Artículos (Ingeniería Energética)

URI permanente para esta colecciónhttps://hdl.handle.net/11441/11362

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Enhancing the building resilience in a changing climate through a passive cooling roof: A case study in Camas (Seville, Spain)
(Elsevier, 2024-10-15) Monge Palma, Rafael; Castro Medina, Daniel; Guerrero Delgado, Maria Del Carmen; Sánchez Ramos, José; Montero Gutiérrez, Paz; Álvarez Domínguez, Servando; Universidad de Sevilla. Departamento de Ingeniería Energética; Ministerio de Ciencia, Innovación y Universidades (MICINN). España; Universidad de Sevilla. TEP143: Termotecnia
Renovating buildings is a crucial mission for the coming decades to combat energy inefficiencies and produce a resilient building stock. The inefficient thermal envelope has significant implications for occupants, especially for families lacking the financial resources to maintain a healthy and comfortable indoor environment. In scenarios where households cannot afford or utilize HVAC systems and high temperatures are more frequent, building retrofits should prioritize reducing heat loss in winter and passively lowering indoor temperatures in the cooling season. This work introduces a new solution to enhance the liveability of a social housing building in southern Spain by integrating a double-skin roof with a conventional retrofit strategy, which incorporates passive cooling techniques – night ventilation and an evaporative cooling system – for effective heat dissipation based on available commercial solutions. An extensive monitoring campaign was conducted over three years to evaluate the thermal comfort of occupants and the risk of overheating in naturally conditioned buildings before and after renovation following two impact assessment methods: real-time data-based and simulation-based. The real-time data-based method compared the indoor conditions of a dwelling with a conventionally retrofitted roof to one with a double-skin roof, indicating that the dynamic roof maintains a ceiling temperature lower than the air temperature throughout the summer while the conventional roof acts as a heating surface. On the other side, the simulation-based method compared the observed indoor conditions with a double-skin roof enabled during 2023 to the initial stage and a double-skin roof disabled scenario, using calibrated building energy models. The natural cooling roof solution almost eliminates the overheating events, leading to a reduction of 94.1% and 76.9% in discomfort degree-hours compared to the initial stage according to the ASHRAE adaptative and Fanger comfort models, respectively. Additionally, the results indicate that conventional retrofits can increase the risk of overheating when a cooling system is not considered. Integrating a cool roof solution requires only an extra implementation cost of 31€/m2 compared to a conventional solution, having an operational cost that represents less than 3% of the minimum monthly income in the social housing district.
Transient performance modelling of solar tower power plants with molten salt thermal energy storage systems
(Elsevier, 2024-09-01) Tagle-Salazar, D.; Cabeza, Luisa F.; Prieto Ríos, Cristina; Universidad de Sevilla. Departamento de Ingeniería Energética; European Commission (EC); Ministerio de Ciencia, Innovación y Universidades (MICINN). España; European Union (UE); Ministerio de Ciencia e Innovación (MICIN). España; Agencia Estatal de Investigación. España; Generalitat de Catalunya; Universidad de Sevilla. TEP143: Termotecnia
Concentrating solar power (CSP) has emerged as a dynamic and promising technology, demonstrating a burgeoning market potential for power generation through the utilization of solar thermal resources. Notably, global installed capacity has witnessed a substantial uptick in recent years, indicative that this technology is increasing traction worldwide. To optimize the utilization of CSP systems, particularly during periods of low or absent solar radiation, the integration of thermal energy storage (TES) systems using molten salts has become a prevailing strategy. This research introduces an innovative transient modelling tailored for the comprehensive annual performance analysis of a solar tower power plant coupled to a two-tank TES system, incorporating molten salts as the storage medium. The modelling of the power plant is conducted using OpenModelica, a versatile software platform renowned for its capability in system-level modelling and simulation. The simulation outcomes encompass a power plant configuration boasting a turbine gross output of 110 MWe. The results of performance parameters are subsequently contrasted with those generated by commercially available software tool, effectively corroborating the accuracy and effectiveness of the proposed simulation approach. The obtained results demonstrate a favourable concurrence in the transient behaviour of performance parameters, considering heat flows, state of charge, net power, and others, with a discrepancy of less than 1 % in annual production when benchmarked against a commercial software reference. Particularly, the incorporation of the local heat loss due to assembly defects within the thermal modelling of the TES system exerts a discernible albeit relatively minor influence on the overall performance of the power plant. The occurrence of local heat loss primarily stems from distortions or imperfections within the construction, including the structure, insulation layers, or foundation, thereby creating thermal bridges between the storage fluid and the external ambient environment. This impact, while small, is not negligible, as it introduces the potential for the power block to unexpectedly shut down owing to TES system depletion, a behaviour that is challenging to simulate when neglecting local heat loss.
