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Energies, Volume 4, Issue 6 (June 2011), Pages 845-1009

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Research

Jump to: Review

Open AccessArticle Impact of Turbulence Intensity and Equivalence Ratio on the Burning Rate of Premixed Methane–Air Flames
Energies 2011, 4(6), 878-893; doi:10.3390/en4060878
Received: 29 March 2011 / Revised: 6 May 2011 / Accepted: 18 May 2011 / Published: 27 May 2011
Cited by 7 | PDF Full-text (1046 KB) | HTML Full-text | XML Full-text
Abstract
Direct Numerical Simulations (DNS) have been conducted to study the response of initially laminar spherical premixed methane–air flame kernels to successively higher turbulence intensities at five different equivalence ratios. The numerical experiments include a 16-species/25-step skeletal mechanism for methane oxidation and a multicomponent
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Direct Numerical Simulations (DNS) have been conducted to study the response of initially laminar spherical premixed methane–air flame kernels to successively higher turbulence intensities at five different equivalence ratios. The numerical experiments include a 16-species/25-step skeletal mechanism for methane oxidation and a multicomponent molecular transport model. Highly turbulent conditions (with integral Reynolds numbers up to 4513) have been accessed. The effect of turbulence on the physical properties of the flame, in particular its consumption speed Sc, which is an interesting measure of the turbulent flame speed ST has been investigated. Local quenching events are increasingly observed for highly turbulent conditions, particularly for lean mixtures. The obtained results qualitatively confirm the expected trend regarding correlations between u′/SL and the consumption speed: Sc first increases, roughly linearly, with u′/SL (low turbulence zone), then levels off (bending zone) before decreasing again (quenching limit) for too intense turbulence. For a fixed value of u′/SL, Sc/SL varies with the mixture equivalence ratio, showing that additional parameters should probably enter phenomenological expressions relating these two quantities. Full article
(This article belongs to the Special Issue Advancement in Combustion Sciences and Technology)
Open AccessArticle A Phenomenological Model for Prediction Auto-Ignition and Soot Formation of Turbulent Diffusion Combustion in a High Pressure Common Rail Diesel Engine
Energies 2011, 4(6), 894-912; doi:10.3390/en4060894
Received: 11 April 2011 / Revised: 5 May 2011 / Accepted: 6 May 2011 / Published: 3 June 2011
PDF Full-text (609 KB) | HTML Full-text | XML Full-text
Abstract
A new phenomenological model, the TP (Temperature Phase) model, is presented to carry out optimization calculations for turbulent diffusion combustion in a high-pressure common rail diesel engine. Temperature is the most important parameter in the TP model, which includes two parts: an auto-ignition
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A new phenomenological model, the TP (Temperature Phase) model, is presented to carry out optimization calculations for turbulent diffusion combustion in a high-pressure common rail diesel engine. Temperature is the most important parameter in the TP model, which includes two parts: an auto-ignition and a soot model. In the auto-ignition phase, different reaction mechanisms are built for different zones. For the soot model, different methods are used for different temperatures. The TP model is then implemented in KIVA code instead of original model to carry out optimization. The results of cylinder pressures, the corresponding heat release rates, and soot with variation of injection time, variation of rail pressure and variation of speed among TP model, KIVA standard model and experimental data are analyzed. The results indicate that the TP model can carry out optimization and CFD (computational fluid dynamics) and can be a useful tool to study turbulent diffusion combustion. Full article
(This article belongs to the Special Issue Advancement in Combustion Sciences and Technology)
Open AccessArticle Parametric Investigation of Optimum Thermal Insulation Thickness for External Walls
Energies 2011, 4(6), 913-927; doi:10.3390/en4060913
Received: 28 April 2011 / Revised: 24 May 2011 / Accepted: 27 May 2011 / Published: 7 June 2011
Cited by 8 | PDF Full-text (279 KB) | HTML Full-text | XML Full-text
Abstract
Numerous studies have estimated the optimum thickness of thermal insulation materials used in building walls for different climate conditions. The economic parameters (inflation rate, discount rate, lifetime and energy costs), the heating/cooling loads of the building, the wall structure and the properties of
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Numerous studies have estimated the optimum thickness of thermal insulation materials used in building walls for different climate conditions. The economic parameters (inflation rate, discount rate, lifetime and energy costs), the heating/cooling loads of the building, the wall structure and the properties of the insulation material all affect the optimum insulation thickness. This study focused on the investigation of these parameters that affect the optimum thermal insulation thickness for building walls. To determine the optimum thickness and payback period, an economic model based on life-cycle cost analysis was used. As a result, the optimum thermal insulation thickness increased with increasing the heating and cooling energy requirements, the lifetime of the building, the inflation rate, energy costs and thermal conductivity of insulation. However, the thickness decreased with increasing the discount rate, the insulation material cost, the total wall resistance, the coefficient of performance (COP) of the cooling system and the solar radiation incident on a wall. In addition, the effects of these parameters on the total life-cycle cost, payback periods and energy savings were also investigated. Full article
Open AccessArticle Textural Characterization and Energetics of Porous Solids by Adsorption Calorimetry
Energies 2011, 4(6), 928-947; doi:10.3390/en4060928
Received: 20 February 2011 / Revised: 13 April 2011 / Accepted: 28 April 2011 / Published: 10 June 2011
Cited by 1 | PDF Full-text (461 KB) | HTML Full-text | XML Full-text
Abstract
An adsorption microcalorimeter was designed and built in our laboratory and used for the determination of differential adsorption heats in different samples of porous solids: activated carbon granules, activated carbon pellets, an activated carbon monolith and a zeolite sample. This work shows the
