Carnot Cycle and Heat Engine Fundamentals and Applications II

This second Special Issue connects both the fundamental and application aspects of thermomechanical machines and processes. Among them, engines have the largest place (Diesel, Lenoir, Brayton, Stirling), even if their environmental aspects are questionable for the future. Mechanical and chemical processes as well as quantum processes that could be important in the near future are considered from a thermodynamical point of view as well as for applications and their relevance to quantum thermodynamics. New insights are reported regarding more classical approaches: Finite Time Thermodynamics F.T.T.; Finite Speed thermodynamics F.S.T.; Finite Dimensions Optimal Thermodynamics F.D.O.T. The evolution of the research resulting from this second Special Issue ranges from basic cycles to complex systems and the development of various new branches of thermodynamics

Optimization of environmentally friendly solar assisted absorption cooling systems

La optimización de los sistemas de conversión de energía gana cada vez más importancia debido a su impacto ambiental y los limitados recursos de combustibles fósiles. Entre estos sistemas los de refrigeración tienen una contribución creciente en el consumo total de energía y en las emisiones de CO2. Los sistemas de absorción operados con energía solar son una de las alternativas más sostenibles frente a los sistemas de refrigeración convencionales. Por lo tanto, este trabajo se centra en su mejora siguiendo los métodos de optimización termo-económica y de programación matemática. El análisis exergético y la optimización termo-económica basada en el método estructural se han realizado para distintas configuraciones de ciclos de refrigeración por absorción con las mezclas de trabajo agua-LiBr y amoniaco-agua. En la sección de programación matemática se incluye la optimización multi-objetivo (frontera de Pareto), la optimización bajo incertidumbre de los precios de la energía, el uso de varios indicadores de impacto ambiental y el efecto del impuesto sobre las emisiones de CO2. Los resultados demuestran que se pueden obtener reducciones importantes del impacto ambiental frente a los sistemas convencionales. Los sistemas de refrigeración solar no sólo son atractivos para reducir el impacto ambiental, sino también pueden ser económicamente competitivos. Su implantación dependerá, en gran medida, del impuesto sobre las emisiones de CO2 y del coste de la energía.Optimizations of energy conversion systems become more important because of their environmental impact and the limitations of the fossil fuel resources. Among these systems cooling and refrigeration machines have an increasing share in the total energy consumption and contribution to CO2 emissions. Solar assisted absorption cooling systems are sustainable alternatives compared to the conventional cooling systems. Hence, this work is focused on improving the sustainability of cooling systems following the thermoeconomic optimization and mathematical programming approaches. In the first approach the energy, exergy and structural analysis are performed for different configurations of water/LiBr and ammonia/water absorption cooling cycles. In the second approach multi-objective optimization (Pareto frontier), optimization under uncertainty of energy prices, different environmental impact indicators, and the effect of CO2 emissions tax to reduce the global warming are discussed. The results of the multi-objective optimization show that a significant environmental impact reduction can be obtained. Results indicate that these systems are attractive not only to reduce the environmental impact but also in incurring the economic benefits. However, its practical impact largely depends on the CO2 emissions tax and the increase in the energy price

Thermoeconomic Analysis of Organic Rankine Cycle Using Zeotropic Mixtures

The selection of the working fluid is an important part of design and optimization of ORC system as it effects the systems efficiency, design of ORC components, stability, safety and environmental impact. Present study aims to investigate the performance of ORC system using pure working fluids and zeotropic mixtures for low temperature geothermal heat source on the basis of thermodynamic and economic parameters of ORC system. Evaporator, expander, condenser and feed pump models are developed in MATLAB. The control volume approach is adopted for evaporator and condenser model with appropriate database of heat transfer and pressure drop correlations. For comparison, pure working fluids are taken as the base case. The ORC system with pure working fluid and zeotropic mixture under same heat and sink source conditions are optimized using multi objective genetic algorithm for maximum exergy efficiency and minimum specific investment cost. The exergy efficiency of ORC system with zeotropic mixture is improved by 14.33% compared to pure working fluid. The exergy destruction in evaporator and condenser is reduced by 24~30%. The fraction of more volatile component in zeotropic mixture effected the thermal and economic performance of ORC system, for current study the mass fraction of 40% of R245fa corresponds to optimum exergy efficiency and specific investment cost. For same condensing pressure and expander power, area of evaporator for pure working fluids and zeotropic mixture is also calculated. The required heat transfer area for zeotropic mixture is approximately 13% less than required for pure working fluid

