R. Cipollone - Academia.edu (original) (raw)
Papers by R. Cipollone
Journal of Physics: Conference Series
Engine thermal management can reduce significantly CO2 emissions in road vehicles without alterin... more Engine thermal management can reduce significantly CO2 emissions in road vehicles without altering sensibly the engine layout. However, more efficient auxiliaries also participate to fuel consumption saving and, therefore, to CO2 emissions reduction. Typically, centrifugal cooling pumps are adopted as circulating devices, but their efficiency varies highly with rotational speed, wasting energy during real operation despite being optimized at the design point. Instead, volumetric pumps keep a high efficiency also far from it, enhancing the overall engine efficiency. In this paper, the performances of a screw-type volumetric pump have been compared with those of a centrifugal pump considering the same cooling circuit of a mid-size engine for passenger vehicles. Both pumps have been designed to satisfy the cooling flow rate required by the engine during a homologation cycle, while verifying their capability to cool the engine operating at maximum power. Once prototyped, the pumps perfo...
Energy Conversion and Management
Designs, 2019
The paper presents an extensive investigation of a small-scale sliding vane rotary expander opera... more The paper presents an extensive investigation of a small-scale sliding vane rotary expander operating with R245fa. The key novelty is in an innovative operating layout, which considers a secondary inlet downstream of the conventional inlet port. The additional intake supercharges the expander by increasing the mass of the working fluid in the working chamber during the expansion process; this makes it possible to harvest a greater power output within the same machine. The concept of supercharging is assessed in this paper through numerical computational fluid dynamics (CFD) simulations which are validated against experimental data, including the mass flow rate and indicated pressure measurements. When operating at 1516 rpm and between pressures of 5.4 bar at the inlet and 3.2 bar at the outlet, the supercharged expander provided a power output of 325 W. The specific power output was equal to 3.25 kW/(kg/s) with a mechanical efficiency of 63.1%. The comparison between internal pressu...
In Sliding Vane Rotary Compressors, as well as in most of positive displacement machines, the oil... more In Sliding Vane Rotary Compressors, as well as in most of positive displacement machines, the oil is injected to accomplish sealing and lubrication purposes. However, the oil injection could produce an additional outcome during the compression phase with a great saving potential from the energetic point of view. Being the air inside the cell at a higher temperature than the oil injected, a cooling effect could be achieved so decreasing the mechanical power required for the compression. At the moment, the oil is introduced inside the compressor vanes simply through a series of calibrated holes that are only able to produce solid jets. In this way any effective heat transfer is prevented, as demonstrated by p-V measurements inside the cells during the compression phase. In the current study, a theoretical model of a sprayed oil injection technology was developed and further experimentally validated. The oil was injected along the axial length of the compressor through a number of pres...
International Journal of Refrigeration, 2015
The present work highlights the energy saving potential of the lubricant fluid supplied in Slidin... more The present work highlights the energy saving potential of the lubricant fluid supplied in Sliding Vane Rotary air Compressors. A Lagrangian theoretical model of a sprayed oil injection technology assessed the cooling effect of the lubricant due to the high surface to volume ratio of the oil droplets and predicted a reduction of the indicated power. The model validation was carried out through a test campaign on a mid-size sliding vane compressor equipped with a series of pressure swirl atomizers. The oil injections took place along the axial length of the compressor. The reconstruction of the indicator diagram and the direct measurement of the mechanical power revealed a reduction of the energy consumption close to 7 % using an injection pressure of 20 bar. A parametric analysis on the injection pressure and temperature and on the cone spray angle was eventually carried out to identify an optimal set of operative injection parameters.
Journal of Physics: Conference Series, 2015
This paper analyzes the performances of an evaporator for small scale waste heat recovery applica... more This paper analyzes the performances of an evaporator for small scale waste heat recovery applications based on bottoming Organic Rankine Cycles with net output power in the range 2-5 kW. The heat recovery steam generator is a plate heat exchanger with oil as hot stream and an organic fluid on the cold side. An experimental characterization of the heat exchanger was carried out at different operating points measuring temperatures, pressures and flow rates on both sides. The measurement data further allowed to validate a numerical model of the evaporator whereas heat transfer coefficients were evaluated comparing several literature correlations, especially for the phase-change of the organic fluid. With reference to a waste heat recovery application in industrial compressed air systems, multiple off-design conditions were simulated considering the effects of oil mass flow rate and temperature on the superheating of the organic fluid, a key parameter to ensure a proper operation of the expansion machine, thus of the energy recovery process.