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An adsorption microcalorimeter was designed and built in our laboratory and used for the determination of differential adsorption heats in different samples of porous solids: activated carbon granules, activated carbon pellets, an activated carbon monolith and a zeolite sample. This work shows the relationship between adsorption heat and the pore size of different porous solids using adsorption of NH3, CO and N2O. The result shows that the thermal effect can be related with textural properties and superficial chemical groups of the studied porous solids. The values of differential heats of N2O adsorption in the investigated systems have shown that this interaction is weaker than that with CO. Small amounts of N2O are chemisorbed in the investigated systems. For the room temperature adsorption of N2O, the strongest active sites for the interaction with Brönsted acid groups in the ACM structure were identified. The values determined are between −60 kJ/mol and −110 kJ/mol for ZMOR and ACM, respectively, for the adsorption of N2O and −95 kJ/mol and −130 kJ/mol for the adsorption of CO. Full article
Open AccessArticle Energy Saving Evaluation of the Ventilated BIPV Walls
Energies 2011, 4(6), 948-959; doi:10.3390/en4060948
Received: 17 January 2011 / Revised: 30 May 2011 / Accepted: 10 June 2011 / Published: 14 June 2011
Cited by 5 | PDF Full-text (873 KB) | HTML Full-text | XML Full-text
Abstract
This study integrates photovoltaic (PV) system, building structure, and heat flow mechanism to propose the notion of ventilated Building-Integrated Photovoltaic (BIPV) walls. The energy-saving potential of the ventilated BIPV walls was investigated via engineering considerations and computational fluid dynamics (CFD) simulations. The results
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This study integrates photovoltaic (PV) system, building structure, and heat flow mechanism to propose the notion of ventilated Building-Integrated Photovoltaic (BIPV) walls. The energy-saving potential of the ventilated BIPV walls was investigated via engineering considerations and computational fluid dynamics (CFD) simulations. The results show that the heat removal rate and indoor heat gain of the proposed ventilated BIPV walls were dominantly affected by outdoor wind velocity and airflow channel width. Correlations for predicting the heat removal rate and indoor heat gain, the reduction ratio of the indoor heat gain, CO2 reduction, and induced indoor air exchange are introduced. Full article
(This article belongs to the Special Issue Advances in Solar Energy)
Open AccessArticle SVR with Hybrid Chaotic Immune Algorithm for Seasonal Load Demand Forecasting
Energies 2011, 4(6), 960-977; doi:10.3390/en4060960
Received: 24 March 2011 / Revised: 7 June 2011 / Accepted: 14 June 2011 / Published: 17 June 2011
Cited by 12 | PDF Full-text (314 KB) | HTML Full-text | XML Full-text
Abstract
Accurate electric load forecasting has become the most important issue in energy management; however, electric load demonstrates a seasonal/cyclic tendency from economic activities or the cyclic nature of climate. The applications of the support vector regression (SVR) model to deal with seasonal/cyclic electric
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Accurate electric load forecasting has become the most important issue in energy management; however, electric load demonstrates a seasonal/cyclic tendency from economic activities or the cyclic nature of climate. The applications of the support vector regression (SVR) model to deal with seasonal/cyclic electric load forecasting have not been widely explored. The purpose of this paper is to present a SVR model which combines the seasonal adjustment mechanism and a chaotic immune algorithm (namely SSVRCIA) to forecast monthly electric loads. Based on the operation procedure of the immune algorithm (IA), if the population diversity of an initial population cannot be maintained under selective pressure, then IA could only seek for the solutions in the narrow space and the solution is far from the global optimum (premature convergence). The proposed chaotic immune algorithm (CIA) based on the chaos optimization algorithm and IA, which diversifies the initial definition domain in stochastic optimization procedures, is used to overcome the premature local optimum issue in determining three parameters of a SVR model. A numerical example from an existing reference is used to elucidate the forecasting performance of the proposed SSVRCIA model. The forecasting results indicate that the proposed model yields more accurate forecasting results than the ARIMA and TF-ε-SVR-SA models, and therefore the SSVRCIA model is a promising alternative for electric load forecasting. Full article
(This article belongs to the Special Issue Intelligent Energy Demand Forecasting)
Open AccessArticle Petri Net Model and Reliability Evaluation for Wind Turbine Hydraulic Variable Pitch Systems
Energies 2011, 4(6), 978-997; doi:10.3390/en4060978
Received: 11 March 2011 / Revised: 8 June 2011 / Accepted: 16 June 2011 / Published: 23 June 2011
Cited by 8 | PDF Full-text (804 KB) | HTML Full-text | XML Full-text
Abstract
Based on an analysis of the working principles of the hydraulic variable pitch system of a wind turbine, a novel Petri net model and reliability evaluation method are proposed. First, Petri net theory is adopted to build a model for each discrete state
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Based on an analysis of the working principles of the hydraulic variable pitch system of a wind turbine, a novel Petri net model and reliability evaluation method are proposed. First, Petri net theory is adopted to build a model for each discrete state of the operation of the hydraulic pitch system of the wind turbine and at the same time a fault Petri net model is established. Then through qualitative analysis and quantitative calculations based on the fault Petri net, the system reliability indexes are obtained. During the qualitative analysis process, in order to more conveniently find the minimal cut sets of the fault Petri net, a Visual C++ 6.0-based algorithm is compiled and the minimal cut sets are tested correctly with another method. During the quantitative calculation process, the fault probability has been obtained from the equations according to the fault probability of libraries and transitions between different states. Not only does the proposed Petri net describe the structure, function and operation of the hydraulic pitch system with a graphic language, but the fault Petri net model can also clearly express the logical relations among faults. The novel Petri net model offers simple calculations and the prospect of broad applicability and the new reliability evaluation method provides an important reference for the performance evaluation of these systems. Full article
(This article belongs to the Special Issue Wind Energy 2011)
Figures

