Journal of Energy Engineering

To improve grid-connected inverter operation performance, a power oscillation and current harmonic suppression coordinate control strategy that considers the problem of overcurrent is proposed in this work. First, the internal relationship between power fluctuation suppression and current balance is analyzed, and then, combining dynamic regulation of the active and reactive power settings, the peak value of the grid-connected current is limited within a safe range. Second, a simplified Fourier transform algorithm is proposed for the detection of fundamental positive and negative sequence vector components and band-pass filtering the three-phase input signals. By simplifying the transform and introducing a recursion algorithm, the online computational complexity is reduced and the controller based on this algorithm is used as an inner current loop regulator. Finally, the controller was investigated using simulations, and experimental results indicated that the output power quality of the grid-connected inverter under unbalanced grid voltages can be substantially improved.

Agricultural and waste-derived solid biomass fuels are available in vast amounts for the generation of sustainable energy. Since these fuels usually have rather low heating values, low bulk densities and are disadvantageous concerning their storage behavior, the torrefaction of such materials (low-temperature pyrolysis between 200°C and 320°C) represents an interesting procedure to improve their fuel properties. After the torrefaction of vine prunings for 30 min at 200°C and 220°C was performed in a pilot hearthtype reactor located in Ptolemais-Greece, the lower heating value (LHV) was increased by 3.7% and 10.5%, respectively, leading to important cost reductions during transport and storage. A comparative analysis of chemical properties between raw material and torrefied material is presented followed by calculating fuel-specific indices concerning corrosion risk, aerosol formation, and slagging tendency. Based on the ${\mathrm{NO}}_{\mathrm{x}}$ emission index, a lower conversion was predicted for the torrefied fuel than for the untreated fuel. High aerosol emissions are expected for raw fuel, even higher aerosol emissions for the torrefied fuel. According to the measured ash melting temperatures and calculation of the ${\mathrm{R}}_{\mathrm{s}}$ index, raw fuel and torrefied fuel at 200°C present medium trend for deposit formulation, whereas there is a high trend for deposit formulation in the case of torrefied fuel at 220°C.

Buildings consume large amounts of energy, and lighting and maintaining a comfortable temperature consume a substantial amount of this energy. It is of significance to dwell on creative technology that takes advantage of solar energy for light and heat supply. As a consequence, this study offered an investigation on a novel building envelope material by means of the polymethyl methacrylate resin embedded into concrete, which can provide excellent illumination from natural light and an excellent combination of shielding performance and clarity. The light transmission and thermal conductivity of resin translucent cement-based material (RTCM) were measured by the optical power method and flat plate method, respectively. The building energy consumption and daylight level were evaluated through energy and daylighting simulation with the help of Autodesk Ecotect Analysis 2011 software. The natural lighting coefficient increased by nearly 100%, and the lighting uniformity improved by nearly 50%. The operating time of the artificial lighting device was shortened from 72% to 41%. In addition, the cooling/heating load in the present test conditions could be reduced by nearly 20%. The results revealed that RTCM had excellent light transmittance and thermal conductivity. RTCM could effectively improve the indoor daylight condition and visual comfort.

Lignite usually has a high moisture content and low calorific value, and should be predried before combustion to enhance power generation efficiency. Steam extracted from steam turbine and boiler exhaust gas are often applied in lignite predrying systems. However, the bleeding gas from the steam turbine reduces its output, and the exhaust gas originating from the boiler has insufficient drying capacity. In the present work, a new lignite power plant integrated with a solar drying system is proposed. A solar energy collection and storage tank system were employed to solve the problem of low heat density and instability of solar energy. Thermodynamic analysis results show that the area of reflectors declines at a decreasing rate with an increase in the direct normal irradiation (DNI). The power generation efficiencies of a solar drying lignite power plant (SDPP) and steam extraction drying power plant (SEDPP) can be increased by 0.68% and 0.33% for every $0.1\mathrm{kg}/\mathrm{kg}$ rise in the drying degree. When the drying degree is 0.3 and DNI is $0.5\mathrm{kW}/{\mathrm{m}}^2$, the economic analysis indicates that the simple payback periods for a conventional lignite power plant, SDPP, and SEDPP are 2.38, 3.20, and 2.53 years, respectively. In addition, the solar-to-electricity efficiency declines at a decreasing rate with increasing drying degree. The power generation efficiency of SDPP with dryer exhaust recovery is increased by 0.83% for each $0.1\mathrm{kg}/\mathrm{kg}$ increase in the drying degree.

