Journal of Energy Engineering

In this paper, an optimal control method is proposed for a piezoelectric vortex-induced vibrations (VIV) energy harvester. The harvester comprises a blunt cylinder attached to the tip of a flexible beam. The beam is a composite cantilever that is partially covered by piezoelectric plates. A nonlinear model is derived for the VIV of the harvester by using the Euler–Lagrange principle with the unsteady aerodynamic force due to vortex shedding. To achieve the maximum energy production, an optimal controller is designed using the model predictive control (MPC) method. The MPC design problem turned out to be a linear quadratic optimization problem that is solved by efficient numerical methods. The closed-loop response of the MPC scheme is studied through extensive numerical simulation for several working conditions. The results showed that, compared with the conventional methods, the MPC scheme significantly increases the output electrical power of the VIV harvester.

One of the most critical pollutant emissions in spark ignition (SI) engines is hydrocarbon (HC) emissions, which are partially incomplete combustion products. In this study, the upper surface of a piston was covered with ceramic material with a high heat reserve in order to reduce HC emissions from SI engines and to increase engine performance. However, when the upper surface of the piston was coated with a high heat reserve material, ${\mathrm{NO}}_x$ emissions released from the engine especially under full load conditions increased compared with the standard case, due to increased temperatures inside the cylinder. Water was injected into the intake manifold to control ${\mathrm{NO}}_x$ emissions. As a result of the experimental studies carried out, it was found out that in the thermal barrier–layer engine there was a 3.5% increase in effective power and a 4.9% decrease in specific fuel consumption compared with the standard case. HC emissions decreased by 36% and ${\mathrm{NO}}_x$ emissions increased by 11.1%. When water injection was applied to the engine, HC emissions decreased by 43% and ${\mathrm{NO}}_x$ emissions decreased by as much as 24.8% compared with the standard engine data. Engine performance parameters improved by 3.44% compared with the standard case.

In this study, simple and recuperative organic Rankine cycles (ORCs) were designed as the bottoming cycle to a simple gas turbine. After the design, the performance of the ORC engines was analyzed for varying turbine inlet temperature and pressure. During the study, eight different working fluids were selected for the design of the ORCs to identify the best-performing working candidate, namely, benzene, cyclohexane, ethanol, methanol, R21, R152a, toluene, and trans-2-butane. For all turbine inlet pressure values, the maximum performance was obtained from methanol for simple ORC (sORC) and from trans-2-butane for recuperative ORC (rORC). The maximum net power production, thermal efficiency, and exergy efficiency of the sORC were obtained with methanol at 45 bar 350°C, achieving 1967 kW, 24.5%, and 48.9%, respectively. For rORC, the maximum net power production, thermal efficiency, and exergy efficiency were obtained with trans-2-butane at 40 bar 240°C as 2,523 kW, 31.1%, and 62.4%, respectively. The highest net power production, thermal efficiency, and exergy efficiency of the gas turbine (GT)-ORC combined cycle are found at 40 bar and 240°C for rORC, reaching 8,723 kW, 47.63%, and 67.33%, respectively. This means that almost $\mathrm{1,605}\mathrm{kg}\text{-}{\mathrm{CO}}_2/\mathrm{h}$ reduction in ${\mathrm{CO}}_2$ emission is possible with the use of rORC as a bottoming cycle in the GT. When the total heat input from the fuel in the burner of the GT is considered, it is observed that the power production of the GT-rORC combined cycle can be increased up to 40.7%. In order to identify optimum performance under real operating conditions, the designed system can be used by ORC engine designers, manufacturers, and in facilities where simple gas turbines are available.