Energy Procedia, 2016
Pumping work in energy recovery units based on Organic Rankine Cycles (ORC) can severely affect t... more Pumping work in energy recovery units based on Organic Rankine Cycles (ORC) can severely affect the net power output recovered. Nevertheless, in recent years scientific and industrial communities mainly focused on expanders' development. In order to address this lack of know-how and equipment, the current paper presents the development of a positive displacement ORC pump based on the sliding vane rotary technology. The machine was installed in a power unit for low-medium grade thermal energy recovery that operated with oil at 70-120°C as upper thermal source and tap water as lower one. Working fluid was R236fa while cycle pressure ratio ranged from 2.8 to 3.7. The ORC pump was also tested at different revolution speeds such that mass flow rate varied between 0.05 kg/s and 0.12 kg/s. These experimental data were further used to validate a comprehensive one-dimensional model that takes into account fluid dynamic filling and emptying processes, closed vane transformation and leakages at blade tip, rotor slots and end walls clearances. Viscous and dry friction phenomena occurring between components in relative motion were additionally considered. A full operating map of the sliding vane pump was eventually retrieved to explore multiple off-design operating conditions. The parametric and modular structure of the model will act as a design platform to outline enhanced ORC sliding vane pump prototypes.
Recent studies on the use of 3D Computational Fluid Dynamics (CFD) for the analysis and design of... more Recent studies on the use of 3D Computational Fluid Dynamics (CFD) for the analysis and design of sliding vane machines has proved beneficial for the detailed evaluation and optimisation of the vane expanders for a given working fluid and operating condition. The authors have earlier developed a customised rotor grid generator for integration with commercial CFD solvers and validated it for use in typical small-scale ORC expanders for waste heat recovery. In this paper, this customised grid generation is extended to an open source CFD solver OpenFOAM, by using a connectivity methodology originally developed for roots blower and twin-screw machines. The control of the rotor grid deformation is through a user code integrated within the flow solver. A case study of the reference ORC expander operating with R245fa was used for validation. The available experimental data for three operating conditions are compared with the results calculated with ANSYS CFX and OpenFOAM-v1912 solvers. During the filling and expansion process, the internal pressure traces are accurately captured by both the solvers and the difference is within 0.05 bar with measurements. However, between the outlet port closure and inlet port opening process the pressure and temperature prediction with OpenFOAM solver is considerably different from the ANSYS CFX solver. It was observed that the OpenFOAM solver is resulting into a non-physical low temperature zone upstream to the tangency region of the rotor and the stator that goes below 80℃. Overall, CFD solution obtained with the commercial solver ANSYS CFX is much more stable and robust than the open source OpenFOAM solver. The generic nature of the deforming grid generation used with an open source CFD solver presented in the paper allows broadening of the utilisation of CFD modelling tools for the design of vane machines.
