Journal of Energy Engineering

The charging/discharging characteristics and life cycle of a lithium-ion battery are significantly dependent on the battery thermal performance. In this study, the three-dimensional numerical model was developed to explore the effects of thermal conductivities of the battery, holding plate, and diameter of venting holes on the thermal behaviors of the stagger-arranged battery pack cooled by longitudinal airflow. The numerical model was validated by our previous experimental results. Numerical results illustrated that the thermal conductivities of the battery and holding plate have nearly no effect on the thermal behaviors of the 18650 lithium-ion battery pack; therefore, the traditional epoxy ($k_{\mathrm{hp}}{=0.2\mathrm{W}·\mathrm{m}}^{-1}{·\mathrm{K}}^{-1}$) is an effective material for the holding plate with the advantages of low cost, excellent insulation, and thermal conductivity properties. The heat-transfer coefficient between the air coolant and battery or holding plates does not gradually decrease along the horizontal airflow direction due to the periodic thinning and damaging of the flow boundary layer caused by the venting holes, which indicates that the venting holes can improve the overall heat-transfer performance of the battery pack. At last, comprehensively considering the effects of the diameter of the venting holes on thermal characteristics, cooling efficiency, and structural strength, the appropriate diameter of the venting holes should be 4 mm for the 18650 lithium-ion battery with holding plates.

In this work, a lab-scale external receiver with a xenon lamp set was designed to study optical and thermodynamic properties, and its benchmark was also introduced. Eighteen stainless-steel tubes were placed on the receiver to absorb radiant energy from the xenon lamps and achieve light-to-heat conversion. The indirect method was used to obtain the optical efficiency of the xenon lamp setup, and the heat-flux distribution on the surface of the receiver had an average heat flux of $99.4\mathrm{kW}/{\mathrm{m}}^2$. Furthermore, the experimental method was used to study the temperature change of the receiver during the startup, stabilization, and shutdown of the receiver. A numerical simulation was conducted using commercially available software with the realizable $k\text{-}\epsilon$ model and the discrete ordinates model as the radiative transfer equation to valid the experimental result. The temperatures of the back and front of the receiver were obtained by thermocouples and an infrared thermal imager, respectively. The temperature of the back of the receiver rose rapidly after the lamps were turned on, and the temperature of the heat receiver remained unchanged when it was stable. The velocity of the molten salt was also studied, and the maximum speed was $1.9\mathrm{m}/\mathrm{s}$. The temperature increases of the experiment and simulation were approximately 4°C and 4.2°C, respectively, and the temperature of the tube wall was 40°C higher than that of the molten salt. The comparison of the experiment results indicate that the deviation between the receiver’s back temperatures in the simulation and experiment was basically within 5%, indicating consistency, and the thermal efficiency of the receiver was approximately 85%.

The atomization mechanism of the gas-liquid multiphase flow through an internally mixing twin-fluid Y-jet atomizer has been studied by examining both the internal and external flow patterns. Superheated steam and light fuel oil (LFO) are used as working fluids. The flow is numerically modeled using the compressible Navier-Stokes equations; the hybrid large eddy simulation approach through wall-modeled large eddy simulations (WMLES) is used to resolve the turbulence with the large eddy simulations, whereas the Prandtl mixing length model is used for modeling the subgrid-scale structures, which are affected by operational parameters. A volume-of-fluid to discrete phase model (VOF-to-DPM) transition mechanism is utilized along with dynamic solution-adaptive mesh refinement to predict the initial development and fragmentation of the gas-liquid interface through VOF formulations on a sufficiently fine mesh, while DPM is used to predict the dispersed part of the spray on the coarser grid. Two operational parameters, namely, gas-to-liquid mass flow rate ratio (GLR) and liquid-to-gas momentum ratio, are compared; the latter is found to be an appropriate operational parameter to describe both the internal flow and atomization characteristics. It is confirmed that the variation in the flow patterns within the mixing port of the atomizer coincides with the variation of the spatial distribution of the spray drops.

With the development of energy markets and the introduction of renewable energy certificates (RECs), a regional integrated energy system (RIES) may participate in an energy wholesale market flexibly. In this paper, a bilevel optimization problem is formulated to determine the optimal management strategies of an RIES, including trading in the markets of electricity, natural gas, and RECs. In the bilevel model, an energy supplier (ES) purchases energy from energy wholesale markets and sets retail prices of energy products at the upper level to maximize its profit. At the lower level, various user aggregators (UAs) determine individual energy consumption strategies. The clearing prices of electricity, natural gas, and REC markets are determined asynchronously at the lower level. This nonlinear problem is then transformed into a mixed-integer linear programming problem using the incremental method and strong duality theory, which enables the problem to be solved efficiently. Finally, case studies are carried out to demonstrate the feasibility and effectiveness of the proposed method and the impacts of the RECs.