Enhancement of heat transfer through the incorporation of copper metal wool in latent heat thermal energy storage systems
(Elsevier, 2024-09) Ribezzo, Alessandro; Morciano, Matteo; Zsembinszki, Gabriel; Risco Amigó, Sara; Mani Kala, Saranprabhu; Borri, Emiliano; Bergamasco, Luca; Fasano, Matteo; Chiavazzo, Eliodoro; Prieto Ríos, Cristina; Cabeza, Luisa F.; Universidad de Sevilla. Departamento de Ingeniería Energética; European Union (UE). H2020; Ministerio de Ciencia e Innovación (MICIN). España; Agencia Estatal de Investigación. España; Generalitat de Catalunya; Universidad de Sevilla. TEP143: Termotecnia
The design of thermal energy storage (TES) tank is the key part that can limit charging and discharging process. Most research findings highlight that the use of fins augments the heat transfer rate. This work experimentally investigates the use of aligned copper wools as fillers to enhance the thermal performance of a lab-scale shell-and-tube TES tank filled with phase change material (PCM). Two copper wools with different fibre thicknesses were chosen and discretely laid around the TES tank tubes in two design patterns. Accordingly, five shell-and-tube TES tank configurations were obtained, including the reference, for performance evaluation. The TES tank was loaded with n-octadecane as PCM for all the cases studied. The results showed up to a 16 % reduction in melting time with the inclusion of copper wool. The TES tank significantly increased the mean power during charging (53 %) and discharging (205 %). The addition of metal wool into the TES tank enables the PCM to release the heat at a constant temperature during the entire phase transition process. And the overall efficiency of the TES tank was found to get improved. Therefore, a copper wool integrated TES tank would be a beneficial addition to thermal energy storage systems.
PVT potential for a small-scale brewing process: A case study
(Elsevier, 2024-08) Pino, Alan; Pino Lucena, Francisco Javier; Cabello González, Gracia María; Navas Herrera, Sergio Jesús; Guerra Macho, José Julio; Universidad de Sevilla. Departamento de Ingeniería Energética; Universidad de Sevilla. TEP:143: Termotecnia
Reported cases of solar energy integration in industrial brewing processes are mostly found in medium-sized and large breweries. Given the brewing process's requirement for low-temperature heat and cold, a solar-assisted polygeneration system proves to be suitable. Microbreweries typically lack steam boilers, often relying on gas burners or electric resistors for heat supply. Additionally, small vapor-compression chillers are common for cold production. A hybrid photovoltaic-thermal (PVT) system has the potential to preheat brewing water and generate electricity. This study evaluates the energy output and economic viability of PV and PVT systems installed on a microbrewery's roof, utilizing actual heat and cold load profiles from a Spanish microbrewery. Energy yield calculations are based on simulations using TRNSYS. In a hot coastal Mediterranean location, the largest proposed PVT system could cover up to 26.4 % of electric consumption (self-consumption) and fulfill 47.6 % of the heat demand for water preheating. These figures decrease to 23.2 % (electricity) and 42.4 % (heat) for an inland temperate Mediterranean site, and to 27.6 % (electricity) and 35.7 % (heat) for a central European location. While the electric yield matches between a high-efficiency PV system and similar-sized PVT systems (difference between −1.3 % and −10 % for unglaze, and −5% to −15 % for glaze), the PVT's energy yield surpasses PV by up to 67 %, location and system size dependent, when considering useful heat. However, the PVT system is less economic-effective compared to PV, resulting in a payback period exceeding 12 years. Research and development efforts should focus on improving manufacturing techniques to reduce system costs
Quantitative analysis of high-frequency radiometric databases. Application to the case of Seville