Modelling, thermoeconomic analysis and optimization of hybrid solar-biomass organic Rankine cycle power plants

The need for modern energy systems to embrace the requirements of energy security, sustainability and affordability in their designs has placed emphatic importance on exploitation of renewable resources, such as solar and wind energy, etc. However, these resources often lead to reduced reliability and dispatchability of energy systems; less-efficient conversion processes; high cost of power production; etc. One promising way to ameliorate these challenges is through hybridization of renewable energy resources, and by using organic Rankine cycle (ORC) for power generation. Thus, this PhD research project is aimed at conceptual design and techno-economic optimization of hybrid solar-biomass ORC power plants. The methodologies adopted are in four distinct phases: - First, novel hybrid concentrated solar power (CSP)-biomass scheme was conceived that could function as retrofit to existing CSP-ORC plants as well as in new hybrid plant designs. Thermodynamic models were developed for each plant sub-unit, and yearly techno-economic performance was assessed for the entire system. Specifically, the ORC was modelled based on characteristics of an existing CSP-ORC plant, which currently operates at Ottana, Italy. Off-design models of ORC components were integrated, and their performance was validated using experimental data obtained from the aforementioned real plant. - Second, detailed exergy and exergoeconomic analyses were performed on the proposed hybrid plant, in order to examine the system components with remarkable optimization potentials. The evaluation on optimization potentials considered intrinsic irreversibilities in the respective components, which are imposed by assumptions of systemic and economic constraints. This has been termed enhanced exergy and enhanced exergoeconomic analyses here. - Third, the techno-economic implications of using siloxane mixtures as ORC working fluid were investigated, with the aim of improving heat transfer processes in the ORC plant. The studied fluid pairs were actively selected to satisfy classical thermodynamic requirements, based on established criteria. - Fourth, the biomass retrofit system was optimized multi-objectively, to minimize biomass consumption rate (maximize exergetic efficiency) and to minimize exergy cost rate. Non-dominated Sorting Genetic Algorithm (NSGA-II) was adopted for multi-objective optimization. The conceptual scheme involves parallel hybridization of CSP and biomass systems, such that each is capable of feeding the ORC directly. Results showed that the proposed biomass hybridization concept would increase both thermodynamic efficiency and economic performance of CSP-ORC plants, thereby improving their market competitiveness. Total exergy destroyed and exergy efficiency were quantified for each component, and for the whole system. Overall system exergetic efficiency of about 7 % was obtained. Similarly, exergoeconomic factor was obtained for each system component, and their implications were analysed to identify system components with high potentials for optimization. Furthermore, it was observed that thermodynamic performance of the hybrid plant would be optimized by using siloxane mixtures as ORC working fluid. However, this would result in larger heat exchange surface area, with its attendant cost implications. Lastly, biomass combustion and furnace parameters were obtained, which would simultaneously optimize exergetic efficiency and exergy cost rate for the hybrid plant. In sum, a novel scheme has been developed for hybridizing solar and biomass energy for ORC plants, with huge potentials to improve techno-economic competitiveness of solar-ORC systems

