Journal of Energy Engineering

Thermal batteries have become irreplaceable energy-storage devices in the field of high-temperature power supplies with the rapid development of energy technology. Electrolyte materials with a low melting point and high ionic conductivity are being widely studied. This paper presents a review of electrolytes (including halides and nitrates) used in thermal batteries. In addition, the electrochemical and physicochemical properties of different electrolytes are compared comprehensively and further discussed.

Smart health monitoring based on a wireless sensor network plays a crucial role in maintaining the efficiency and safety of railway systems during operation, while the power source of the railway monitoring system remains a problem. Considering the mechanical energy produced by the rail vibration to be a sustainable and environment friendly power source, we propose a sponge-supported triboelectric nanogenerator (S-TENG) device as an energy harvester for the railway monitoring system. A high-density sponge is utilized under the tribo-pair as an innovative flexible buffer structure. The initial gap between the tribo-pair is properly designed according to the rail vibration amplitude to guarantee that the two dielectric materials can get into contact, while the rail with displacement beyond the initial gap will compress the sponge instead of squashing the tribo-pair, so as not to break the tribo-pair and to improve the output performance by enhancing the contact force between the tribo-pair. The feasibility of the sponge base is proved through a mechanical test, and a series of well-designed experimental tests are carried out to study the output performance of S-TENG with various loading conditions. To further investigate the applicability of S-TENG in railway monitoring, we establish a theoretical model for S-TENG output performance combined with a metro train-floating slab track model and simulate the output characteristics of S-TENG under train operation.

This paper presents a computational study of the effects of nitrogen and sulfur oxides doping on the ignition of methane-air mixtures under marine engine–like conditions. The performance of four detailed chemical kinetic mechanisms, appropriately coupled with nitrogen and sulfur chemistry reactions, is first assessed against literature experiments. An assembled mechanism is thus adopted and used to investigate ${\mathrm{NO}}_x\text{-}{\mathrm{SO}}_x$ doping effects on the ignition of homogeneous methane mixtures for a wide variation of pressure, temperature, equivalence ratio, and doping concentrations. Extensive rate-of-production analysis is performed in order to delineate chemical effects on ignition. The present results confirm that, in general, the addition of either NO or ${\mathrm{NO}}_2$ reduces ignition delay time. ${\mathrm{NO}}_2$ is found to be more drastic than NO at intermediate pressure; this trend is milder at high pressure. The effects of ${\mathrm{SO}}_2$ on ignition chemistry are not significant. An outcome of the present study is thus an operating grid, relevant for controlling marine engine combustion. The assembled mechanism, subject to reduction, can be used in marine engine computational fluid dynamics (CFD) studies.

The suppression of soot generated from acetylene nonpremixed combustion was investigated by following the numerical simulation method. The combustion and soot formation were predicted by the eddy-dissipation and Moss–Brookes models, respectively. The rate of soot formation was decreased by applying acoustic oscillation. The influences of oscillating velocity, frequency, flow rate of acetylene, and Reynolds number on the rate of soot formation were studied. Results showed that the maximum efficiency of soot suppression exceeded 90%. An increase in Reynolds number resulted in enhanced soot suppression efficiency. It is considered that the boundary layer of the soot particles was reduced when the Reynolds number increased. This could potentially result in the enhancement of mass transfer, thus causing the reoxidation of the soot in the oxidation zone. Reoxidation of soot resulted in reduced soot generation. The flame temperature increased simultaneously.

Recent developments in power system and internet technology introduced blockchain technology to energy trading. In addition, the growing penetration of distributed energy resources made the division of distribution systems into microgrids a tempting solution for technical and economical problems. In this paper, the feasibility of applying blockchain technology as an accounting system for energy trading within each island and between interconnected islands is considered. The distribution system is considered after being optimally divided into islands. Energy hubs, aggregated thermostatically controlled loads and aggregated electric vehicles (EVs) are considered. Optimal demand-side management is applied taking into consideration the uncertainties arising from renewable energy sources due to their nature, load forecasting, energy price due to bidding actions accompanying energy transactions, and energy exchange in EV parking stations due to EV availability patterns. The blockchain-based energy trading (BET) system is considered in three steps. The first step is carried out considering EV parking stations for energy trading between EVs and then between parking stations and island consumers with billing transfer between different blockchains. The second step considers the trading between prosumers and consumers within each island. In the third step, the BET system is applied for energy trading between interconnected islands. The feasibility of the proposed energy trading system is validated using a realistic case of the distribution system of Alexandria, Egypt. The simulation results show the positive impact of applying blockchain-based energy trading on energy cost.

The study addresses proton exchange membrane fuel cell (PEMFC) internal temperature predictions and the designed thermal management strategy based on the predicted temperature. The effect of temperature difference on PEMFC operation performance is also explored to verify the feasibility of this thermal management strategy. First, a PEMFC thermal model is built using MATLAB/Simulink version 2019. The effectiveness of this model is confirmed by comparing with the calculated experimental bench thermal power under identical working conditions. An urban dynamometer driving schedule (UDDS) is simulated in a self-built experimental test. In the progress of simulating the UDDS in the experimental test bench, the PEMFC coolant outlet temperature is also monitored by the temperature sensor. Second, the PEMFC operation temperature is predicted with a Kalman filtering algorithm based upon the thermal model. The feasibility of the algorithm is evaluated by comparing the predicted and monitored temperatures. The result also shows that it is useful to predict the operating temperature in real time. Finally, two different experimental projects are implemented to further explore the effectiveness of the temperature prediction algorithm. The predicted temperature is designed as the core of the PEMFC thermal management strategy in one of the experiment projects. The effect of temperature differences is analyzed by monitoring single-cell voltage differences. The temperature difference can be controlled over a more reasonable range adopting this designed management strategy. A lower temperature difference benefits PEMFC operating performance.

