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A general regenerative model of the Otto engine cycle working with an ideal Bose gas is used to discuss the influence of quantum degeneracy, regeneration and finite rate heat transfer on the performance of the cycle. Based on the ...
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A general regenerative model of the Otto engine cycle working with an ideal Bose gas is used to discuss the influence of quantum degeneracy, regeneration and finite rate heat transfer on the performance of the cycle. Based on the model, expressions for some important parameters, such as the power output and efficiency of the Bose—Otto engine cycle, are derived analytically. By means of numerical calculation and illustration, the influence of the compression ratio of the two isochoric processes and the regenerator effectiveness on the performance of the cycle are discussed and evaluated in detail. Moreover, the general optimal performance characteristics of the cycle are revealed. This analysis could provide a general theoretical tool for the optimal design and operation of real power plants.
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We study the performance of an endoreversible magnetic Otto cycle with a working substance composed of a single quantum dot described using the well-known Fock-Darwin model. We find that tuning the intensity of the parabolic trap ...
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We study the performance of an endoreversible magnetic Otto cycle with a working substance composed of a single quantum dot described using the well-known Fock-Darwin model. We find that tuning the intensity of the parabolic trap (geometrical confinement) impacts the proposed cycle's performance, quantified by the power, work, efficiency, and parameter region where the cycle operates as an engine. We demonstrate that a parameter region exists where the efficiency at maximum output power exceeds the Curzon-Ahlborn efficiency, the efficiency at maximum power achieved by a classical working substance.
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This paper focuses on the overall performances of Otto, Atkinson, and Diesel air standard cycles. This study compares performance of these cycles with regard to parameters such as variable specific heat ratio, heat transfer loss, ...
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This paper focuses on the overall performances of Otto, Atkinson, and Diesel air standard cycles. This study compares performance of these cycles with regard to parameters such as variable specific heat ratio, heat transfer loss, frictional loss, and internal irreversibility based on finite-time thermodynamics. The relationship between thermal efficiency and compression ratio, and between power output and compression ratio of these cycles are obtained by numerical examples. In this study, it is assumed that during the combustion process, the heat transfer occurs only through the cylinder wall. The heat transfer is affected by the average temperature of both the cylinder wall and the working fluid. The results show that for each cycle, with the increase of the compression ratio in the specific mean piston speed, power output and thermal efficiency first increase and after reaching their maximum value, start to decrease. The results also indicate that maximum power output and maximum thermal efficiency of an Atkinson cycle could be higher than the values of these parameters in Diesel cycle and Otto cycle in the same operating conditions. The maximum power output and the maximum thermal efficiency of the Otto cycle have the lowest value among studied cycles. By increasing the mean piston speed, power output and thermal efficiency of Atkinson, Diesel, and Otto cycles start to decrease. The results of this study provide guidance for the performance analysis and show the improvement areas of practical Otto, Atkinson, and Diesel engines.
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We examine the performance of a finite-time, endoreversible Otto heat engine with a working medium of monolayer or multilayered graphene subjected to an external magnetic field. As the energy spectrum of multilayer graphene under ...
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We examine the performance of a finite-time, endoreversible Otto heat engine with a working medium of monolayer or multilayered graphene subjected to an external magnetic field. As the energy spectrum of multilayer graphene under an external magnetic field depends strongly on the number of layers, so too does its thermodynamic behavior. We show that this leads to a simple relationship between the engine efficiency and the number of layers of graphene in the working medium. Furthermore, we find that the efficiency at maximum power for bilayer and trilayer working mediums can exceed that of a classical endoreversible Otto cycle. Conversely, a working medium of monolayer graphene displays identical efficiency at maximum power to a classical working medium. These results demonstrate that layered graphene can be a useful material for the construction of efficient thermal machines for diverse quantum device applications.
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An irreversible cycle model of the micro-/nanoscaled Otto engine cycle with internal friction loss is established. The general expressions of the work output and efficiency of the cycle are calculated based on the finite system th...
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An irreversible cycle model of the micro-/nanoscaled Otto engine cycle with internal friction loss is established. The general expressions of the work output and efficiency of the cycle are calculated based on the finite system thermodynamic theory, in which the quantum boundary effect of gas particles as working substance and the mechanical Casimir effect of gas system are considered. It is found that, for a micro-/nanoscaled Otto cycle devices, the work output Wand efficiency η of the cycle can be expressed as the functions of the temperature ratio x of the two heat reservoirs, the volume ratio r_V and the surface area ratio r_A of the two isochoric processes, the dimensionless thermal wavelength λ and other parameters of cycle, while for a macroscaled Otto cycle devices, the work output W_0 and efficiency η_0 of the cycle are independent of the surface area ratio r_A and the dimensionless thermal wavelength λ. Further, the influence of boundary of cycle on the performance characteristics of the micro-/nanoscaled Otto cycle are analyzed in detail by introducing the output ratio W/W_0 and efficiency ratio η/η_0. The results present the general performance characteristics of a micro-/nanoscaled Otto cycle and may serve as the basis for the design of a realistic Otto cycle device in micro-/nanoscale.
