Journal of Energy Engineering

Energy systems including electricity, heat/cooling, and gas supply systems represent a very important part of the infrastructure in Russia. This paper presents a general framework of integrated energy systems. Elements of the concept of integrated energy systems are suggested. The explanation of the concept elements is given as a three-layer structure of integrated energy systems in three dimensions. The problems of integrated control of electric and heat networks deal with issues of combined calculation of operating conditions of the electric and heat networks integrated in the intelligent energy supply system. A mathematical description of the problems is presented. The results of two illustrative case studies are shown and explained. The first case study represents research on an emergency situation at the supergrid level of the energy system layers after an accident on a pipeline of the gas transportation network. The second case study represents research of interdependency of power and heat supply minigrids in emergency conditions on the example of a city district. Preferable future work is discussed.

Rapid development of the hydroelectric power industry has raised concerns about the stability of hydroturbine units among the scientific and engineering communities. Most existing approaches that model hydropower stations focus on the design of the hydroturbine governing system or on analysis of the complex forces acting on hydraulic turbine generators. These models fail to comprehensively study the impact of such forces on the stability of hydropower stations. This study provides a novel model for analyzing the stability of generators that are subjected to increasing excitation currents. The results highlight a significant difference between the dynamic response of the shafting system and governing system for values of the excitation current lower than 880 A. Conversely, the fluctuations affecting the two subsystems appear to be consistent when the excitation current exceeds 880 A. Finally, the response of the whole system appears to be subject to random vibrations when the excitation current is 1,380 A. These findings offer a useful insight into the dynamic response of hydropower systems and their safe and stable operation.

Solar thermal power plants with central receiver systems are promising candidates for the harvest of solar energy. However, the development and application of volumetric receivers are restricted owing to the nonuniformity of incident heat flux distribution, which may reduce thermal efficiency and even lead to structural damage. In the present work, the influence of thermal conductivity and radiation distribution on the thermal response of porous receivers is studied. On this basis, a transient thermal model was developed. It was found that porous media receivers with larger thickness will ensure that the thermal energy of the receivers will be fully taken advantage of by flowing air and improve the efficiency of the whole system. For porous receivers exposed to concentrated solar radiation with a Gaussian distribution, the temperature distribution along the radial direction also distributes in a Gaussian shape, with a mean temperature the same as that of uniform distribution heat flux. In working conditions where the intensity of concentrated solar radiation changes rapidly, the rate of temperature increase/decrease may be too high, which may cause damage to receivers.

This manuscript aimed to seek influencing factors of energy consumption in China’s energy-intensive industries employing the generalized logarithmic mean Divisia index (LMDI) and input-output analysis. The research stated clearly that decomposition factors covered energy structure, energy intensity, industry structure, complete demand, final demand structure, and final demand total effect. The results showed that the decrease of energy consumption in energy-intensive industries heavily relied on energy intensity and industry structure. However, final demand total effect, which specifically involved the investment demand and export expansion, was a dominant element driving energy consumption growth. Accordingly, speeding up the industrial structure adjustment, improving the import and export mix, and reducing energy intensity have been the primary approaches to decrease energy consumption in energy-intensive industries. These approaches would accelerate the target of a 16% decline in energy intensity compared with 2010 in China’s Twelfth Five-Year Plan. Moreover, this research has crucial theoretical and practical significance on the implementation of energy policy in China.

A 12.9-L heavy-duty (HD) compression ignition engine was operated with diesel-ignited propane. Propane was fumigated into the intake and held a constant 84% of total fuel by energy while diesel was direct-injected at 310 crank angle degrees (CAD). Intake manifold pressure was varied from 135 to 220 kPa (5 to 17.135 psig) for two different exhaust gas recirculation (EGR) valve positions (fully closed and fully open) using a variable nozzle turbo and EGR valve. The engine was operated at a constant speed of 1,500 revolutions per minute (rpm) at constant load of 5 bar brake mean effective pressure (BMEP), which was representative of a typical low load condition for this operating condition (25% full load BMEP). All operating conditions were studied for combustion characteristics, fuel conversion efficiency (FCE), and engine-out emissions. Increasing the intake manifold pressure with a closed EGR valve resulted in lowering brake specific nitrogen oxide emissions (BSNOx) below $0.26\mathrm{g}/\mathrm{kW}\text{-}\mathrm{h}$ and also decreased brake specific hydrocarbons emissions (BSHC) with the trade-off of higher brake specific carbon monoxide emissions (BSCO) and lower FCE. Increasing the intake manifold pressure with an open EGR valve increased the BSNOx levels at all conditions but also lowered BSCO and BSHC values while increasing FCE relative to closed EGR-valve conditions. An intake manifold pressure of 168 kPa with negligible EGR levels was shown to result in optimal efficiency and emissions levels while applying EGR at the same intake manifold pressure gave an increase of significant FCE with the cost of little gain in BSNOx.

In this study, an advanced cogeneration plant based on a 100-MW aeroderivative intercooled gas turbine (ICGT) engine and large two-pass reverse osmosis (RO) desalination system is analyzed thermodynamically. The proposed model has been developed using specialized software and validated with manufacturers’ published data. Saline water is simulated using the latest physical properties available in the literature and treated as a real mixture. Combined energetic and exergetic performance criteria for the design of a cogeneration plant is presented as being, today, the most efficient method for accurate assessment of performance, which also permits quantification of system deficiencies. The performance of the proposed plant was investigated using different loads, ambient temperatures, pressure ratios, and feed water temperatures. The results show an intercooler system improves cogeneration plant performance despite having a negative impact on the combustion chamber performance because of its reduction of compressed air temperature. The ICGT engine is considered the best available choice to integrate with a RO unit because of its high pressure ratio and low power consumption in the compressors. From an operational perspective, full load and low ambient and high feed-water temperatures are highly recommended. The exergetic efficiency of the ICGT engine, RO system, and cogeneration plant are shown to be 44.3, 32.83, and 47.6%, respectively. From a sustainability perspective, the exergetic-environmental efficiency is slightly affected by ambient temperature, whereas it is highly affected by load variation. Based upon the obtained results, numerous possibilities are presented to improve the performance of cogeneration plants.

