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Abstract: Knocking combustion in spark-ignition (SI) engines is an abnormal combustion phenomenon which can constrain the engine performance and thermal efficiency. It can also result in severe permanent engine damage under certain operating conditions. This paper systematically reviews the engine knock phenomenon, including the mechanisms, influencing factors, consequences and detection methods etc. It introduces the visualization researches, simulations and some judging indexes of engine knock. Three mathematical models which can predict the engine knock, and various kinds of methods of suppressing knock are summarized. Finally, this paper puts forward some new suggestions on the weakness in the researches of knocking combustion. [Copyright &y& Elsevier]

Abstract: A desalination system is a complex multi energy domain system comprising power/energy flow across several domains such as electrical, thermal, and hydraulic. The dynamic modeling of a desalination system that comprehensively addresses all these multi energy domains is not adequately addressed in the literature. This paper proposes to address the issue of modeling the various energy domains for the case of a single stage flash evaporation desalination system. This paper presents a detailed bond graph modeling of a desalination unit with seamless integration of the power flow across electrical, thermal, and hydraulic domains. The paper further proposes a performance index function that leads to the tracking of the optimal chamber pressure giving the optimal flow rate for a given unit of energy expended. The model has been validated in steady state conditions by simulation and experimentation. [Copyright &y& Elsevier]

The simulation model is the key point for obtaining an operation strategy because of the complexity of the distributed CCHP system. However, simplified simulation models are currently employed to formulate a system operation strategy in most studies. To investigate whether the simulation model accuracy will influence the operation cost substantially, several detailed simulation models are proposed in this paper. An analysis and a comparison are performed on operation cost by testing the simplified simulation model and the detailed simulation model, respectively. The results indicate that the operation cost obtained by the detailed model is larger than the simplified model. However, the detailed model performs better in terms of the rationality of the operation strategy. To investigate further the performance of the two models in guiding actual system operation, a case study is conducted. The results indicate that 2240 ¥/day, accounting for 2.5% of the total daily cost, is reduced when the detailed model is used to formulate the operation strategy, demonstrating that the detailed model is superior to the simplified model when the economy and rationality of the optimal operation strategy are considered. [ABSTRACT FROM AUTHOR]

Abstract: Waste heat recovery by means of a Rankine Cycle is a promising approach for achieving significant reductions in fuel consumption and, as a result, exhaust emissions of passenger car engines. This approach is already well established in industrial applications such as gas and steam power plants or ship propulsion systems. While these systems are mainly designed for stationary operation, the behaviour in highly dynamic operating conditions becomes more important when the principle is transferred to a passenger car engine. Knowledge of the dynamic response of the employed heat exchangers plays an important role in performance prediction and control system design of the steam cycle. Hence, a dynamic model of the exhaust gas heat exchanger employing the moving-boundary principle was developed and is presented in this paper. The model describes both design operation and the heat-up procedure of the component. For achieving high model accuracy in the resulting broad range of operating conditions, new approaches for modelling wall temperature distribution and zone switching were developed. Simulations of stationary operating points as well as the response to typical disturbances of the system’s input variables are in good agreement with test bench measurements. The model is used to develop a control system for dynamic operation on the test bench. Further studies of the operating characteristics reveal varying dynamic behaviour depending on the heat flow rate from exhaust gas to working fluid as well as coupling of evaporation pressure and outlet steam temperature. [Copyright &y& Elsevier]

Abstract: This paper is focused on the control of air-feed system of Polymer Electrolyte Membrane Fuel Cell (PEMFC). This system regulates the air entering in the cathode side of the fuel cell. The control objective is to maintain optimum net power output by regulating the oxygen excess ratio in its operating range, through the air compressor. This requires controllers with a fast response time in order to avoid oxygen starvation during load changes. The problem is addressed using a robust nonlinear second order sliding mode controller in cascaded structure. The controller is based on sub-optimal algorithm, which is known for its robustness under disturbances and uncertainties. The controller performance is validated through Hardware-In-Loop (HIL) simulation based on a commercial twin screw air compressor and a real time fuel cell emulation system. The simulation results show that the controller is robust and has a good transient performance under load variations and parametric uncertainties. [Copyright &y& Elsevier]

