1,720,991 research outputs found
A Novel Organic Rankine Cycle (ORC) for High Temperature Applications
Full text linkThe current experimental ORC setups for long-haul Heavy Duty Diesel Engines (HDDE) are not reaching the desired fuel savings within the expected costs. Pathways to improve ORC performance and cost-effectiveness remain a major challenge facing the automotive sector. This paper presents the conceptual overview and simulation results (using Aspen HYSYS) of a novel ORC especially tailored for high temperature heat sources (300-400°C) in truck applications. With a fundamental revision of the expansion and heat transfer characteristics, the advantage of the proposed novel ORC included an equivalent performance to the conventional ORC despite a 20% reduction in the total heat transfer area and a 40% reduction in the size of the expansion machine. This resulted in a 15% improvement in the Cost/kW value of the system, whilst offering 5.1% improvement in engine thermal efficiency at highway driving conditions
Organic Rankine cycle – review and research directions in engine applications
Full text linkWaste heat to power conversion using Organic Rankine Cycles (ORC) is expected to play an important role in CO2 reductions from diesel engines. Firstly, a review of automotive ORCs is presented focusing on the pure working fluids, thermal architectures and expanders. The discussion includes, but is not limited to: R245fa, ethanol and water as fluids; series, parallel and cascade as architectures; dry saturated, superheated and supercritical as expansion conditions; and scroll, radial turbine and piston as expansion machines. Secondly, research direction in versatile expander and holistic architecture (NOx + CO2) are proposed. Benefits of using the proposed unconventional approaches are quantified using Ricardo Wave and Aspen HYSYS for diesel engine and ORC modelling. Results indicate that, the implementation of versatile piston expander tolerant to two-phase and using cyclopentane can potentially increase the highway drive cycle power by 8%. Furthermore, holistic architecture offering complete utilisation of charge air and exhaust recirculation heat increased the performance noticeably to 5% of engine power at the design point condition
Waste heat recovery using fluid bottoming cycles for heavy duty diesel engines
Full text linkA typical long-haul heavy duty Diesel engine currently rejects up to 50% of the total fuel energy in the form of heat. Due to increasing CO2 emissions and fuel costs, there is a growing interest in techniques that can even partially utilise this wasted resource to improve the overall system efficiency. Fluid Bottoming Cycles (FBC) including Rankine and organic Rankine cycles offer one means towards converting waste heat into usable power. This thesis investigates the potential of FBCs to improve the net power of two computationally modelled (Ricardo WAVE V8.1) 10 litre engine platforms operating at Euro 6 emission levels. The heat to power conversion potential of a FBC largely depends on the selected working fluid, its associated cycle operating mode and the system architecture. Firstly, a detailed systematic methodology for the selection and evaluation of pure working fluids was developed and applied using an advanced chemical process modelling tool (Aspen HYSYS V7.3). Using cycle and fluid fundamentals, screening criteria, and ranking indices, the methodology identified ethyl iodide, methanol, R30, acetone, R152 and E152a as the most suitable fluids amongst the 1800 synthetic, organic and inorganic fluids. Secondly, by varying the expansion inlet parameters, simulations were conducted using 10 pure, dry, isentropic and wet working fluids. The aim was to reduce cycle irreversibilities, highlight the significant sensitivity and performance results, provide directions for practical implementation, and offer new opportunities in energy conversion. For the low, medium and high thermal boundary conditions respectively, liquid expansion (E152a), low pressure limited superheat expansion (methanol, R30, acetone) or dry supercritical expansion (R152), and high pressure limited superheat expansion (using the high temperature organic fluids) were identified as techno-economic optimum. These optimal ORC operating modes achieved efficiencies 65-77% of the theoretical cycle limits. Finally, 13 combinations of thermal and sub-system architectures were methodically analysed and classified in terms of their level of complexity, average system power and relative size. To provide tailored solutions, the pure working fluid methodology was additionally adapted to examine over 750 water blends and 700 organic blends. Aqueous blends of 3-Methyl-1-Butanol and 1-propanol were found to be best suited to the dual pressure and the dual cycle systems. Furthermore, the ethanol-toluene blend was preferred for the high temperature recuperated cycle. The dual cycle system (aqueous blend and E152a combination) showed the maximum potential and produced an average of 7.5% of additional engine crankshaft power
An innovative Organic Rankine Cycle system for integrated cooling and heat recovery