(Springer, 2024) Pérez Aparicio, Elena; Moreno Tejera, Sara; Silva Pérez, Manuel Antonio; Lillo Bravo, Isidoro; Universidad de Sevilla. Departamento de Ingeniería Energética; Universidad de Sevilla. TEP122: Termodinámica y Energías Renovables
The short-term variability of solar resource is one of the main challenges faced by the large-scale implementation of photovoltaic (PV) systems today; this will increase as the installed power of solar PV increases. To evaluate its influence on electrical grid operation, it is essential to analyse the variability of solar resource based on high-frequency data, 30 s and shorter. In this study, the high-frequency measurements of Global Horizontal Irradiation (GHI) and Direct Normal Irradiation (DNI) recorded every 5 s at the radiometric station of the University of Seville for 20 years are analysed and characterised. For this purpose, a corrected database for GHI and DNI was obtained from the application of a correction methodology. To understand the reliability of this database it is required to know its uncertainty. This work proposes a methodology to quantify the uncertainty of high-frequency radiometric databases whose wrong data have been corrected. Applying it, the daily uncertainty is 2.69% for GHI and 4.07% for DNI. To characterize the distribution of the database, the distribution of high frequency kt and kb indices are modelled providing the fitting parameters. To characterize the variability of high-frequency measurements, transition matrices are proposed, which allow identifying both the magnitude and frequency of jumps. The results obtained show that jumps of up to 800 W/m2 occur in both GHI and DNI. In the case of GHI, the percentage of jumps equal to or greater than 500 W/m2 is 1.36%, about 43,000 jumps in a year in measurements every 5 s.
Multi-Objective optimisation of oil demisters geometry for Ultra-Low charge ammonia chillers
(Elsevier, 2024-08) Expósito Carrillo, José Antonio; Gomis Payá, Ignacio; Salmerón Lissén, José Manuel; Sánchez de la Flor, Francisco José; Ruiz Pardo, Álvaro; Universidad de Sevilla. Departamento de Ingeniería Energética; Ministerio de Ciencia e Innovación (MICIN). España; Universidad de Sevilla. TEP143: Termotecnia
Driven by global climate objectives, the pursuit for eco-friendly refrigeration solutions has catalysed impressive advancements in the sector. Ammonia, a historically utilized refrigerant, is now widely adopted in light industrial applications, largely due to the growth of Ultra-Low Charge package chillers. Opportunities, however, persist for refining system components to further diminish refrigerant charge, fostering safer and more efficient solutions. This paper focuses on optimizing the oil separator geometry of an experimentally tested Ultra-Low Charge ammonia chiller. The principal aim and novelty is to lower the specific refrigerant charge while enhancing the separation efficiency and the pressure drop performance. Assessing the separation efficiency involves an analytical model grounded in the “orbit-equilibrium” concept, while the pressure drop is evaluated with consideration of liquid particles presence. Utilizing the validated model, a Multi-Objective Optimization process driven by the eaMuPlusLambda algorithm produces geometries able to reduce the cut-size diameter by 1.4 % up to 15.4 %, pressure drop by 66.7 % up to 89.1 %, and internal volume by 51.3 % up to 68.9 %, compared to the baseline setup. This accomplishment stems from meaningful parameter adjustments, encompassing a 12.1 – 30.0 % decrease in the main diameter, 35.8 % reduction in the main height, 25.4 – 41.2 % contraction in the outlet diameter, 10.9 – 47.1 % augmentation in the inlet diameter, and the vortex finder elimination. Consequently, this translates to a 5% to 14% decrease in the chiller’s specific charge. This study intends an initial step in optimizing oil separators for Ultra-Low Charge ammonia chillers, presenting prospects for specific charge reduction and inciting further exploration through experimental testing or Computational Fluid Dynamics.