The present work examines numerically the breakup of water droplets exposed to gas flows at Mach numbers $\mathrm{Ma}>1$, which resemble the ambient conditions encountered in the injection systems of supersonic combustion ramjet (scramjet) engines. A computational fluid dynamics (CFD) model is utilized that solves the compressible Navier-Stokes equations, the energy equation, and the mass conservation in volume fraction form [volume of fluid (VOF) method] along with two equations of state to model the density variations of the two phases. In addition, a coupled VOF/Lagrange model is employed to capture the appearance of microdroplets, which are smaller than the smallest grid cell. As a first step, a two-dimensional planar simulation (water column) is performed at conditions of $\mathrm{Ma}=1.47$ in order to validate the numerical model; its results are compared against published experimental and numerical data. Good agreement is observed for the temporal evolution of droplet shape, the streamwise deformation, and the leading-edge displacement, as well as the shock wave reflection. Subsequently, the validated model is utilized to perform a three-dimensional (3D) simulation at $\mathrm{Ma}=1.23$, which corresponds to the conditions of previous experimental studies, and its results are compared against the experimental data as well as the results from previous numerical studies, showing good agreement. Furthermore, surface instabilities are observed at the droplet surface initiated by interfacial instabilities due to the shearing effect and the interaction with the shock wave, pertaining to Kelvin-Helmholtz and Rayleigh-Taylor instabilities, despite the stabilizing contribution of surface tension; viscosity effects are found to play an insignificant role.

Economic cost for sizing and feasibility for scheduling are the tasks to be addressed to design a renewable energy system. Thus, in this paper, the design of a standalone hybrid renewable energy system was a task in which the sizing was accomplished by optimizing the economic cost, and the load scheduling was carried out maximizing the state of charge of the battery and considering the system did not collapse. The algorithm used to implement the optimization problem was a heuristic optimization algorithm named JAYA. Once the size was determined, an online scheduling strategy was proposed to solve the scheduling problem. This strategy was compared with the results of several heuristic optimization algorithms (JAYA, PSO, and TLBO) in order to test and check its validity. Instead of using current data, a predictive value of renewable resources and loads was used both for the scheduling optimization and the scheduling strategy. The results showed that the proposed scheduling strategy presented similar solutions than the scheduling optimization and with a better computation effort.

The effects of exhaust gas recirculation (EGR) on combustion, performance, and exhaust emissions in direct injection (DI) diesel engines are assessed in a primarily numerical study under the influence of various EGR rates using two different strategies, that is, under constant engine fueling rate (FR) or air/fuel ratio (AFR). The analysis uses an in-house, comprehensive, two-zone diesel combustion model, which separates the in-cylinder working medium into an unburned zone (air, or air plus EGR gas) and a burned one into which fuel is injected from the injector-nozzle holes that are burned with the entrained gas mass from the unburned zone. The validity of the model computations is appraised positively compared to relevant experimental data, such as diagrams of in-cylinder pressures and temperatures, heat release rate (HRR), and nitric oxide (NO) and soot (smoke) emissions, with tests acquired in the laboratory on a standard, experimental, monocylinder, DI, naturally-aspirated (N/A) diesel engine at various operating conditions. A perplexity occurs in the literature of using either constant FR or AFR in the EGR strategy (sometimes overlooked), which can lead to an erroneous interpretation and comparison of the obtained results. This is delineated in this study by using its numerical results that supply insight into the local combustion and emissions formation mechanisms, identifying the important parameters in each case that affect the engine behavior under various operating conditions, in the light of the existing NO–smoke trade-off and the impact on engine power-output and efficiency. The results can be useful for optimizing the emissions and efficiency in each case, and assist with their implications for better designing of the related electronic control unit (ECU) in diesel engines bearing EGR systems.

