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Abstract Environmental performance assessment has been on the forefront of global economic growth discussions for the past decades. The study of efficiency growth and convergence is important to enable countries to evaluate their uses of inputs and embrace technologies to increase productivity. Using the Malmquist-Luenberger productivity index, this paper investigated the environmental performance of a panel of 104 countries over the period 1980 to 2016. Absolute and conditional beta convergence was analyzed and the possibility of clustering based on the club convergence was also analyzed. The findings show that average global environmental efficiency growth over the period is 1.3%. Convergence in environmental growth is conditional on industrial structure, globalization and energy price. The results also indicate the formation of club clusters in a sub sample of every decade but not in the entire period of study. Policy implications are also suggested.

Abstract The feasibility on a residential energy supply network using multiple cogeneration systems, known as combined heat and powers, is investigated by an optimization approach. The target residential energy supply network is based on a microgrid of residential cogeneration systems without electric power export, and featured by power and heat interchanges among cogeneration systems and hot water supply network where produced hot water is supplied to multiple residence units through networked pipes. First, an optimal operational planning model is developed on the basis of mixed-integer linear programming, where energy loss characteristics of connecting pipes between storage tanks are originally modeled by considering the influence of hot water retention. Second, a hot water demand calculation model considering energy loss from networked pipes is developed to reduce the solution space of the optimization problem. The developed models are then applied to a residential energy supply network for a housing complex composed of multiple 1-kWe gas engine-based cogeneration systems and 20 residence units. The results show that the energy-saving effect of the residential energy supply network is dominated by the power interchange and decreases with an increase in the number of residence units involved in the hot water supply network.

Abstract To produce a bio-oil having a high concentration of furfural, corn stover was fast-pyrolyzed using ZnCl 2 in a fluidized bed reactor at 330–430 °C. The effects of various parameters such as reaction temperature, water- and acid-washing prior to pyrolysis, and ZnCl 2 content on the product and furfural yields were investigated. Moreover, solvent extraction was conducted using toluene at different mass ratios of bio-oil/toluene to recover furfural from the obtained bio-oil. The maximum yield of bio-oil was 59 wt%. The bio-oil mainly comprised acetic acid, α-hydroxyketones, and furfural. The maximum furfural yield was 11.5 wt% when the feed material was water-washed, impregnated with 18.5 wt% ZnCl 2 , and pyrolyzed. Although acid-washing removed alkali and alkaline earth metals much more efficiently than water-washing, water-washing was better than acid-washing for the furfural production. Toluene extraction was very effective to recover furfural from bio-oil. The maximum recovery rate (82%) was achieved at a bio-oil/toluene ratio of 1:4.

Abstract In this paper, a spark advance self-optimization strategy is presented for lean-burn operation mode of spark-ignition (SI) engine which aims on-board combustion phase tuning to achieve high efficiency under a probability constraint of knocking events. Firstly, the effects of spark advance (SA) on combustion phase under lean-condition are analyzed in a statistical perspective based on experiments. Then, based on conclusion of the analysis, a SA control scheme, which combines extremum seeking loop with likelihood-based knock limit control loop, is proposed to optimize SA for maximal fuel economy with knock probability threshold. Finally, experimental validation results are demonstrated that are conducted on a test bench with a V6 commercial SI engine.

Abstract Wave energy plays a vital role in providing renewable energy in coastal areas. Several factors need to be considered for optimum site selection and type of the wave energy converter. Some factors such as impact of climate variation, exploitable storage of wave energy and its trend, design wave condition (as a representative of construction cost), accessibility and availability are related to the local sea state, while the characteristics of the Wave Energy Converter (WEC) need to be considered in the prediction power supply. Hence, this study focuses on the impact of different criteria on the selection of the appropriate location/WECs combinations and offers a Multi-Criteria Approach (MCA). The proposed multi-criteria approach combines the above-mentioned factors into one factor to consider both the efficiency of WECs as well as sea state to assist decision makers when planning for a pilot project. The approach was then applied to the wave condition of three locations previously suggested as hotspots for wave energy extraction. Comparison of MCA index in the stations with different types of WECs provided a more comprehensive view on the suitability of a location for a near-future pilot project and selection of the most efficient WEC.