PREDICTIVE CONTROL OF POWER GRID-CONNECTED ENERGY SYSTEMS BASED ON ENERGY AND EXERGY METRICS

Building and transportation sectors account for 41% and 27% of total energy consumption in the US, respectively. Designing smart controllers for Heating, Ventilation and Air-Conditioning (HVAC) systems and Internal Combustion Engines (ICEs) can play a key role in reducing energy consumption. Exergy or availability is based on the First and Second Laws of Thermodynamics and is a more precise metric to evaluate energy systems including HVAC and ICE systems. This dissertation centers on development of exergy models and design of model-based controllers based on exergy and energy metrics for grid-connected energy systems including HVAC and ICEs. In this PhD dissertation, effectiveness of smart controllers such as Model Predictive Controller (MPC) for HVAC system in reducing energy consumption in buildings has been shown. Given the unknown and varying behavior of buildings parameters, this dissertation proposes a modeling framework for online estimation of states and unknown parameters. This method leads to a Parameter Adaptive Building (PAB) model which is used for MPC. Exergy destruction/loss in a system or process indicates the loss of work potential. In this dissertation, exergy destruction is formulated as the cost function for MPC problem. Compared to RBC, exergy-based MPC achieve 22% reduction in exergy destruction and 36% reduction in electrical energy consumption by HVAC system. In addition, the results show that exergy-based MPC outperforms energy-based MPC by 12% less energy consumption. Furthermore, the similar exergy-based approach for building is developed to control ICE operation. A detailed ICE exergy model is developed for a single cylinder engine. Then, an optimal control method based on the exergy model of the ICE is introduced for transient and steady state operations of the ICE. The proposed exergy-based controller can be applied for two applications including (i) automotive (ii) Combined Heat and Power (CHP) systems to produce electric power and thermal energy for heating purposes in buildings. The results show that using the exergy-based optimal control strategy leads to an average of 6.7% fuel saving and 8.3% exergy saving compared to commonly used FLT based combustion control. After developing thermal and exergy models for building and ICE testbeds, a framework is proposed for bilevel optimization in a system of commercial buildings integrated to smart distribution grid. The proposed framework optimizes the operation of both entities involved in the building-to-grid (B2G) integration. The framework achieves two objectives: (i) increases load penetration by maximizing the distribution system load factor and (ii) reduces energy cost for the buildings. The results show that this framework reduces commercial buildings electricity cost by 25% compared to the unoptimized case, while improving the system load factor up to 17%

A study of organic Rankine cycle systems with the expansion process performed by twin screw machines

The prediction of the performance of energy systems that recover power from low grade heat is one of the most important requirements for reducing their investment cost and optimising system efficiency. The aim of this work was to study, model and analyse an Organic Rankine cycle (ORC) system using a twin screw expander to generate the power output, with HFC-245fa, as the working fluid. A software package (Power Plant Performance Prediction Program), simulating ORC system performance was therefore prepared for this purpose. Major components were represented by proper units and relations between the system’s constituents defined. The preferred analytical procedure depends on both the system complexity and the requirements of the study. In this case, the whole cycle was simulated in order to obtain a good understanding of its behaviour with the aim of estimating its optimum operating conditions. The procedure adopted was to start from a basic case and then improve it, in a realistic way, in order to evaluate the system potential. Performance indicators, like thermal efficiency, specific net output, total UA and surface of the heat exchangers, as well as the relative cost of the system all need to be taken into account but it is impossible to optimise all of them simultaneously. The design value for these parameters is therefore a matter of choice, or compromise. Efficiencies of ORC systems were calculated based on the assumption that the working fluid entered the expander as wet vapour. For the heat source and sink conditions chosen for this study, the overall cycle efficiency was estimated as approximately 6% using R245fa. This and the power output are highly dependent on the ambient air temperature when using air-cooled condensers. Allowing for a small degree of subcooling at the condenser exit, it is shown that the heat recovery should be maximised

Study of Organic Rankine Cycles for Waste Heat Recovery in Transportation Vehicles