In order to investigate the effects of a Ce-based fuel-borne catalyst (FBC) on the catalytic oxidation of soot particles from a diesel engine, a naphthenic acid cerium solution was selected as the FBC, which was blended with diesel fuel at four ratios. Experimental studies on the smoke emissions, particle size, soot oxidation characteristics, and diesel particulate filter (DPF) catalytic regeneration were conducted on a light-duty diesel engine fueled with FBC fuels. The experimental results show that FBC fuels can improve the fuel economy and reduce the exhaust gas temperature and smoke emissions. The particle mass distribution moves to the small particle size, the proportion of accumulation mode particles increase, and the proportion of the coarse mode particles decrease when the engine is fueled with FBC fuels. The soot oxidation temperature decreases with the FBC ratio increasing, and the DPF regeneration temperature can be reduced as diesel engine fueled with FBC.

The effects of the cetane number (CN) and latent heat of vaporization (LHV) of diesel/n-butanol fuel on the hydrocarbon (HC) emission and combustion process at various oxygen intake concentrations (${\mathrm{C}}_{\mathrm{oxy}}$) were studied in a modified four-cylinder light-duty diesel engine. Three fuels were studied in this experiment: neat diesel (B00), diesel blending with 20% n-butanol by volume (B20), and diesel blending with 20% n-butanol and 0.7% 2-ethylhexyl nitrate by volume (B20+EHN). The conclusion reached is that the ignition delay period has a decisive influence on HC emissions and the combustion process. A comparison of the B20 and B00 fuels reveals that, as ${\mathrm{C}}_{\mathrm{oxy}}$ decreases, the degree of the influence of the LHV on in-cylinder combustion temperature (IT) and combustion duration (CD) gradually increases, and the degree of influence of CN gradually decreases. Additionally, the increasing in-cylinder average temperature difference is the primary factor for the increase in the difference between the HC emissions of the two fuels, whereas the influence of CD is relatively weak. A comparison of the B20+EHN with B20 fuels revealed their different in-cylinder average temperatures that resulted from the influence of their CN on the combustion phase were mainly responsible for the different HC emissions of the two fuels; this difference becomes increasingly obvious as ${\mathrm{C}}_{\mathrm{oxy}}$ decreases.

Renewable energy has the characteristics of fluctuation and intermittence due to environmental conditions; the fluctuation of output power affects the operation of the power grid. To combat these fluctuations, a control strategy for the battery energy-storage system using a deep-learning adaptive-dynamic algorithm is proposed in this work. First, power-fluctuation rate feedback control is used to suppress the power fluctuation from the renewable energy source. Second, by introducing an adaptive-dynamic algorithm based on a deep belief network, the charging and discharging power of the battery energy-storage system with secondary regulation is achieved. Finally, the validity of the methods is verified by a series of examples using available data for wind and photovoltaic sources. It was found the proposed control strategy is highly effective for suppression of unwanted fluctuations.

In subtropical areas, the heat-source tower (HST) heat pumps are more competitive than air-source heat pumps because they avoid frosting and absorb latent heat from ambient air. The configurations of HST, such as spray directions (upward spray or downward spray), air flowing directions (upward flowing or downward flowing), internal structures (with or without packing), and liquid–gas ratios all have impact on the performance of heat and mass transfer. To study the impacts of these configurations on the performance of HST, the present study conducted experiments for an open-type HST working under different configurations. Then the thermal efficiencies and energy efficiency ratios of HST under different configurations were calculated and compared. Moreover, the regression analysis of thermal efficiency and energy efficiency ratio of HST was undertaken. The results showed that the performance of the upward spraying HST was better than that of the downward spraying HST. For upward spraying HST, the performance of HST with air flowing upward was higher than that of HST with air flowing downward. The performance decreased with the increase of the liquid–gas ratio, and the HST with packing was better than that without packing. The regression equations of thermal efficiency and energy efficiency ratio were in good agreement with the experimental data.

In many office buildings, an air-handling unit (AHU) in a variable air volume (VAV) system is operated using discharge air temperature (DAT) simply fixed at a particular set point. However, this simply fixed control causes a variety of inefficiencies related to cooling energy. Therefore, this study compares the cooling energy consumption of the fixed-control strategy, which fixes the AHU DAT at a specific temperature, and the cooling energy consumption of an AHU DAT set point reset strategy based on the outdoor air (OA) temperature, which proportionally controls the AHU DAT according to the change of the OA temperature. Commercially available software was used to compare the AHU DAT control methods of fixed control and the AHU DAT set point reset strategies. The comparison results show that the effect of reducing the total cooling energy consumption in summer (June to August) is negligible; however, in spring (March to May) and autumn (September to November), it was found to be significant compared with the single-fixed-control method. Therefore, if a method of proportionally controlling the AHU DAT is implemented, as in the case of the AHU DAT set point reset based on the OA temperature, it could be an advanced control scheme to improve energy efficiency, especially by reducing the energy consumption of the chiller, which accounts for the highest proportion of the total cooling energy consumption.