Energy Conversion and Management, 2021
Abstract Waste heat recovery (WHR) in internal combustion engines (ICEs) is very interesting oppo... more Abstract Waste heat recovery (WHR) in internal combustion engines (ICEs) is very interesting opportunity for reducing fuel consumption and CO2 emissions. Among the different heat sources within an ICE, exhaust gases are certainly the most suitable for potential recovery. The most promising technology is represented by power units based on organic Rankine cycles (ORCs). Unfortunately, their actual efficiency is far from that obtainable using only thermodynamic evaluations: low efficiencies of small-scale machines, strong off-design conditions, and backpressure effect are the main reasons. To improve the conversion efficiency, this paper presents a combined solution, coupling two thermodynamic cycles: Joule-Brayton and Rankine-Hirn ones. The first (top cycle) considers supercritical CO2 as the working fluid and the second considers an organic fluid (R1233zDe, bottom cycle). The combined recovery unit inherently introduces further complexity, but realizes an overall net efficiency 3–4% higher than that of a single ORC-based recovery unit. The hot source is represented by the exhaust gas of an IVECO F1C reciprocating engine, considering twelve experimental operating conditions that fully represent its overall behaviour. The combined unit was modelled via a software platform in which the main components of the ORC unit were experimentally validated. The best thermodynamic choices of the top and bottom cycles, as well as their mutual interference, were identified under the condition of maximum power recoverable; this implies an overall optimization of the combined unit considered as an integrated system. Moreover, the components must be handled when off-design conditions (produced by the unavoidable variations of the hot source) occur: insufficient heat transferred to the two working fluids, produced by an over- or under-designed heat exchanger, would prevent the proper operation of the two units, thereby reducing the final mechanical power recovered. To address this critical issue, the three main heat exchangers were designed and sized for a suitable ICE working point, and their behaviour verified to guarantee a suitable maximum temperature of the supercritical CO2 and full vaporisation of the organic fluid. These two conditions assure the operability of the combined recovery system in a wide range of engine working points and a maximum recovered mechanical power up to 9% with respect to the engine brake one.
Applied Thermal Engineering, 2021
Abstract Internal Combustion Engine (ICE) cooling system is receiving a new technological interes... more Abstract Internal Combustion Engine (ICE) cooling system is receiving a new technological interest for the influence it has on primary harmful and CO2 emissions reduction. Improvements on pump efficiency are requested to reduce its required energy during real on-the-road operation. Present technology always considers centrifugal pumps whose efficiency is highly dependent on rotational speed: consequently, pumps designed to have a very high efficiency at design point, show poor performances during usual operation, wasting energy. This study aims to assess the screws pumps potentiality to substitute the traditional centrifugal pumps for engine cooling. The main advantage is that positive displacement pumps have an efficiency ideally non-dependent on rotational speed, flow rate and head delivered, so having requirements that can fit more the engine cooling features. A novel comprehensive zero-dimensional mathematical model has been formulated to predict the performances of triple-screw pumps, in terms of volumetric, indicated and mechanical efficiency as a function of main operating conditions of the pump. A wide experimental activity has been done, resulting in a good agreement with predictions in spite of the manufacture of the pump, which privileges a low-cost solution as it is requested for the specific sectors of application. The model, once experimentally validated, demonstrates a high validity as virtual platform for a model-based design, thus offering the possibility to include design aspects particularly suitable for engine cooling systems. At last, by simulating the World Harmonized Transient Cycle on an F1C IVECO 3l engine, the triple-screw pump shows an average efficiency about 8% greater than that of the centrifugal pump, leading to an energy saving equal to 18.5%. This result leads the way to the use of screws pumps also in the engine cooling system of an on-the-road vehicle, which could represent a new potential application, never considered before.
Applied Thermal Engineering, 2020
Abstract Internal combustion engines evolution has recently gained additional push, in relation t... more Abstract Internal combustion engines evolution has recently gained additional push, in relation to their environmental impact on global warming and air quality deterioration mainly in high congested areas, like urban environments. Several innovative technologies have been introduced in the market and many others are under development in order to reduce CO2 emissions during homologation cycles, including real driving emission tests. Among them, great attention has been paid to the waste heat recovery, since it can assure a significant improvement on overall engine efficiency and, so, fuel saving and CO2 emission reduction. A novel opportunity can be represented by directly exploiting the residual pressure and temperature of the flue gases through an Inverted Brayton cycle (IBC), in which the gases are expanded at a pressure below the environmental one, cooled down and then recompressed to the environmental value. The real useful power of an IBC-based recovery unit is strictly related to the behavior of the machines chosen as IBC turbine and compressor (pressure ratio vs. mass flow rate and efficiencies), considering that they run at the same speed, resulted by the equilibrium of a common shaft. Therefore, an experimentally based mathematical model has been developed to evaluate the coupling of an IBC-based recovery unit with a turbocharged diesel engine, operating on a dynamic test bed. In particular, experimental data of the engine have been used as boundary conditions of the IBC group and real operating maps of radial turbine and compressor have been considered. In this way, the actual room of recovery of the unit has been assessed, evaluating also the trade-off produced by backpressure induced on the engine by the IBC-based recovery unit, which hadn't been investigated yet. An overall net efficiency increase close to 3.4% has been demonstrated with respect to the original efficiency of the engine, when operates close to the maximum power. The analysis is concluded evaluating the correct functioning of the after-treatment devices of the engine: sufficiently higher temperature has to be assured to guarantee right pollutants abatement.