Abstract: In this paper, a Maximum Power Point (MPP) tracking technique is proposed for the Fuel Cell (FC) stacks based on a modified Extremum Seeking (mES) control that slightly improves the performances of the classical ES control schemes. A higher value of the search speed obtained for the same tracking accuracy is demonstrated for the proposed mES control in comparison with the classical ES control schemes. The analysis made for the mES control in frequency domain reveals interesting relationships to design the control parameters, the values of closed loop gain and the dither amplitude, to obtain the imposed performance related to the search speed and tracking accuracy. The search speed will increase proportionally with the product of both control parameters, so it is practically limited for safe reasons. Finally, in the dynamical operation of the FC stack, a higher loop gain means a shorter time to catch the next MPP. Simulations show that the performances mentioned above are effective for the mES control based on a band pass filter scheme. [Copyright &y& Elsevier]

Abstract: The present paper aims to study the performance of the hybrid systems based on the fuel cell stack developed by Siemens-Westinghouse coupled with four different commercially available recuperated micro-turbines. The different systems considered were studied through the development of appropriate simulation models validated with available data. Full and part load performance of those systems are presented and discussed. For the part load operation two control strategies were adopted by maintaining either the SOFC stack temperature or the turbine exit temperature constant. The part load results have shown large variations in SOFC stack and turbine exit temperatures. Those data must be taken into account in order to avoid system malfunctions and to ensure long lifetime. The smaller (among the four considered) the micro-turbine coupled with the Siemens-Westinghouse SOFC generator, the more efficient the corresponding hybrid system. It was also revealed that when the power requirements are low, the designer may choose a larger micro-turbine than the required, as the system operates efficiently also at higher loads than the base and could satisfy peak energy demands. [Copyright &y& Elsevier]

Abstract: In energy and environment field models are constructed, in general, based on well-defined physical phenomena and properties. Calibration and uncertainty analysis hold a particular interest because models represent a simplification of reality and, therefore, it is necessary to quantify to what degree they are imperfect before employing them in design, prediction and decision making processes. Integrated building energy models attempt to describe the effect of various internal and external actions (weather, occupancy, appliances, etc.) through physical relations (both algebraic and differential) and they are being widely used to design and operate high performance buildings, which are an essential component of a global energy strategy to reduce carbon emission and fossil sources depletion. An approach oriented to systems and able to integrate effectively field measured data and computer simulations for calibration in the modeling process has the potential to revolutionize the way buildings are designed and operated, and to stimulate also the development of new technologies and solutions in the field. The research presented in this paper aims to represent an initial step towards this integrated approach. [Copyright &y& Elsevier]

Abstract: In this paper, a novel purposely designed dynamic simulation model for the performance analysis of solar heating and cooling systems is presented. The investigated system layouts are based on single stage LiBr–H2O absorption chillers and on both evacuated tube and concentrating photovoltaic thermal solar collectors. Furthermore, both electric chiller and gas fired heater backup system are considered. Such model is implemented in a computer code written in MATLAB. Here, the optimisation of several system design and operating parameters in terms of energy saving is also carried out. A code to code analysis is performed comparing the obtained simulation results vs. those achieved by a TRNSYS model available in literature. The simulation code for the concentrating photovoltaic thermal solar collectors is validated by experimental data. A good agreement among results is observed in both the cases. A suitable case study referred to a building including both offices and dwellings located in Northern and Southern Italy is presented. High primary energy savings are obtained for some of the investigated system layouts. By evacuated tube collectors solar field such savings can reach 74%, while shifting to concentrating photovoltaic thermal solar collectors they often surpass 100%. The system economic profitability strongly depends on future scale economies and eventual public funding. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental and numerical study on evaluation of thermal response and performance of prototype precast-high strength concrete (PHC) energy pile. Short-term field thermal response tests (TRTs) were conducted for the PHC energy piles installed in partially saturated weathered granite soil deposit, in which two types of heat exchangers were considered: W and 3U-shaped heat exchangers. The TRTs were successfully simulated by three-dimensional finite element analyses employing quasi-steady-state convective heat transfer boundary condition. The numerical model was applied to simulate 3-day TRTs, and the simulation results were used for assessing effective thermal conductivity and thermal resistance. Besides, continuous and intermittent operation simulations of the energy piles were performed, and for the results of performance analyses, discussion was made to evaluate energy efficiency of the prototype PHC piles. [Copyright &y& Elsevier]