The laminar combustion characteristics of premixed shale gas/air flames were studied by spherical expansion flame experiments and chemical kinetics simulations. The influence of the initial temperature, the initial pressure, and the equivalent ratio on the laminar flame propagation process was analyzed. The variation of the laminar burning velocity and the flame stability with the initial conditions is discussed. The change trend of the reactants and products in the shale gas laminar flame was studied. The relationships between the important free radicals, the adiabatic flame temperature, and the laminar burning rate were analyzed. The results show that the initial temperature had little influence on the chemical reaction rate, the flame propagation process was stable, and the $\mathrm{H}+\mathrm{OH}$ mole fraction peak increased, which was the main reason for the enhancement of the laminar burning velocity. When the initial pressure increased, the chemical reaction rate increased obviously, the concentration of H, O, and OH decreased, the velocity of flame propagation was slowed, and the stability of the front flame was reduced. When the equivalent ratio was 1.0, the velocity of the laminar flame was the fastest, the inhibition effect of the lean mixture on the velocity of the flame propagation was stronger than that of the concentrated mixture, and with the increase of the equivalence ratio, the front flame became stable.

This paper presents the results of simulation engine test bed tests on the impact of diesel fuel additives. These hold detergent properties in the form of polyisobutylene succinimide (PIBSI) chemical structures of various molecular masses, and the intent is to assess the effect of these on the formation of internal diesel injector deposits (IDIDs). The work focused on products with masses ranging from 2000 to 4000 Da (daltons). In addition, contrary to similar papers in which the molecular mass was increased via changes of polyisobutylene (PIB) anhydride, the molecular mass was controlled by means of amine weight and additive structure changes by attaching other PIB chains to the detergent molecules. Moreover, less harsh test conditions, closer to the actual engine operation, were adopted in the tests. The outcome of the project implementation suggested, among other things, that in the case of diesel fuel additives synthesized for the project objectives, as PIBSI substances, their molecule mass affects the formation of organic polymer amide IDID-type deposits in fuel injectors of a diesel engine fueled with diesel fuel.

Chlorella vulgaris is widely distributed in China and has the advantages of high oil content, short growth cycle, and wide growth space. Chlorella vulgaris biodiesel fuel (CVBF) made from Chlorella vulgaris has great development potential. In this study, the preparation, composition, and physicochemical properties of CVBF in China were analyzed, and the performance, emissions, and combustion characteristics of B0 and B5 (5% v/v CVBF and 95% diesel) in nonroad diesel engines were compared. The results show that CVBF has different physical and chemical properties than diesel fuel. The brake power and torque output of B5 is lower than B0, and the brake specific fuel consumption and brake specific energy consumption are higher. The maximum in-cylinder pressure and heat release rate of B5 is lower than B0, while the rate of cylinder pressure is higher, and the corresponding crankshaft angles are all advanced. The ignition delay and the premixed combustion duration of B5 are longer, while the diffusion combustion duration and the total combustion duration are slightly shorter. B5 has slightly higher ${\mathrm{NO}}_{\mathrm{X}}$ emissions, but less CO emissions. B5 can significantly reduce unburned hydrocarbon and smoke emissions, especially at high loads. Low-level CVBF blends can partially replace diesel fuel, with the advantages of improved combustion processes and effective emissions reduction.

This research designed a multigeneration system that meets the energy requirement of a rural community in Nigeria. This system is powered by the biogas produced from maize silage and chicken manure. Nigeria is the most populous nation in Africa, but the country is faced with serious electricity challenges. About 40% of Nigerians still do not have access to electricity, and most of these people dwell in rural communities. The multigeneration system developed in this research produces power, cooling, hot air, hot water, and hot air for green houses. Three power cycles are used for power production, namely the Brayton cycle, the Rankine cycle, and the organic Rankine cycle. The system was analyzed at the steady state condition with more emphasis on the energy and exergy performance. The Emure-Ekiti community in Southwestern Nigeria was used as a case study for this research. The estimated power requirement for this area is 944 kW, and the multigeneration system designed in this study produces 969.8 kW of electricity. The overall energy and exergy efficiency of the multigeneration system are 62.72% and 23.49%, respectively.

This paper investigated the optimal use of surplus low-pressure steam in the Khangiran gas refinery, Iran. To manage energy and reduce surplus steam waste for heat sources at 150°C, three scenarios were proposed to use this energy. In these scenarios, while considering the thermodynamic conditions of steam, it was proposed to use an organic Rankine cycle with pure and mixture working fluids and a Kalina cycle, which is capable of producing power from low-temperature sources. Finally, all the scenarios were evaluated in terms of energy, exergy and exergoeconomic, and optimum conditions were specified. The results indicated that the organic Rankine cycle with isobutane as the working fluid had the best performance with a power output of 249.8 kW. Moreover, the optimal binary mixture was isopentane/cyclohexane (0.85-0.15, by mole fraction) and the power output was 279.6 kW. When using mixing fluids, the net power of the system was observed to increase by 12%. The results also revealed that the best ternary mixture was isohexane/R245fa/R365mfc (0.17-0.33-0.50, by mole fraction) and that the related net power output was 283.7 kW, which was higher than that of the binary mixture.