Regulations for ICE-based transportation in the EU seek carbon dioxide emissions lower than 95 g CO2/km by 2020. In order to fulfill these limits, improvements in vehicle fuel consumption have to be achieved. One of the main losses of ICEs happens in the exhaust line. Internal combustion engines transform chemical energy into mechanical energy through combustion; however, only about 15-32% of this energy is effectively used to produce work, while most of the fuel energy is wasted through exhaust gases and coolant. Therefore, these sources can be exploited to improve the overall efficiency of the engine. Between these sources, exhaust gases show the largest potential of Waste Heat Recovery (WHR) due to its high level of exergy. Regarding WHR technologies, Rankine cycles are considered as the most promising candidates for improving Internal Combustion Engines. However, the implementation of this technology in modern passenger cars requires additional features to achieve a compact integration and controllability in the engine. While industrial applications typically operates in steady state operating points, there is a huge challenge taking into account its impact in the engine during typical daily driving profiles. This thesis contributes to the knowledge and characterization of an Organic Rankine Cycle coupled with an Internal Combustion Engine using ethanol as working fluid and a swash-plate expander as expansion machine. The main objective of this research work is to obtain and quantify the potential of Organic Rankine Cycles for the use of residual energy in automotive engines. To do this, an experimental ORC test bench was designed and built at CMT (Polytechnic University of Valencia), which can be coupled to different types of automotive combustion engines. Using these results, an estimation of the main variables of the cycle was obtained both in stationary and transient operating points. A potential of increasing ICE mechanical efficiency up to 3.7% could be reached at points of high load installing an ORC in a conventional turbocharged gasoline engine. Regarding transient conditions, a slightly simple and robust control based on adaptive PIDs, allows the control of the ORC in realistic driving profiles. High loads and hot conditions should be the starting ideal conditions to test and validate the control of the ORC in order to achieve high exhaust temperatures that justify the feasibility of the system. In order to deepen in the viability and characteristics of this particular application, some theoretical studies were done. A 1D model was developed using LMS Imagine.Lab Amesim platform. A potential improvement of 2.5% in fuel conversion efficiency was obtained at the high operating points as a direct consequence of the 23.5 g/kWh reduction in bsfc. To conclude, a thermo-economic study was developed taking into account the main elements of the installation costs and a minimum Specific Investment Cost value of 2030 €/kW was obtained. Moreover, an exergetic study showed that a total amount of 3.75 kW, 36.5% of exergy destruction rate, could be lowered in the forthcoming years, taking account the maximum efficiencies considering technical restrictions of the cycle components.Las normativas anticontaminantes para el transporte propulsado por motores de combustión interna alternativos en la Unión Europea muestran límites de emisión menores a 95 g CO2/km para el año 2020. Con el fin de cumplir estos límites, deberán ser realizadas mejoras en el consumo de combustible en los vehículos. Una de las principales pérdidas en los Motores de Combustión Interna Alternativos (MCIA) ocurre en la línea de escape. Los MCIA transforman la energía química en energía mecánica a través de la combustión; sin embargo, únicamente el 15-32% de esta energía es eficazmente usada para producir trabajo, mientras que la mayor parte es desperdiciada a través de los gases de escape y el agua de refrigeración del motor. Por ello, estas fuentes de energía pueden ser utilizadas para mejorar la eficiencia global del vehículo. De estas fuentes, los gases de escape muestran un potencial mayor de recuperación de energía residual debido a su mayor contenido exergético. De todos los tipos de Sistemas de Recuperación de Energía Residual, los Ciclos Rankine son considerados como los candidatos más prometedores para mejorar la eficiencia de los MCIA. Sin embargo, la implementación de esta tecnología en los vehículos de pasajeros modernos requiere nuevas características para conseguir una integración compacta y una buena controlabilidad del motor. Mientras que las aplicaciones industriales normalmente operan en puntos de operación estacionarios, en el caso de los vehículos con MCIA existen importantes retos teniendo en cuenta su impacto en el modo de conducción cotidianos. Esta Tesis contribuye al conocimiento y caracterización de un Ciclo Rankine Orgánico acoplado con un Motor de Combustión Interna Alternativo utilizando etanol como fluido de trabajo y un expansor tipo Swash-plate como máquina expansora. El principal objetivo de este trabajo de investigación es obtener y cuantificar el potencial de los Ciclos Rankine Orgánicos (ORC) para la recuperación de la energía residual en motores de automoción. Para ello, una instalación experimental con un Ciclo Rankine Orgánico fue diseñada y construida en el Instituto Universitario "CMT - Motores Térmicos" (Universidad Politécnica de Valencia), que puede ser acoplada a diferentes tipos de motores de combustión interna alternativos. Usando esta instalación, una estimación de las principales variables