Tight-sandstone gas reservoirs have low porosity and permeability, dissimilar pore types, and generally high clay content. Partial saturation leads to local fluid flow induced by seismic waves, resulting in velocity dispersion and attenuation, and this is the reason why the dissipation factor ($Q^{-1}$) (inverse quality factor) is highly sensitive to fluid saturation. A relation between $Q$ and saturation can be based on the self-consistent approximation and poroelasticity theory, to build, in principle, a two-dimensional (2D) rock-physics template. However, there is an ambiguity in the process of estimation because one value of $Q$ may correspond to two saturations. Thus, this paper addresses this limitation. Moreover, a well-log in the Sichuan Basin and reported experimental data show that these reservoirs may have a high clay content, which affects the estimation. To take into account this factor, the hydration effect of clay is considered in the framework of the double double-porosity theory of wave propagation. Ultrasonic measurements were performed on a tight sandstone and the spectral-ratio method was used to estimate $Q$. Then, three-dimensional (3D) rock-physics templates are built by introducing the phase velocity ratio ($V_P/V_S$), clay content, and seismic $Q$ estimated with an improved frequency-shift method. The template is calibrated and tested with ultrasonic, well-log, and seismic data and applied to estimate reservoir porosity, clay content, and gas saturation on 2D and 3D seismic data.

Renewable energy resources like biogas fuel are highly needed to overcome the increasing demands on energy and to allow more efficient power transformation. Biogas is not investigated adequately in homogenous charge compression ignition (HCCI) engines and no specific chemical kinetics were proposed for its combustion in HCCI engines. In this study, a reaction mechanism had been proposed to simulate biogas combustion in HCCI engines. A combined mechanism reduction algorithm, using a graph-based approach and sensitivity analysis, was used to reduce a full detailed mechanism for C1-C4 hydrocarbon fuels. The resulted mechanism consists of 42 species and 328 reactions that were selected to predict the ignition delay time of the HCCI ignition process. The new mechanism was implemented in a modified multizone combustion model using CANTERA flow reactions and MATLAB software. Many combustion parameters, including pressure and temperature profiles, ignition time, produced work, and heat release rate, were estimated. It was found that HCCI engines fueled with biogas can be an effective option for power generation applications at wide range of ${\mathrm{CH}}_4\text{-}{\mathrm{CO}}_2$ ratios. Furthermore, the reaction mechanism showed high ability in predicting the experimental data at HCCI operation conditions over a wide range of temperature (500–2,000 K) and equivalence ratios (0.4–1.8). This allows further investigations of the mechanism for combustion and emissions prediction at many different operation conditions.

It has been a significant challenge to ensure high-efficiency, stable power supplies in complementary wind–hydropower generation systems, and there are increasing concerns about power curtailment and uncertainty control issues. Pumped-storage technology, which stores energy when it is in excess and provides energy in times of shortage, has been found to be a viable solution to enhance system flexibility and energy efficiency. This study investigated a hybrid wind–hydropower generation system with integrated pumped storage for which the hourly optimized scheduling was assessed using a developed mixed-integer nonlinear mathematical model. The hourly uncertainties involved in wind and hydropower were measured using the $k$-nearest neighbor algorithm and fuzzy theory, respectively, and dynamic programming was employed to assess the reservoir storage capacity changes during constant periods. With the actual application to a wind–hydro generation system in China, nine hourly scheduling scenarios for different seasons and available reservoir capacities were investigated, from which it was found that the hybrid system was highly self-sufficient in the normal season, and that pumped-storage technology was able to improve wind power efficiency in the case region.

Coal-water slurries are promising fuels for thermal power engineering. One of the main problems with their combustion is formation of fairly large (with characteristic sizes of more than 1 mm) droplets during spraying with nozzles. It results in their late ignition in the furnaces of steam and hot water boilers. The aim of this work is to establish by experimental results distribution of coal-water fuel droplets by size with the addition of isopropyl alcohol after coaxial spraying and justify the effectiveness of using this alcohol as the third component that affects the number and diameter of fuel droplets after spraying. It was found that the number of small droplets (no more than 100 micrometers) in the jet increases by 19% in comparison with typical coal-water fuel after spraying coal-water fuel prepared on the basis of lignite due to the introduction of IPA (no more than 3% by weight). Concentration of small droplets (no more than 100 µm) increases by 16% after spraying coal-water slurry prepared on the basis of long-flame coal and addition of no more than 3% by weight of isopropyl alcohol in comparison with typical coal-water fuel. Increase in the proportion of isopropyl alcohol in the slurry composition to no more than 5% by weight is the reason for increase of sufficiently large (more than 400 micrometers) droplets of such fuel after spraying by 14%. The number of fuel droplets of small sizes decreases similarly to large fragments after spraying coal-water slurry prepared on the basis of lean coal with small weight (no more than 3%) additives of isopropyl alcohol. Increase in the viscosity of fuels in several times is conditioned by increase in the concentration of the third component. This significantly degrades jet characteristics after spraying. The expansion angle of the jet increases by 20%. Medium-sized droplets (200–600 micrometers) and fairly large fragments (more than 600 micrometers) prevail in the jet. Concentration of droplets up to 200 micrometers in the diameter decreases. The results obtained are of sufficient practical significance, because they illustrate the possibility of increasing the number of small fuel droplets after spraying. The efficiency of insertion a small amount (no more than 3% by weight) of isopropyl alcohol additive into the composition of coal-water fuel was experimentally proven, and the application feasibility results in the analysis of optimal ignition conditions for droplets of alcohol-coal-water slurries in conditions corresponding to the combustion chambers of steam and hot water boilers.