The chemical kinetics mechanism is an important factor to accurately predict the combustion characteristics of constant-volume bomb (CVB). In this study, an n-heptane oxidation mechanism constructed by Wang et al. is introduced to study the correlation of the ignition behaviors with the mechanism constructed by Chang et al. The effects of the similarity factor method in the analysis of ignition behaviors of fuel in CVB were repeatedly verified by changing the important spraying parameters: injection pressure and hole diameter. Through further verification, it was found that the combustion process was controlled at approximately 850 K and stoichiometric ratio mixture of fuel/air in CVB, which corresponds to the negative temperature coefficient region at stoichiometric ratio mixture in shock tube (ST). The mechanism verified by the experiment under the condition in ST can reflect the chemical ignition in CVB. In addition, the similarity factor method was less dependent on the chemical re... [more]

A study was carried out to determine in-tube evaporation and condensation performance of enhanced heat transfer tubes (EHT) using R410A, with the results being compared to a plain tube. The test tubes considered in the evaluation include: plain, herringbone (HB) and spiral (HX) microgrooves, herringbone dimple (HB/D), and hydrophobic herringbone (HB/HY). Experiments to evaluate the condensation were conducted at a saturation of 318 K, and at 279 K for evaporation. Mass flux (G) ranged between 40 to 230 kg m−2s−1. Condensed vapor mass decreased from 0.8 to 0.2; and the mass of vaporized vapor increases from 0.2 to 0.8; heat flux increased with G. Inlet and outlet two-phase flow patterns at 200 kg m−2s−1 were recorded and analyzed. Enhanced tube heat transfer condensation performance (compared to a plain tube) increased in the range from 40% to 73%. The largest heat transfer increase is produced by the herringbone−dimple tube (HB/D). In addition to providing drainage, the herringbone gro... [more]

The wind power systems of variable velocity using a doubly-fed induction generator dominate large-scale electrical generation within renewable energy sources. The usual control goal of the wind systems consists of maximizing the wind energy capture and streamlining the energy conversion process. In addition, these systems are an intermittent energy source due to the variation of the wind velocity. Consequently, the control system designed to establish a reliable operation of the wind system represents the main challenge. Therefore, emulating the operation of the wind turbine by means of an electric motor is a common strategy so that the controller design is focused on the induction generator and its connection to the utility grid. Thus, we propose to emulate the dynamical operation of a wind turbine through a separately excited DC motor driving by a sensor-less velocity controller. This controller is synthesized based on the state-feedback linearization technique combined with the supe... [more]

In boilers operating in modern power plants, thick-walled elements of complex shapes, such as valves, superheater headers, T-pipes, Y-pipes, four-way pipes, and elbows, are especially prone to fatigue processes. Higher operation parameters and more frequent startups may speed up fatigue damage in these elements. Such damage is a local phenomenon and is caused by thermomechanical fatigue (TMF). This paper presents a method designed for predicting the behavior of components subjected to variable temperature and mechanical loading conditions. This method combines the results of measurements of operating parameters of devices under industrial conditions with those obtained using finite element modeling (FEM). Particular attention was given to the influence of the time-dependent heat transfer coefficient on the local thermomechanical stress−strain behavior of the material. It was stated that heat transfer conditions have a significant impact on local transient stresses and depend on the ope... [more]

Over the last 15 years, photovoltaics (PV) in Vietnam has experienced development. The increased installed capacity of PV requires more land for installation sites as well as for manufacturing the plants’ component and waste treatment during the plants’ decommissioning. As a developing country, in which more than 80% of the population’s livelihood depends on agriculture, there are concerns about the competition of land for agriculture and solar development. This paper estimates the life-cycle land-use requirement for PV development in Vietnam, to provide the scientific-based evidence for policy makers on the quantity of land required, so that the land budget can be suitably allocated. The direct land-use requirement for PV ranges from 3.7 to 6.7 m2 MWh−1 year, and the total fenced area is 7.18 to 8.16 m2 MWh−1 year. Regarding the life-cycle land use, the land occupation is 241.85 m2a and land transformation is 16.17 m2 per MWh. Most of the required land area is for the installation of... [more]

