycle considered consists of multiple evaporators, liquid accumulator, compressor, condenser and expansion valves. In contrast with conventional refrigeration systems with liquid-to-liquid heat exchangers for temperature control where the critical heat flux (CHF) is not a major concern, refrigeration systems for high heat flux removal have to ensure that the incoming heat flux is lower than the CHF to prevent device burnout. Since the superheated region in the evaporator has much lower heat transfer coefficient than the two-phase region, the evaporator exit should be two-phase for ensure sufficiently high CHF. The two-phase evaporator exit necessitates the inclusion of a heated liquid accumulator for the safe operation of the compressor to ensure only saturated vapor enters the compressor. The evaporators and condenser of the cycle are modeled by the mass balance, momentum balance, and energy balance equations. Due to the future utilization of microchannels to enhance heat transfer in heat exchangers, the momentum equation, rarely seen in previous modeling efforts, is included here to capture potentially significant pressure drops. The expansion valve and compressor are modeled as static components. The accumulator is modeled to regulate the active refrigeration charge of the system and to provide just enough heat to the outflow of the evaporator such that the inflow of the compressor is always saturated vapor. Based on the steady-state model, the static system design issues include determining the total refrigerant charge of the system to accommodate the varying operation conditions, sizing of the compressor and accumulator, and finding the optimal operation condition for given incoming heat flux to optimize the Coefficient of Performance (COP) while satisfying the CHF and other constraints. The steady-state model will be validated on a testbed currently in construction. The testbed consists of a reciprocating compressor with variable frequency drive, a plate condenser, a heated accumulator (tank with electric heater), three evaporators with immersed electrically controlled heaters, and one electronic expansion valve for each evaporator.
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Vorraro, Giovanni, and James W. G. Turner. "Numerical assessment of the performance and emissions of a compact Wankel rotary engine applied as a range extender on the BMW i3 model." In 2023 JSAE/SAE Powertrains, Energy and Lubricants International Meeting. 10-2 Gobancho, Chiyoda-ku, Tokyo, Japan: Society of Automotive Engineers of Japan, 2023. http://dx.doi.org/10.4271/2023-32-0068.
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<div class="section abstract"><div class="htmlview paragraph">Amongst all the hybrid-vehicles technologies and layouts, range-extended electric vehicles are the ones with the real prospect to reduce the emissions produced by the thermal machine when in driving conditions, while assuring an adequate range for the common user. The BMW i3 represents one of the most successful series hybrid electric vehicles, having been on the market since 2013. Given the complexities of a hybrid layout employing both thermal and electrical machines, the range extender must have compactness and lightweight characteristics in addition to a suitable power output for the vehicle. Usually, standard 4- stroke small-displacement engines are employed for this application, with the BMW i3 employing a 2- cylinder range extender. More interestingly, a Wankel rotary engine can provide the same amount of mechanical power by reducing the weight and the volume of nearly a third to the equivalent 4-stroke engine. In this study a numerical assessment of the Advanced Innovative Engineering UK (AIE UK) 225CS Wankel rotary engine as a range extender for the BMW i3 was carried out. A full vehicle model of the BMW i3 was built in Siemens Simcenter Amesim 2021.2 to evaluate the behaviour of the aforementioned engine as a range extender. The engine sub-model used was a Mean Value Engine Model (MVEM) set up by implementing the experimental data collected during previous experimental campaign while the BMW i3 chassis sub-model was characterised by using the publicly available data from an Argonne National Laboratory benchmarking project (vehicle weight, front surface, drag coefficient, tires dimensions, etc.). Finally the model was tested over the standard Worldwide harmonized Light vehicles Test Procedure (WLTP) driving cycle in both Charge Depleting and Charge Sustaining modes.</div></div>
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Fan, Xiaowei, Xianping Zhang, Xinli Wei, Fang Wang, and Xiaojing Zhang. "Performance Assessment of Blends of CO2 With Eco-Friendly Working Fluids for Heat Pump Applications." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-63354.
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Since pure CO2 as refrigerant has some disadvantages failing to meet requirements, binary blends of CO2 (or R744) with other eco-friendly working fluids, R290, R1270, R170, RE170 and HFC134a are proposed in this paper to be used for medium temperature heat pump systems. The eco-friendly refrigerant mixtures can reduce the heat rejection pressure as that for pure CO2, and meanwhile suppress the flammability, explosivity as that for pure HCs or RE170. Based on the pinch point of heat transfer, the numerical models of heat pump cycle using CO2-based mixture are developed. With a comprehensive consideration of heating coefficient of performance (COPh), optimum heat rejection pressure, volumetric heating capacity, discharge temperature, the binary mixture CO2/R290 is determined as the most suitable working fluid for the given heat pump application. Compared to pure CO2, the optimum heat rejection pressure of mixture for 95/5, 90/10, 85/15 and 80/20 is decreased by 0.82, 0.94, 1.06 and 1.86MPa respectively for heat sink outlet temperature of 65°C. The experimental testrig is designed and set up for the transcritical heat pump system. The experimental study with different CO2 mass fraction has been carried out, which conducts a study on the variations of heat pump performance, component’s mass fraction and working fluid charge. The experimental results validated the CO2/R290 natural mixture proposed in theory. The experimental results provide useful references on the optimization and improvement of CO2/R290 heat pump testrig.