Continuous electrical power supplies are crucial for the success of deep-sea missions given the need for power to energize sensors, actuators, or light sources to monitor activities in deep murky waters. Therefore, viable renewable energy sources installed at seabed could be the solution for the success of these types of missions. In this work, three types of energy harvesters tethered to a buoy through a long inflexible cable for operation at seabed are presented. The first harvester uses an alternator to produce electricity to charge a battery pack whereas the second one is based on a mass-magnet-spring translational system. In addition, the third harvester (base-excitation type) uses periodic waves to linearly move the magnet via a inflexible rod. The harvesters are actuated by the motion of the buoy resulting from the waves at the surfaces of the sea/ocean. The simulation results show that the alternator-based harvester was capable of producing 3,650 W, which is enough to power a small monitoring station. Furthermore, this power level is based on 1.0-m-high waves. Effect of the wave amplitude ($Yo$) on the induced electrical power (PW) for charging the batteries and the actual mean wave height in the test location will be more indicative of the power available for recharging the batteries. However, the mass-spring harvester and the base-excitation type harvester produced only 0.000135 W and 0.537 W, respectively.

Energy conservation is important in this modern era because of its high demand in transportation systems coupled with the depletion of fossil fuels. Biodiesel is thus an alternative fuel to replace conventional diesel. This study investigates the effect of chamber pressure ($P_{amb}$) and chamber temperature ($T_{amb}$) on biodiesel spray penetration length ($S_L$) and spray pattern ($S_P$) characteristics in a constant-volume vessel, under rotary engine working conditions, using spray visualization and image processing techniques. Furthermore, a three-dimensional (3D) direct-injection rotary engine model was developed and used for computational fluid dynamics (CFD) simulation studies of biodiesel distribution, mixture forming, and combustion process at different injection timing (IT) in the cylinder. Results indicate that increasing $P_{amb}$ decreases $S_L$ and broadens $S_P$, while increasing $T_{amb}$ decreases $S_L$ and narrows $S_P$. At advanced IT, biodiesel diffuses and disperses, and at retarded IT, which is the suitable rate for combustion, biodiesel concentrates and narrows. Compared with the original scheme [80° crank angle before top dead center (CA BTDC)], $P_{\max }$ increases by 16.79%, ${\varphi }_{\max }$ decreases by 28.75%, NO and CO change a little, and ${\mathrm{CO}}_2$ decreases. Its drawback is a 15.65% increase in soot formation.

The proton-exchange membrane fuel cell (PEMFC) is the most promising fuel cell technology because of the high power density and fast start-up. However, PEMFCs have not yet been commercialized on a large scale due to many technical problems. One of the key challenges for optimum fuel cell performance is maintaining the PEMFC at a proper temperature. This paper proposes a temperature fuzzy control strategy to adjust the stack temperature. A mathematical model of the cooling circuit was established to facilitate the control design. Then a kind of improved quantum particle swarm optimization (IQPSO) was introduced to optimize fuzzy control rules. The established model and fuzzy controllers were simulated and analyzed. The results of proportional integral derivative (PID) control, fuzzy-PID control (FPID), and fuzzy-PID control method with IQPSO algorithm (IQPSO-FPID) were compared. Simulation results showed that the IQPSO-FPID can meet many control objectives and improve control performance.

Electric power is a critical commodity of the modern world where demand for electricity has been increasing significantly in the last decades, and it is expected to keep increasing in the future. Several socioeconomic factors affect and get affected by the electric sector development, but the literature falls short in studying such relationships in a holistic approach. The goal of this paper is to study how the electric power sector development (i.e., electrical power consumption per capita and electrical losses during distribution) is associated with the socioeconomic indicators of economic growth, human development, and corruption. The research methodology comprises a series of statistical tests, such as the correlation analysis, linear regression, panel analysis, polynomial regression, and Granger causality testing. The findings show that there is generally a relationship between electrical power consumption on one side as well as economic growth, human development, and corruption on the other side. This relationship emerges when studying all the data from all countries as a whole but not necessarily for each country separately. In general, countries that have healthier economies, more advanced human development, and low corruption tend to have higher electrical consumption per capita. Regarding the causality between the parameters, results show that there is no causality effect on the short term between electrical power consumption and any of the socioeconomic indicators under investigation. Also, it was found that there is generally a positive relationship between low corruption and low electrical power losses. In countries with higher corruption, there are large amounts of electric power that is lost (i.e., the power is generated but is not billed). However, overall, an analysis of the relationship between corruption and electric power losses are mixed and hard to interpret. Ultimately, this research emphasizes that the dynamics of the electrical power sector should be examined from the economic and social perspectives and not only the engineering technical perspective.