Nowadays, the attention of designers and service providers is especially focused on energy efficiency and integration of renewable energy sources (RES). However, the knowledge on smart devices and automated, easily applicable algorithms for optimizing heating consumption by effectively taking advantage of solar heat gains, while avoiding overheating, is limited. This paper presents a simple method for taking into account the influence of solar heat gains in the form of solar radiation for the purposes of forecasting or controlling thermal power for heating of buildings. On the basis of field research carried out for seven buildings (five residential buildings and two public buildings) during one heating season, it was noticed that it was justified to properly narrow down the input data range included in the building energy model calculations in order to obtain a higher accuracy of calculations. In order to minimize the impact of other external factors (in particular wind speed) affecti... [more]

Solar energy usage is thriving day by day. These solar panels are installed to absorb solar energy and produce electrical energy. As a result, the efficiency of solar panels depends on different environmental factors, namely, air temperature, dust (aerosols and accumulated dust), and solar incidence, and photovoltaic panel angles. The effects of real conditions factors on power and efficiency of photovoltaic panels are studied in this paper through testing the panel in real environmental tests. To study the mentioned parameters precisely, two panels with different angles are used. The case study is regarding a region of Tehran, Iran, in summer and winter seasons. The results show that panel efficiency during winter is higher than summer due to air temperature decrement. It is discovered that among air pollutants, Al and Fe have the most share in polluting the air that affect the photovoltaic efficiency. Moreover, measuring the accumulated dust on the panels shows more amount in winter... [more]

In petroleum engineering, imbibition is one of the most important elements for the hydraulic fracturing and water flooding processes, when extraneous fluids are introduced to the reservoir. However, in unconventional shale formations, osmosis has been often overlooked, but it can influence the imbibition process between the working fluid and the contacting formation rocks. The main objective of this study is to understand effects of fluid−rock interactions for osmosis-associated imbibition in unconventional formations. This paper summarizes previous studies on imbibition in unconventional formations, including shale, tight carbonate, and tight sandstone formations. Various key factors and their influence on the imbibition processes are discussed. Then, the causes and role of osmotic forces in fluid imbibition processes are summarized based on previous and recent field observations and laboratory measurements. Moreover, some numerical simulation approaches to model the osmosis-associate... [more]

In the process of studying the steady-state performance and component matching of adaptive cycle engines with convertible fan system, it was found that the front fan and aft fan stage have a unique matching problem when the mode select valve is closed and engine is operating at higher Mach number conditions. The cause of this matching problem was studied with numeric simulation in this paper. Based on the features of adaptive cycle engines with convertible fan system, the possible methods and their feasibilities of solving this matching problem were also discussed. According to the results, the flow rate adjustment capacity of the aft fan stage directly determines the occurrence and severity of this matching problem. The matching problem can be ameliorated in some extent by either reducing the design second bypass ratio or adjusting the variable geometry mechanisms, but it cannot be completely solved at the aspect of component matching mechanism.

The dissemination of low-carbon technologies, such as urban photovoltaic distributed generation, imposes new challenges to the operation of distribution grids. Distributed generation may introduce significant net-load asymmetries between feeders in the course of the day, resulting in higher losses. The dynamic reconfiguration of the grid could mitigate daily losses and be used to minimize or defer the need for network reinforcement. Yet, dynamic reconfiguration has to be carried out in near real-time in order to make use of the most updated load and generation forecast, this way maximizing operational benefits. Given the need to quickly find and update reconfiguration decisions, the computational complexity of the underlying optimal scheduling problem is studied in this paper. The problem is formulated and the impact of sub-optimal solutions is illustrated using a real medium-voltage distribution grid operated under a heavy generation scenario. The complexity of the scheduling problem... [more]

