Renewable energy-based generation of electrical energy is currently experiencing rapid growth in electrical grids [...]

The stable operating region of a photovoltaic (PV) cascaded H-bridge (CHB) grid-tied module level inverter is extended by adopting the hybrid modulation strategy. However, the traditional single hybrid modulation method is unable to regulate the DC-side voltage of each module precisely, which may aggravate the fluctuation of modules’ DC-side voltages or even cause the deviation of modules’ DC-side voltages under some fault conditions and, thus, degrade the energy harvesting of PV panels. To tackle this problem, a switching modulation strategy for PV CHB inverter is proposed in this paper. When the CHB inverter is operating in normal mode, the hybrid modulation strategy containing the zero state is adopted to suppress DC-side voltage fluctuation, thereby, improving the output power of PV modules. When the CHB inverter is operating in fault mode owing to failing solar panels, the hybrid modulation strategy without the zero state is utilized to make the DC-side voltages reach the referenc... [more]

A better understanding of turbulent premixed flame propagation is the key for improving the efficiency of fuel consumption and reducing the emissions of spark ignition gasoline engines. In this study, we measure turbulent burning velocities (ST) of pre-vaporized iso-octane/air mixtures over wide ranges of the equivalence ratio (φ = 0.9−1.25, Le ≈ 2.94−0.93), the root-mean-square (r.m.s.) turbulent fluctuating velocity (u′ = 0−4.2 m/s), pressure p = 1−5 atm at T = 358 K and p = 0.5−3 atm at T = 373 K, where Le is the effective Lewis number. Results show that at any fixed p, T and u′, Le < 1 flames propagate faster than Le > 1 flames, of which the normalized iso-octane ST/SL data versus u′/SL are very scattering, where SL is the laminar burning velocity. But when the effect of Le is properly considered in some scaling parameters used in previous correlations, these large scattering iso-octane ST/SL data can be collapsed onto single curves by several modified general correlations, regardl... [more]

The effects of three kinds of oxygenated fuel blends—i.e., ethanol-gasoline, n-butanol-gasoline, and 2,5-dimethylfuran (DMF)-gasoline-on fuel consumption, emissions, and acceleration performance were investigated in a passenger car with a chassis dynamometer. The engine mounted in the vehicle was a four-cylinder, four-stroke, turbocharging gasoline direct injection (GDI) engine with a displacement of 1.395 L. The test fuels include ethanol-gasoline, n-butanol-gasoline, and DMF-gasoline with four blending ratios of 20%, 50%, 75%, and 100%, and pure gasoline was also tested for comparison. The original contribution of this article is to systemically study the steady-state, transient-state, cold-start, and acceleration performance of the tested fuels under a wide range of blending ratios, especially at high blending ratios. It provides new insight and knowledge of the emission alleviation technique in terms of tailoring the biofuels in GDI turbocharged engines. The results of our works sh... [more]

Stress interference of multiplied fractures has significant influences on the propagation behavior of hydraulic fractures in roads, bridges, clay formations, and other forms of engineering. This paper establishes a crossing criterion and initiation angle model with comprehensive consideration of remote stress, stress intensity near the tip of fracture, and stress interference of multiplied fractures. Compared with the existing crossing criterion and initiation angle model, the ability to cross natural fractures decreases. Furthermore, the secondary initiation angle decreases with consideration of multiplied fracture propagation. The length of hydraulic fractures and natural fractures has little influence on the secondary initiation angle. With the increase in fracture space, the stress interference between fractures decreases, and as a result, the initiation angle begins to increase and then decrease. Differing from the propagation behavior of single fracture, the initiation angle basi... [more]

Negative impacts from the dominant use of petroleum-based transportation have propelled the globe towards electrified transportation. With this thrust, many technological challenges are being encountered and addressed, one of which is the development and availability of fast-charging technologies. To compete with petroleum-based transportation, electric vehicle (EV) battery charging times need to decrease to the 5−10 min range. This paper provides a review of EV fast-charging technologies and the impacts on the battery systems, including heat management and associated limitations. In addition, the paper presents promising new approaches and opportunities for power electronic converter topologies and systems level research to advance the state-of-the-art in fast-charging.