Full text linkConverting a portion of the waste heat into usable power by implementing Rankine and Organic Rankine Cycles (ORC) on long-haul trucks is seen as a potential way to improve the overall system efficiency. To identify techno-economical heat sources across the drive cycle of a Heavy Duty Diesel Engine (HDDE), an energy and exergy analysis was performed on all the available heat streams. As a result, to recover the combined exhaust gases and coolant heat, a reference cascade system was analysed. Owing to the nature of this application, a size vs. performance optimisation was performed for the cascade system utilising water and R245fa fluid combination. Despite a 1.8% Brake Thermal Efficiency (BTE) improvement, the key consideration in the research and development efforts for ORC systems was identified as the investigation of technical paths that may improve the practicality of such a heat-to-power conversion concept. For this, simple holistic solutions were considered vital to meet the impending CO2 regulations. To provide a potential solution, an innovative dual-pressure ORC system is therefore proposed to partially address the shortcomings of the cascade system. This innovative system is a function of new working fluids (i.e. water blends), its associated cycle operating mode and a novel architecture (i.e. direct engine block heat recovery). A screening and evaluation methodology applied to water–organic blends is presented. Simulations conducted in Aspen HYSYS V8 showed that, compared to the reference cascade system, the proposed dual-pressure system has the potential to deliver an average of 20% improvement in the system power, a 50% reduction in the total heat exchanger footprint, and a reduced system complexity. These advantages bode well for an integrated and relatively compact engine cooling and exhaust heat recovery solution for future automotive HDDEs. Implementation of the proposed system at mid-speed high-load engine operating condition increased the overall BTE from 41.4% to a maximum of 43.6%
An innovative organic Rankine cycle approach for high temperature applications
Full text linkOrganic Rankine Cycles (ORC) using toluene and hexamethyldisiloxane (MM) are put forward as a means of improving the efficiency of automotive heavy duty engines, and provide a reference for comparison in this study. Despite an efficiency improvement potential of 4–4.7%, the current ORC approach is not reaching the required fuel savings within the expected costs. As such, innovative pathways to improve the ORC performance and cost-effectiveness are of great importance to the research community. This paper presents a partial solution by means of a conceptual overview and simulation results for ORCs especially tailored for high-temperature applications. A fundamental revision of the heat transfer and expansion characteristics is presented, without increasing the system integration complexity. These characteristics are attributed to the use of formulated organic blends with toluene and MM as a significant blend component. The developed 22 criteria blend screening methodology is presented. Simulation results show that for an equivalent expansion volume flow ratio, and product of heat transfer coefficient and area, the blends offer a 22–24% improvement in the net power. This resulted in a 15–18% cost savings compared to the reference ORC. The simulations were conducted in Aspen HYSYS V8 using the Peng-Robinson and Wilson fluid property packages
A Novel Integrated Cooling and Heat Recovery System Using Organic Rankine Cycle for Diesel Engines
Full text linkDiesel engines offer at least two sources for heat recovery, namely, engine coolant and exhaust gases. The continued trend of cooler engine intake temperatures and engine downsizing now means that the charge air cooling has additionally become a noticeable load on the engine cooling module. There exists key challenges in integrating multiple heat sources, and hence, heat recovery has been typically suggested as an add-on solution using either high temperature heat (i.e. exhaust gases) or low temperature heat (i.e. engine coolant). This paper proposes a novel process integration, termed, the dual process system, to recover exhaust heat and also provide cooling for the charge air. This system is a function of innovative approaches in system architecture (non-isothermal cascade condenser, liquid expander), working fluids (water-organic zeotrope, environment friendly refrigerant) and cycle operation (trilateral flash cycle). The system is simulated using an advanced chemical process modelling tool, Aspen HYSYS. As a case study, steady-state heat recovery was considered at the rated condition from a 12.8 litre engine model. Simulation results showed that the use of the dual process system on new engine platforms can potentially offer 7.2% of additional engine crankshaft power. This corresponded to a 55% increase in power generation compared to the two conventional independent heat recovery cycles targeting the high temperature and the low temperature heat sources
A study of organic Rankine cycle systems with the expansion process performed by twin screw machines
No full textThe 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
A Novel Integrated Cooling and Heat Recovery System Using Organic Rankine Cycle for Diesel Engines
Full text linkDiesel engines offer at least two sources for heat recovery, namely, engine coolant and exhaust gases. The continued trend of cooler engine intake temperatures and engine downsizing now means that the charge air cooling has additionally become a noticeable load on the engine cooling module. There exists key challenges in integrating multiple heat sources, and hence, heat recovery has been typically suggested as an add-on solution using either high temperature heat (i.e. exhaust gases) or low temperature heat (i.e. engine coolant). This paper proposes a novel process integration, termed, the dual process system, to recover exhaust heat and also provide cooling for the charge air. This system is a function of innovative approaches in system architecture (non-isothermal cascade condenser, liquid expander), working fluids (water-organic zeotrope, environment friendly refrigerant) and cycle operation (trilateral flash cycle). The system is simulated using an advanced chemical process modelling tool, Aspen HYSYS. As a case study, steady-state heat recovery was considered at the rated condition from a 12.8 litre engine model. Simulation results showed that the use of the dual process system on new engine platforms can potentially offer 7.2% of additional engine crankshaft power. This corresponded to a 55% increase in power generation compared to the two conventional independent heat recovery cycles targeting the high temperature and the low temperature heat sources
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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