An enhanced understanding of the pressurized pyrolysis process is of great importance for advanced coal utilization technologies. In this study, a nonisothermal thermogravimetric analysis was conducted to investigate the pyrolysis characteristics of two different ranks of coal. The samples were heated at a constant heating rate of $10°\mathrm{C}/\min$ up to 900°C under the pressures varying from atmospheric to 2 MPa (20 bars). Experimental results show that the pressurized conditions cause a reduction in devolatilization rates at temperatures above 400°C, and total volatile yields at the final temperature decrease by 12–18% with increasing pressure up to 2 MPa (20 bars). With regard to the ranks of coal investigated, devolatilization processes of bituminous coal are more strongly influenced by pressure conditions than those of subbituminous coal. Two kinds of global $n$th-order reaction models were used to predict the thermal behavior of coal during the pressurized pyrolysis process, and a reasonable fit to the experimental data could be achieved for all the applied pressures.

Ammonia (${\mathrm{NH}}_3$) is considered as a combustion fuel, hydrogen carrier, and heat-recovery and working fluid within locomotive propulsion-system configurations. Thermodynamic and environmental analyses and assessments are conducted for a modern two-stroke diesel-fueled locomotive and the proposed ${\mathrm{NH}}_3$ configurations. The present study proposes and comparatively assesses the potential long-term solutions for sustainable, clean rail transportation. The diesel locomotive is considered as the baseline system, with energetic and exergetic efficiencies of 33 and 31%. The two alternative configurations—${\mathrm{NH}}_3$ diesel–fueled locomotive, and with the integration of onboard ${\mathrm{H}}_2$ fuel production—have energetic utilization efficiencies of 34.3 and 35.7%, and exergetic utilization efficiencies of 31.4 and 32.6%, respectively. The air-contaminant emissions are evaluated based on diesel fuel reduction, and reduction by selective catalytic reduction using ${\mathrm{NH}}_3$. The greenhouse gas emissions are reduced by up to 53%.

Effervescent atomizers have a number of significant advantages over conventional injectors. They can operate at much lower injection pressures, their atomization performance is largely insensitive to fuel physical properties, and very fine atomization can be achieved at lower air flow-rates when compared to air-blast atomizers. Despite these advantages, there is a lack of quantitative data describing the near-field atomization zone, which is difficult to probe due to the unstable nature of effervescent fragmentation. This lack of data has prevented a fundamental understanding of this atomization mode and delayed the development of advanced numerical models. Here, the near-field characteristics of a series of effervescent sprays are examined using advanced image processing. The study provides new quantitative insights into the nature of the regime transitions that occur as a function of the gas-to-liquid ratio (GLR). The distinct regime transitions, noted through quantitative measurements of the liquid jet outer diameter, closely coincide with previously quoted bubble type and transitional tree-regime transitions. The distribution of the outer diameter of the ejected air-laden liquid jet progresses from bimodal at low GLR values ($<0.5\%$) to monomodal distribution at a higher GLR. Measurements of ligament thickness in the near field have allowed for direct evaluation of a previously developed analytical model that predicts droplet Sauter mean diameter (SMD) as a function of the GLR. This model has been confirmed here over a wider GLR range by using number-based conditioning and further extended into a simple analytical model that can estimate the total number of objects generated per unit time.

For heavily curtailed wind power caused by the coexistence of large-scale wind power and high-penetration combined heat and power (CHP) units, especially during the winter heating period in northern China, the flexible operation of CHP units with the introduction of thermal energy storage (TES) and heating load flexibility is very helpful for reducing wind power curtailment in northern China. Therefore, based on the construction of a two-stage trading mode in the day-ahead market, which consists of the conventional energy market and peak regulation market, a three-level optimization method is proposed for integrating heating loads and storage control through the coordinated operation of CHP units and TES devices and heating load management. Thus, the operation mode of CHP units can be optimized to supply peak regulation capacity for curtailed wind power under a certain agreed peak regulation price. Finally, the typical influence factors, such as the capacity of TES devices, the agreed peak regulation price, and the different operation modes, will be discussed to demonstrate the resulting economic benefit and curtailed wind power consumption.

In view of the polygeneration technology of coal pyrolysis/circulating fluidized bed combustion, circulating ash and coal were layered in the pyrolysis reactor to investigate the secondary catalytic reaction of circulating ash on the primary volatiles of coal pyrolysis. The influence factors of the location types of ash and coal, the mass ratio of ash to coal, ash composition, and ash particle size were studied. Increasing the mass ratio of ash to coal increases the number of the catalytic active sites. Circulating ash rich in ${\mathrm{Fe}}_2{\mathrm{O}}_3$ significantly promotes the increase of gas product yield and the decrease of liquid product yield. Circulating ash increases the yields of ${\mathrm{CO}}_2$ and ${\mathrm{C}}_2^{+}$ but decreases the ${\mathrm{H}}_2$ yield significantly. The yields of ${\mathrm{CH}}_4$ and ${\mathrm{C}}_2^{+}$ for Zhaotong brown coal increase more than Shenmu bituminous coal. Combined with the thermogravimetric analyzer–mass spectrometer, the secondary catalytic effect of circulating ash on the primary volatiles of coal pyrolysis is evidenced mainly in the promotion of hydrocracking reaction of large molecular hydrocarbons. This study may provide reference for the optimization of the industrial scale of coal pyrolysis by solid heat carrier.