The changes in blood glucose levels are a key indicator of fish health conditions and are closely correlated to their stress levels. Here, we developed a self-powered glucose biosensor (SPGB) consisting of a needle-type enzymatic biofuel cell (N-EFC), which was operated underwater and connected to a charge pump integrated circuit (IC) and a light emitting diode (LED) as the indicator. The N-EFC consisted of a needle bioanode, which was inserted into the caudal area of a living fish (Tilapia) to access biofuels, and a gas-diffusion biocathode sealed in an airtight bag. The N-EFC was immersed entirely in the water and connected to a charge pump IC with a capacitor, which enabled charging and discharging of the bioelectricity generated from the N-EFC to blink an LED. Using a smartphone, the glucose concentration can be determined by observing the LED blinking frequencies that are linearly proportional to the blood glucose concentration within a detection range of 10−180 mg/dL. We have suc... [more]

Natural gas hydrates samples are rare and difficult to store and transport at in situ pressure and temperature conditions, resulting in difficulty to characterize natural hydrate-bearing sediments and to identify hydrate accumulation position and saturation at the field scale. A new apparatus was designed to study the acoustic properties of seafloor recovered cores with and without hydrate. To protect the natural frames of recovered cores and control hydrate distribution, the addition of water into cores was performed by injecting water vapor. The results show that hydrate saturation and types of host sediments are the two most important factors that govern the elastic properties of hydrate-bearing sediments. When gas hydrate saturation adds approximately to 5−25%, the corresponding P-wave velocity (Vp) increases from 1.94 to 3.93 km/s and S-wave velocity (Vs) increases from 1.14 to 2.23 km/s for sandy specimens; Vp and Vs for clayey samples are 1.72−2.13 km/s and 1.10−1.32 km/s, respe... [more]

A commercial 43 m wind turbine blade was tested under static loads. During these tests, loads, displacements, and local strains were recorded. In this work, the blade was modeled using the finite element method. Both a segment of the spar structure and the full-scale blade were modeled. In both cases, conventional outer mold layer shell and layered solid models were created by means of an in-house developed software tool. First, the boundary conditions and settings for modeling the tests were explored. Next, the behavior of a spar segment under different modeling methods was investigated. Finally, the full-scale blade tests were conducted. The resulting displacements and longitudinal and transverse strains were investigated. It was found that for the considered load case, the differences between the shell and solid models are limited. Thus, it is concluded that the shell representation is sufficiently accurate.

To improve the reactor efficiency, this study investigated the influence of temperature on the biological hydrogen methanation (BHM) in trickle-bed reactors (TBR). Rising temperatures increase the metabolic activity of methanogenic microorganisms, thus leading to higher reactor specific methane formation rates (MFR). In order to quantify the potential for improved performance, experiments with four different operating temperatures ranging from 40 to 55 °C were carried out. Methane content increased from 88.29 ± 2.12 vol % at 40 °C to 94.99 ± 0.81 vol % at 55 °C with a stable biological process. Furthermore, a reactor specific methane formation rate (MFR) of up to 8.85 ± 0.45 m³ m−3 d−1 was achieved. It could be shown that the microorganisms were able to adapt to higher temperatures within hours. The tests showed that TBR performance with regard to BHM can be significantly increased by increasing the operating temperature.

