Abstract
Waste heat recovery via Organic Rankine Cycle (ORC)-based power units represents one of the most promising solutions to counteract the effects of CO2 emissions on climate change. Nevertheless, several aspects are still limiting its development on the on-the-road transportation sector. Among these aspects, the significant variations of the conditions of the hot source (exhaust gases) are a crucial point. Therefore, the components of the ORC-based unit operate far from the design point if the main operating parameters of the plant are not suitably controlled. The maximum pressure of the cycle is one of the most important variables to be controlled for the importance it has on the effectiveness of the recovery and on safety of operation. In this paper, a wide experimental and theoretical activity was performed in order to define the operating parameters that mostly affect the maximum pressure of the recovery unit. The results showed that the mass flow rate provided by the pump and the expander volumetric efficiency were the main drivers that affect the plant maximum pressure. Subsequently, through a validated model of the expander, a diagnostic map was outlined to evaluate if the expander and, consequently, the whole plant were properly working.
Highlights
To date, the transport sector is responsible of 14% of the total amount of anthropogenic greenhouse gas emissions [1], so the efforts of the scientific and technical community are focused on the development of technologies whose introduction allows to reduce this contribution, matching with the increasingly restrictive requests of the international governments and organizations [2,3].Among the technologies that ensure the CO2 reduction, waste heat recovery (WHR) from exhaust gases, based on Organic Rankine Cycle (ORC) units, is one of the most attractive alternatives [4].approximately 30% of fuel energy is lost through the exhaust gases [5], whose enthalpy content is almost equal to the engine mechanical useful power [6]
Despite that the ORC-based power unit is a quite conventional technology for stationary applications, it requires some more efforts in the transportation sector, in order to define the most suitable layout, the choice of components, and the level of integration with the engine: Reliability, robustness, and effectiveness in transient situations [7] are the main requirements, taking into account the boundary condition imposed by the specific on board application
In order to find the main driver that defines the maximum pressure of the ORC-based power, an extensive experimental campaign was performed on a fully instrumented ORC-based power unit bottomed to the exhaust gases of a 3 liters supercharged diesel engine for light duty application
Summary
The transport sector is responsible of 14% of the total amount of anthropogenic greenhouse gas emissions [1], so the efforts of the scientific and technical community are focused on the development of technologies whose introduction allows to reduce this contribution, matching with the increasingly restrictive requests of the international governments and organizations [2,3].Among the technologies that ensure the CO2 reduction, waste heat recovery (WHR) from exhaust gases, based on Organic Rankine Cycle (ORC) units, is one of the most attractive alternatives [4].approximately 30% of fuel energy is lost through the exhaust gases [5], whose enthalpy content is almost equal to the engine mechanical useful power [6]. Despite that the ORC-based power unit is a quite conventional technology for stationary applications, it requires some more efforts in the transportation sector, in order to define the most suitable layout, the choice of components, and the level of integration with the engine: Reliability, robustness, and effectiveness in transient situations [7] are the main requirements, taking into account the boundary condition imposed by the specific on board application. This application should face issues related to the components encumbrances and weight on a vehicle, backpressure effect on the engine [8,9], proper fitting of the condenser in Energies 2019, 12, 1970; doi:10.3390/en12101970 www.mdpi.com/journal/energies.
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