Flow field plays an important role in proton exchange membrane fuel cell (PEMFC) performance. Excellent flow field configuration promotes the transport of reactant gases in the membrane electrode assembly (MEA), effectively removing liquid water. In this study, a three-dimensional, two-phase model of PEMFC with a wave parallel flow field is developed. The results reveal that wave parallel flow fields are overall better than conventional parallel flow field in promoting reactant gases transport, removing liquid water accumulated in microporous layer and avoiding thermal stress concentration in the membrane. Due to the periodic geometric characteristics of the wave flow channel, the gas flow velocity of the wave parallel flow fields is more uniform than that of conventional parallel flow field. Moreover, the results show that large amplitude and short wave length in the wave parallel flow fields can improve the PEMFC output power. Specifically, at an operating voltage of $0.6\mathrm{V}$, the maximum power in the wave parallel flow field is 34.75% higher than that of conventional parallel flow field.

This paper tested one cylinder of a modified light-duty 4-cylinder diesel engine to study the coupling effect of 1.8-bar pressure and oxygen concentration (Coxy) on the combustion process of diesel (B00), $\mathrm{diesel}/n$-butanol (B20) and $\mathrm{diesel}/n\text{-}\mathrm{butanol}/2\text{-}\mathrm{ethylhexyl}$ nitrate ($\mathrm{B}20+\mathrm{EHN}$), with emphasis on the analysis of the influence of combustion state parameters on emission generation. The research results showed that the difference between B00 fuel and B20 fuel in hydrocarbon (HC) and CO emissions was caused mainly by the combustion duration (CD) when the gas circuit concentration was 12%–17%, whereas when the gas circuit Coxy was 9%–12%, the HC and CO emissions were the result of the combined action of the two factors of in-cylinder combustion temperature (IT) and CD. The main influencing factor of ${\mathrm{NO}}_x$ emission difference was IT. However, the main influencing factor of soot emission difference at 11%–17% gas circuit Coxy was the ignition delay period (ID), and at 9%–11% gas circuit Coxy it was the in-cylinder combustion temperature. Further research on the emissions difference between B00 fuel and $\mathrm{B}20+\mathrm{EHN}$ fuel showed that ID plays a decisive role in the reduction of HC and CO emissions.

The increasing demand for gas turbines motivates the need to improve their performance and reduce the associated exhaust pollutants. Steam injection is an effective technique for boosting power because it increases the thermal efficiency, therefore saving fuel. However, in previous studies, the steam-injection process was designed based on a system of prespecified operating parameters without consideration of change. The present work conducted optimization analysis of a steam-injected gas turbine (STIG) engine to determine the optimum amount of steam for injection into the combustion chamber at specific operating conditions, namely pressure ratio and turbine inlet temperature (TIT) to produce maximum efficiency and decrease wasted water. Design point analysis showed that the injection of the optimum steam-to-air (SA) ratio increased engine efficiency by 31%, increased output power by 76.8%, and decreased specific fuel consumption by 23.8% compared with the simple cycle. Off-design analysis changing the operating conditions was conducted to plot the operating curves of efficiency and specific power against the SA ratio in each scenario. The optimum operation locus of the system for which the efficiency was maximum was traced, and an equation for the system’s optimal operation as a function of TIT was formulated. Finally, the optimized and noncontrolled STIG engines were compared to show superior performance of the controlled engine.

The study evaluated the effects of nanoparticle mixture ratios on the thermal performance of a flat plate collector (FPC) fitted with a torque stirrer operating with ${\mathrm{Al}}_2{\mathrm{O}}_3$–ZnO/water nanofluid. ${\mathrm{Al}}_2{\mathrm{O}}_3$ and ZnO nanoparticles with an average size of 29 and 70 nm, respectively, were used to synthesize ${\mathrm{Al}}_2{\mathrm{O}}_3$–ZnO/water nanofluid at $1:1$ (50% by volume ${\mathrm{Al}}_2{\mathrm{O}}_3$ and 50% by volume ZnO), $2:1$ (66.66% by volume ${\mathrm{Al}}_2{\mathrm{O}}_3$ and 33.34% by volume ZnO), and $1:2$ (33.34% by volume ${\mathrm{Al}}_2{\mathrm{O}}_3$ and 66.66% by volume ZnO) mixture ratios using a two-step synthesis method. Correlation models were developed for the specific heat capacity, thermal conductivity, and viscosity properties of the hybrid nanofluid based on experimentally obtained data. Meteorological data from Nicosia, Cyprus were used to develop a model to observe the effect of a range of temperatures, volume concentrations, and mass flow rates on the performance of the collector. An economic analysis was performed on the system to observe the cost implications of using the hybrid nanofluids to its efficiency gains. The results showed that the mixture ratio of the nanoparticles in the hybrid nanofluids affects both the thermal and exergetic performance of the collector. The thermal efficiency of the FPC increased with the mass flow rate. The highest efficiency recorded in the collector for all mixture ratios of the hybrid nanofluid was at a 0.1% volume concentration. Accounting for the work done by the torque stirrer, there was a net energy gain in the system; however, the economic analysis showed that nanofluids are more beneficial when used in large-scale installations.

