查看更多>>摘要：Dimethyl ether is a new-generation alternative fuel to mitigate cold-start issues in compression ignition engines. It has a higher cetane number and offers superior spray atomization and fuel evaporation characteristics. This simulation study compares dimethyl ether and baseline diesel sprays and their evaporation characteristics in a constant volume spray chamber. Fuel properties greatly influence spray atomization and evaporation characteristics. This study is based on the Eulerian-Lagrangian approach adopted in the Reynolds-averaged Navier-Stokes framework. The liquid spray penetration obtained by simulation matched well with the experimental results of dimethyl ether and baseline diesel. Spray model constants were tuned for diesel and dimethyl ether separately, as the fuel properties of both test fuels are completely different. These tuned models were used to simulate dimethyl ether and diesel sprays at fixed fuel injection timings and ambient conditions. Results showed a lower spray penetration length for dimethyl ether than baseline diesel because of the flash boiling of dimethyl ether. Smaller diameter droplets formed due to dimethyl ether's lower viscosity, density, surface tension, and higher evaporation rate. The reduction in Sauter mean diameter was quite sharp after the start of injection for the dimethyl ether. Diesel spray showed retarded spray atomization and evaporation characteristics compared to dimethyl ether. The vapor penetration length of both fuels was almost the same; however, the vapor mass fraction was higher for dimethyl ether than baseline diesel. Dimethyl ether spray exhibited superior spray atomization and improved evaporation of fuel droplets.
查看更多>>摘要：The current research investigates the spray behavior of lemon peel oil (LPO) and butanol in a controlled environment under various engine-like conditions. The liquid spray morphology of both fuel blends is captured using a standard Mie scattering technique, and the liquid spray penetration length is compared to a baseline fuel isooctane. In order to simulate and create engine-like conditions, these experiments are carried out in a constant volume chamber under various pressure and temperature conditions. Furthermore, the combustion quality of binary and ternary blends is studied using an optical gasoline direct injection engine at three different injection timings. According to the constant volume spray study, isooctane has the shortest penetration. Because of its higher boiling point, LPO has a longer liquid spray penetration length. Despite its lower boiling point, butanol penetrates better than isooctane. The temperature was also discovered to influence liquid spray tip penetration length more than pressure significantly. In-cylinder combustion imaging results also revealed that injection timing significantly impacts combustion. Although butanol improves combustion, LPO-dominant blends demonstrated more diffusion burning due to poor evaporation characteristics. The blends prepared for the study were similar to gasoline in combustion conditions. It was discovered that these blends ran optimally without requiring any modifications to existing engines, even though late injection is recommended to improve combustion quality and peak performance.
查看更多>>摘要：A nonlinear system identification approach was used to exploit the nonlinearly in the exergy of the system and reduce it into two or more interconnected elements. The Hammerstein-Wiener (H-W) methodology was adopted to describe the dynamics of a passive thermal system using a combination of nonlinear and linear blocks. Here, the linear block is a discrete transfer function, which symbolizes the dynamic component of the model. The proposed model was validated using the state functions measured for the solar air collector. The mean absolute percentage error (MAPE) for enthalpy changes falls in the domain of -0.01% to 0.01%, whereas it varied from -0.06% to 0.02% as the entropy of the system changed with time. Similarly, the MAPE encountered while evaluating the exergy of the system was in the closed interval of-0.066% to -0.0017%. The average exergy gain by the H-W model across the 1st and IInd passages was, respectively, 0.90 kJ • kg~(-1) (8.10 g• s~(-1)), 0.61kJ•kg~(-1) (10.10 g•s~(-1)) and 0.46 kJ•kg~(-1) (12.10 g•s~(-1)); and 0.57 kJ•kg~(-1) (8.10 g•s~(-1)), 0.48 kJ•kg~(-1) (10.10 g•s~(-1)), and 0.79 kJ • kg~(-1) (12.10 g•s~(-1)). The proposed model exhibited good fitting with the validation data.