(1) Background: To increase the biochemical productivity and to reduce the production cost of microalgal biodiesel, this study aimed to investigate the effects of CO₂ on biomass, fatty acids, carbon-hydrogen, and biochemical accumulation of the marine diatom, Amphora coffeaeformis RR03 (A. coffeaeformis) RR03. (2) Methods: Fatty acid composition of the dry biomass of A. coffeaeformis RR03 was analysed using Gas chromatography-mass spectrometry (GC-MS). (3) Results: The results showed that A. coffeaeformis RR03 contained high biomass productivity and biochemical composition in different cultivation conditions. A. coffeaeformis RR03 showed maximum growth of 5.2 × 10⁶/mL on 21st day cultivation under CO₂ supply. The bio-crude oil production from A. coffeaeformis RR03 was 36.19 megajoule (MJ). GC-MS analysis found that the dry biomass of A. coffeaeformis RR03 contained maximum of 47.72% fatty acids of 16-octadecanoic acid methyl ester (10:12) and 19.58% pentadecanoic acid, 13-methyl-, and... [more]

This paper presents a Modified Perturb & Observe (P&O) Maximum power point tracking (MPPT) algorithm using fuzzy logic-based variable step size to overcome some of the limitations associated with the conventional P&O MPPT tracking method to improve the transient response and reduce the steady-state terminal voltage oscillations. The proposed MPPT algorithm was implemented and tested on an indoor emulated PV source that is constructed from a conventional solar panel and a DC power supply, a boost DC-DC converter and a dSPACE-based MPPT controller. The advantage of implementing this testing platform for MPPT is easy implementation and indoor testing of MPPT algorithms and DC-DC power converters. Thus, dependency on atmospheric conditions such as irradiance level can be avoided. Details of the emulated PV source mathematical model and electrical characteristics, the proposed MPPT algorithm via dSPACE, simulation and test results were presented in the paper.

This paper proposes a method to charge a lithium ion battery with an integrated compensator. Unlike the conventional charging method which uses separate voltage/current compensators based on a constant voltage-constant current charge profile, the proposed method uses a single compensator. The conventional method requires a complicated design process such as separate plant modeling for compensator design and the compensator tuning process in the frequency domain. Moreover, it has the disadvantage of a transient state between the mode change. However, the proposed method simplifies the complicated process and eliminates the transient response. The proposed compensator is applied to the LLC resonant converter and is designed to provide smooth and reliable performance during the entire charging process. In this paper, for the compensator design, the frequency domain models of the LLC resonant converter at the constant voltage and constant current charging mode are derived including the imp... [more]

In order to enhance the mass transfer efficiency between gas⁻liquid interfaces, NaClO₂ mist generated by an ultrasonic humidifier was used to remove NO from simulated flue gas. The effects of some key parameters (the gas flow rate, the NaClO₂ concentration in the solution, the inlet NO concentration, the NaClO₂ solution pH) on NO removal efficiency were investigated preliminarily. The results showed that NaClO₂ mist could oxidize NO with a much higher efficiency compared with other mists containing either NaClO or H₂O₂ as oxidants. With an increase in the gas flow rate from 1.5 to 3.0 L·min−1, the atomizing rate of the NaClO₂ solution increased almost linearly from 0.38 to 0.85 mL·min−1. When the gas flow rate was 2.0 L·min−1, a complete removal of NO had been reached. NO removal efficiency increased obviously with an increase in the NaClO₂ concentration in the solution. With an increase in the inlet NO concentration, the ratio of NO in the flue gas and NaClO₂ in the mist increased alm... [more]

One-quarter of the world’s population lives without access to electricity. Unfortunately, the generation technology most commonly employed to advance rural electrification, diesel generation, carries considerable commercial and ecological risks. One approach used to address both the cost and pollution of diesel generation is renewable energy (RE) integration. However, to successfully integrate RE, both the stochastic nature of the RE resource and the operating characteristics of diesel generation require careful consideration. Typically, diesel generation is configured to run heavily loaded, achieving peak efficiencies within 70⁻80% of rated capacity. Diesel generation is also commonly sized to peak demand. These characteristics serve to constrain the possible RE penetration. While energy storage can relieve the constraint, this adds cost and complexity to the system. This paper identifies an alternative approach, redefining the low load capability of diesel generation. Low load diesel... [more]