del ciclo fue obtenida tanto en puntos estacionarios como en transitorios. Un potencial de mejora en torno a un 3.7 % puede ser alcanzada en puntos de alta carga instalando un ORC en un motor gasolina turboalimentado. Respecto a las condiciones transitorias, un control sencillo y robusto basado en PIDs adaptativos permite el control del ORC en perfiles de conducción reales. Las condiciones ideales para testear y validar el control del ORC son alta carga en el motor comenzando con el motor en caliente para conseguir altas temperaturas en el escape que justifiquen la viabilidad de estos ciclos. Para tratar de profundizar en la viabilidad y características de esta aplicación particular, diversos estudios teóricos fueron realizados. Un modelo 1D fue desarrollado usando el software LMS Imagine.Lab Amesim. Un potencial de mejora en torno a un 2.5% en el rendimiento efectivo del motor fue obtenido en condiciones transitorias en los puntos de alta carga como una consecuencia directa de la reducción de 23.5 g/kWh del consumo específico. Para concluir, un estudio termo-económico fue desarrollado teniendo en cuenta los costes de los principales elementos de la instalación y un valor mínimo de 2030 €/kW fue obtenido en el parámetro de Coste Específico de inversión. Además, el estudio exergético muestra que un total de 3.75 kW, 36.5 % de la tasa de destrucción total de exergía, podría ser reducida en los años futuros, teniendo en cuenta las máximas eficiencias considerando restricciones técnicas en los componentes del ciclo.Les normatives anticontaminants per al transport propulsat per motors de combustió interna alternatius a la Unió Europea mostren límits d'emissió menors a 95 g·CO2/km per a l'any 2020. Per tal d'acomplir aquests límits, s'hauran de realitzar millores al consum de combustible dels vehicles. Una de les principals pèrdues als Motors de combustió interna alternatius (MCIA) ocorre a la línia d'escapament. Els MCIA transformen l'energia química en energia mecànica a través de la combustió; però, únicament el 15-32% d'aquesta energia és usada per produir treball, mentre que la major part és desaprofitada a través dels gasos d'escapament i l'aigua de refrigeració del motor. Per això, aquestes fonts d'energia poden ser utilitzades per millorar l'eficiència global del vehicle. Considerant aquestes dues fonts d'energia, els gasos d'escapament mostren un potencial major de recuperació d'energia residual debut al seu major contingut exergètic. De tots els tipus de Sistemes de Recuperació d'Energia Residual, els Cicles Rankine són considerats com els candidats més prometedors per millorar l'eficiència dels MCIA. No obstant, la implementació d'aquesta tecnologia en els vehicles de passatgers moderns requereix un desenvolupament addicional per aconseguir una integració compacta i una bona controlabilitat del motor. Mentre que les aplicacions industrials normalment operen en punts d'operació estacionaris, en el cas dels vehicles amb MCIA hi han importants reptes a solucionar tenint en compte el funcionament en condicions variables del motor i el seu impacte en la manera de conducció quotidiana del usuari. Aquesta Tesi contribueix al coneixement i caracterització d'un Cicle Rankine Orgànic (ORC) acoblat amb un motor de combustió interna alternatiu (MCIA) utilitzant etanol com a fluid de treball i un expansor tipus Swash-plate com a màquina expansora. El principal objectiu d'aquest treball de recerca és obtenir i quantificar el potencial dels ORCs per a la recuperació de l'energia residual en motors d'automoció. Per aconseguir-ho, una instal·lació experimental amb un ORC va ser dissenyada i construïda a l'Institut "CMT- Motores Térmicos" (Universitat Politècnica de València). Esta installació pot ser acoblada a diferents tipus de MCIAs. Mitjançant assajos experimentals en aquesta installació, una estimació de les principals variables del cicle va ser obtinguda tant en punts estacionaris com en punts transitoris. Un potencial de millora al voltant d'un 3.7% pot ser aconseguida en punts d'alta càrrega instal·lant un ORC acoblat a un motor gasolina turboalimentat. Pel que fa a les condicions transitòries, un control senzill i robust basat en PIDs adaptatius permet el control del ORC en perfils de conducció reals. Les condicions ideals per a testejar i validar el control de l'ORC són alta càrrega al motor començant amb el motor en calent per aconseguir altes temperatures d'escapament que justifiquen la viabilitat d'aquests cicles. Per tractar d'aprofundir en la viabilitat i característiques d'aquesta aplicació particular, diversos estudis teòrics van ser realitzats. Un model 1D va ser desenvolupat usant el programari LMS Imagine.Lab Amesim. Un potencial de millora al voltant d'un 2.5% en el rendiment efectiu del motor va ser obtingut en condicions transitòries en els punts d'alta càrrega com una conseqüència directa de la reducció de 23.5 g/kWh al consum específic. Per concloure, un estudi termo-econòmic va ser desenvolupat tenint en compte els costos dels principals elements de la installació i un valor mínim de 2030 €/kW va ser obtingut en el paràmetre del Cost Específic d'Inversió. A més, l'estudi exergètic mostra que un total de 3.75 kW, 36.5% de la taxa de destrucció total d'exergia, podria ser recuperat en un pròxim, considerant restriccions tècniques en els components del cicle i tenint en compte les màximes eficiències que es poden aconseguir.Royo Pascual, L. (2017). Study of Organic Rankine Cycles for Waste Heat Recovery in Transportation Vehicles [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/84013TESI