In the present study of energy and exergy, the raw biogas is chosen as the less reactive inducted renewable fuel in dual-fuel mode (DFM). Further, some crucial parameters like global fuel-air equivalence ratio (${\mathrm{\Phi }}_{\mathrm{global}}$), intake charge preheating, and various liquid oxygenated fuels blended with diesel as the pilot fuel are considered to improve the DFM engine performance. The experiments at part and higher loads are carried out at the engine’s standard compression ratio (CR) and injection timing (IT). The parameters examined are the energy and exergy potential of fuel input, cooling water, exhaust gas, exergy destruction, energy efficiency, exergy efficiency, entropy generation, energy and exergy recovery from the exhaust, and emissions. Energy, exergy and emissions are noticed to be improved significantly at higher loads, with preheating, and with the use of blends of oxygenated pilot fuels at optimum ${\mathrm{\Phi }}_{\mathrm{global}}$. The superior results are found with the ternary blends of diethyl ether (TB-DEE) as the pilot fuel. At higher load of $21.78\mathrm{N}·\mathrm{m}$ with TB-DEE blend (pilot fuel), the maximum energy recovery, exergy recovery, reductions of CO and Unburnt hydrocarbon (HC) of 26.99%, 36.03%, 51.72%, and 67.39%, respectively, are estimated in comparison with the case without preheating.

This work presents a numerical study on transmission performance of ellipsoidal windows used in receivers under concentrated solar irradiation. The Monte Carlo ray tracing method is used to analyze the transmission of concentrated solar radiation through an ellipsoidal window. The effects of concentrator shape error (1–3 mrad) and geometry parameters of the window, including window height (30–60 mm), radius of concave region (20–55 mm), and shape factor (0–100 mm), on the transmittance are examined. It is found that the transmittance increases with the increase of shape factor and window height and the decrease of the slope error of the concentrator. The dependence of the transmittance on the radius of the concave region is nonmonotonic. To maximize window transmittance, a single-variable nonlinear optimizer is used to optimize the concave region radius. The results indicate that the transmittance can be increased by 1.7% at most by increasing the shape factor, within the parameter range. Only if the window height is greater than a certain critical value, could the transmittance of the ellipsoidal window be significantly higher than that of plane window. The critical value increases with the increasing slope error and decreasing shape factor, varying from 20 to 40 mm. The transmittance of the ellipsoidal window with optimal parameter can range up to 98.9%, which is 7.82% higher than that of flat window. The conclusions drawn from the present study could be useful for the design and application of ellipsoidal windows to reduce reflection losses of windowed receiver.

A novel methodology is suggested in this study, with the aim of assessing the impact of the road grade on a vehicle’s performance and emissions. This methodology consists of creating multiple sinusoidal elevation profiles that simulate a vehicle trip between consecutive peaks and valleys with the total net elevation being zero. A light commercial vehicle is considered, powered by a turbocharged diesel engine, and the baseline trip is the worldwide harmonized light-duty vehicles test cycle (WLTC). A detailed engine-mapping approach is used as the basis for the results, with experimentally derived correction coefficients applied to account for engine transient operation. Engine-out NO and soot are the examined pollutants, as well as fuel, energy consumption, and ${\mathrm{CO}}_2$ emissions. Results from this study show that there is a noteworthy increase in emissions, even for a zero net elevation trip, with the magnitude of this increase being proportional to the trip root mean square (RMS) grade. For the engine/vehicle studied, higher RMS grade values (approximately 5%) result in a 3.5% increase in $\mathrm{fueling}/{\mathrm{CO}}_2$ emissions, 5.6% increase in NO emissions, and 7.9% increase in soot emissions; on the other hand, lower RMS grade values (approximately 2%) have $\mathrm{fueling}/{\mathrm{CO}}_2$ emissions remaining practically unchanged but still showcase a slight increase in NO and soot emissions (1.8% and 2.6%, respectively).