Energy Procedia, 2016
ORC represents an effective challenge in the waste heat recovery from ICEs. In spite of technolog... more ORC represents an effective challenge in the waste heat recovery from ICEs. In spite of technological aspects, its thermodynamic design still deserves attention. Mixtures of pure fluids show interesting properties able to improve exergetic efficiency of the Rankine cycle, thanks to the positive slope of the phase changing. They can reduce also ODP and GWP, helping the replacement trends of working fluids. The paper optimizes cycle exergetic efficiency considering mixtures of pure fluids. The use of hydrocarbons in mixtures is particularly suitable and when used in limited fractions with other organic fluids they loses the limits related to the flammability. R245fa is a fluid that obtains a large net power increase when used in mixtures with hydrocarbons, compared to pure fluid an optimized R245fa/benzene mixture, for instance, attains an 11% net power increase.
SAE Technical Paper Series, 2015
The design of the powertrains for transportation on the road is even more oriented to the emissio... more The design of the powertrains for transportation on the road is even more oriented to the emission reduction. Recently, greenhouse gases commitments added new technological challenges. Energy recovery from exhaust gases has a great potential considering the amount of mechanical or electrical work which could be generated on board. The paper considers the recovery which could be obtained from the exhaust gases expanding them in an additional turbine (turbo compounding). An engine model has been developed and validated thanks to an extensive experimental activity which concerned the F1C Iveco engine equipped with a Variable Geometry Turbine (VGT). Two potential technologies are presented and the recovery has been calculated by the model which behaves as a virtual engine platform. Energy recoverable has been estimated referring to engine operating points which reproduce the NEDC and the ESC13 approval cycle.
Journal of Physics: Conference Series
Engine thermal management can reduce significantly CO2 emissions in road vehicles without alterin... more Engine thermal management can reduce significantly CO2 emissions in road vehicles without altering sensibly the engine layout. However, more efficient auxiliaries also participate to fuel consumption saving and, therefore, to CO2 emissions reduction. Typically, centrifugal cooling pumps are adopted as circulating devices, but their efficiency varies highly with rotational speed, wasting energy during real operation despite being optimized at the design point. Instead, volumetric pumps keep a high efficiency also far from it, enhancing the overall engine efficiency. In this paper, the performances of a screw-type volumetric pump have been compared with those of a centrifugal pump considering the same cooling circuit of a mid-size engine for passenger vehicles. Both pumps have been designed to satisfy the cooling flow rate required by the engine during a homologation cycle, while verifying their capability to cool the engine operating at maximum power. Once prototyped, the pumps perfo...
Energy Conversion and Management
Designs, 2019
The paper presents an extensive investigation of a small-scale sliding vane rotary expander opera... more The paper presents an extensive investigation of a small-scale sliding vane rotary expander operating with R245fa. The key novelty is in an innovative operating layout, which considers a secondary inlet downstream of the conventional inlet port. The additional intake supercharges the expander by increasing the mass of the working fluid in the working chamber during the expansion process; this makes it possible to harvest a greater power output within the same machine. The concept of supercharging is assessed in this paper through numerical computational fluid dynamics (CFD) simulations which are validated against experimental data, including the mass flow rate and indicated pressure measurements. When operating at 1516 rpm and between pressures of 5.4 bar at the inlet and 3.2 bar at the outlet, the supercharged expander provided a power output of 325 W. The specific power output was equal to 3.25 kW/(kg/s) with a mechanical efficiency of 63.1%. The comparison between internal pressu...