Hybrid photovoltaic and thermal (PVT) collectors with sheet-and-tube water-based flat-plate structure (simplified as STWF-PVT) are very popular because of their simple structure and ease of manufacture. Generally, their performance is closely related to their structure, especially the location arrangement of photovoltaic (PV) cells. In this work, the authors present three kinds of PVT collectors with different PV cell locations, denoted as PVT-1, PVT-2, and PVT-3, representing a conventional air-gap STWF-PVT collector whose PV cells are stuck on its solar absorber, a new air-gap STWF-PVT collector whose PV cells are fixed on the bottom of its glass cover, and a zero-air-gap STWF-PVT collector, respectively. Experiments and computational fluid dynamics (CFD) analyses were carried out to investigate the performance of these STWF-PVT collectors, by means of various comparisons with a pure thermal collector. The effects of the PVT configuration and the covering factor of the PV cells on the collector performance were discussed. Among these PVTs, the PVT-1 behaves with the greatest overall efficiency, followed by PVT-3 and PVT-2 in turn, whereas PVT-3 is proven to have the highest photoelectric conversion efficiency of PV cells, followed by PVT-2 and PVT-1. In summary, PVT-3 is much preferred by the customers who want more electricity than thermal energy, and PVT-1 is the first choice for a comprehensive evaluation of electrical and thermal energy. The authors hope this work is useful for STWF-PVT collector design, especially for the location design of PV cells and air gap.

Syngas is considered a promising renewable fuel because of its superior emission characteristics and high flexibility with respect to its production and utilization. However, its composition can vary widely, which poses challenges with its use in practical systems. In this regard, fundamental studies dealing with its combustion and emission behavior can provide valuable input for designing such systems. This paper reports a computational study on the structure, thermal-diffusive instability, and extinction of syngas premixed counterflow flames. One-dimensional (1D) and two-dimensional (2D) simulations are performed using validated computational fluid dynamics (CFD)–based codes and a chemistry model with 52 species and 544 reactions. Results focus on the effects of stretch, preferential diffusion, and radiation on flame characteristics. The effect of preferential diffusion is to increase and decrease the peak heat release rate with strain rate for lean and rich syngas flames, respectively. Similarly, the flame temperature is higher and lower than the adiabatic flame temperature for lean and rich flames, respectively. In addition, for lean flames, the flame temperature exhibits nonmonotonic variation, first increasing and then decreasing with strain rate as the flame approaches extinction. At low strain rates ($k<25{\mathrm{s}}^{-1}$), the effect of radiation is to reduce flame temperature and burning rate and to cause extinction at very low strain rates. Thus, flame radiation leads to two extinction limits in terms of strain rates. Temporal evolution of the extinction process at high strain rates indicates that extinction starts locally near the centerline, and this region subsequently spreads radially until the flame extinguishes globally. Simulations are also used to examine correlations between stretch and burning rate. Lean flames are found to be diffusively unstable ($Ma<0$), and their propensity toward instability increases as the mixture becomes leaner or $H_2$ content in syngas increases. Conversely, rich syngas flames are diffusively stable ($Ma>0$), and their propensity toward instability decreases as the mixture becomes richer or $H_2$ content increases. These results are consistent with previous studies dealing with spherical flames burning $H_2$ and hydrocarbon fuels.

Single-cylinder diesel engines are widely used because of their low cost and high adaptability, and they have become the main power for industry and agriculture in developing countries. The inability of meeting increasing requirements for energy saving and environmental protection have become the primary bottleneck problems for diesel engines. The high cost of various advanced technologies for emission control limits their application. In this study, an economic single-cylinder diesel engine to lower emissions is designed. The four-valve technology and high-pressure injection system with electrical unit pump are adopted. Both the numerical simulation and experimental results indicate that the fuel consumption can be 10% lower than that of other engines on the same power level. The noxious gas emission has been measured up to the emission standards in China, the United States, and Japan on nonroad diesel engines. Meanwhile, the life-cycle cost of the new engine consisting of initial and maintenance expenses is lower than traditional engines. The technology of the economic single-cylinder diesel engine proposed in this study is believed to have remarkable market value and deep impact to the governmental decision makers, and to greatly contribute to easing the sharp conflict between economic development and environmental pollution, especially in developing countries.

In this study, a 470-MWh natural gas combined cycle–combined heat and power plant (NGCC-CHP) in Beijing is the research object. For the industrial NGCC-CHP plant, the introduction of 90% postcombustion carbon capture (PCC) highlighted an outstanding issue: limited low-pressure steam allocation between district heating and ${\mathrm{CO}}_2$ capture. This work evaluates four options for providing the energy necessary for the amine reboiler when most of the low-pressure (LP) steam was extracted for district heating: electric heating of the reboiler, direct natural gas firing of the amine reboiler, a standalone gas-fired boiler to generate low-pressure steam, and integration via supplementary firing of the heat recovery steam generator. The study focused on net power output, ${\mathrm{CO}}_2$ capture level, ${\mathrm{CO}}_2$ emission intensity, and profit ratio. The results show that supplementary firing improves the steam turbine power output up to 135.84 MWh with the firing of 217.65 MW of additional natural gas, whereas the net equivalent efficiency is approximately 50.2%. The integration via supplementary firing of the heat recovery steam generator (HRSG), therefore, is shown to have a higher technical and economic performance advantage over other options.

Adoption of methane scavenged prechamber has been considered as a promising solution to extend the lean limit of large-bore natural gas engines. In this paper, the effects of prechamber energy fraction, Miller cycle, excess air ratio, intake temperature, fuel methane number, and engine load are examined by a full set of experiments and detailed analysis on a single-cylinder large-bore natural gas engine. The results indicate that brake thermal efficiency (BTE) could be improved by increasing prechamber energy fraction, reducing excess air ratio, and using fuel with a higher methane number. It is also observed that brake thermal efficiency is higher at higher engine loads. Moreover, knock intensity is shown to be higher at higher prechamber energy fractions, higher intake temperatures, and lower methane numbers. For a methane scavenged prechamber engine, the cyclic variation of indicated mean effective pressure is maintained at a low level, attributed to the strong ignition energy. However, reducing air excess ratio and utilizing valve timing with a higher Miller degree are capable of reducing cyclic variation to a lower level. Additionally, carbon monoxide (CO) emissions are lower at higher prechamber energy fractions, higher excess air ratios, and lower Miller degree, which first increases and then decreases with the increase of methane number. Hydrocarbon emissions could be controlled by increasing intake temperature, reducing prechamber energy fraction and excess air ratio, and using a higher Miller degree. Meanwhile, lower NOx emissions can be obtained by raising prechamber energy fraction and excess air ratio. It is also deduced that implementation of higher Miller degree has positive effect on NOx reduction.