Experimental analysis of NOx reduction through water addition and comparison with exhaust gas recycling
(Elsevier, 2019-02) Serrano Reyes, Javier; Jiménez-Espadafor Aguilar, Francisco José; Lora, A.; Modesto-López, Luis B.; Gañán-Calvo, Alfonso M.; López-Serrano, J.; Universidad de Sevilla. Departamento de Ingeniería Aeroespacial y Mecánica de Fluidos; Universidad de Sevilla. Departamento de Ingeniería Energética; Ministerio de Economía y Competitividad (MINECO). España; Ministerio de Educación y Ciencia (MEC). España; Universidad de Sevilla. TEP137: Máquinas y Motores Térmicos; Universidad de Sevilla. TEP219: Física de Fluidos y Microfluídica
The diesel engine requirements regarding the reduction of exhaust emissions, especially nitrogen oxide (NOx) and particulate matter (PM) are becoming more stringent year by year. A current method used for NOx control is exhaust gas recirculation (EGR). However, this approach significantly increases the production of soot for medium and high rates. Water addition can also be used for NOx control, achieving 50% NOx reduction rates in relation to EGR with a lower production of soot and without additional carbon monoxide (CO) and hydrocarbons (HC) substantially. This paper analyses the weaknesses and the strengths of adding water into the intake manifold with a flow-blurring injector for NOx reduction on a current technology diesel engine with multiple injection thorough a proprietary tool for heat release rate that considered real gas properties. A reduction of NOx emissions around 60–70% was achieved with water injection at different loads and speeds. Besides, a clear relationship was established between the minimum attainable NOx emission and the thermal capacity of the load (air plus water), this result stablish the hard relationship between NOx formation and combustion chamber temperature and therefore shows the strong dependence of the Zeldovich mechanism.
Classification of days according to DNI profiles using clustering techniques
(Elsevier, 2017-04) Moreno Tejera, Sara; Silva Pérez, Manuel Antonio; Ramírez Santigosa, Lourdes; Lillo Bravo, Isidoro; Universidad de Sevilla. Departamento de Ingeniería Energética; Universidad de Sevilla. TEP122: Termodinámica y Energías Renovables
A methodology to classify days as a function of the state of the sky for Concentrated Solar Power (CSP) plant operation is proposed. For this purpose, three indexes are used to characterize the energy, variability and time distribution of the DNI and to define the type of days by means of clustering techniques. Two sets of indexes are tested and compared. The energy of days is represented by the transmittance index, kb. Two indexes are used to characterize the variability of the DNI: persistence index of the instantaneous kb values (POPD) and Variability Index (VI). Equivalent indexes have been previously used to classify the types of days using Global Horizontal Irradiation (GHI). A novel index to define the time distribution of the DNI daily energy is introduced. Clustering analysis is applied to thirteen years (2000–2012) of 10-min DNI measurements recorded in Seville (37.40°N, 6.01°W) by the Group of Thermodynamics and Renewable Energy (GTER) at the University of Seville. The k-medoids algorithm is used for cluster analysis. Through the use of well-known internal validity indexes and with the help of the L-method, the optimum number of clusters (types of days) is found to be 10. The results are compared with the assessment carried out by five experts on a reference set composed of DNI daily curves from two years (2010 and 2011). This comparison reveals a better coincidence when the clustering is performed using VI.
Evaluation of classification methods according to solar radiation features from the viewpoint of the production of parabolic trough CSP plants
(Elsevier, 2018-06) Moreno Tejera, Sara; Silva Pérez, Manuel Antonio; Ramírez Santigosa, Lourdes; Lillo Bravo, Isidoro; Universidad de Sevilla. Departamento de Ingeniería Energética; Universidad de Sevilla. TEP122: Termodinámica y Energías Renovables
In this work, the representativeness of the day-types classified according to the solar radiation features by two classification methods is evaluated from the perspective of the production of two parabolic trough plants. A new methodology to characterize the representativeness of the day-types using a novel index is proposed, based on the characterization of the daily production. As a previous step to the use of a classification method, the evaluation methodology helps to select the most adequate model and to improve it from the perspective of a concentrated solar power project. This methodology is applied to 16 years of measurements from Seville (Spain) classified by two methods: a method based on daily clearness index values (kt), and a method that uses clustering techniques to define the day-types. From the application of the methodology to the clustering classification some improvements are identified and applied. As a result, from the 10 day-types identified by the clustering classification method a new classification based on 8 day-types with different features for each type of plant is proposed. The use of this classification to estimate the daily yield outperforms the results obtained with the kt classification, with a mean yearly RMSE value more than 20% lower.