Abstract: The Energy Performance of Buildings Directive (EPBD recast, 2010/31/EU) requires Member States to define minimum requirements of energy performance of buildings and building components with a view to achieving cost-optimal levels. In order to calculate the cost optimal level of minimum energy performance, Member States are required to create a set of reference buildings, at national or regional level, to be used in the calculations. This paper introduces to the concept of reference buildings and to the state of art at an international level. In particular, a general methodology for the creation of reference buildings is illustrated. A case study of an office building as a reference building for the Italian existing building stock is then shown. The process concerning the building definition and modeling was carried out by means of dynamic energy simulation program EnergyPlus. [Copyright &y& Elsevier]

Abstract: A multivariable control strategy is needed to ensure high efficiency and load-following capability in the operation of waste heat recovery power plants. In this paper, a generalized predictive controller is proposed for a waste heat recovery process operating on an organic Rankine cycle. The simulation results show that the proposed control strategy not only can achieve good transient and steady response along with decoupling performance, but also can obtain satisfactory disturbance rejection performance. [Copyright &y& Elsevier]

Abstract: This paper is devoted to the development of inverted-type bulk heterojunction solar cells based on zinc oxide (ZnO) interlayers, poly-3-hexylthiophene (P3HT) and PCBM using simple synthesis procedures and deposition techniques. We compare device structures and performances consisting of poly-3-hexylthiophene (P3HT) polymer and PCBM in contact with three different types of ZnO interlayers: a ZnO backing interlayer alone using spin coating process; nanorod ZnO interlayers from Zn2+:HO− solutions using deep coating process and finally nanorod ZnO interlayers from Zn2+:HO− solutions onto ZnO backing interlayer using spin coating process. The best device configuration is fabricated in a ZnO backing interlayer/nanorod ZnO interlayer by spincoating process/P3HT:PCBM/Gold cell architecture which exhibits a power conversion efficiency of 2.73% under 100mW/cm2 AM 1.5G simulated solar emission. Atomic force microscopy (AFM) and photovoltaic device measurements are used to study the morphology and device performance of the three different types of ZnO interlayers. [Copyright &y& Elsevier]

Abstract: The aim of this study is to develop representative simulation building energy data sets and benchmark models for the Egyptian residential sector. This study reports the results of a recent field survey for residential apartment buildings in Egypt. Two building performance simulation models are created reflecting the average energy consumption characteristics of air-conditioned residential apartments in Alexandria, Cairo and Asyut. Aiming for future evaluation of the cost and energy affects of the new Egyptian energy standard this study established two detailed models describing the energy use profiles for air-conditioners, lighting, domestic hot water and appliances in respect to buildings layout and construction. Using EnergyPlus simulation tool the collected surveyed data was used as input for two building simulation models. The simulation models were verified against the apartment characteristic found in the survey. This paper presents details of the building models including the energy use patterns and profiles created for this study. [Copyright &y& Elsevier]

Abstract: Solar powered solid desiccant cooling system is a good alternative to conventional vapor compression system. In this paper, a novel solar driven desiccant coated heat exchanger cooling (SDCC) system is proposed. In order to validate the feasibility of such system and to predict system performance, an integrated system model is established by combing the mathematical models of different components. The model is adopted to evaluate system performance under Shanghai summer condition with high temperature as well as high humidity ratio. It is found that SDCC system can provide satisfied supply air to conditioned indoor space from 8:00 to 17:00 in June and July, the biggest cooling powers are 2.9kW and 3.5kW, and corresponding solar COP are 0.22 and 0.24 respectively. In August, the system needs relatively short switch time (less than 2min) to provide satisfied supply air, and the corresponding cooling power can reach to 5kW. To make a good compromise between system performance and system constitution, 2min is recommended as the switch time under simulated condition in August. Also, effects of main design parameters on system performance are calculated and discussed. [Copyright &y& Elsevier]