This paper details a quantitative joint Reynolds number, equivalence ratio, wall material, and quenching distance imaging experiment designed to investigate OH radical behavior near the walls in premixed methane–air combustion. Different wall materials, such as AZ31B, 316STS, and AlN, are studied. The greater the Reynolds number, the lower the maximum fluorescence intensity of the flame. When the distance between walls is 7 mm, two areas of high counts could be found, located on both sides of the bottom; the middle area has no OH radical signal at all. This is the repetitive extinction/reignition phenomenon of radicals. The order of the maximum fluorescence intensity in the flame between the six materials is $304\mathrm{STS}>316\mathrm{STS}>{\mathrm{Al}}_2{\mathrm{O}}_3>\mathrm{quartz}>\mathrm{AlN}>\mathrm{AZ}31\mathrm{B}$. The order of the quenching distance of OH radicals is $\mathrm{AZ}31\mathrm{B}>\mathrm{AlN}>\mathrm{quartz}>{\mathrm{Al}}_2{\mathrm{O}}_3>316\mathrm{STS}>304\mathrm{STS}$. For the same material, the greater the maximum fluorescence intensity, the smaller the quenching distance.

A comparison of energy and exergy analyses for an air conditioning system with and without an air membrane heat and mass exchanger was performed. The study considered several key performance parameters, including coefficient of performance, second law efficiency, exergy destruction rate, evaporative cooling rate, compressor input power, fuel depletion ratio, relative irreversibility, productivity lack, exergetic factor, and exergetic improvement potential. A membrane significantly improves the second law efficiency, while it has only a small effect on the coefficient of performance. However, in the presence of a membrane both the required cooling energy and the required input power decrease significantly. In addition, the total exergy destruction rate is lower when a membrane is used, and the evaporator has the highest irreversibility ratio compared with the other components. The total exergy destruction decreases, on average, by more than 50% when a membrane is used compared with the case when no membrane is used. Therefore, the second law efficiency increases when a membrane is used and this study reveals that it increases by more than 5%.

Solar glass with high transmittance and low reflectance is used as glazing in solar-thermal collectors or photovoltaic modules; however, in field conditions the glazed surface can be the subject of fouling; therefore, additional prerequisites are targeting self-cleaning features while preserving or enhancing the glass optical properties. This study presents the results obtained by applying silica-based layers to the solar glass surfaces; the surface properties are tailored by controlling the roughness to modify the optical properties and improve surface wettability, supporting self-cleaning mechanisms. The sol-gel silica nanoparticles are deposited in optimized conditions, with and without titanium dioxide and gold nanoparticles; the thin layers are analyzed by X-ray diffraction, contact angle, optical measurements, and atomic force microscopy. The roughness values are influenced by the chemical composition, with lower values for the layers containing only silica and increased values when ${\mathrm{TiO}}_2$ and Au nanoparticles are added. The layers have a predominant polar component of surface tension ($>95\%$), supporting good wettability, up to enhanced superhydrophilic features as compared with the uncoated solar glass. Additionally, the investigations under simulated solar radiation outline self-cleaning features in methylene blue removal, as a combined effect of photocatalysis and superhydrophilicity.

Retailers purchase electric energy from the wholesale market and sell it to the customers at regulated fixed prices in deregulated power systems. A retailer has multiple choices for electricity procurement, such as spot market, bilateral contracts, and a self-generating facility. However, the retailer faces challenges such as the pool price and electricity demand uncertainty. To meet these challenges, this paper proposes a midterm framework based on the information gap decision theory (IGDT) to evaluate the robust or opportunity strategy. In this approach, the composition of two conflicting portfolio investment goals is considered including obtaining high expected portfolio return and selling price designation, as well as controlling risk. A real case study is used to demonstrate the effectiveness of the proposed framework.

This paper proposes a stochastic day-ahead scheduling framework for integrated energy systems (IES) considering uncertain wind power generation and multienergy loads. The structure and modeling of the IES consisting of electrical, natural gas, and heating networks are presented. The network constraints of the electricity network, natural gas network, and heating network are formulated and incorporated into the optimization model. Uncertainties of hourly wind power and multienergy loads are taken into account by creating multiple representative scenarios with different probabilities using Monte Carlo simulation. The stochastic scheduling model is formulated as a mixed integer linear programming (MILP) problem by linearizing the nonlinear constraints, with the objective function of minimizing the total expected operation cost. Numerical results validate the proposed model and demonstrate the impact of natural gas and heating network on IES operation.

Combustion of premixed methane/air in a hybrid porous burner is experimentally studied. The burner is filled with alumina pellets in the preheating zone and silicon carbide foams with a gap in the combustion region. Different lengths and locations of gap are evaluated to identify how the geometric parameters affect flame stability, flame temperature, and pollutant emission (CO, HC, and ${\mathrm{NO}}_x$). The maximum stable flame range is obtained when the gap length is 15 mm and located between the packed alumina pellets and silicon carbide foams. When the gap is inside the foam region, the flame always stabilizes in the porous region regardless of the foam before or after the gap. The flame temperature decreases with the increase of gap length or with the decrease of foam region after the gap. The CO emission and the flame temperature exhibit opposite tendencies with the variation of flame speed. The HC emission increases with the increase of gap length $\delta$ or when the gap moves to the downstream. It implies that the preheating effect caused by the gap location is dominant to the formation of HC emission. The ${\mathrm{NO}}_x$ emission is 4 ppm, which is relatively low attributable to the lower flame temperature.