Sequential pyrolysis of biomass and gasification of the resultant char generate syngas. The Aspen Plus software was used to simulate a two-stage high-temperature cyclone pyrolysis and gasification of corn straw and rice husk. The effects of the pyrolyzer temperature (700°C–1,400°C) and of the gasification agent (air/steam) on the products of both pyrolysis and gasification, and on the gasifier temperature were assessed. Pyrolysis of biomass generates gases that are rich in ${\mathrm{H}}_2$ and CO, and solid residues amounting to 14%–35% of the feedstock mass, depending on the process temperature. High pyrolysis temperatures promote the ${\mathrm{H}}_2$ and CO formation. Burning half the mass of the pyrolysis gas ensures energy sufficiency in the pyrolyzer. The CO concentration in the gasification syngas increases with input $\mathrm{O}/\mathrm{C}$ ratios increasing from 0.1 to 1, and decreases with $\mathrm{O}/\mathrm{C}>1$. Gasification in steam-enriched air initially promotes the formation of ${\mathrm{H}}_2$ and, to a lesser extent, enhances the CO concentrations in the output syngas as the amount of ${\mathrm{H}}_2\mathrm{O}$ increases; eventually they both reach maximum values and then decrease. In gasification processes, 30%–60% fractions of steam in air are recommended.

For decades, Darrieus turbines have shown their advantage over other turbines for providing hydropower. Most studies tend to be conducted with the turbine in its vertical axis configuration, while few have examined the horizontal axis configuration. In this paper, we undertake a computational fluid dynamics (CFD) analysis that investigates blade profile alternatives to improve the efficiency of a horizontal axis Darrieus turbine under more natural flow conditions. An inlet boundary layer profile and a confined domain are imposed to represent river conditions. Four blade profiles are tested under various tip-speed ratios using a three-bladed turbine. The developed model is based on an unsteady $k\text{-}\omega$ shear stress transport (SST) turbulence closure associated with a very-fine-grid mesh. The model methods are first validated against open-channel experimental results published in the literature and show less than 13% discrepancy. The S1046 blade profile is shown to improve the power coefficient $C_p$ by 14% compared to the NACA0018 blade profile. The S809 blade profile exhibits the lowest performance in the dynamic stall and transition regions. For high tip-speed ratios, the FXLV152 profile produces the highest local efficiency power coefficient. The influence of the blade number is also quantified. The four- and two-bladed S1046 configurations achieve the highest power coefficients in the low and high tip-speed ratio regions, respectively.

A theoretical investigation is performed to comparatively evaluate the impact of water addition to the intake air (humidification) or in water-diesel fuel emulsion on the performance and emissions in a turbocharged (T/C), heavy-duty direct injection (HDDI) diesel engine. Specifically, three water addition strategies are examined, i.e., intake air humidification, combustion of water-diesel emulsion considering increasing the injector nozzle-hole diameter for keeping constant the injection duration with increasing water content, and combustion of water-diesel emulsion considering a variable injection duration with increasing water content. In all cases, three water percentages were considered: 10%, 20%, and 30% by weight. In all cases examined, the engine brake power output was kept constant corresponding to a speed of 1,800 rpm and to 25%, 50%, 75%, and 100% of full load, equal to those corresponding to the baseline case without water addition. From the examination of the theoretical results, it is shown that the use of water-fuel emulsion with increased injection duration results in higher cylinder pressures and bulk gas temperatures during the premixed combustion phase compared to the other two water addition strategies, whereas water-fuel emulsion with constant injection duration promotes the intensification of the diffusion combustion phase compared to the other two water induction strategies. The use of both water-fuel emulsion strategies result in a significant reduction of cumulative soot formation rate compared to intake air humidification. Overall, it can be concluded that the use of water-fuel emulsion with constant injection duration can result in a simultaneous increase of brake thermal efficiency and significant reduction of exhaust soot and NO values at both partial and full engine load; thus, it is the most beneficial water addition strategy of those examined in this study.