Abstract: The residential buildings in Hong Kong are often developed into highrise central core blocks due to limited buildable land and dense population. The lift lobbies in these buildings are enclosed without windows and their floor heights are restricted to not more than 2.8m. Electric lighting is switched on continuously for 24h a day. This paper investigated an alternative way to provide lighting for the enclosed space by solar energy via a remote source solar lighting system. The detailed analysis on different layouts of typical lift lobbies are reported first and then the remote source solar lighting system is proposed, which is composed of a simple heliostat and side-emitting fiber optic. Simulation on the light transmission performance in the system was carried out by the ZEMAX-EE. An experiment was carried out to validate the simulation results. The validated simulation results can reveal the performance of the side-emitting fiber optic lighting system. The results show that the proposed remote source solar lighting system can be applied as an alternative lighting system to illuminate the enclosed lift lobby at daytime in clear sky condition. [Copyright &y& Elsevier]

Abstract: There are various architectural features of a residential building that can influence its indoor climate and electricity consumption, such as thermal insulation, window size, glazing material, albedo of building façade and orientation. In addition to these architectural features, shading effects (either by external objects or by the building itself) can also affect the thermal performance of a building. External shading effects are mainly caused by nearby trees or buildings, while shading effect imposed by the building itself usually depends on the layout design of the building, i.e. building shape and layout arrangement of the flats on each floor. Some flats in a building may receive a shading effect from adjacent flats located in the same building block. When architects or building designers conduct the layout design of a building, a number of factors such as building regulations, site limitations, scenic view, noise control, natural ventilation and daylight utilization will be considered. The thermal performance of a building is one of the major issues that should be taken into account. The objective of this study is to assess the thermal performance of residential buildings under the effect of adjacent shading in subtropical Hong Kong. A literature survey was carried out to identify typical layout designs of residential buildings from the past two decades. Building energy simulations were conducted for residential building blocks with different layout designs. It is found that adjacent shading effect has a substantial impact on the thermal performance of residential buildings. The findings are reported in this paper. [Copyright &y& Elsevier]

Abstract: The use of fuel cell systems for distributed residential power generation represents an interesting alternative to traditional thermoelectric plants due to their high efficiency and the potential recovering of the heat generated by the internal electrochemical reactions. In this paper the study of a micro cogenerative (CHP) energy system based on a Proton Exchange Membrane fuel cell (PEMFC) is reported. With the aim to evaluate the performance and then the feasibility of this non-conventional energy system, in consideration of thermal and electrical basic demand of a multifamily apartment blocks, a zero-dimensional PEMFC model in Aspen Plus environment has been developed. A simulations sequence has been carried out at different operating conditions of the fuel cell (varying temperature, pressure and relative humidity). Subsequently, on the basis of the obtained results, an energy/exergy analysis has been conducted to define the optimal operating conditions of the PEMFC that ensures the most efficient use of the energy and exergy inputs. [Copyright &y& Elsevier]

Abstract: This paper presents a study on optimization of a fixed bed tri-reformer reactor (TR). This reactor has been used instead of conventional steam reformer (CSR) and auto thermal reformer (CAR). A theoretical investigation has been performed in order to evaluate the optimal operating conditions and enhancement of methane conversion, hydrogen production and desired H2/CO ratio as a synthesis gas for methanol production. A mathematical heterogeneous model has been used to simulate the reactor. The process performance under steady state conditions was analyzed with respect to key operational parameters (inlet temperature, O2/CH4, CO2/CH4 and steam/CH4 ratios). The influence of these parameters on gas temperature, methane conversion, hydrogen production and H2/CO ratio was investigated. Model validation was carried out by comparison of the reforming model results with industrial data of CSR. Differential evolution (DE) method was applied as a powerful method for optimization. Optimum feed temperature and reactant ratios (CH4/CO2/H2O/O2) are 1100K and 1/1.3/2.46/0.47 respectively. The optimized TR has enhanced methane conversion by 3.8% relative to industrial reformers in a single reactor. Methane conversion, hydrogen yield and H2/CO ratio in optimized TR are 97.9%, 1.84 and 1.7 respectively. The optimization results of tri-reformer were compared with the corresponding predictions from process simulation software operated at the same feed conditions. [Copyright &y& Elsevier]