This work explores the influence of lateral heat losses from a phase change material (PCM) storage tank on the performance of a storage integrated solar thermophotovoltaic (SISTPV) system by means of an analytical model. The heat losses from the lateral surface of the PCM tank are modeled using Newton’s law of cooling by prescribing a heat-loss coefficient on the lateral surfaces. The results show that at high heat losses, low thermal efficiencies are realized. Correspondingly larger solar concentrations are required to fully melt the PCM tank. At low heat losses, such as can be expected when using thermal insulation on the lateral surfaces, approximately 40% thermal efficiency can be realized. The results also demonstrate that a high absorber area:length of PCM tank squared (SR) ratio enables the system to have a high thermal efficiency. For a high-SR, low-heat-loss design case, having a high taper ratio, high area ratio between absorber area and inlet hole area, and small PCM tank length all achieve higher thermal efficiencies. It is expected that these SISTPV systems will be designed at steady-state to be fully molten in order to maximize thermal energy storage via the latent heat of the PCM. The analytical model developed here can be used to predict the design conditions under which the PCM tank will be fully molten.

This paper describes the development of several piezoelectric prototypes capable of harvesting energy from the action of traffic on roadways. It provides a brief overview of piezoelectric theory to show that the relationship between the power generated and the applied stress has a quadratic form. The amount of energy available for harvesting is explored through finite element simulations of the strain energy in pavements under moving tire loads. The prototypes developed involve various configurations of cylindrical and prismatic piezoelectric elements. Exploratory analysis shows that it is desirable to alternate the polarity of stacked piezoelectric elements and connect them in parallel to avoid generating unmanageably high voltages. The prototypes are tested in uniaxial compression under sinusoidal loading at a frequency of 10 Hz. Curves are fitted to the electrical power versus stress laboratory data. For a single pass of a 44.48-kN truck tire load, the electrical power generated is estimated to be between 1.0 and 1.8 W. A number of traffic scenarios are considered for translating this power output into energy. The estimated annualized cost of the harvesters and the amount of electric energy produced per year is used to compute the levelized cost of energy (LCOE) for this technology. For the most promising harvester the LCOE is between $\$19/\mathrm{kWh}$ and $\$4.8/\mathrm{kWh}$, depending on traffic level.

In accordance with current industrial waste heat and heat requirements, a new steam heat pump system used for recovering industrial waste heat is proposed in this paper which consists of a vapor compression–type high-temperature heat pump (VCHTHP) and an injector heat pump. As the experimental results show, if the primary steam is superheated vapor at 300°C and 3.5 MPa, and the secondary steam is 0.20–0.22 MPa, then compressible steam with a condensing temperature of approximately 160°C can be obtained with a maximum entrainment ratio of 0.39. Through a combination of the VCHTHP and the injector heat pump, the entire heat pump system can recover waste heat from industrial sewage at a temperature of 80°C to produce compressible steam with a condensing temperature of approximately 160°C and a coefficient of performance (COP) of the optimum condition of 1.19. If the compressible steam is used to heat the reboilers in a chemical plant, 28% more high-pressure steam can be saved compared with that from the original heating system, with power consumption only taking 32.5% of the recovered heat.

The increasing penetration of renewable energy (RE) brings nonnegligible uncertainties to a power system, which should be carefully considered in the day-ahead scheduling for better RE utilization and higher power supply reliability. However, stochastic unit commitment of multitype power is a challenging problem considering the uncertainties of RE and the complicated characteristics of different power. This paper specifically focuses on the modeling and optimization approach for multitype power sources stochastic unit commitment (MPSSUC) with high penetration of RE and multiple uncertainties using interval number programming (INP). The MPSSUC model is established considering the elaborate characteristics of thermal power, hydropower, wind power and pumped storage power. The uncertainties of wind energy, natural water inflow, and power load are depicted by interval numbers. A novel particle swarm optimization–based bilevel solving approach is proposed for MPSSUC optimization, which preserves the interval properties of INP for better accommodation of uncertainties. Case studies on the IEEE 118-bus system and a realistic power system show that this study can effectively improve the RE accommodation while maintaining operation benefit. Analyses on the uncertainty level influence, trade-off between cost and robustness, and the operation characteristics by water regimens are also presented.

Employing thermal energy storage (TES) for combined heat and power (CHP) can improve flexibility in an integrated electric-thermal system (IETS) and therefore is beneficial to the accommodation of variable renewable energy sources (RESs). In general, there are two kinds of thermal storage: active thermal storage (ATS) and passive thermal storage (PTS). Active thermal storage capacity, provided by devices designed for special purposes, is generally fully exploited; passive thermal storage capacity, defined as the TES capacity provided by system components such as pipelines and building envelopes, has yet to be employed. To explore the possibility of using ATS and PTS for flexibility enhancement in the IETS, this paper presents a unified model of an IETS with both ATS and PTS in which heat transfer is included. In the proposed model, ATS is expressed by a phase-change TES device, and PTS is expressed by pipelines and heat consumers. Then, for the operation of the integrated system with both ATS and PTS, a dispatch model is presented, which can be simplified to a system with only ATS or only PTS by setting different boundary conditions. Finally, a test system is set up to verify the proposed model. The impact of factors such as transport time delays and temperature variation ranges in PTS is also analyzed in the test system. Results show that both ATS and PTS can provide extra flexibility in system operation and thus promote wind power accommodation.

In a wind farm, the wind data of the anemometers are used to evaluate the local wind resource. The position of the anemometer in a wind farm influences the wind resource evaluation significantly. In this paper, the position optimization of the anemometer related to flow field simulation of a wind farm is studied. The computational fluid dynamics method is introduced for airflow simulation. Based on the similarity of the flow field and the wind data of a single anemometer in the wind farm, a residual correction method is introduced to determine the boundary wind speeds and the flow field of the wind farm. Subsequently, a performance index is proposed through analyzing the characteristics of the residual correction method, acting as the optimization principle for anemometer positioning. The effectiveness of the performance index is tested by a case on a randomly generated terrain and a case with measured wind data in a real wind farm. The results indicate that the best anemometer position after optimization is not the one with highest elevation. Furthermore, the wind data of the optimized anemometer position can help to improve the numerical flow field results as well as saving much computational cost compared to the one with highest elevation. It is suggested that the proposed performance index can be used as the guidance for the anemometer positioning when designing a wind farm.