In Sliding Vane Rotary Compressors, as well as in most of positive displacement machines, the oil... more In Sliding Vane Rotary Compressors, as well as in most of positive displacement machines, the oil is injected to accomplish sealing and lubrication purposes. However, the oil injection could produce an additional outcome during the compression phase with a great saving potential from the energetic point of view. Being the air inside the cell at a higher temperature than the oil injected, a cooling effect could be achieved so decreasing the mechanical power required for the compression. At the moment, the oil is introduced inside the compressor vanes simply through a series of calibrated holes that are only able to produce solid jets. In this way any effective heat transfer is prevented, as demonstrated by p-V measurements inside the cells during the compression phase. In the current study, a theoretical model of a sprayed oil injection technology was developed and further experimentally validated. The oil was injected along the axial length of the compressor through a number of pres...
International Journal of Refrigeration, 2015
The present work highlights the energy saving potential of the lubricant fluid supplied in Slidin... more The present work highlights the energy saving potential of the lubricant fluid supplied in Sliding Vane Rotary air Compressors. A Lagrangian theoretical model of a sprayed oil injection technology assessed the cooling effect of the lubricant due to the high surface to volume ratio of the oil droplets and predicted a reduction of the indicated power. The model validation was carried out through a test campaign on a mid-size sliding vane compressor equipped with a series of pressure swirl atomizers. The oil injections took place along the axial length of the compressor. The reconstruction of the indicator diagram and the direct measurement of the mechanical power revealed a reduction of the energy consumption close to 7 % using an injection pressure of 20 bar. A parametric analysis on the injection pressure and temperature and on the cone spray angle was eventually carried out to identify an optimal set of operative injection parameters.
Journal of Physics: Conference Series, 2015
This paper analyzes the performances of an evaporator for small scale waste heat recovery applica... more This paper analyzes the performances of an evaporator for small scale waste heat recovery applications based on bottoming Organic Rankine Cycles with net output power in the range 2-5 kW. The heat recovery steam generator is a plate heat exchanger with oil as hot stream and an organic fluid on the cold side. An experimental characterization of the heat exchanger was carried out at different operating points measuring temperatures, pressures and flow rates on both sides. The measurement data further allowed to validate a numerical model of the evaporator whereas heat transfer coefficients were evaluated comparing several literature correlations, especially for the phase-change of the organic fluid. With reference to a waste heat recovery application in industrial compressed air systems, multiple off-design conditions were simulated considering the effects of oil mass flow rate and temperature on the superheating of the organic fluid, a key parameter to ensure a proper operation of the expansion machine, thus of the energy recovery process.
Energy Procedia, 2016
Pumping work in energy recovery units based on Organic Rankine Cycles (ORC) can severely affect t... more Pumping work in energy recovery units based on Organic Rankine Cycles (ORC) can severely affect the net power output recovered. Nevertheless, in recent years scientific and industrial communities mainly focused on expanders' development. In order to address this lack of know-how and equipment, the current paper presents the development of a positive displacement ORC pump based on the sliding vane rotary technology. The machine was installed in a power unit for low-medium grade thermal energy recovery that operated with oil at 70-120°C as upper thermal source and tap water as lower one. Working fluid was R236fa while cycle pressure ratio ranged from 2.8 to 3.7. The ORC pump was also tested at different revolution speeds such that mass flow rate varied between 0.05 kg/s and 0.12 kg/s. These experimental data were further used to validate a comprehensive one-dimensional model that takes into account fluid dynamic filling and emptying processes, closed vane transformation and leakages at blade tip, rotor slots and end walls clearances. Viscous and dry friction phenomena occurring between components in relative motion were additionally considered. A full operating map of the sliding vane pump was eventually retrieved to explore multiple off-design operating conditions. The parametric and modular structure of the model will act as a design platform to outline enhanced ORC sliding vane pump prototypes.