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The goal of this research is to evaluate the effect of adding different concentrations of biodiesel to ethanol, analyzing its heating value, viscosity, flash point and density. Eight different compositions were carried out (4 blen...
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The goal of this research is to evaluate the effect of adding different concentrations of biodiesel to ethanol, analyzing its heating value, viscosity, flash point and density. Eight different compositions were carried out (4 blends with soybean biodiesel and 4 with castor bean oil), by varying the percentage of biodiesel at 1%, 3%, 5% and 10% (m/m) hydrous ethanol. The highest heating value increase was achieved in the blend with 10% soybean biodiesel (+8.70%). The blend with 10% castor bean biodiesel showed a viscosity increase of 23.8% whereas blends with 5% castor bean oil and 10% soybean biodiesel presented a viscosity increase of 15%. The flash point for blends with 10% soybean and castor bean biodiesel increased by just over 1 degrees C, improving safety condition in the handling of the fuel. The density exceeded the specified limit of 1.42% for the blend with 10% castor bean oil. This parameter is dependent on the amount of water present in ethanol, which in this study achieved the maximum limit, thus making the density of the blends exceed the threshold.
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Finite-time thermodynamic analysis of an air-standard Otto cycle is performed in this paper. The relation between net work output and efficiency of the cycle is derived. The maximum net work Output and the corresponding efficienc...
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Finite-time thermodynamic analysis of an air-standard Otto cycle is performed in this paper. The relation between net work output and efficiency of the cycle is derived. The maximum net work Output and the corresponding efficiency bound of the cycle with heat transfer considerations are also Found. Detailed numerical examples are given. the result obtained herein provide a guide to the per- Formance evaluation and improvement for practical Otto engines.
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The technology of electricity production by a mini-thermal power plant, operating on combined cycles of Otto and Rankine, is considered. The main aspects of the investigation methodology are outlined. It is shown that the design a...
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The technology of electricity production by a mini-thermal power plant, operating on combined cycles of Otto and Rankine, is considered. The main aspects of the investigation methodology are outlined. It is shown that the design and layout parameters of all the major energy elements of the developed technology allow implementing it in a block and modular version; and the efficiency of electricity supply for the proposed technology will be at least 50 %.
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Recent theoretical and experimental studies in quantum heat engines show that, in the quasi-static regime, it is possible to have higher efficiency than the limit imposed by Carnot, provided that engineered reservoirs are used. Th...
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Recent theoretical and experimental studies in quantum heat engines show that, in the quasi-static regime, it is possible to have higher efficiency than the limit imposed by Carnot, provided that engineered reservoirs are used. The quasi-static regime, however, is a strong limitation to the operation of heat engines, since an infinitely long time is required to complete a cycle. In this paper we propose a two-level model as the working substance to perform a quantum Otto heat engine surrounded by a cold thermal reservoir and a squeezed hot thermal reservoir. Taking advantage of this model we show a striking achievement, that is to attain unity efficiency even at non-null power.
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This work compares the fundamental thermodynamic underpinnings (i.e. working fluid properties and heat release profile) of various combustion strategies with engine measurements. The approach employs a model that separately tracks...
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This work compares the fundamental thermodynamic underpinnings (i.e. working fluid properties and heat release profile) of various combustion strategies with engine measurements. The approach employs a model that separately tracks the impacts on efficiency due to differences in rate of heat addition, volume change, mass addition, and molecular weight change for a given combination of working fluid, heat release profile, and engine geometry. Comparative analysis between the measured and modeled efficiencies illustrates fundamental sources of efficiency reductions or opportunities inherent to various combustion regimes. Engine operating regimes chosen for analysis include stoichiometric spark-ignited combustion and lean compression-ignited combustion including homogeneous charge compression ignition, spark-assisted homogeneous charge compression ignition, and conventional diesel combustion. Within each combustion regime, the effects of engine load, combustion duration, combustion phasing, compression ratio, and charge dilution are explored. Model findings illustrate that even in the absence of losses such as heat transfer or incomplete combustion, the maximum possible thermal efficiency inherent to each operating strategy varies to a significant degree. Additionally, the experimentally measured losses are observed to be unique within a given operating strategy. The findings highlight the fact that to create a roadmap for future directions in internal combustion engine technologies, it is important to not only compare the absolute real-world efficiency of a given combustion strategy but also to examine the measured efficiency in context of what is thermodynamically possible with the working fluid and boundary conditions prescribed by a strategy.
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