Based on the applications of thermal control for bearing structures, this paper conducts an investigation of the thermal performance of a metallic lattice structure filled with phase change material (PCM). The transient temperature variations of a composite sample under constant heat flux are measured experimentally. The effects of porosity, heating orientation, and heat flux are discussed. A three-dimensional numerical model employing the enthalpy-porosity method is also established and validated. The results show that the heat transfer process in a metallic truss structure filled with PCM can be divided into three regions: sensible heat region before melting, latent heat region, and sensible heat region after melting. The temperature control time for a sample with PCM is approximately 4.0 times of that without PCM because of the latent heat absorption of the PCM. The sample with the larger porosity has a lower back-surface temperature and a longer melting duration time. Furthermore, the liquid fraction and temperature near the metallic trusses are higher than at other locations in the sample. The temperature difference between metallic trusses and PCM can be a major driving force of natural convection under top heating. The present study may provide beneficial guidance for the design of a thermal control system with a metallic truss structure.

Organic Rankine cycle (ORC) is a more efficient way to recover exhaust heat from medium- and small-scale gas turbines than conventional steam power cycles. Plate-fin heat exchangers (PFHEs) were applied as the evaporator and recuperators because gas-liquid and gas-gas heat transfers occurred. This study focused on the preliminary system design and off-design analysis of the gas turbine (GT)–ORC combined cycle. Therefore, optimum-rated parameters for the ORC and geometric parameters for the PFHEs were designed first. Based on the established off-design model and constant pressure control approach, off-design simulations were done and results showed that the combined cycle efficiency decreased monotonically with the decline of GT load. However, the ORC still had good performance and played a more important role in the combined cycle under low-load conditions. Moreover, sensitivity simulations concluded that the ambient temperature impacted the combined cycle performance mainly by the gas turbine under high-load conditions and the ORC under low-load conditions. In addition, the ORC had better performance with higher ambient temperature. This model can provide reference parameters for detailed design of the GT-ORC combined cycle and predict its off-design performance under variable conditions.

Energy consumption in data centers is growing rapidly due to their increasing numbers, scales, and densities. Coordinated operation of the information devices and cooling system is an effective way to lower the energy cost in data centers. Previous studies covered various types of optimization and control approaches, but oversimplified heat transfer models were employed. In this paper, the heat transfer procedures in the data center are studied using numerical simulations of computational fluid dynamics. By neglecting the natural convection of the air, solving the temperature field is decoupled from the velocity field. With this feature, the temperature field for real cases can be calculated by linear superposition of multiple precalculated elementary procedures, saving significant computational time. Based on this technique, an optimized control strategy is proposed to adjust the outlet temperatures of computer room air conditioners (CRACs), with the objective of enhancing cooling efficiency and, in the meantime, preventing information devices from overheating.

Nowadays, many health, environmental, and economic concerns are associated with fossil fuel use, and therefore the improvement of new and advanced technologies and the use of renewable fuels are key issues for the sustainable development of the planet. The aim of this research is the plan of new power systems for future urban centers rising on reclaimed industrial areas; an innovative and convenient mode to exploit the solar energy is proposed using solar thermal power to replace the bled-off steam in regenerative Rankine power cycles. The main idea is the concept that exploitation of solar power in solar thermal–aided power-generation plants can be more cost- and energy-effective than using it in exclusively solar plants, especially in medium-temperature systems. For this purpose, the paper deepens an investigation about biomass-solar combination in a regenerative Rankine cycle system with superheating, substituting the steam bleeds by solar power for feed water preheating process. In biomass-solar combined configuration, the conversion efficiency of solar energy is appraised to compare the exploitation of solar energy in power plants characterized by different plant configurations. The calculated global and exergetic efficiencies are assumed as optimization factors for the best plant configurations, changing regeneration parameters and steam pressure.

It has been proven that the turbocharger turbine operates differently under unsteady flow conditions as compared to steady flow. Despite this, the turbine wheel is still designed under the assumption of steady flow conditions. This results in overprediction of the efficiency during actual conditions, which are always pulsating because of the reciprocating nature of an internal combustion engine. The difficulties in characterizing turbine behavior under pulsating flow conditions is attributable to complexities in characterizing the mass flow imbalance and its deviation from steady-state conditions. This paper attempts to describe the mass flow hysteresis properties that occur as a result of the filling and emptying phenomena as the flow frequency is increased from 20 to 60 Hz for vaned and vaneless turbine stators. The phenomena, coupled with difficulties in obtaining instantaneous mass flow rate, resulted in a complex experimental arrangement. Results indicated that the hysteresis properties of each frequency differ substantially, depending on the differences of the propagation velocity between the bulk flow and pressure. The hysteresis loop for vaned turbines also seems to have a larger range than its vaneless counterpart.

This study was conducted to investigate the spray characteristics of n-butanol, using a diesel spray for comparison. Spray tip penetration and spray cone angle were tested and analyzed. A high-speed photographic system was employed to observe the spray evolution, and a common-rail system and constant-volume chamber were used to change the pressure. The results show that the n-butanol spray penetrates faster than the diesel spray while under the same conditions. The experimental trend lines support the axial development model constructed by Hiroyasu and Arai on the grounds of a similar proportional relation to time after the start of injection, and the empirical equations provide reasonable approximations to the experimental measurements of the spray tip penetration.