Abstract: This paper presents a model-based supervisory and optimal control strategy for central chiller plants to enhance their energy efficiency and control performance. The optimal strategy is formulated using simplified models of major components and the genetic algorithm (GA). The simplified models are used as the performance predictors to estimate the system energy performance and response to the changes of control settings and working conditions. Since the accuracy of the models has significant impacts on the overall prediction results, the models used are linear in the parameters and the recursive least squares (RLS) estimation technique with exponential forgetting is used to identify and update the model parameters online. That is to ensure that the linear models can provide reliable and accurate estimates when working condition changes. The GA, as a global optimization tool, is used to solve the optimization problem and search for globally optimal control settings. The performance of this strategy is tested and evaluated in a simulated virtual system representing the actual central chiller plant in a super high-rise building under various working conditions. The results showed that this strategy can save about 0.73–2.55% daily energy of the system studied, as compared to a reference strategy using conventional settings. [ABSTRACT FROM AUTHOR]

Abstract: Stirling engines (SE) are a market-ready technology suitable for residential cogeneration of heat and electricity to alleviate the increasing demand on central power grids. Advantages of this external combustion engine include high cogeneration efficiency, fuel flexibility, low noise and vibration, and low emissions. To explore and assess the feasibility of using SE based cogeneration systems in the residential sector, there is a need for an accurate and practical simulation model that can be used to conduct sensitivity and what-if analyses. A simulation model for SE based residential scale micro-cogeneration systems was recently developed; however the model is impractical due to its functional form and data requirements. Furthermore, the available experimental data lack adequate diversity to assess the model’s suitability. In this paper, first the existing model is briefly presented, followed by a review of the design and implementation of a series of experiments conducted to study the performance and behaviour of the SE system and to develop extensive, and hitherto unavailable, operational data. The empirical observations are contrasted with the functional form of the existing simulation model, and improvements to the structure of the model are proposed based upon these observations. [Copyright &y& Elsevier]

Abstract: In this paper, the model for the multi-deck medium temperature display cabinets is developed with the integration of CFD and cooling coil sub-models. The distributed method is used to develop the cooling coil model with the airside inputs from the outputs of the CFD model. Inversely, the airside outputs from the cooling coil model are used to update the boundary conditions of the CFD model. To validate this cabinet model, a multi-deck medium temperature display cabinet refrigerated with a secondary refrigerant cooling coil was selected as a prototype and mounted in an air conditioned chamber. Extensive tests were conducted at constant space air temperature and varied relative humilities. The cabinet model has been validated by comparing with the test results for the parameters of air at different locations of the flow path, and temperatures of refrigerant and food product, etc. The validated model is therefore used to explore and analyse the cabinet performance and control strategies at various operating and design conditions. [Copyright &y& Elsevier]

Abstract: Co-utilization of natural gas and biomass is a successful way to make efficient use of them for chemical production and power generation, for biomass is rich in carbon while natural gas is rich in hydrogen. The present paper therefore proposes a new polygeneration system taking biomass and natural gas as materials for methanol production and power generation. The new polygeneration system can achieve the optimal ratio of H2 to CO for methanol production by adjusting input ratio of natural gas to biomass without any energy penalty. Thus, the suggested system can eliminate CO to H2 shift process and CO2 remove process, which can avoid material and energy destruction; however, those processes are otherwise necessary in individual biomass to methanol plant. Moreover, the new system eliminates the CO2 addition process; however, the addition of CO2 is necessary in individual natural gas to methanol plant, which causes extra energy penalty. This system combined chemical production and power generation together, in order to achieve the cascaded utilization of chemical and physical energy of natural gas and biomass. In a further way, we investigated the key processes, to maximize the utilization of energy and improve system performance. A thermo-chemical process taking biomass and natural gas as co-feedstock is compared with the systems that only taking either biomass or natural gas as resource for methanol production and power generation. The evaluation and calculation of the systems are carried out by help of Aspen Plus process simulator. The evaluation results indicate that, the new polygeneration system can reduce materials input at least 9% compared with individual systems with same output. In a further way, the effect of natural gas to biomass feed ratio on system performance is also investigated. The research results show that, the proposed polygeneration system would be expected to realize efficient utilization of biomass and natural gas, and offer a possibility of developing new technologies for biomass and natural gas based systems. [Copyright &y& Elsevier]