This paper introduces a sliding-mode-based extremum-seeking algorithm aimed at generating optimal set-points of wind turbines in wind farms. A distributed extremum-seeking control is directed to fully utilize the captured wind energy by taking into consideration the wake and aerodynamic properties between wind turbines. The proposed approach is a model-free algorithm. Namely, it is independent of the model selection of the wake interaction between the wind turbines. The proposed distributed scheme consists of two parts. A dynamic consensus algorithm and an extremum-seeking controller based on sliding-mode theory. The distributed consensus algorithm is exploited to estimate the value of the total power produced by a wind farm. Subsequently, sliding-mode extremum-seeking controllers are intended to cooperatively produce optimal set-points for wind turbines within the farm. Scheme performance is tested via extensive simulations under both steady and varying wind speed and directions. The... [more]

The present work addresses the issues related to the capacity fading of spinel LiMn2O4, such as Mn leaching and Jahn−Teller distortion and suggests an advanced TiN-coated LiAl0.1Mn1.9O4 (LAMO) cathode material as an electrode for lithium-ion batteries. TiN coating layers with the same thickness but a different porosity cover the LiAl0.1Mn1.9O4 electrode via reactive magnetron sputtering, and present promising electrochemical behavior. In contrast with the pristine LiAl0.1Mn1.9O4, the dense TiN-coated LiAl0.1Mn1.9O4 electrode demonstrates a remarkable long-term cycling by reducing the contact area of the electrode/electrolyte interface, resulting in structure stabilization.

Reassessment of the fatigue life for wind turbine structural components is typically performed using deterministic methods with the same partial safety factors as used for the original design. However, in relation to life extension, the conditions are generally different from the assumptions used for calibration of partial safety factors; and using a deterministic assessment method with these partial safety factors might not lead to optimal decisions. In this paper, the deterministic assessment method is compared to probabilistic and risk-based approaches, and the economic feasibility is assessed for a case wind farm. Using the models also used for calibration of partial safety factors in IEC61400-1 ed. 4, it is found that the probabilistic assessment generally leads to longer additional fatigue life than the deterministic assessment method. The longer duration of the extended life can make life extension feasible in more situations. The risk-based model is applied to include the risk... [more]

Medium and heavy-duty battery electric trucks (BETs) may play a key role in mitigating greenhouse gas (GHG) emissions from road freight transport. However, technological challenges such as limited range and cargo carrying capacity as well as the required charging time need to be efficiently addressed before the large-scale adoption of BETs. In this study, we apply a geospatial data analysis approach by using a battery electric vehicle potential (BEVPO) model with the datasets of road freight transport surveys for analyzing the potential of large-scale BET adoption in Finland and Switzerland for trucks with gross vehicle weight (GVW) of over 3.5 t. Our results show that trucks with payload capacities up to 30 t have the most potential for electrification by relying on the currently available battery and plug-in charging technology, with 93% (55% tkm) and 89% (84% tkm) trip coverage in Finland and Switzerland, respectively. Electric road systems (ERSs) would be essential for covering 51%... [more]

The detonability of polyethylene pyrolysis products (pyrogas) in mixtures with air is determined for the first time in a standard pulsed detonation tube based on the measured values of deflagration-to-detonation transition run-up time. The pyrogas is continuously produced in a gas generator at decomposition temperatures ranging from 650 to 850 °C. Chromatographic analysis shows that at a high decomposition temperature (850 °C) pyrogas consists mainly of hydrogen, methane, ethylene, and ethane, and has a molecular mass of about 10 g/mol, whereas at a low decomposition temperature (650 °C), it mainly consists of ethylene, ethane, methane, hydrogen, propane, and higher hydrocarbons, and has a molecular mass of 24−27 g/mol. In a pulsed detonation mode, the air mixtures of pyrogas with the fuel-to-air equivalence ratio ranging from 0.6 to 1.6 at normal pressure are shown to exhibit the detonability close to that of the homogeneous air mixtures of ethylene and propylene. On the one hand, thi... [more]