Liquefied petroleum gas (LPG) fuel has a high octane number and high heating value. These features make LPG a rather convenient alternative fuel for spark-ignition engines. On the other hand, using only LPG in diesel engines is not possible due to its low cetane number. However, LPG and diesel can be used in dual-fuel mode, a method that does not require significant modifications in diesel engines. In LPG-diesel dual-fuel mode, nitrogen oxide (${\mathrm{NO}}_{\mathrm{x}}$) emissions and knock intensity increase due to the rises in cylinder pressure and temperature, depending on LPG combustion and heat release characteristics under high load conditions. In this study, direct water injection with an electronic control method was utilized to reduce ${\mathrm{NO}}_{\mathrm{x}}$ and knock intensity in an engine running on LPG-diesel dual-fuel mode under full load conditions. For using LPG in a dual-fuel engine operating under full load without causing any damage, it is determined that the most convenient LPG ratio is 30% at the maximum. The test results obtained using neat diesel fuel are referred to as the standard engine data and are used in the comparisons for better understanding the results obtained. Direct water injection was applied into the engine cylinder at various ratios. During experiments, the ratio of injected water mass to fuel mass consumed in a cycle is set to 60%, 80%, and 100%, respectively. Increases in pressure, temperature, knock intensity, hydrocarbon (HC), and ${\mathrm{NO}}_{\mathrm{x}}$ emissions were observed in dual-fuel mode and are presented in comparison with the standard engine data. Consequently, specific fuel consumption, smoke opacity, and ${\mathrm{CO}}_2$ values were significantly reduced. By applying direct water injection and using diesel-LPG dual fuel of 30% LPG, significant improvements in engine performance parameters resulted, and ${\mathrm{NO}}_{\mathrm{x}}$ emissions in the dual-fuel condition reduced to lower levels than the standard engine data. Moreover, using direct water injection in dual-fuel mode reduced the increase in the combustion rate of fuel, but this increased the knock intensity.

The spatial-temporal distribution of electric vehicle (EV) charging loads can be improved by implementing optimized charging scheduling, and by the joint planning of a distribution network (DN) and a charging network of EVs. In this paper, such a joint planning scheme was studied and modeled as two-level optimization model. In the upper level of the optimization, a joint planning model of a DN and a charging network of EVs with distributed photovoltaic (PV) systems and/or energy storage (ES) units is constructed to minimize the total cost. Then the optimized results of the DN and the EV charging network construction plan are used as the inputs of the lower-level operation model. In the lower-level operation optimization, an optimal charging scheduling approach is proposed to minimize the sum of the DN’s operation cost and the traffic congestion cost. The spatial-temporal distribution of the charging demand, under an optimized charging strategy, is used as feedback for the upper-level optimization model, which effectively can reduce the scale of the DN and the charging network construction. The proposed joint planning model was demonstrated through applications in a city in China.

The study aims to evaluate the combined effects of alcohols as additives to diesel and exhaust-gas recirculation (EGR) on combustion and emission characteristics of a common-rail diesel engine. Tested fuels were prepared with 25% ethanol, 25% $n$-butanol, 25% $n$-pentanol, and 50% $n$-pentanol by volume, referred to as E25, B25, P25, and P50, respectively. The effects of different alcohol contents and a wide range of EGR ratios on combustion and emissions characteristics, especially particulate emissions, were investigated. The results demonstrate that with EGR ratios increasing, for each fuel, the peak of cylinder pressure decreases and the peak of heat release rate increases, both of which are delayed. The premixed combustion phase of alcohol/diesel blends is larger than that of pure diesel. Furthermore, alcohol contents and EGR ratios have obvious effects on indicated thermal efficiency (ITE). ITE increases after the addition of alcohol to diesel, but falls as EGR increases. Regarding emissions, the particulate number concentration of each fuel shows a unimodal distribution versus particulate size. At low and medium EGR ratio situation ($<40\%$), the peak particulate number concentration increases quickly and the particulate size grows larger with increased EGR ratios. The total particulate number concentrations (TPNCs) of alcohol/diesel blends are much lower than pure diesel except for $n\text{-}\mathrm{pentanol}/\mathrm{diesel}$ blends. But when EGR ratio continually increases, the peaks of particulate number concentration and the particulate size decrease. For almost all EGR ratios, the TPNCs of P25 and P50 are much higher than those of E25 and B25.