查看更多>>摘要：Hybrid drive wind power generation systems (WPGSs) equipped with speed-regulating differential mechanisms (SRDMs) have emerged as a promising solution for integrating large-scale wind energy into the power grid without the need for partially or fully rated converters. This article presents a comprehensive study on the dynamic analysis and parameter optimization of the SRDM-based transmission, with the aim of providing a sound foundation for the design and performance improvement of hybrid drive WPGSs. This study first formulates the kinematics, power flow, and mechanical efficiency of the SRDM and then proposes an effective parameter configuration model for optimizing the speed ratios of the key link units. The objective function is set as the minimum peak power required for speed regulation by the SRDM. Furthermore, to deal with the unique mechanical features such as dual power inputs, continuously variable transmission, and time-varying steering mechanism, an appropriate nonlinear dynamic modeling method of the SRDM transmission is developed. The torsion-translation vibration equations are derived and solved using the Runge-Kutta numerical integral method, considering randomly changing wind speed inputs and time-varying internal/external excitations. Results reveal that the sun gear experiences severe vibrations with the maximal and average vibration displacements of 0.563 mm and 0.112 mm, respectively, in the circumferential direction, while the planet gear exhibits complex frequency responses. Finally, specialized case studies are demonstrated to verify the proposed approaches, showing the satisfactory on-grid operating performance of the proposed SRDM-based WPGSs.
查看更多>>摘要：Enhancing nocturnal productivity holds promise for boosting the effectiveness of solar desalination setups. Current research concentrates on an innovative strategy: the integration of paraffin wax and Jatropha biodiesel as a composite energy storage material (CESM) to amplify distilled water output during nighttime. The composite material, comprising Jatropha biodiesel and paraffin wax in a 1:1 ratio by weight, is meticulously examined for its impact on productivity, juxtaposed against a conventional solar still (CSS). Results reveal a substantial improvement in thermal conductivity with CESM, exhibiting a noteworthy 20.37%% surge compared to pure paraffin wax. Furthermore, a solar still with biodiesel and phase change material (SSBDPCM) is pitted against a CSS, with continuous monitoring of water and absorber temperatures alongside distillate production. The findings illustrate that SSBDPCM achieves a 16% upsurge in water temperature and a 10% elevation in absorber temperature compared to CSS. Impressively, SSBDPCM achieves a staggering 63% increase in distillate production, yielding 3.6 l/m~2 and 3.4 l/m~2, in sharp contrast to CSS, which only manages 2.2 l/m~2 and 2.1 l/m~2 over a two-day test period. Furthermore, a comprehensive cost analysis showcases the economic superiority of SSBDPCM over CSS. SSBDPCM demonstrates a compelling 29.2% reduction in cost per liter and a significant 25.9% decrease in the payback period in comparison to CSS. These compelling outcomes underscore the substantial potential of the SSBDPCM approach in delivering heightened efficiency and cost-effectiveness, paving the way for a promising advancement in solar stills.
查看更多>>摘要：Continued social and mobility development has caused a sharp increase in the number of waste tires, increased environmental pollution, and waste of limited resources. Agricultural residues as a bioresource, which has drawn increased attention in recent years. The ther-mochemical conversion of waste tires and agricultural residues and their mixtures offers important prospects for scientific development, which can provide energy security and a much reduced environmental footprint. In this paper, pyrolysis of waste tires and its co-pyrolysis with maize stalk, wheat straw, cotton stalk, rape straw, or peanut shell agricultural residues, in mass ratios of 1∶1 were investigated at different heating rate using thermogravimetric analysis. The kinetic parameters were calculated using Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) kinetic models at heating rates of 20, 30, and 50 °C/min. The synergistic effect between waste tires and agricultural residues was explored by calculating the deviation between the experimental and calculated values. The results showed the presence of a synergistic effect between the co-pyrolysis of waste tires and the residual agricultural residues. In the kinetic analysis, activation energies of waste tires, agricultural residues, and their mixtures were calculated using the two models. The reaction followed a multistage reaction mechanism. The differential thermo-gravimetry behavior of the mixture was similar to the weighted aggregate results of the waste tire and agricultural waste samples, pyrolyzed separately. These results provide some insights into the combined treatment of waste tires and agricultural waste residues.