The tri-reforming process was employed for syngas production from biogas at elevated pressures in this study. In the tri-reforming process, air and water were added simultaneously as reactants in addition to the main biogas components. The effects of various operating parameters such as pressure, temperature and reactant composition on the reaction performance were studied numerically. From the simulated results, it was found that methane and carbon dioxide conversions can be enhanced and a higher hydrogen/carbon monoxide ratio can be obtained by increasing the amount of air. However, a decreased hydrogen yield could result due to the reverse water⁻gas shift reaction. A higher level of methane conversion and hydrogen/carbon monoxide ratio can be obtained with increased water addition. However, negative carbon dioxide conversion could result due to the water⁻gas shift and reverse carbon dioxide methanation reactions. The dry reforming reaction resulting in positive carbon dioxide conver... [more]

State of charge (SOC) and state of health (SOH) are two significant state parameters for the lithium ion batteries (LiBs). In obtaining these states, the capacity of the battery is an indispensable parameter that is hard to detect directly online. However, there is a strong correlation relationship between this parameter and battery internal resistance. This article first shows a simple and effective online internal resistance detection method. Secondly, the relationship between the measured internal resistance and the LiBs capacity is established by linear fitting. Finally, the capacity through internal resistance conversion is applied in SOC estimation. The estimation results show that this method can effectively enhance the SOC estimation accuracy regardless of temperature change and battery degradation.

Small-scale decentralized polygeneration systems have several energetic, economic and environmental benefits. However, using multiple energy sources and providing multiple energy services can lead to complicated studies which require advanced optimization techniques for determining optimal solutions. Furthermore, several parameters can influence the design and performance of a polygeneration system. In this study, the effects of heat load, renewable generation and storage units on the optimal design and performance of a polygeneration system for a hypothetical hospital located in northern Italy are investigated. The polygeneration system shows higher performance compared to the reference system, which is based on the separate generation of heat and power. It reduces fuel consumption by 14⁻32%, CO₂ emissions by 10⁻29% and annualized total cost by 7⁻19%, for various studied scenarios. The avoided fuel and electricity purchase of the polygeneration system has a positive impact on the econ... [more]

Integrated energy system (IES) has received increasing attention in micro grid due to the high energy efficiency and low emission of carbon dioxide. Based on the technology of combined heat and power (CHP), this paper develops a novel operation mechanism with community micro turbine and shared energy storage system (ESS) for energy management of prosumers. In the proposed framework, micro-grid operator (MGO) equipped with micro turbine and ESS provides energy selling business and ESS leasing business for prosumers. Prosumers can make energy trading with public grid and MGO, and ESS will be shared among prosumers when they pay for the rent to MGO. Based on such framework, we adopt a cooperative game for prosumers to determine optimal energy trading strategies from MGO and public grid for the next day. Concretely, a cooperative game model is formulated to search the optimal strategies aiming at minimizing the daily cost of coalition, and then a bilateral Shapley value (BSV) is proposed t... [more]

Energy extracted from the ocean can provide a source of regular and foreseeable electrical production at higher energy densities than any other renewable energy resource. The marine current resource is potentially great and is focused in several sites around the world. The knowledge of the energy potential, its constraints and availability are all prerequisites to determine the possibilities for the implementation of infrastructure to produce energy. They are also required to anticipate the structuring of energy routes and to respond to increasing technological needs. Several Moroccan regions want to take advantage by their coastal domain and play a role in the development of the tidal energy sector. They also want to benefit from the associated economic advantages knowing that the Mediterranean coast length is 550 km and the Atlantic length is 3000 km, respectively. The Copernicus Marine Service ocean products provide key input for such technologies, as they can be employed to help ev... [more]