Solar resource assessment in Seville, Spain. Statistical characterisation of solar radiation at different time resolutions
(Elsevier, 2016-07) Moreno Tejera, Sara; Silva Pérez, Manuel Antonio; Lillo Bravo, Isidoro; Ramírez Santigosa, Lourdes; Universidad de Sevilla. Departamento de Ingeniería Energética; Universidad de Sevilla. TEP122: Termodinámica y Energías Renovables
The characterisation of the solar resource of a site is essential for different phases of solar energy projects. While only rough estimates of yearly levels of solar irradiation (global or direct, depending on the technology) are needed in their very early stages, the required depth of the assessment increases as the project advances, including long-term estimates that can only be obtained through a statistical analysis of a continuous and long-term database of solar radiation measurements. This paper provides the results of a statistical analysis of thirteen years of Global Horizontal Insolation (GHI) measurements and Direct Normal Insolation (DNI) measurements from Seville, Spain (37.4°N, 6.05°W) at different time resolutions, i.e. from annual to nearly instantaneous (5-s). In addition, a new methodology for gap-filling is proposed which keeps the frequency distribution of the original dataset and reduces the uncertainty of the aggregated values (hourly, daily, monthly, yearly) due to the gaps. Some relevant results of this analysis are: (a) the instantaneous values of GHI and DNI have bimodal distributions, although of different characteristics, in agreement with the results of some works developed in similar climate locations; (b) the frequency distributions of the instantaneous and 10-min clearness index (kt) and beam fraction index (kb) are almost identical, suggesting 10 min as a good time resolution for the simulation of Concentrated Solar Power (CSP) systems oriented to feasibility analyses; (c) the distributions of hourly kt and kb values, show significant differences with respect to the instantaneous ones; (d) the difference between the percentile 99 (P99) of the instantaneous GHI and its maximum value is very high, because of the enhancement effect due to the cloud reflection, while for the DNI the corresponding values are much closer. The comparison with the results of other locations of similar climates suggest that these results can be extrapolated, at least, to other locations of similar climates. Other, more site-specific, results are: (a) the number of typical overcast days in summer is extremely low, while it takes its maximum value in December, suggesting this month as the best for maintenance operations that require halting the operation of CSP plants; (b) the annual mean daily values are 4.98 kW h m−2 for GHI and 5.68 kW h m−2 for DNI, with a low inter-annual variability and a greater monthly variability which depends on the season. The monthly and yearly average values from Seville have been compared with three long-term databases derived from satellite images. The best concordance in GHI values is found with NASA’s Surface Meteorology and Solar Energy (NASA SSE), but NASA SSE provides significantly higher DNI values compared to the Seville database. A comparison of one year of DNI and GHI measurements recorded at two locations, Durban (South Africa) and Abu Dhabi (United Arab Emirates), with high solar potential is also addressed.
A proposed methodology for quick assessment of timestamp and quality control results of solar radiation data
(Elsevier, 2015-06) Moreno Tejera, Sara; Ramírez Santigosa, Lourdes; Silva Pérez, Manuel Antonio; Universidad de Sevilla. Departamento de Ingeniería Energética; Universidad de Sevilla. TEP122: Termodinámica y Energías Renovables
To evaluate the solar resource at a site, the period of measurements analyzed must be as long as possible. In solar radiation database, a quality control that identifies errors and labels the data by means of different flags or indicators is fundamental. Reading and interpretation of flagged data can usually be tedious due to the large numbers of data that have to be handled. This article presents a new type of graphical representation that facilitates the identification and interpretation of data quality by using their flagged values. These graphs represent the results of quality control (QC) for up to one year of measurements with any recording frequency on the same graph, making it easier to identify frequent errors such as incorrect timestamp. The utility of this visual tool to identify the most common errors found in quality control of solar radiation data is exemplified by applying it to the QC performed to 4 databases registered at different locations in Spain. The quality control process followed the recommendations of the Baseline Solar Radiation Network (BSRN).