This study develops a mixed-integer linear programming (MILP) model integrating energy system optimization and benefit allocation scheme of the building distributed heating network. Based on the proposed model, the minimized annual total cost, energy generators configuration, optimal operation strategy and heating pipeline lay-out of the distributed energy network can be determined. Moreover, four benefit allocation schemes (Shapely, the Nucleolus, DP equivalent method, Nash-Harsanyi) based on cooperative game theory are employed to deal with the benefit (reduced annual cost) assignment among the building clusters, while considering the stability and fairness of each scheme. As a case study, a local area including three buildings located in Shanghai, China is selected for analysis. The simulation results indicate that the ground coalition in which all buildings cooperate with each other by sharing and interchanging the thermal energy yields the best economic performance for the distributed energy network as a whole. In addition, different allocation schemes may result in diversified outcomes in terms of the fairness and stability, which are measured by the Shapley-Shubik Power Index and the Propensity to Disrupt value, respectively. For the current case study, the Shapely value method is recognized to be the most acceptable allocation scheme from both viewpoints.

Abstract This study aimed to investigate the free gas accumulation behavior in a reservoir using a multiple-well system for methane hydrate production achieved by depressurization. Twenty-year simulations of gas production from a large-scale 3D methane hydrate reservoir model with different reservoir permeabilities were conducted, and the effects of different reservoir and operating conditions on the free gas accumulation behavior were fully examined. The simulation results indicated that the free gas accumulation behavior was affected by the reservoir permeability, and methane gas was inclined to accumulate within a certain permeability range, which was defined as the “free gas accumulation zone” for the first time. For an actual methane hydrate reservoir with a porosity of 0.31–0.51 and an initial hydrate saturation of 0.34–0.54, the free gas accumulation zone was estimated to be 37–145 mD at most. On the other hand, a low wellbore pressure could contribute to enhancing gas recovery by narrowing the free gas accumulation zone. In addition, the free gas accumulation zone was dramatically enlarged with the increase in well spacing, so a proper well spacing should be carefully designed to avoid the free gas accumulation zone. The prediction method proposed in this study could be applied to future commercial gas production from actual methane hydrate deposits achieved by depressurization using multiple-well systems.

Abstract Multiple unexpected uncertainty factors can occur when measuring gas turbine engine data, and the quality of the measured data can directly affect the accuracy of gas turbine engine models during performance adaptation. In the present study, a new performance adaptation method for aero gas turbine engines is proposed to improve prediction accuracy, by effectively processing a large amount of measured data. Adaptation factors were obtained to match the engine model and the measured data of every single operating point. These adaptation factors were then used to adjust the compressor performance, bleed air flow, engine thrust, and exhaust gas temperature. A data clustering technique was employed to exclude physically non-reasonable data points from the time series adaptation factors. The correlations for the adaptation factors were generated by using selected centroids from the clustered data, then the correlations were applied to the engine simulation. As a result, the values in the adapted engine model were in good agreement with transient measurement data. This confirms that the proposed performance adaptation method can be used to generate accurate gas turbine engine models using time series measurement data.

Abstract The application of the power generated by the proposed magnetic energy-harvesting suspension (MEHS) is to power a wireless sensor in the MEHS. In this paper, the generated powers of the MEHS at various excitations have been theoretically analyzed and experimentally validated. Firstly, the dynamic mechanism of the proposed MEHS is revealed and investigated. Secondly, the analysis expression of energy harvesting is obtained to find the related variables that affect the energy harvesting, and the influence parameters on the energy harvesting characteristics are analyzed numerically. The experimental tests are carried out to verify the numerical analysis and investigate the effect of various excitations and external load resistances on the energy harvesting characteristics. Experimental results demonstrate that the maximum output power of the MEHS can be obtained by changing the excitation frequency, excitation amplitude and external load resistance. Furthermore, the peak output power is generated when the excitation frequency is equal to the natural frequency, and the generated peak output power is 0.34 W at the excitation frequency 3.3 Hz. Meanwhile, the self-powered sensing experiments of the MEHS have been successfully verified in the laboratory, which lays the foundation for further application in a real vehicle.