This study explores the impact of clean energy and non-renewable energy consumption on CO2 emissions and economic growth within two phases (formative and expansion) of renewable energy diffusion for three selected countries (France, Spain, and Sweden). The vector autoregression (VAR) model is estimated on the basis of annual data disaggregated into quarterly data. The Granger causality results reveal distinctive differences in the causality patterns across countries and two phases of renewables diffusion. Clean energy consumption contributes to a decline of emissions more clearly in the expansion phase in France and Spain. However, this effect seems to be counteracted by the increases in emissions due to economic growth and non-renewable energy consumption. Therefore, clean energy consumption has not yet led to a decoupling of economic growth from emissions in France and Spain; in contrast, the findings for Sweden evidence such a decoupling due to the neutrality between economic growth... [more]

In order to reduce fuel consumption and reduce the deviation between the final battery state-of-charge (SOC) value and the target value at the same time, a novel double-layer multi-objective optimization method is proposed, which adopts an improved ant colony optimization (ACO) algorithm and the equivalent fuel consumption minimization strategy (ECMS) considering mode switching. The proposed strategy adopts a two-layer structure. In the inner layer, the ECMS considering mode switching was adopted to optimize the working mode and working point, so as to achieve the goal of reducing fuel consumption. In the outer layer, aiming at the shortcomings of traditional ACO, the heuristic factor and adaptive volatilization factor were introduced. An improved ACO method was proposed to optimize the equivalent factor, so as to achieve the goal of reducing the deviation between the final value of SOC and the target value. In order to verify the effectiveness of the proposed algorithm, it is compared... [more]

Initial temperature has a promoting effect on laminar burning velocity, while initial pressure and dilution rate have an inhibitory effect on laminar burning velocity. Equal laminar burning velocities can be obtained by initial condition coupling with different temperatures, pressures and dilution rates. This paper analysed the equivalent distribution pattern of laminar burning velocity and the variation pattern of an equal weight curve using the coupling effect of the initial pressure (0.1−0.3 MPa), initial temperature (323−423 K) and dilution rate (0−16%). The results show that, as the initial temperature increases, the initial pressure decreases and the dilution rate decreases, the rate of change in laminar burning velocity increases. The equivalent effect of initial condition coupling can obtain equal laminar burning velocity with an dilution rate increase (or decrease) of 2% and an initial temperature increase (or decrease) of 29 K. Moreover, the increase in equivalence ratio lead... [more]

This article presents an estimation of the temperature decrease in the vicinity of a salt cavern due to its leaching. The one-dimensional radially symmetry models of a salt cavern were considered and described. The initial temperature of rock salt massif was assumed as 50 ∘C and temperature of leaching water varied seasonally from 6 ∘C to 20 ∘C. A significant influence of the season of the leaching process, beginning on the final temperature distribution was found. The model takes into account: convection coefficient changes depending on temperature of brine and rock formation and heat effects caused by salt dissolution. Numerical results are compared with measurements data on the field of cavern volume increasing with time as the function of flow of leaching water and its temperature. The accuracy of the cavern volume increasing versus time was assumed as good—both quantitative and qualitative.

Many applications (electric vehicles, renewable energies, low-voltage DC grids) require simple, high-power density and low-current ripple-boost converters. Traditional step-up converters are limited when large transformation ratios are involved. In this work is proposed a step-up converter that brings together the characteristics of high gain, low ripple, and high-power density. From the converter proposal, a mathematical analysis of its operation is first performed, including its static transfer function, stress of components, and voltage and current ripples. Furthermore, it provides a design example for an application of Vin = 48 V to Vo = 270 V and 500 W. For its implementation, two different wide bandgap (WBG) semiconductor models have been used, hybrid GaN cascodes and SiC MOSFETs. Finally, the experimental results of the produced prototypes are shown, and the results are discussed.