Probabilistic assessment of concentrated solar power plants yield: The EVA methodology
(Elsevier, 2018-08) Fernández Peruchena, Carlos María; Vignola, Frank; Gastón, Martín; Silva Pérez, Manuel Antonio; Moreno Tejera, Sara; Universidad de Sevilla. Departamento de Ingeniería Energética; Universidad de Sevilla. TEC122: Termodinámica y Energías Renovables
Understanding the long-term temporal variability of solar resource is fundamental in any assessment of solar energy potential. The variability of the solar resource (as shown by historical solar data) plays a significant role in the statistical description of the future performance of a solar power plant, thus influencing its financing conditions. In particular, solar-power financing is mainly based on a statistical quantification of the solar resource. In this work, a methodology for generating meteorological years representative of a given annual probability of exceedance of solar irradiation is presented, which can be used as input in risk assessment for securing competitive financing for Concentrating Solar Thermal Power (CSTP) projects. This methodology, which has been named EVA, is based on the variability and seasonality of monthly Direct Normal solar Irradiation (DNI) values and uses as boundary condition the annual DNI value representative for a given probability of exceedance. The results are validated against a 34-year series of net energy yield calculated at hourly intervals from measured solar irradiance data and meteorological, and they are also supplemented with the analysis of uncertainty associated to the probabilities of exceedance estimates. Relations between DNI and CSTP energy yields at different time scales are also analyzed and discussed.
A statistical characterization of the long-term solar resource: Towards risk assessment for solar power projects
(Elsevier, 2016-01) Fernández Peruchena, Carlos María; Ramírez, Lourdes; Silva Pérez, Manuel Antonio; Moreno Tejera, Sara; Universidad de Sevilla. Departamento de Ingeniería Energética; Universidad de Sevilla. TEP192: Termodinámica y Energías Renovables
In this study, a statistical characterization of annual solar irradiation series is presented which can be used as input in risk assessment for securing competitive financing for solar power projects. To perform this task, an analysis of annual Direct Normal solar Irradiation (DNI) and Global Horizontal solar Irradiation (GHI) probability density functions has been carried out, showing that annual DNI and GHI distributions are described by Weibull and normal functions, respectively. Normal fitting of annual GHI distributions yields uncertainties in mean parameter below 1%, and uncertainties in standard deviation parameter of ∼12%. Weibull fitting of annual DNI distributions yields uncertainties in scale parameter of ∼1%, and uncertainties in shape parameter of ∼15%. For each location analyzed in this study, the estimated regression coefficients (and their uncertainties) of annual solar irradiation distributions fitting are used to obtain percentile values and their respective associated uncertainties. The greatest uncertainties are associated with the lower percentiles, being 1st percentile uncertainty ∼1.6% and ∼4% for GHI and DNI respectively. Finally, according to the results obtained in this work, a minimum of 11 years of GHI and 15 years of DNI are recommended for their statistical characterization.
Failure analysis of an overhead valve train system in urban buses
(Elsevier, 2019-02) Vélez Godiño, José Antonio; Torres-García, Miguel; Jiménez-Espadafor Aguilar, Francisco José; Palomo Guerrero, Daniel; Universidad de Sevilla. Departamento de Ingeniería de la Construcción y Proyectos de Ingeniería; Universidad de Sevilla. Departamento de Ingeniería Energética
This work is focused on the study of the failures identified in the valve train system of two different types of engines, one diesel and one fed by compressed natural gas, both pertaining to a fleet of urban buses. The studied failure has been reported in >20 different units, the affected elements being both the cams (material removal at the cam nose) and the tappets (hard plate removal and strong tappet core deformation) and requiring the vehicles to be out of service until being repaired. In order to determine the root cause of the failure, the performed analyses have covered the lube oil characteristics, the kinematic chain status, highlighting the review of the camshaft modal response and the behaviour of the valves springs, and, finally, the verification of the selection regarding both the material and heat treatment of the camshaft.