The microenvironment of the electrodes in a polymer electrolyte membrane fuel cell (PEMFC) is critical to its performance and is significantly affected by the distribution of water and heat along the cell. In this work, the temperature and relative humidity (RH) distributions at both anode and cathode were for the first time investigated simultaneously via in situ measurement. Through this method, we successfully evaluate the effects of coflow and counterflow arrangements on cell performance and the uncoupling characteristics of temperature and RH. The experimental results show that coflow has better coupling characteristics than counterflow between the anode and cathode, especially at high current density. At low and medium current densities, the temperature and RH distributions are more uniform in counterflow mode at the same degree of humidification, producing better performance. At high current density, a bigger temperature difference and severe water flooding were observed in the cell in counterflow mode, with adverse effects on performance and durability. We evaluate a number of other conditions that give us greater insight into the influence of fuel cell design and operating conditions. This work paves the way for the optimization of bipolar plates and water–heat management in PEMFCs.

Mechanical damage to the membrane of the electrode assembly (MEA) in a proton electrolyte membrane fuel cell (PEMFC) is one of the main factors influencing its durability. In this study, a two-dimensional finite-element model is developed for a metal bipolar plate stack. We focus on studying the stress concentration phenomenon in the MEA of a PEMFC containing complete sealing components in an assembled state by considering the factors of assembly load, sealing structure, and sealing material. The results indicate that stresses are clearly concentrated in the area of the membrane under the edge of the rib of the bipolar plate on both sides of the sealing structure. Even if the average pressure on the MEA is only 0.43 MPa, the local stress is greater than 6 MPa, potentially leading to the plastic deformation of the membrane. At the joint between the frame and gas diffusion layer, the shear stress on the membrane is unusually high. Optimally designing the sealing structure, including a suitable layout of the joint, the selection of the ration of the sealing gasket height to the sealing groove depth, and the selection of the frame with material properties close to those of the membrane, will alleviate the stress concentration effectively.

This work used a three-dimensional, two-phase, and nonisothermal model to compare performances of proton exchange membrane (PEM) fuel cells with a parallel, interdigitated, or serpentine flow field when wavelike gas channels (GCs) are or not employed, to determine which flow field needs wavelike GCs more than the others. The comparisons showed that the performance enhancement is the most pronounced for the parallel flow field, whereas the enhancement was significantly reduced for the serpentine and interdigitated flow fields when wavelike GCs are adopted. For the parallel flow field, oxygen transport into the gas diffusion layer (GDL) and liquid water removal from the cathode porous electrode were enhanced remarkably by wavelike GCs. As a result, more oxygen was transported into the catalyst layer (CL) to participate in electrochemical reactions, leading to better cell performance. However, subrib convection in the interdigitated and serpentine flow fields weakened the role of wavelike GCs, so that the performance was not improved greatly for the two flow fields. The influence of the amplitude to wavelength ratio, aspect ratio of wavelike GCs, and cathode flow rate in the parallel flow field were investigated. The results show that the optimal amplitude to wavelength ratio is 0.6, which yields a 13.44% increase in the power density compared with straight GCs. The wavelike GCs had greater enhancement when small channel aspect ratios were employed or when the cell operated at larger cathode flow rates. The simulations provide useful guidance for practical PEM fuel cell flow field designs.

Natural resources in the current scenario of energy production and consumption demands appropriate management. Due to increasing urbanization worldwide, energy consumption optimization has become fundamental, including in the building sector. Many authors mention bioclimatic architecture as an intelligent way to achieve energy efficiency, reducing energy consumption while providing thermal comfort for the users. This paper aims to evaluate the energetic performance of a bioclimatic pilot plant in Bioclimatic zone 2. The methodology to evaluate the energetic performance of the bioclimatic building was developed from hygrothermal measurements and simulations in eQUEST version 3.65. The building was compared to its similar nonbioclimatic one by changing its envelope characteristics in the simulation. The results show the efficiency of bioclimatic strategies, which ensures the building’s thermal and hygrometric stability, besides thermal comfort conditions most of the time. Consequently, these strategies allow one to reduce about 25% of the electric energy consumption compared to the nonbioclimatic building.