Recent studies on the use of 3D Computational Fluid Dynamics (CFD) for the analysis and design of... more Recent studies on the use of 3D Computational Fluid Dynamics (CFD) for the analysis and design of sliding vane machines has proved beneficial for the detailed evaluation and optimisation of the vane expanders for a given working fluid and operating condition. The authors have earlier developed a customised rotor grid generator for integration with commercial CFD solvers and validated it for use in typical small-scale ORC expanders for waste heat recovery. In this paper, this customised grid generation is extended to an open source CFD solver OpenFOAM, by using a connectivity methodology originally developed for roots blower and twin-screw machines. The control of the rotor grid deformation is through a user code integrated within the flow solver. A case study of the reference ORC expander operating with R245fa was used for validation. The available experimental data for three operating conditions are compared with the results calculated with ANSYS CFX and OpenFOAM-v1912 solvers. During the filling and expansion process, the internal pressure traces are accurately captured by both the solvers and the difference is within 0.05 bar with measurements. However, between the outlet port closure and inlet port opening process the pressure and temperature prediction with OpenFOAM solver is considerably different from the ANSYS CFX solver. It was observed that the OpenFOAM solver is resulting into a non-physical low temperature zone upstream to the tangency region of the rotor and the stator that goes below 80℃. Overall, CFD solution obtained with the commercial solver ANSYS CFX is much more stable and robust than the open source OpenFOAM solver. The generic nature of the deforming grid generation used with an open source CFD solver presented in the paper allows broadening of the utilisation of CFD modelling tools for the design of vane machines.
Energy Conversion and Management, 2021
Abstract Waste heat recovery (WHR) in internal combustion engines (ICEs) is very interesting oppo... more Abstract Waste heat recovery (WHR) in internal combustion engines (ICEs) is very interesting opportunity for reducing fuel consumption and CO2 emissions. Among the different heat sources within an ICE, exhaust gases are certainly the most suitable for potential recovery. The most promising technology is represented by power units based on organic Rankine cycles (ORCs). Unfortunately, their actual efficiency is far from that obtainable using only thermodynamic evaluations: low efficiencies of small-scale machines, strong off-design conditions, and backpressure effect are the main reasons. To improve the conversion efficiency, this paper presents a combined solution, coupling two thermodynamic cycles: Joule-Brayton and Rankine-Hirn ones. The first (top cycle) considers supercritical CO2 as the working fluid and the second considers an organic fluid (R1233zDe, bottom cycle). The combined recovery unit inherently introduces further complexity, but realizes an overall net efficiency 3–4% higher than that of a single ORC-based recovery unit. The hot source is represented by the exhaust gas of an IVECO F1C reciprocating engine, considering twelve experimental operating conditions that fully represent its overall behaviour. The combined unit was modelled via a software platform in which the main components of the ORC unit were experimentally validated. The best thermodynamic choices of the top and bottom cycles, as well as their mutual interference, were identified under the condition of maximum power recoverable; this implies an overall optimization of the combined unit considered as an integrated system. Moreover, the components must be handled when off-design conditions (produced by the unavoidable variations of the hot source) occur: insufficient heat transferred to the two working fluids, produced by an over- or under-designed heat exchanger, would prevent the proper operation of the two units, thereby reducing the final mechanical power recovered. To address this critical issue, the three main heat exchangers were designed and sized for a suitable ICE working point, and their behaviour verified to guarantee a suitable maximum temperature of the supercritical CO2 and full vaporisation of the organic fluid. These two conditions assure the operability of the combined recovery system in a wide range of engine working points and a maximum recovered mechanical power up to 9% with respect to the engine brake one.
Applied Thermal Engineering, 2021
Abstract Internal Combustion Engine (ICE) cooling system is receiving a new technological interes... more Abstract Internal Combustion Engine (ICE) cooling system is receiving a new technological interest for the influence it has on primary harmful and CO2 emissions reduction. Improvements on pump efficiency are requested to reduce its required energy during real on-the-road operation. Present technology always considers centrifugal pumps whose efficiency is highly dependent on rotational speed: consequently, pumps designed to have a very high efficiency at design point, show poor performances during usual operation, wasting energy. This study aims to assess the screws pumps potentiality to substitute the traditional centrifugal pumps for engine cooling. The main advantage is that positive displacement pumps have an efficiency ideally non-dependent on rotational speed, flow rate and head delivered, so having requirements that can fit more the engine cooling features. A novel comprehensive zero-dimensional mathematical model has been formulated to predict the performances of triple-screw pumps, in terms of volumetric, indicated and mechanical efficiency as a function of main operating conditions of the pump. A wide experimental activity has been done, resulting in a good agreement with predictions in spite of the manufacture of the pump, which privileges a low-cost solution as it is requested for the specific sectors of application. The model, once experimentally validated, demonstrates a high validity as virtual platform for a model-based design, thus offering the possibility to include design aspects particularly suitable for engine cooling systems. At last, by simulating the World Harmonized Transient Cycle on an F1C IVECO 3l engine, the triple-screw pump shows an average efficiency about 8% greater than that of the centrifugal pump, leading to an energy saving equal to 18.5%. This result leads the way to the use of screws pumps also in the engine cooling system of an on-the-road vehicle, which could represent a new potential application, never considered before.