Innovative power train configurations for aircraft auxiliary power units focused on reducing carbon footprint
(Elsevier Masson, 2020-11) Jiménez-Espadafor Aguilar, Francisco José; Vélez Godiño, José Antonio; Universidad de Sevilla. Departamento de Ingeniería de la Construcción y Proyectos de Ingeniería; Universidad de Sevilla. Departamento de Ingeniería Energética; Ministerio de Economía y Competitividad (MINECO). España
Auxiliary power units constitute a non-negligible source of pollution not only in flight conditions but also at airports and their surrounding areas. This work compiles a technical feasibility assessment focused on the analysis of innovative alternatives to the traditional aircraft gas turbine based auxiliary power unit arrangement. The proposed innovations involve both new power train configurations and the use of different fuels, with the purpose of reducing both the primary energy consumption and the environmental impact of these systems. The core innovation proposed here consists in the use of a supercharged rotary engine as an alternative configuration to traditional auxiliary power units in aircraft. The rotary engine can achieve higher thermal efficiencies than gas turbines, which corresponds to a lower specific fuel consumption and, thus, a lower carbon footprint. Additionally, the proposed alternatives will involve hybrid configurations, providing thermal energy generation with electrical storage devices. Finally, the assessed arrangements will be based on the “more electric aircraft” concept, which implies a simplification of the aircraft non-propulsive power system design and allows the addition of batteries to the generating unit. In order to perform this assessment, different thermal models and simulations have been developed, allowing the quantification of the improvements related to the alternative proposed configuration.
Experimental analysis of late direct injection combustion mode in a compression-ignition engine fuelled with biodiesel/diesel blends
(Elsevier, 2022-01-15) Vélez Godiño, José Antonio; Torres-García, Miguel; Jiménez-Espadafor Aguilar, Francisco José; Universidad de Sevilla. Departamento de Ingeniería de la Construcción y Proyectos de Ingeniería; Universidad de Sevilla. Departamento de Ingeniería Energética; Junta de Andalucía
A compression ignition reciprocating internal combustion engine has been modified to allow operation with late direct injection of rapeseed biodiesel fuel blends. The purpose of these modifications is to reduce both the engine's carbon footprint and emission of nitrogen oxides and soot, without decreasing performance or using expensive emission post-treatment systems. The experimental part of this work is based on the measurement of the main pollutants being emitted and the analysis of the combustion process, which is accomplished by the study of the heat release rate curve. This curve is derived from the experimental chamber pressure data, in combination with a zero-dimensional thermodynamic model assuming a perfect mixing reactor with temporal variation in volume and chemical composition, temperature-dependent properties and heat losses. The analysis of the experimental results allows deepening the knowledge of the combustion process in a compression ignition engine with late direct injection using different biodiesel blends. There is a significant reduction (>50%) of emissions of nitrogen oxides in comparison with the original configuration. This allows considering the modified configuration as an advanced combustion mode, intermediate between conventional compression ignition engines and homogeneous charge compression ignition combustion mode.
Simulation of HCCI combustion in air-cooled off-road engines fuelled with diesel and biodiesel
(Elsevier, 2018-08) Vélez Godiño, José Antonio; Jiménez-Espadafor Aguilar, Francisco José; Torres-García, Miguel; Universidad de Sevilla. Departamento de Ingeniería de la Construcción y Proyectos de Ingeniería; Universidad de Sevilla. Departamento de Ingeniería Energética; Ministerio de Economía y Competitividad (MINECO). España
The present work describes the elaboration of a predictive tool consisting on a phenomenological multi-zone model, applicable to the simulation of HCCI combustion of both diesel and biodiesel fuels. The mentioned predictive tool is created with the aim to be applied in the future to perform engine characterization during both pre-design and post-design stages. The methodology applied to obtain the proposed predictive model is based on the generation of an analytical mechanism that, given a set of regression variables representing the engine operative conditions, provides the user with the optimal figures for the scaling coefficients needed to particularize both the ignition delay and the heat release rate functional laws, which rule the combustion development in the proposed multi-zone model for HCCI engines. The validation of the proposed predictive multi-zone model consists on the comparison between chamber pressure curve derived from the simulations and experimental data based on a DEUTZ FL1 906 unit modified in order to allow HCCI combustion operation mode using diesel EN590 and rapeseed biodiesel. Finally, evidences of the capabilities of the proposed model to be used as a predictive tool applicable to the analysis of off-road engines under HCCI conditions are provided, consisting in the characterization and optimization of the operational maps related to both Brake Specific Fuel Consumption and NOx emissions.
