Xxxciclo Del Dottorato Di Ricerca in Ingegneria E Architettura
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UNIVERSITÀ DEGLI STUDI DI TRIESTE XXX CICLO DEL DOTTORATO DI RICERCA IN INGEGNERIA E ARCHITETTURA CURRICULUM INGEGNERIA MECCANICA, NAVALE, DELL’ENERGIA E DELLA PRODUZIONE WASTE HEAT RECOVERY WITH ORGANIC RANKINE CYCLE (ORC) IN MARINE AND COMMERCIAL VEHICLES DIESEL ENGINE APPLICATIONS Settore scientifico-disciplinare: ING-IND/09 DOTTORANDO SIMONE LION COORDINATORE PROF. DIEGO MICHELI SUPERVISORE DI TESI PROF. RODOLFO TACCANI CO-SUPERVISORE DI TESI DR. IOANNIS VLASKOS ANNO ACCADEMICO 2016/2017 Author’s Information Simone Lion Ph.D. Candidate at Università degli Studi di Trieste Development Engineer at Ricardo Deutschland GmbH Early Stage Researcher (ESR) in the Marie Curie FP7 ECCO-MATE Project Author’s e-mail: • Academic: [email protected] • Industrial: [email protected] • Personal: [email protected] Author’s address: • Academic: Dipartimento di Ingegneria e Architettura, Università degli Studi di Trieste, Piazzale Europa, 1, 34127, Trieste, Italy • Industrial: Ricardo Deutschland GmbH, Güglingstraße, 66, 73525, Schwäbisch Gmünd, Germany Project website: • ECCO-MATE Project: www.ecco-mate.eu Official acknowledgments: The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme FP7/2007-2013/ under REA grant agreement n°607214. Abstract 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 the 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 waste 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, carried out in collaboration with Ricardo, an international engineering consulting company, is to introduce an innovative 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 further 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’s 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 demonstrate 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 first case study is focused on an agricultural tractor Diesel engine application, using engine data obtained from Ricardo’s testing activities. These data are the starting point for the investigation of the performance of different ORC architectures and working fluids, as well as for the exploitation of EGR wasted heat and the integration of the system with a preliminary study of the vehicle thermal management and cooling system. The results obtained show how the recovery of EGR heat can be beneficial both in terms of ORC system’s performance increase and decreased impact on the vehicle cooling system. A parallel exhaust gas and EGR ORC architecture is able, in principle, to allow around 10% maximum fuel saving, still considering a good trade-off with cooling radiator dimensions and parasitic fan consumption increase, when using water-steam, toluene or ethanol as possible working fluids. The second case study refers to a 1.5 MW, four-stroke, Diesel engine power generator, generally used for auxiliary power production on board ships. A detailed thermodynamic model of the engine has been developed in the commercial software Ricardo WAVE and the performance have been calculated at varying exhaust backpressure levels, in order to represent different possible designs for an ORC boiler fitted on the exhaust side of the engine. Three turbocharging systems have been assessed: a fixed geometry turbocharger, a turbocharger with Waste-Gate (WG) and a Variable Geometry Turbocharger (VGT). An ORC thermodynamic model has been then implemented, considering simple or recuperated architectures and different suitable working fluids, in order to assess the potential for exhaust gas heat recovery. From the simulations’ results, on the engine side, the VGT system allows to better withstand i the adverse effect of the ORC boiler backpressure, while at the same time fulfilling the requirements for combustion air-fuel ratio and maximum turbocharger exhaust temperature. Additionally, a recuperated ORC, running with acetone, allows a fuel consumption reduction between 9.1 and 10.2%, depending on the boiler design backpressure. Flammability and health hazards could however still be a problem, when installing the system onboard ships, even though an intermediate oil loop can mitigate the issues, separating the hot engine exhaust gas from the ORC working fluid. The third case study is focused on a 13.6 MW, low-speed, two-stroke, Diesel engine propulsion unit, typically installed in bulk carriers, oil tankers and container ships. A thermodynamic model of the engine, in typical IMO Tier II configuration, has been developed and validated, in Ricardo WAVE, based on the experimental data supplied by the project partner Winterthur Gas & Diesel (WinGD). Starting from the validated baseline model, a Low Pressure (LP) EGR circuit has been implemented for IMO Tier III operations, and the engine thermodynamic performance and characteristics evaluated in order to understand the impact of the emission reduction strategy on the engine fuel consumption and possible waste heat sources exploitable through the use of ORCs. A general increase of the heat available to be recovered can be evinced when using EGR, especially for the Scavenge Air Cooler (SAC) and the exhaust gas economizer. Four different ORC architectures, and two different working fluids (water-steam and R1233zd(E)) have been assessed, with the scope of obtaining the highest power production from the recovery of the waste heat. When combining the different ORC architectures, in order to try to fully exploit the engine waste heat available, a combined system with a water-steam Rankine cycle on the exhaust gas side and a refrigerant-based ORC recovering jacket cooling water and SAC heat, in an innovative two-stage SAC configuration, has been estimated to bring 5.4% fuel economy benefit in Tier II operation, and 5.9% in Tier III (at full load). The results achieved show the possibility of mitigating the increased fuel consumption effect of EGR operations using waste heat recovery systems. A preliminary economic feasibility analysis shows how a fuel cost savings of about 4% to 5.7% can be expected. The second and third case studies show how engine simulation tools can be used to assess the engine performance under different operational strategies, while at the same time, supplying the right boundary conditions for the evaluation of the performance of the waste heat recovery system, saving time and expensive test campaigns. However, a more synergic approach should be considered, when evaluating the combined engine-ORC systems. For this reason, the last case study aims to set the basics, and open the path, to a new methodology which can be helpful to understand the overall system and optimize its combined performance. In particular, a model of a four-stroke, 200 kW, Diesel engine, for on-highway trucks applications, has been developed in Ricardo WAVE. Innovative post-processing routines, developed in MATLAB, have been used to calculate a detailed First and Second Law analysis, for every engine operating point which can be simulated. The ORC models, for different architectures and working fluids, have also been adapted in order to calculate a complete energy and exergy balance. The calculation of the exergy destruction terms, for every sub-system of the overall engine-ORC powertrain, allows also to highlight where the main inefficiencies concentrate, thus helping to propose improvement strategies. Once energy and exergy streams are known, it has been possible to implement a techno and thermo- economic analysis, allowing