Abstract: The ground-coupled heat pump (GCHP) system is becoming attractive for air-conditioning in some moderate-weather regions due to its high energy efficiency and reliable operation capability. However, when the technology is used in buildings where there is only cooling load in hot-weather areas like Hong Kong, the heat rejected into the ground by the GCHP systems will accumulate around the ground heat exchangers (GHE). This heat accumulation will result in degradation of system performance and increment of system operating costs. This problem can be resolved by using the hybrid ground-coupled heat pump (HGCHP) system, which uses supplemental heat rejecters to reject the accumulated heat. This paper presents a practical hourly simulation model of the HGCHP system by modeling the heat transfer process of the system’s main components. The computer program based on this hourly simulation model can be used to calculate the hour-by-hour operation data of the HGCHP system. As a case study, both a HGCHP system and a traditional GCHP system are designed for a hypothetic private residential building located in Hong Kong, and the economic comparisons are conducted between these two types of systems. The simulation results show that the HGCHP system can effectively solve the heat accumulation problem and reduce both the initial costs and operating costs of the air-conditioning system in the building. [Copyright &y& Elsevier]

Abstract: Accurate performance simulation and estimation of gas turbine engines is very useful for gas turbine manufacturers and users alike and such a simulation normally starts from its design-point. When some of the engine component parameters for an existing engine are not available, they must be estimated in order that the performance analysis can be started. Therefore, the simulated design-point performance of an engine may be slightly different from its actual performance. In this paper, a Genetic Algorithm (GA) based non-linear gas turbine design-point performance adaptation approach has been presented to best estimate the unknown component parameters and match available design-point engine performance. In the approach, the component parameters may be compressor pressure ratios and efficiencies, turbine entry temperature, turbine efficiencies, engine mass flow rate, cooling flows, by-pass ratio, etc. The engine performance parameters may be thrust and SFC for aero engines, shaft power and thermal efficiency for industrial engines, gas path pressures and temperatures, etc. To select the most appropriate to-be-adapted component parameters, a sensitivity analysis is used to analyze the sensitivity of all potential component parameters against the engine performance parameters. The adaptation approach has been applied to an industrial gas turbine engine to test the effectiveness of the approach. The approach has also been compared with a non-linear Influence Coefficient Matrix (ICM) based adaptation method and the advantages and disadvantages of the two adaptation methods have been compared with each other. The application shows that the sensitivity analysis is very useful in the selection of the to-be-adapted component parameters and the GA-based adaptation approach is able to produce good quality engine models at design-point. Compared with the non-linear ICM-based method, the GA-based performance adaptation method is more robust but slower in computation and relatively less accurate. [Copyright &y& Elsevier]

Abstract: A methodology for optimum sizing of different components (i.e., rotor diameter, electrical generator rating, and battery capacity) of a standalone wind–battery system is proposed in this paper. On the basis of time series simulation of the system performance along with different design constraints, the entire set of feasible design options, also known as the design space, has been identified on a rotor diameter vs. rated power diagram. The design space of a standalone wind–battery system identifies the entire envelope within which a feasible system may be designed. The optimum configuration of the standalone system is identified on the basis of minimum cost of energy (US$/kWh). It is observed that the cost of energy is sensitive to the magnitude of average demand and the wind regime. Sensitivity of the capital cost on the minimum cost of energy is also studied. [Copyright &y& Elsevier]

Abstract: This paper describes the fabrication, experimentation and simulation stages of converting a 165l domestic electric refrigerator to a solar powered one. A conventional domestic refrigerator was chosen for this purpose and was redesigned by adding battery bank, inverter and transformer, and powered by solar photovoltaic (SPV) panels. Various performance tests were carried out to study the performance of the system. The coefficient of performance (COP) was observed to decrease with time from morning to afternoon and a maximum COP of 2.102 was observed at 7 AM. Simulations regarding economic feasibility of the system for the climatic conditions of Jaipur city (India) were also carried out using RETScreen 4. It was observed that the system can only be economically viable with carbon trading option taken into account, and an initial subsidy or a reduction in the component costs – mainly SPV panels and battery bank. [Copyright &y& Elsevier]