Simplified model to correct thermopile pyranometer solar radiation measurements for photovoltaic module yield estimation
(Elsevier, 2020-02) Lillo Bravo, Isidoro; Larrañeta, Miguel; Núñez Ortega, Elías; González Galván, Rocío; Universidad de Sevilla. Departamento de Ingeniería Energética; Universidad de Sevilla. TEP122: Termodinámica y Energías Renovables
This article presents and evaluates the performance of a simplified model to generate 10-min global horizontal synthetic solar radiation data that would correspond to the measurements of a calibrated photovoltaic monocrystalline cell. The model, which only requires global horizontal solar radiation data measured with a thermopile pyranometer as input, is based on the characterization of the relation between the data measured with a thermopile pyranometer and a calibrated cell as a function of the sky condition and the solar elevation. We have used an extensive solar radiation database for the location of Seville (Spain) for the training of the model that has been tested in Seville and Lancaster (USA), showing satisfactory results and suggesting a global applicability with no local adaptation or calibration requirement. The model shows the best results for high levels of solar radiation and solar elevations and decreases its performance on days with high levels of diffuse irradiation and for very low solar elevation angles. We obtain a daily RMSD between measured and synthetic data of 1.9% in Seville and 5.2% in Lancaster. The frequency distribution of the synthetic datasets shows a KSI of 3.7 W/m2 in Seville and 8.6 W/m2 in Lancaster. We also evaluate the ramp rates of measured and synthetic sets through the KSI of the measured and synthetic ramp rates sets, obtaining 0.11 W/m2۰min in Seville and 0.20 W/m2۰min in Lancaster.
Generation of synthetic solar datasets for risk analysis
(Elsevier, 2019-07) Larrañeta, Miguel; Fernández Peruchena, Carlos María; Silva Pérez, Manuel Antonio; Lillo Bravo, Isidoro; Grantham, A.; Boland, J.; Universidad de Sevilla. Departamento de Ingeniería Energética; Junta de Andalucía; Universidad de Sevilla. TEP122: Termodinámica y Energías Renovables
In this paper, we present a method for the synthetic generation of long-term time series of coupled 1-min global horizontal solar irradiance (GHI) and direct normal solar irradiance (DNI). This method requires an input of 10–15 annual time series of hourly DNI and GHI values that can be retrieved from satellite-based irradiance databases, and produces 100 years of 1-min solar radiation values that can be used for risk analysis or as input for solar plants performance simulation in a wide range of scenarios. The method consists of the conjunction of three steps. The first one, based on a stochastic procedure, is used to generate 100 years of monthly DNI and GHI values. The second step consists of the subsequent generation of daily irradiation values. To that end we have used a bootstrapping technique. The synthetic daily sequences have the same serial correlation structure as the observed data. The last step consists of the generation of 100 years of 1-min solar irradiance data out of the daily values based on the non-dimensionalization of the daily profiles by the clear sky envelope approach. The method has been applied for the location of Seville showing satisfactory results in terms of cumulative distribution functions (CDFs) of the synthetic data. We obtain an average monthly KSI (Kolmogorov-Smirnov test integral) index of 0.11 kWh/m2 for GHI and 0.26 kWh/m2 for DNI. The minimum KSI value is 0.07 kWh/m2 for GHI and 0.15 kWh/m2 for DNI obtained in January. The maximum KSI value is 0.19 kWh/m2 for GHI and 0.34 kWh/m2 for DNI obtained in June and August respectively.
Assessing the feasibility of retrofitting parabolic trough power plants with integrated photovoltaic systems for grid integration
(Elsevier, 2024-11) López Álvarez, José Antonio; Larrañeta, Miguel; Lillo Bravo, Isidoro; Silva Pérez, Manuel Antonio; Universidad de Sevilla. Departamento de Ingeniería Energética; Ministerio de Ciencia e Innovación (MICIN). España; European Union (UE); Junta de Andalucía; Universidad de Sevilla. TEP122: Termodinámica y Energías Renovables
This study addresses the optimization issues of a Parabolic Trough (PT) power plant by retrofitting it with a photovoltaic (PV) plant to find the optimal configuration for already operational Concentrated Solar Power (CSP) plants. A simulation tool based on Modelica and OpenModelica has been developed to analyze and optimize the performance of CSP/PV hybrid plants under several grid limitation scenarios, one of which includes an electrical heater to utilize the PV surplus, considering the impact of hybridization on their overall performance and therefore also on their economic viability. The results obtained provide clear insights into how different configurations of CSP and PV plants interact and how certain variables, such as the PV ratio and thermal storage size, influence the overall performance of the hybrid plant.

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