查看更多>>摘要：The purpose of this article is to expound recovery of low-grade heat deriving from cooling data center electronics, in order to sustain a thermodynamic cycle of the Rankine type, using cryogenic nitrogen as the working fluid. A novel conception of an energy plant is proposed and considered where these resources are available. The evaporator, built in a closed and thermally insulated vessel, is the key component. Liquid nitrogen is evaporated by means of an immersed serpentine, which provides for thermal power and produces pressurized gas. A supplementary reservoir acts as superheater, as well as buffer. The plant is completed with a turbo-expander that generates power and a pump to recirculate the fluid. A thermodynamic model is developed. A dimensioning procedure for all the subsystems is reported, while a verification analysis is made to detect the maximum pressure that can be exerted. Hence, an in-depth parametric analysis is made for two-plant layout scenarios, based on the presence (1) and absence (2) of the supplementary tank. The simulations are aimed at determining all the operating parameters of the plant, as well as the performance. The results show that pressure is beneficial for performance, presenting scenario 1 as better than scenario 2. The maximum nitrogen pressurization is 12 bar, which corresponds to an electric efficiency of 31.5%, under a thermal supply of 2.79 kW per 1 kW of net electric power produced.
Juan FajardoCamilo NegretteDaniel YabrudyDeibys Barreto...
121702.1-121702.12页
查看更多>>摘要：Established or create new ones to plan the cleaning tasks of the heat exchangers. In this work, a maintenance strategy is developed for a preheating train under the Maintenance Centered on Energy Efficiency (MCEE) methodology, where it is sought to integrate the information of the principles of the second law of thermodynamics with economic variables to use parameters. The modification of the maintenance justification parameter (J) is proposed, adding two new maintenance indicators (W and X). Each one seeks to evaluate an essential criterion for the maintenance area: economic viability, technical feasibility, and benefits, toward the other exchangers in the network after cleaning a specific component. A criticality diagram and a criticality matrix are used. The heat exchangers are grouped into subassemblies, with the leading group consisting of the key heat exchangers (KHEX), the elements of which have a significant impact on the efficiency of the preheat train. For their part, the regions are composed of components whose performance is less considerable than that of the KHEX. In total, 34 maintenance activities will be carried out, distributed among the 25 interchanges of the network. The planning of a program of cleaning activities according to the maintenance strategy based on the methodology of the MCEE establishes a substantial scientific contribution due to the almost null existence of exergetic studies applied to the management of maintenance tasks and focused mainly on the preheating of trains.
查看更多>>摘要：The present work investigates the cyclic variability of a single-cylinder spark ignition engine fueled with gasoline/natural gas. Return maps and symbol sequence analysis are used to analyze the cycle dynamics at different engine loads and mixture strength. Cycle dynamics is found to be stochastic in nature at high engine loads with low cyclic variability. The frequency of deterministic patterns with close coupling between consecutive cycles is found to be high at low loads with high cyclic variability. In comparison to gasoline, the deterministic effects are found to be more predominant for natural gas fueled engine. The paper also demonstrates that the identification of deterministic patterns and omitting them through an efficient engine management system brings the engine to a stable state from unstable state. The research provides an estimate of how much better engine performance could be achieved with the knowledge of determinism in the system and the subsequent application of this knowledge for efficient engine control.
Madeleine C. OliverMunjal ShahJanna MartinekKarthik Nithyanandam...
121704.1-121704.11页
查看更多>>摘要：Sustainable energy technologies often use fluids with complex properties. As an example, sulfur is a promising fluid for use in thermal energy storage (TES) systems, with highly nonlinear thermophysical properties. The viscosity of liquid-phase sulfur varies by four orders of magnitude due to polymerization of sulfur rings between 400 K and 500 K, followed by depolymerization of long rigid chains, and a decrease in viscosity, as temperature increases. These properties may compromise the accuracy of long-established empirical correlations in the design of TES systems. This work uses computational fluid dynamics to compute steady-state free convection heat transfer coefficients of sulfur in concentric cylinders at temperatures between 400 K and 600 K. The results show that uneven distributions of high and low-viscosity sulfur in the system cause variations in flow patterns and highly nonlinear heat transfer coefficients as temperature gradients increase. As a result, existing empirical correlations for describing system performance become inaccurate. Comparisons of simulation results to predictions from well-established literature correlations show that deviations may surpass 50%. Nusselt versus Rayleigh number correlations for heat transfer are significantly affected by the loss of self-similarity. The analysis proves that existing correlations are not able to capture the complex properties of sulfur in this temperature range, suggesting that alternative modeling techniques are needed for the design and optimization of sulfur TES systems. These challenges are unlikely to be limited to sulfur as a working fluid or TES but will appear in a range of energy systems.
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