Open AccessArticle Energy Use in Day Care Centers and Schools
Energies 2011, 4(6), 998-1009; doi:10.3390/en4070998
Received: 27 May 2011 / Revised: 22 June 2011 / Accepted: 23 June 2011 / Published: 27 June 2011
Cited by 7 | PDF Full-text (119 KB) | HTML Full-text | XML Full-text
Abstract
Typically the aim in the construction process is to calculate the energy, space and cost efficiency in the design phase. These factors’ influence on decision making extends to the whole building process. How these decisions affect the use of the building and user
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Typically the aim in the construction process is to calculate the energy, space and cost efficiency in the design phase. These factors’ influence on decision making extends to the whole building process. How these decisions affect the use of the building and user satisfaction as well as maintenance is still not that well understood. This study analyses different schools and day care centers and their energy as well as primary energy use. The buildings are located in southern Finland. Each building has had different objectives with respect to energy efficiency in the design phase. Our objective was to find out how those decisions made in the design and construction phase have influenced the overall energy performance of the building compared to existing building stock of similar building type. The results show that the studied buildings had lower thermal energy consumption compared to existing building stock. Thus the special attention in the design phase allowed achieving the desired goal. However, for the electricity consumption such a correlation could not be found. One of the reasons could be also different service level of buildings (more equipment). Also other quality values could not be compared since such data were not available from the existing building stock. As many earlier studies have indicated users have a high influence on the energy consumption. In the future, when feed-back from the users are obtained it will be interesting to analyze the results and compare what kind of influence that user behavior will have on the overall energy consumption of the studied buildings. Full article
(This article belongs to the Special Issue Energy Savings in the Domestic and Tertiary Sectors 2011)

Review

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Open AccessReview Environmental Impacts and Costs of Hydrotreated Vegetable Oils, Transesterified Lipids and Woody BTL—A Review
Energies 2011, 4(6), 845-877; doi:10.3390/en4060845
Received: 1 February 2011 / Revised: 30 March 2011 / Accepted: 19 May 2011 / Published: 25 May 2011
Cited by 32 | PDF Full-text (559 KB) | HTML Full-text | XML Full-text
Abstract
This article reviews and compares assessments of three biodiesel fuels: (1) transesterified lipids, (2) hydrotreated vegetable oils (HVO), and (3) woody biomass-to-liquid (BTL) Fischer-Tropsch diesel and selected feedstock options. The article attempts to rank the environmental performance and costs of fuel and feedstock
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This article reviews and compares assessments of three biodiesel fuels: (1) transesterified lipids, (2) hydrotreated vegetable oils (HVO), and (3) woody biomass-to-liquid (BTL) Fischer-Tropsch diesel and selected feedstock options. The article attempts to rank the environmental performance and costs of fuel and feedstock combinations. Due to inter-study differences in goal and study assumptions, the ranking was mostly qualitative and intra-study results are emphasized. Results indicate that HVO made from wastes or by-products such as tall oil, tallow or used cooking oil outperform transesterified lipids and BTL from woody material, both with respect to environmental life cycle impacts and costs. These feedstock options are, however, of limited availability, and to produce larger volumes of biofuels other raw materials must also be used. BTL from woody biomass seems promising with good environmental performance and the ability not to compete with food production. Production of biofuels from agricultural feedstock sources requires much energy and leads to considerable emissions due to agrochemical inputs. Thus, such biodiesel fuels are ranked lowest in this comparison. Production of feedstock is the most important life cycle stage. Avoiding detrimental land use changes and maintaining good agricultural or forestry management practices are the main challenges to ensure that biofuels can be a sustainable option for the future transport sector. Full article
(This article belongs to the Special Issue Biomass and Biofuels)

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