Exergy as a measure of sustainable retrofitting of buildings

This study presents a novel optimization methodology for choosing optimal building retrofitting strategies based on the concept of exergy analysis. The study demonstrates that the building exergy analysis may open new opportunities in the design of an optimal retrofit solution despite being a theoretical approach based on the high performance of a Carnot reverse cycle. This exergy-based solution is different from the one selected through traditional efficient retrofits where minimizing energy consumption is the primary selection criteria. The new solution connects the building with the reference environment, which acts as “an unlimited sink or unlimited sources of energy”, and it adapts the building to maximize the intake of energy resources from the reference environment. The building hosting the School of Architecture at the University of Navarra has been chosen as the case study building. The unique architectural appearance and bespoke architectural characteristics of the building limit the choices of retrofitting solutions; therefore, retrofitting solutions on the façade, roof, roof skylight and windows are considered in multi-objective optimization using the jEPlus package. It is remarkable that different retrofitting solutions have been obtained for energy-driven and exergy-driven optimization, respectively. Considering the local contexts and all possible reference environments for the building, three “unlimited sinks or unlimited sources of energy” are selected for the case study building to explore exergy-driven optimization: the external air, the ground in the surrounding area and the nearby river. The evidence shows that no matter which reference environment is chosen, an identical envelope retrofitting solution has been obtaine

BUBBLE-PUMP-DRIVEN SOLAR ABSORPTION AIR CONDITIONING FOR RESIDENTIAL APPLICATIONS

Large-scale heat-driven absorption cooling systems are currently available in the marketplace for industrial applications. The high temperature is required in the generator for driving this absorption chiller. For this reason, this type of chiller was originally designed to use direct-fired gas. However, the low efficiency of this cooling cycle restricts its use in small-scale applications. The concept of a solar-driven absorption chiller can satisfy the increasing demand for air conditioning without contributing greenhouse gases to the global environment. This research contributes to providing an efficient air conditioning driven by low temperature solar heat and independent of grid electricity, which may be useful in remote residential communities. The performance of 10 kW absorption and adsorption cooling systems were compared for the selection of a suitable cooling technology that can be driven by low temperature heat source such as a flat plate solar collector. Analysis revealed that under any operating conditions, the coefficient of performance (COP) of the absorption cooling system is higher. However, absorption chillers have a lower efficiency than traditional compression refrigeration systems, when used for small scale applications. Hence, energy and exergy analyses were conducted to evaluate the performance of a solar-driven air-cooled ammonia-water absorption chiller for residential air conditioning. Low driving temperature heat sources were optimized (70~80℃) and the efficiencies (COP=0.6, exergetic efficiency=32%) of the system were evaluated. The highest exergy losses were identified in the absorption process (63%) followed by the generator (13%) and the condenser (11%). In order to replace the only electrical component (pump) in an absorption chiller and make it independent of grid electricity, a solar-thermal-driven bubble pump was introduced in a vapor absorption refrigeration (VAR) cycle. This solar-thermal-driven pump can circulate the solution to the absorber and the generator to create the necessary refrigerant vapor for cooling. An analytical model of a bubble pump was developed and experimental work was conducted. Furthermore, a dimensional analysis was performed, considering bubble pump geometry and the solution properties. The bubble pump performance was defined in terms of non-dimensional parameters which can be used in all bubble-pump-driven absorption refrigeration systems. Experimental and theoretical results for a new refrigerant-absorbent solution (LiCl-H2O) were compared, and the flow regime (slug flow) was determined for the highest pump efficiency. Moreover, in order to employ the advantages of high performance, the bubble pump was incorporated into a simulation of a water-based vapor absorption refrigeration cycle. A new absorbent-refrigerant pair (LiCl-H2O) for a bubble-pump-operated VARS was proposed and a thermodynamic comparison was made between LiBr-H2O and LiCl-H2O systems. Finally, energy, exergy and advanced exergy analyses were performed on this proposed refrigeration cycle, and the exergy losses due to the internal irreversibilities of each component and the effect of the irreversibilities of the other components were determined. The avoidable exergy destruction was identified pertaining to the potential improvement of the overall system structure. The highest avoidable endogenous exergy losses occurred in the generator