Vertical-axis wind turbines (VAWTs) may be subjected to varying degrees of turbulence in practice. In the present study, the computational fluid dynamics (CFD) method and improved delayed detached eddy simulation (IDDES) turbulence model are adopted to investigate the effects of turbulence intensity on the aerodynamic performance of single and dual straight-bladed VAWTs. The reliability of the numerical model is verified by available experiments. Then, the power performance, wake characteristics, and turbulence statistics distribution of a single VAWT under different inlet conditions are analyzed. Besides, the aerodynamic interaction between two arrayed VAWTs in the turbulent flow are explored. The results show that higher turbulence intensities could significantly improve the power coefficients of the VAWT under low and medium inflow velocities. The aerodynamic loads on the blade are enlarged by the turbulent flow, and more fluctuations occur around the rotor. The strong ambient turbulence could provide constant momentum supplement for the turbine wake and accelerate the wake recovery. Moreover, the atmospheric turbulence has a positive effect on the total power output of dual VAWTs in a tandem arrangement.

Many methods have been developed to reduce emissions from marine heavy-fuel oil (HFO) engines. The effects of exhaust gas recirculation (EGR), Miller cycle, humid air motor (HAM), and start of injection (SOI) were investigated on the combustion and emissions characteristics of a large two-stroke HFO marine engine using computational fluid dynamics (CFD) coupled with chemical reaction mechanisms. A multicomponent-sulfur mechanism was developed to determine the effect of sulfur content on the combustion and emissions characteristics of the HFO marine engine and found that the peak in-cylinder pressure and ${\mathrm{NO}}_{\mathrm{x}}$ emissions decreased by approximately 0.08 MPa and $1.2\mathrm{g}/\mathrm{kW}·\mathrm{h}$, respectively, when sulfur content was reduced from 5% to 0%, which suggests that sulfur content has little effect on in-cylinder pressure and ${\mathrm{NO}}_{\mathrm{x}}$ emissions. A multicomponent surrogate fuel mechanism was then used in CFD simulations to compare different ${\mathrm{NO}}_{\mathrm{x}}$ emissions reductions strategies. In order of effectiveness in reducing ${\mathrm{NO}}_{\mathrm{x}}$ emissions, the strategies were EGR, HAM, SOI, and the Miller cycle. Only EGR reduced ${\mathrm{NO}}_{\mathrm{x}}$ emissions below the regulated limits. Coupling strategies were investigated to balance indicated specific fuel consumption (ISFC) and ${\mathrm{NO}}_{\mathrm{x}}$ emissions. An EGR ratio of 21% coupled with the miller cycle degree of 20 (M20) method reduced ${\mathrm{NO}}_{\mathrm{x}}$ emissions to $3.14\mathrm{g}/\mathrm{kW}·\mathrm{h}$, while the same EGR ratio coupled with HAM level of 2 (HAM2) reduced ${\mathrm{NO}}_{\mathrm{x}}$ emissions to $1.43\mathrm{g}/\mathrm{kW}·\mathrm{h}$. Therefore, coupling EGR with Miller cycle and HAM technology were suggested to reduce ${\mathrm{NO}}_{\mathrm{x}}$ emissions from HFO marine engines.

Cascading blackouts of power systems are normally activated by the initial disruptive contingencies under certain conditions. Effective identification of such disruptive contingencies is significant to ensure the reliability and resilience of power systems. This paper focuses on identification of the disruptive contingencies on branches that can result in catastrophic cascading blackouts of power systems. An identification approach based on optimal control is developed to look for the most disruptive contingencies on branches of power networks by treating the disruptive contingencies as control inputs in an optimal control problem. In particular, real-time protective schemes such as generation control and load shedding are incorporated during the sequence of line outages, where such actions are also optimized for preventing the propagation of cascading failures. Moreover, the necessary conditions for determining the most disruptive contingencies on the selected branch are derived by solving a system of nonlinear equations. Extensive simulations are conducted to substantiate the effectiveness and superiority of the proposed identification approach on IEEE bus test systems.