In this paper, a big data-based approach is proposed for the security improvement of an unplanned microgrid islanding (UMI). The proposed approach contains two major steps: the first step is big data analysis of wide-area monitoring to detect a UMI and locate it; the second step is particle swarm optimization (PSO)-based stability enhancement for the UMI. First, an optimal synchrophasor measurement device selection (OSMDS) and matching pursuit decomposition (MPD)-based spatial-temporal analysis approach is proposed to significantly reduce the volume of data while keeping appropriate information from the synchrophasor measurements. Second, a random forest-based ensemble learning approach is trained to detect the UMI. When combined with grid topology, the UMI can be located. Then the stability problem of the UMI is formulated as an optimization problem and the PSO is used to find the optimal operational parameters of the UMI. An eigenvalue-based multiobjective function is proposed, which aims to improve the damping and dynamic characteristics of the UMI. Finally, the simulation results demonstrate the effectiveness and robustness of the proposed approach.

Using multiple energy resources greatly enhances system operating flexibility and efficiency. An energy hub is a vital facility, producing, converting, and storing energy in different forms. Considering heat-power cogeneration and thermal storage capabilities, concentrating solar power (CSP) acts as an energy hub, building physical connections between the power distribution network (PDN) and the district heating network (DHN) in integrated energy systems. The CSP hub, the PDN, and the DHN are respectively formulated to model the economic dispatch of an integrated heat-power distribution system. The linearized DistFLOW model is used to describe the electrical power flow in the PDN. The hydraulic-thermal model is employed to formulate steady-state nodal temperature with constant mass flow rates. Both operating costs and carbon emissions are considered in the objective function, yielding mixed-integer programming with a convex quadratic objective and linear constraints that can be solved by commercial solvers. The effectiveness of the proposed model and the method are validated on a test system in terms of reducing operating costs, carbon emissions, and renewable spillage.

Utilization of biofuels in autoignition engines is important but it is an exciting challenge to invent technologies that will harness the unique chemico-physical characteristics of these novel fuels. This study aims to investigate combustion phases (e.g., start of combustion and autoignition duration) along with emission characteristics of a residue-based biodiesel in autoignition engines. The fuel has been successfully derived from residue of a cooking-oil production process and two blends (B10 and B20, referring to 10 and 20% in volume of the biodiesel in the biodiesel–diesel mixture, respectively) along with fossil diesel (B0) were tested in a common-rail single-cylinder engine operating under a range of speeds (1,400, 1,800, and 2,400 revolutions per minute), loads (25–100%), and injection timing conditions (16–24° before top dead center). Combustion phases were extensively analyzed employing different approaches including in-cylinder pressure derivatives, heat release rate, and engine vibration signals, while particle and NOx formation, two major issues of autoignition engines, are also investigated. Equivalent timing between local maximum and minimum values of in-cylinder pressure derivative observed for B0, B10, and B20 [1.5° of crank angle (DCA) approximately] may suggest a minimal effect of blending ratio on autoignition duration, albeit the start of combustion occurs earlier for B10 and B20 (1–2 DCA) with respect to B0. Particle concentration of B20 decreases up to 30% compared with that of its fossil counterpart, and this is one of the major benefits of utilizing biodiesel in autoignition engines.

A thermal storage unit (TSU) with flat microheat pipe arrays (FMHPAs) as heat transfer core is experimentally investigated in this study. A comprehensive evaluation parameter of the TSU defined as thermal power intensity is proposed. The effects of the length proportion of the air side and the phase-change material (PCM) side on the heat transfer properties of TSU are also examined. Phase-change behavior of the PCM, heat transfer characteristics, and thermal resistance distribution are analyzed and discussed. Results show that the FMHPAs greatly enhanced the heat transfer rate between the air and the PCM. The thermal resistance of the air side is nearly three times greater than that of the PCM side. Keeping the length of the storage section 480 mm long and varying the length of the heating and cooling sections from 130 to 160 mm and 190 mm, the best performance was obtained for the length of 160 mm.

The objective of this study is to investigate the effect of engine speed, intake air temperature, intake air pressure, and compression ratio on combustion and performance characteristics in a homogeneous-charge compression-ignition (HCCI) engine fueled with gasoline surrogate using numerical simulations. The operating range of HCCI combustion with regards to speed and load is fixed considering that the start of ignition together with the heat release rate cannot be controlled directly. In order to design an engine for extended operational range, accurate models are needed that are able to model both combustion and performance. This paper states the outcomes of a modeling study of HCCI combustion using gasoline surrogate, a mixture of hydrocarbons with perfectly acknowledged fuel chemistry. A zero-dimensional single-zone numerical simulation with reduced fuel chemistry was developed and validated. The simulations reveal good agreement aided by the experimental results and capture essential combustion phase trends when engine parameters vary with a minimum percentage of error that is significantly less than 4%. The combustion phase advances and the combustion duration becomes shorter with the increase of intake charge temperature and the decrease of the engine speed. The maximum load successfully increased with increasing the intake pressure. The highest load in this study was 1,086 kPa (10.86 bar) in gross indicated mean effective pressure (IMEPg) at the condition of 200 kPa in intake air pressure and 393 K in intake air temperature. At last, it is found that the intake air pressure gives the most sensitive influence on the HCCI gasoline combustion and performance characteristics.

This work simulates the Suralaya Power Plant Unit 6 boiler located at Cilegon, Banten, in Indonesia for two thermal loads, i.e., 600 and 400 MW under as-found (normal) and reduced-oxygen conditions, by means of computational fluid dynamics (CFD) using a sophisticated software package. The reduced-oxygen condition is an operational scheme that assumes lower mass flow rates of injected air and fuel compared with the as-found ones, but constant or slightly improved thermal efficiency with lower NOx emissions. The results of the CFD simulation were compared against thermodynamic results in the as-found condition cases regarding the overall heat flux and the species concentration, and overall show good agreement because the maximum percentage difference is approximately 14.5% regarding the ${\mathrm{O}}_2$ mole fraction in the 400-MW case. In general, the differences between the two subcases of each investigated thermal load are slight concerning the total heat transfer, the spatial distribution of the heat flux values, the ${\mathrm{CO}}_2$ emissions, and the overall char burnout. More important differences can be noted regarding the CO emissions because the mass and molar concentrations at the main furnace outlet surface almost double in the case of reduced-oxygen conditions in comparison with the case of the as-found ones. Furthermore, it is noted that in all four examined cases the front side of the boiler experiences the highest heat flux values among the boiler tube wall sides. This is attributed to the developed velocity field due to the inclined configuration of the rear boiler tube walls at the proximity of the main furnace outlet surface. In order to minimize the thermal loading of the front side walls and reduce the CO emissions, it would be beneficial to implement a more suitable swirl in the secondary air inlet ports and the development of an overfire air (OFA) system.