Waste heat recovery with Organic Rankine Cycle (ORC) in marine and commercial vehicles Diesel engine applications

Heavy and medium duty Diesel engines, for marine and commercial vehicles applications, reject more than 50-60% of the fuel energy in the form of heat, which does not contribute in terms of useful propulsion effect. Moreover, the increased attention towards the reduction of polluting emissions and fuel consumption is pushing engine manufacturers and fleet owners in the direction of increasing the overall powertrain efficiency, still considering acceptable investment and operational costs. For these reasons, waste heat recovery systems, such as Organic Rankine Cycles (ORC), are undergoing a period of intense research and development. However, in most of engine waste heat recovery studies in literature, the engine side analysis is not considered in a detailed way, even though the engine architecture and the operational behaviour strongly influence the availability of heat sources, and their characteristics, to be recovered using heat recovery systems. As an example, the use of emission reduction strategies, such as Exhaust Gas Recirculation (EGR), can introduce an additional heat source and modify the temperatures in the engine gas lines, thus leading to new possible scenarios for the exploitation of the engine wasted heat. The scope of this work is to introduce a combined engine-waste heat recovery system analysis and design methodology, which could go beyond the traditional development approach, considering both the engine and the ORC system as a synergic and integrated powertrain. For this reason, industry-standard engine gas dynamics simulation software and thermodynamic process simulation techniques have been used and developed in order to study the combined effects and performance of engine-ORC systems in the commercial vehicle and marine sectors, addressing at the same time several development issues, such as: working fluid and layout choice, powertrain thermal management, energy utilization, turbocharging and emission reduction strategies, in the direction of a co-simulation approach, which is one of the industry\u2019s main interests, to reduce development time and costs. After a detailed literature review and modelling approach explanation, four different case studies have been proposed, to show an increasing level of integration between engine and ORC system analysis, addressing also applications which are not commonly considered in literature, such as off-highway vehicles and two-stroke ships propulsion units. The combination of energy, exergy and economic analysis, allows the developer to deeply understand the thermodynamics of the combined engine-ORC systems, addressing all the energy and exergy streams available for heat recovery, highlighting the main sources of inefficiencies in the powertrain, and proposing improvements to increase the overall system efficiency at acceptable investment and operational costs. The methodology can be, in principle and with further developments, applied to any kind of engine-waste heat recovery system powertrain. Moreover, the combined use of emission reduction strategies and new technologies, such as EGR and ORC, can allow to develop clean, but at the same time efficient, propulsion units. However, while for commercial vehicles the recovery of high temperature exhaust gas and EGR heat is more beneficial in terms of compromise between performance, system costs and packaging issues, in the case of large ship propulsion units, the recovery of lower temperature heat sources, such as coolant and scavenge air, could become very interesting for future developments, because of the high amount of heat available, even if at lower temperature levels, suitable for the use of an ORC technology. The results of the proposed case studies show a fuel consumption reduction up to around 5-10% when adopting ORC systems, depending on the application, type of engine, overall system architecture and design point chosen, showing the potential of the technology in the considered sectors