1,720,992 research outputs found
Development and numerical modelling of a supercharging technique for positive displacement expanders
Full text linkThis study presents a novel strategy to enhance the recovery performance of any positive displacement expander technology which aims at the maximization of the power output rather than solely its efficiency. The approach is based on an auxiliary injection of fluid under the same suction conditions as the main intake but during the closed volume expansion phase. The operating principle of the supercharging technology is firstly outlined in theoretical terms, while the benefits over a conventional configuration are numerically assessed with reference to a sliding vane expander for applications based on Organic Rankine Cycles (ORC). The holistic modelling platform used for the benchmarking is preliminarily validated over an experimental campaign in which the vane expander was installed in a heavy-duty automotive ORC system and generated up to 1.9 kW (3% of the engine mechanical power) with an overall efficiency of 51.2%. After the simulation platform is validated, the auxiliary intake line is parameterized in terms of four geometrical quantities and the effects of the supercharging with respect to baseline angular pressure trace are shown. An optimization based on a genetic algorithm is eventually performed and the resulting optimized design led to an average mechanical power increase of 50.6%
On the effects of leakages in Sliding Rotary Vane Expanders
Full text linkRotary Vane Expanders (RVE) are very suitable prime movers for ORC-based power units in on-the-road transportation sector. RVEs suffer volumetric efficiency deficits due to leakages which limit the overall expander efficiency and can vanish their intrinsic benefits with respect to the other prime movers. Making reference to a 2 kW Sliding RVE type (SRVE), the paper presents a theoretical and experimental contribution which goes deep into the effect of leakages inside the machine and aims to quantify their amount and effects on the expander performances. The results showed that the volumetric losses increase the mass flow rate aspirated by the machine if the intake pressure is kept constant. This increase favors a greater recovery from the hot source (up to 50%) but part of it bypasses the vanes, producing a volumetric loss. An interesting feature is that part of this additional mass is exchanged among vanes and this produces a beneficial effect on the indicated power (16.6% increase with respect the ideal case). The resulting knowledge further supported the effectiveness of dual intake expander technology which allows to theoretically reduce the leakages between adjacent vane up to 60–70% ensuring an improvement of expander efficiency
Development and experimental assessment of a Low Speed Sliding Rotary Vane Pump for heavy duty engine cooling systems
No full textModel-based assessment of a feedforward-feedback control strategy for ORC-based unit in waste heat recovery application
Full text linkResearch in the automotive sector is driven by the need to reduce the greenhouse gases emissions, while maintaining the expected vehicle performances. The electrification and hybridization ensure to achieve this goal, anyway, some issues still limit their full development in the international panorama. For this reason, the technological improvement of Internal Combustion Engines (ICEs) plays a crucial role in this transition period, also considering the opportunities related to sustainable fuels. Among the technological solutions allowing to improve ICEs performances, the energy recovery from the exhaust gases through Organic Rankine Cycle (ORC)-based power units are one of the most attractive alternatives, due to the high enthalpic content of the hot source. Despite these benefits, the ICE exhaust gases usually have considerable fluctuation of thermodynamic conditions. For this reason, it is necessary the adoption of a reliable and robust control system to keep the main operating ORC quantities (superheating degree, expander intake pressure and temperature) within a suitable and safe range. ORC control strategies for transportation applications are often based on detailed models that predict the unit behaviour, making use of Proportional-Integrative-Derivative (PID) regulators, whose coefficients are generally tuned through theoretical approaches and dedicated software. In the present work, an innovative control system has been developed, based on the integration of a feedforward (FF) and proportional feedback (FDB) regulating strategies. Despite the simplicity of the proposed approach, it ensures the proper plant operation even under severe fluctuations of the hot source. Particularly, the gain of FDB is based on a constitutive relationship between the expander intake pressure and working fluid mass flow rate. Such gain, indeed, is universally valid, not requiring to be tuned as generally done. The benefits of the proposed strategy are assessed thanks to a comprehensive model of the whole ORC unit, validated through experimental data carried out on a fully instrumented test bench in dynamic working conditions. Results demonstrate the robustness of the feedforward-proportional regulating approach: a superheating degree of 15–20 °C is ensured, keeping the plant power and efficiency close to the design value (1 to2 kW and 4 to6% respectively) even in off-design conditions. Moreover, the safe operating of the expander is guaranteed limiting the maximum temperature excursion under the safety limit of 160 °C
Theoretical and experimental analysis of the impact of a recuperative stage on the performance of an ORC‐based solar microcogeneration unit
Full text linkExperimental validation of a new modeling for the design optimization of a sliding vane rotary expander operating in an orc-based power unit