Oscillating hydrofoils were installed in a water tunnel as a surrogate model for a hydrokinetic cross-flow tidal turbine, enabling the study of the effect of flexible blades on the performance of those devices with high ecological potential. The study focuses on a single tip-speed ratio (equal to 2), the key non-dimensional parameter describing the operating point, and solidity (equal to 1.5), quantifying the robustness of the turbine shape. Both parameters are standard values for cross-flow tidal turbines. Those lead to highly dynamic characteristics in the flow field dominated by dynamic stall. The flow field is investigated at the blade level using high-speed particle image velocimetry measurements. Strong fluid−structure interactions lead to significant structural deformations and highly modified flow fields. The flexibility of the blades is shown to significantly reduce the duration of the periodic stall regime; this observation is achieved through systematic comparison of the flo... [more]

Bio-oils produced by biomass pyrolysis are substantially different from those produced by petroleum-based fuels and biodiesel. However, they could serve as valuable alternatives to fossil fuels to achieve carbon neutral future. The literature review indicates that the current use of bio-oils in gas turbines and compression-ignition (diesel) engines is limited due to problems associated with atomisation and combustion. The review also identifies the progress made in pyrolysis bio-oil spray combustion via standardisation of fuel properties, optimising atomisation and combustion, and understanding long-term reliability of engines. The key strategies that need to be adapted to efficiently atomise and combust bio-oils include, efficient atomisation techniques such as twin fluid atomisation, pressure atomisation and more advanced and novel effervescent atomisation, fuel and air preheating, flame stabilization using swrilers, and filtering the solid content from the pyrolysis oils. Once these... [more]

Increasingly stringent limits for NOx and SO2 emission are forcing the investigation of new reduction methods. This study was conducted to determine the combination of primary measures, i.e., flue gas recirculation (FGR) and excess air effects on sulfur, nitrogen and hydrocarbon emissions, in boiler flue gas. Experimental research was performed using an experimental, small-scale (20 kW) model of an industrial biofuel boiler. During combustion of sunflower seed hulls at different FGR ratios and incomplete combustion regimes, the composition of flue gas (NO, NO2, N2O, HCN, NH3, SO2, SO3, H2S, CO, and CxHy) was compared, allowing an explanation of the determinants of emission concentration changes to be provided. Increasing the flue gas recirculation ratio in the primary air had a positive effect on reducing NOX and CO with certain organic compounds. However, an opposite effect on SO2 was observed. NOX and SO2 concentrations were found to be approximately 500 mg/m3 and 150 mg/m3 under a r... [more]

The relentless spread of photovoltaic production drives searches of smart approaches to mitigate unbalances in power demand and supply, instability on the grid and ensuring stable revenues to the producer. Because of the development of energy markets with multiple time sessions, there is a growing need of power forecasting for multiple time steps, from fifteen minutes up to days ahead. To address this issue, in this study both a short-term-horizon of three days and a very-short-term-horizon of three hours photovoltaic production forecasting methods are presented. The short-term is based on a multimodel approach and referred to several configurations of the Analog Ensemble method, using the weather forecast of four numerical weather prediction models. The very-short-term consists of an Auto-Regressive Integrated Moving Average Model with eXogenous input (ARIMAX) that uses the short-term power forecast and the irradiance from satellite elaborations as exogenous variables. The methods, ap... [more]

Electric vehicles represent a promising opportunity to achieve greenhouse gas (GHG) reduction targets in the transport sector. Integrating them comprehensively into the energy system requires smart control strategies for the charging processes. In this paper we concentrate on charging processes at the end users home. From the perspective of an end user, optimizing of charging electric vehicles might strive for different targets: cost minimization of power purchase for the individual household or—as proposed more often recently—minimization of GHG emissions. These targets are sometimes competing and cannot generally be achieved at the same time as the results show. In this paper, we present approaches of considering these targets by controlling charging processes at the end users home. We investigate the influence of differently designed optimizing charging strategies for this purpose, considering the electrical purchase cost as well as the GHG emissions and compare them with the conven... [more]