Methodology to design a bottoming Rankine cycle, as a waste energy recovering system in vehicles. Study in a HDD engine

• Published in: Applied energy Vol. 104; pp. 758 - 771
• Main Authors: Macián, V., Serrano, J.R., Dolz, V., Sánchez, J.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.04.2013; Elsevier
• Subjects: Applied sciences; Diesel; Energy; Energy. Thermal use of fuels; Engines and turbines; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Organic Rankine Cycle; Rankine cycle; Recover waste power; Recover waste power; Diesel; Organic Rankine Cycle; Rankine cycle; Vehicle; Energetic system; Methodology; Diesel fuel; Engine
• ISSN: 0306-2619; 1872-9118
• DOI: 10.1016/j.apenergy.2012.11.075

► A study for the optimization of a bottoming cycle for recovering various waste heat sources is presented and applied in a HDD engine. ► Water and R245fa are selected as working fluid in the proposed solutions. ► The cycles with water as working fluid produces a higher power output than the solution with R245fa in almost all the operative points. ► The cycle with R245fa as working fluid is the most feasible solution from the point of view of space requirements. ► The effect of the expander machine irreversitibities is discussed. This article describes a methodology for the optimization of a bottoming cycle as a waste heat recovering system in vehicles. The methodology is applied to two particular cases in order to evaluate the preliminary energetic and technical feasibility of the implementation of a bottoming cycle in a heavy duty diesel (HDD) engine considering two different criteria. Initially, a study of the different waste heat sources of the engine is described. In this study, the power and exergy of each heat source is quantified, in order to evaluate which sources are suitable to be used in the bottoming cycle. The optimum working fluids to run the cycles are selected (water and R245fa). Then, the ideal Rankine cycle is optimized for the two different working fluids and different sets of heat sources (all the available heat sources and the sources with high exergy respectively) throughout the engine operating range, reaching a maximum improvement of 15% of the fuel consumption of the engine. Later, a study of the minimum temperature difference between the hot and cold flow of the heat exchangers is described. The improvements in fuel consumption and the size of the installed heat exchanger are related to this temperature difference. Finally, the non-ideal behavior of the machines (pump and expander) is analyzed, obtaining a maximum improvement of 10% in brake specific fuel consumption (bsfc).