This paper compares the annual performance of Integrated Solar Combined Cycles (ISCCs) using different solar concentration technologies: parabolic trough collectors (PTC), linear Fresnel reflectors (LFR) and central tower receiver (CT). Each solar technology (i.e. PTC, LFR and CT) is proposed to integrate solar energy into the combined cycle in two different ways. The first one is based on the use of solar energy to evaporate water of the steam cycle by means of direct steam generation (DSG), increasing the steam production of the high pressure level of the steam generator. The other one is based on the use of solar energy to preheat the pressurized air at the exit of the gas turbine compressor before it is introduced in the combustion chamber, reducing the fuel consumption. Results show that ISCC with DSG increases the yearly production while solar air heating reduces it due to the incremental pressure drop. However, air heating allows significantly higher solar-to-electricity efficie... [more]

During the “13th Five-Year Plan„ period, green energy is the top priority for China. China has realized that natural gas, as a low-carbon energy source, fits with the nation’s energy demand and will play a critical role in the energy transition, but the actual industry development is slower than expected. By analyzing the major gas corporations around the world, the paper finds that the key factors of the sector are supply and price of the energy resource. A comprehensive analysis on domestic and foreign imported gas reveals a trend of oversupply in China in the future. Given the critical import dependence, China has introduced a series of gas price reforms since 2013, which have led to negative impacts on important gas consumption sectors including power generation. With the levelized cost of electricity (LCOE) model, we find that under the prevailing gas supply structure and price level, the economy of utility gas power generation will remain unprofitable, while combined cooling heat... [more]

Pyrolysis and combustion behaviors of three coals (A, B, and C coals) were investigated and their combustion kinetics were calculated by the Freeman⁻Carroll method to obtain quantitative insight into their combustion behaviors. Moreover, the effects of coal size, air flow, oxygen content, and heating rate on coal combustion behaviors were analyzed. Results showed that the three coals have a similar trend of pyrolysis that occurs at about 670 K and this process continuously proceeds along with their combustion. Combustion characteristics and kinetic parameters can be applied to analyze coal combustion behaviors. Three coals having combustion characteristics of suitable ignition temperature (745⁻761 K), DTGmax (14.20⁻15.72%/min), and burnout time (7.45⁻8.10 min) were analyzed in a rotary kiln. Combustion kinetic parameters provide quantitative insights into coal combustion behavior. The suitable particle size for coal combustion in a kiln is that the content of less than 74 μm is 60% to... [more]

In this paper, a fast equalizer for series-connected battery packs with adaptive balancing current control is proposed. As the duty cycle of the power switch in conventional equalizers is kept constant during the equalization process, smaller voltage difference between cells will decrease balancing current and consequently result in extended balancing time, especially in the later phase of equalization. To deal with this problem and take the battery nonlinearity and circuit parameter non-ideality into consideration, an adaptive balancing current control based on a fuzzy logic inference is proposed. The presented approach can adjust the duty ratio adaptively, according to voltages of individual cells and pack, to keep the balancing current nearly constant: Therefore, the balancing time can be shortened and the balancing efficiency can be improved. Finally, experimental results of three compared methods will be given and discussed to validate the feasibility, effectiveness, and performan... [more]

A large amount of energy is consumed by heating and cooling systems to provide comfort conditions for commercial building occupants, which generally contribute to peak electricity demands. Thermal storage tanks in HVAC systems, which store heating/cooling energy in the off-peak period for use in the peak period, can be used to offset peak time energy demand. In this study, a theoretical investigation on stratified thermal storage systems is performed to determine the factors that significantly influence the thermal performance of these systems for both heating and cooling applications. Five fully-insulated storage tank geometries, using water as the storage medium, were simulated to determine the effects of water inlet velocity, tank aspect ratio and temperature difference between charging (inlet) and the tank water on mixing and thermocline formation. Results indicate that thermal stratification enhances with increased temperature difference, lower inlet velocities and higher aspect r... [more]