Applied Thermal Engineering, 2020
Abstract Internal combustion engines evolution has recently gained additional push, in relation t... more Abstract Internal combustion engines evolution has recently gained additional push, in relation to their environmental impact on global warming and air quality deterioration mainly in high congested areas, like urban environments. Several innovative technologies have been introduced in the market and many others are under development in order to reduce CO2 emissions during homologation cycles, including real driving emission tests. Among them, great attention has been paid to the waste heat recovery, since it can assure a significant improvement on overall engine efficiency and, so, fuel saving and CO2 emission reduction. A novel opportunity can be represented by directly exploiting the residual pressure and temperature of the flue gases through an Inverted Brayton cycle (IBC), in which the gases are expanded at a pressure below the environmental one, cooled down and then recompressed to the environmental value. The real useful power of an IBC-based recovery unit is strictly related to the behavior of the machines chosen as IBC turbine and compressor (pressure ratio vs. mass flow rate and efficiencies), considering that they run at the same speed, resulted by the equilibrium of a common shaft. Therefore, an experimentally based mathematical model has been developed to evaluate the coupling of an IBC-based recovery unit with a turbocharged diesel engine, operating on a dynamic test bed. In particular, experimental data of the engine have been used as boundary conditions of the IBC group and real operating maps of radial turbine and compressor have been considered. In this way, the actual room of recovery of the unit has been assessed, evaluating also the trade-off produced by backpressure induced on the engine by the IBC-based recovery unit, which hadn't been investigated yet. An overall net efficiency increase close to 3.4% has been demonstrated with respect to the original efficiency of the engine, when operates close to the maximum power. The analysis is concluded evaluating the correct functioning of the after-treatment devices of the engine: sufficiently higher temperature has to be assured to guarantee right pollutants abatement.
Energy Procedia, 2016
ORC represents an effective challenge in the waste heat recovery from ICEs. In spite of technolog... more ORC represents an effective challenge in the waste heat recovery from ICEs. In spite of technological aspects, its thermodynamic design still deserves attention. Mixtures of pure fluids show interesting properties able to improve exergetic efficiency of the Rankine cycle, thanks to the positive slope of the phase changing. They can reduce also ODP and GWP, helping the replacement trends of working fluids. The paper optimizes cycle exergetic efficiency considering mixtures of pure fluids. The use of hydrocarbons in mixtures is particularly suitable and when used in limited fractions with other organic fluids they loses the limits related to the flammability. R245fa is a fluid that obtains a large net power increase when used in mixtures with hydrocarbons, compared to pure fluid an optimized R245fa/benzene mixture, for instance, attains an 11% net power increase.
SAE Technical Paper Series, 2015
The design of the powertrains for transportation on the road is even more oriented to the emissio... more The design of the powertrains for transportation on the road is even more oriented to the emission reduction. Recently, greenhouse gases commitments added new technological challenges. Energy recovery from exhaust gases has a great potential considering the amount of mechanical or electrical work which could be generated on board. The paper considers the recovery which could be obtained from the exhaust gases expanding them in an additional turbine (turbo compounding). An engine model has been developed and validated thanks to an extensive experimental activity which concerned the F1C Iveco engine equipped with a Variable Geometry Turbine (VGT). Two potential technologies are presented and the recovery has been calculated by the model which behaves as a virtual engine platform. Energy recoverable has been estimated referring to engine operating points which reproduce the NEDC and the ESC13 approval cycle.