Full text linkSliding Rotary Vane Expanders (SVRE) are often employed in Organic Rankine Cycle (ORC)-based power units for Waste Heat Recovery (WHR) in Internal Combustion Engine (ICE) due to their operating flexibility, robustness, and low manufacturing cost. In spite of the interest toward these promising machines, in literature, there is a lack of knowledge referable to the design and the optimization of SVRE: these machines are often rearranged reversing the operational behavior when they operate as compressors, resulting in low efficiencies and difficulty to manage off-design conditions, which are typical in ORC-based power units for WHR in ICE. In this paper, the authors presented a new model of the machine, which, thanks to some specific simplifications, can be used recursively to optimize the design. The model was characterized by a good level of physical representation and also by an acceptable computational time. Despite its simplicity, the model integrated a good capability to reproduce volumetric and mechanical efficiencies. The validation of the model was done using a wide experimental campaign conducted on a 1.5 kW SVRE operated on an ORC-based power unit fed by the exhaust gases of a 3 L supercharged diesel engine. Once validated, a design optimization was run, allowing to find the best solution between two “extreme” designs: a “disk-shaped”—increasing the external diameter of the machine and reducing axial length—and by a “finger-shaped” machine. The predictions of this new model were finally compared with a more complex numerical model, showing good agreement and opening the way to its use as a model-based control tool
Assessment of the differential impact of scroll and sliding vane rotary expander permeability on the energy performance of a small-scale solar-ORC unit
No full textOrganic Rankine Cycle ORC-based power unit is a suitable solution for combined heat and power (CHP) generation in the residential sector currently responsible for an average 28 % energy-related CO2 emissions. The ability to tolerate seasonal daily and hourly fluctuations of the available thermal energy without significant performance compromission - i.e. efficiency of electricity generation and domestic hot water (DHW) fulfillment - is crucial. The need for the plant to work under severe off-design conditions affects the expander selection which for such plants are generally of volumetric technology. The most up-to-date literature addresses scroll-type and sliding vane rotary (SVRE) expanders as the most effective options. For such reason the present paper deals with the experimental assessment of the energy performance of an ORC-based plant equipped with both a customdesign SVRE and a scroll expander. The ORC unit assumes the same plant configuration in the two cases except for the expander layout. SVRE is connected through a mechanical joint to the electric generator whereas the scroll expander shares the same shaft and casing with the electric machine. The former approach ensures to control the expander speed which is set by the dynamic equilibrium in the latter case. The comparative analysis provides useful insights on the relative advantage of both technologies and configuration and a clear indication on the different operating strategy required in each case. SVRE leads to an electric output of the power unit in the 200-700 W range with a 2-6% efficiency whilst scroll expander is associated with a 100-500 W power range and a 2-4% efficiency partly compensated with a shorter starting time and a larger operability range (17-60 g/s). Despite SVRE is regulated in revolution speed its efficiency (20-40 %) is lower than the scroll one (40-60 %). The experimental assessment of the power unit was coupled with an in-depth modeling activity to address the impact of the expander operating conditions mainly on the inlet expander pressure which is close to the upper pressure of the thermodynamic cycle. The model derived from a theoretical analysis of the expander permeability focuses on the effect of the expander revolution speed - variable in the SVRE case constrained in the scroll case - and provides good accuracy with a Root Mean Square Error below 4 % in both cases
An improvement to waste heat recovery in internal combustion engines via combined technologies
No full textWaste 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
Inverted Brayton Cycle for waste heat recovery in reciprocating internal combustion engines
Full text linkEnergy recovery in reciprocating internal combustion engines is one of the most investigated topics for reducingfuel consumption and carbon dioxide emissions in the on-the-road transportation sector. An exhaust gas recoveryopportunity is represented by a power unit with a so-called inverted Brayton cycle (IBC). The gas is used as theworkingfluid, which expands inside a turbine when it falls below atmospheric pressure; after being cooled by anexternal source, it is re-compressed to the atmospheric value. The useful work is the difference between the oneproduced by the turbine and that absorbed by the compressor. In this study, a thermodynamic assessment of theopportunity to apply an IBC-based power unit to a turbocharged diesel engine was conducted, and the mostimportant parameters affecting the range of possible recovery (turbine and compressor efficiencies, pressuredrops) were evaluated, and the pressure ratio was optimized. A conventional bottomed layout shows a recoveryof approximately 1.5% of the engine’s mechanical power when a homologation heavy duty procedure is per-formed. An improved integration, in which the IBC turbine is placed upstream of the turbocharger one, makes itpossible to partially recover the energy losses related to the turbocharger control device, which leads to anaverage recoverable power of approximately 2% of the engine brake power. Concerns about possible watercondensation in the exhaust have also been thoroughly investigated, and they can be managed in temperateweather
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