Compared with conventional aqueous electrolytes, deep eutectic solvents (DES) have been used as the electrolytes of flow batteries for their unique merits, including a wide electrochemical window, ease in preparation, and low vapor pressure. However, the electrochemical and physical characteristics of DES are sensitive to the change of temperature, and there are few related studies. An urgent need exists for research into temperature adaptability of flow batteries with DES electrolytes before they can be utilized practically. This paper studies the electrochemical and transport characteristics of vanadium ions in a DES by varying the operating temperatures. The cyclic voltammetry curves indicate that vanadium ions show a quasi-reversible redox reaction in DES. With the rise of temperature from ambient temperature to 55°C, the gap between oxidation and reduction peaks decreases from 0.271 to 0.248 V at a scan rate of $100\mathrm{mV}/\mathrm{s}$. Both the oxidation and the reduction peak current densities of V(II)/V(III) have a similar incremental trend. Conductivity increases from $2.2\mathrm{mS}/\mathrm{cm}$ at ambient temperature to $11.16\mathrm{mS}/\mathrm{cm}$ at 55°C, whereas the viscosity of DES with vanadium ions decreases sharply. The results prove that operating temperature has a vital effect on the electrochemical reaction and transport characteristics of V(II)/V(III) redox couple in DES, and it deserves further study in cell performance.

Buildings are the largest consumer of energy in the United States from various sectors that includes transportation, industry, commercial, and residential buildings. Leadership in Energy and Environmental Design (LEED) certification program, home energy rating system (HERS), and American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) standards are developed to improve the energy efficiency of the commercial and residential buildings. However, these programs, codes, and standards are used before or during the design and construction phases. For this reason, it is challenging to track whether buildings still could be energy efficient post construction. The primary purpose of this study was to detect the anomalies from the energy consumption dataset of LEED institutional buildings. The anomalies are identified using two different data mining techniques, which are clustering, and isolation Forest (iForest). This paper demonstrates an integrated data mining approach that helps in evaluating LEED energy and atmosphere (EA) credits after construction.

Integrated community energy systems have attracted considerable attention due to their capabilities in supporting distributed generation integration and providing various energy services to customers. However, the rising use of gas-fired generations at the community level is pushing the gas distribution network to its operational boundaries and preventing its further applications. This paper investigates the dynamic interactions and mutual dependence between community energy systems and the gas network through an integrated energy system model. The model incorporates the dynamic behaviors of the gas network, distributed generations and the relevant energy management system. Based on this model, disturbance propagations between the gas network and communities are analyzed from the viewpoint of energy exchanges. Numerical results demonstrate that the change of loads and solar panel outputs can cause large pressure drops of the gas network when microturbines are set to compensate for these variations, and the pressure drop can affect the operation of other gas-fired equipment in surrounding areas. The results also show that different communities can influence each other through the gas network, which indicates some coordination is required in order to restrain adverse interactions as well as their impacts on the gas network.

Developing efficient, sustainable, and affordable buildings requires combinations of passive and active measures that exploit specific onsite features. However, in temperate climates, reducing the heating demand (by south-oriented, triple-glazed curtain walls) has as a direct consequence an increased cooling demand. Using data collected over three years (2013–2015) in a mountain temperate continental climate, this paper analyzes the effect of (passive) natural night ventilation and (active) ceiling cooling on reducing the cooling demand in large office spaces in energy-efficient buildings. The results match those modeled using in-field climatic input data, whereas simulations using interpolated data lead to differences compared with experimental data. The results show that natural night ventilation decreases the cooling demand by 97% in June, and reductions of 33% are reached during the hottest month, August. When involving natural night ventilation and ceiling active cooling (heat pump in reversed mode), 88% coverage of the cooling demand is reached in August. A significant indoor temperature gradient (10°C) is registered during hot days, with peak differences in early afternoon, suggesting a need for customized cooling algorithms.

With the electricity shortage situation becoming increasingly serious, management of the power demand side has practical significance. The feasibility of using a water heater based on an air-source heat pump for storing hot water is analyzed for a hotel in Shanghai, located in the hot summer/cold winter area of China. A detailed dynamic operation strategy for a hot water load shift-peak and fill-valley approach is presented in order to promote power grid cut-peak and fill-valley behavior based on considering key factors such as occupancy, season, utilization efficiency, weather, and electricity price. The heat pump unit’s installed capacity and hot water tank’s volume are discussed. Meanwhile, the influence of two key factors—heat pump coefficient of performance (COP) and electricity price difference between peak and valley—on the energy efficiency and hourly electricity consumption distribution are analyzed. As a consequence, the capacity of the heat-pump water heater and required level of electricity distribution for the domestic hot water system are decreased. In addition, the low-efficiency problems from conventional whole heat-pump water heater systems at low occupancy and partial daily or annual hot water demand are solved. The phenomenon of “a powerful horse pulling a small car” for hotel hot water supply systems is eliminated. The hot water storage scheme effectively encourages electricity load cut peak and fill valley by a hot water load shift peak and fill valley in contrast to conventional schemes. Furthermore, in a broad sense, heat-pump storage of hot water at night has energy saving effects on the entire power grid system depending on heat pump COP and electricity price difference between peak and valley.