• Energy Research

Fuel consumption reduction and CO2 emissions saving are the present drivers of the technological innovation in Internal Combustion Engines for the transportation sector. Among the numerous technologies which ensure such benefits, the role of the cooling pump has been recognized, mainly referred to the possibility to improve engine performances during warm up. During engine homologation, an additional benefit on the fuel consumption can be also reached reducing the energy demand of the pump. In fact, during the cycle, propulsion power requested by the vehicle is low and the importance of the energy absorbed by the pump became significant, since the pump operates far from its maximum efficiency. Indeed, the pump is usually designed at high load working point (Best Efficiency Point, BEP), where the cooling request is maximum: Starting from these design conditions, when the pump operates at lower engine coolant requests (as it happens very frequently and more specifically during the homologation cycle of the engine), its efficiency can be very low. This aspect invites pump designer to take care about the choosing of the design point, privileging engine operating points which are more frequent during real operation. In this paper, a dynamic test bench for engine coolant pumps has been developed and engineered. It has been linked to a software procedure which evaluates, according to a vehicle's mission profile, the propulsion power of the vehicle, the engine speed and, definitively, the pump speed. The knowledge of the cooling circuit and, specifically, the pressure-flow rate relationship of the circuit, allows the calculation of flow rate and pressure delivered in each point of the mission. From the pump efficiency, the instantaneous mechanical power requested by the pump can be calculated, i.e. that subtracted from the engine. The integral of this instantaneous power allows the calculation of the energy requested by the engine over the sequence of operation. The dynamic pump test bench allows to reproduce the real working condition of the pump for a specific sequence of engine operating conditions, and in particular, when this sequence is represented by a homologation WLTP, the one on which emissions and CO2 are measured and referred to an unit of distance (passenger or light duty vehicles). When a Real Driving is specified (as it happens to evaluate the emissions in real driving, RDE), the test bench is able to reproduce the real sequence of operation of the pump as, consequently, the measurement of all relevant quantities. An electrical water pump was designed following the new design concept over a WLTC cycle. Thanks to the comparison between electric and the hydraulic cumulated energy, efficiency of the pump was identified during dynamic working conditions. These experimental results claimed the necessity of a novel design of the pump having resulted an average propulsion power of the pump over the WLTP 10 % lower than the value which would be associated to a pump designed at its BEP when the engine power is maximum.

Abstract Adopting efficient power plants based on renewable energy sources is extremely important to face the challenges of global warming. Concentrated Solar Power Plant (CSP) is a technology option that can achieve the decarbonization target of the electricity sector in large power plants and simultaneously meet the growing demand for electricity. In this study, a CSP plant using air as heat transfer fluid, whose transformations realize a Discrete Ericsson Cycle (DEC), was referenced. Solar fields are based on parabolic trough collectors. The DEC consists of a series of inter-cooled compressions and inter-heated expansions (four and two, respectively, in this paper), whose net result is a useful work. In this paper, a mixture of air and Cr2O3 nanoparticles at different particle concentration has been considered as working fluid to enhance the performances of the compression and expansion transformations in a DEC-based plant. The presence of particles cools the air during compression and heat the air during expansion, approaching isothermal processes. A sensitivity analysis referred to the particle concentration has been discussed and the power and the efficiency of the plant have been discussed outlining benefits and drawbacks. Nanoparticle concentration less that 0,05% in volume (10 % in mass) produce a power and efficiency output increase close to 3 % without any sensible constraint. At higher concentrations, more significant variations are achieved with a 15 % power output increase for a mass concentration of nanoparticles of 50%. Such mass concentration corresponds to just 0.05 % in volume, allowing a potential operativity of the turbomachines. In this condition, the overall CSP efficiency improve by 1.5 percentage points.

Abstract In the present work a novel technology based on a dual injection vane expander has been introduced. The component works on a power unit fed by the exhaust gases of 3L turbocharged diesel engine. The new device was tested in a wide range of operating conditions and its numerical model was validated on the experimental data. The performances of the new machine were compared to those of the original one. The results showed that the dual injection expander provided an increase of the indicated and mechanical power up to 50% and 30%. Mass flow rate can be increased by 30% and this widens the performances of the power unit; this aspect is particularly suitable for a recovery unit fed by the widely changing exhaust gases flow rates in ICEs.

To date, Sliding Vane Pump (SVP) technology is one of the most attractive solution in different technical applications thanks to its reliability and compactness and capability to keep a high efficiency even when it is working far from rated condition. In particular, this feature makes the SVP suitable to be employed for the oil circulation (SVOP) in Internal Combustion Engine (ICE) which is characterized by a wide oil flow rates variation, delivered pressure and temperature variation which causes operating conditions of the pump far from the design point. Flow delivered changes in these machines are produced by varying the eccentricity for a mechanical connection with the engine - or by varying the speed of revolution. The mild hybridization of the powertrains calls for a strong development of electrically assisted engine auxiliaries which undoubtedly makes the flow variations easier to be done, but the presence of an electric motor requires some technological choices not fully assessed, a cost increase and a reliability decrease. The paper presents a mathematical model of a SVOP for oil circulation in ICE, suitably validated by a wide experimental activity. The model integrates a mono and zero-dimensional fluid-dynamic analysis and allows to represent the intimate behaviour of the machine. Moreover, it was employed as virtual platform to discuss pros and cons of different flow rate variation strategies and their effect on the efficiency of the SVOP.

Presently the on-the-road transportation sector is responsible of the 21% of the whole CO2 amount emitted into atmosphere. This pushes the International Governments and Organizations to provide strict limitations in terms of ICEs emissions, also introducing fees payment for the car manufacturers. The vehicle electrification allows certainly to meet these requirements, but the higher cost and the need of a green electricity still limit a widespread diffusion among all social classes. Thus, the technological improvement of internal combustion engine plays a key role in the transition period. Among these technologies, the engine thermal management allows to achieve a good compromise between the CO2 emission reduction and related costs. It was demonstrated that replacing the conventional centrifugal pump of engine cooling system with a sliding vane rotary pump (SVRP), important benefits in terms of CO2 emission reduction can be achieved as centrifugal pump efficiency decreases significantly when the engine works far from the maximum load (i.e. design point of the pump). Nevertheless, the complex thermo-fluid-dynamic phenomena taking place inside a SVRP make its design not immediate, particularly if heavy duty ICE cooling systems are considered. These applications indeed are challenging due to the wide operating range and the huge flow rates which pump must deliver. These operating requirements make difficult the choice of the main design parameters: among the different ones, the pump revolution speed and displaced volume. In the present paper a design strategy is developed for this type of pumps based on a comprehensive mathematical model of the processes occurring, predicting volumetric, indicated and mechanical efficiencies. The model was validated with a wide experimental activity so acting as virtual development platform. The results show how the best global efficiency (0.59) is achieved adopting a dual axial intake port configuration, with a suitable choice result of a trade-off between displaced volume and revolution speed. The analysis also show that the pump keeps its efficiency close to the design one for a wide operating range which is particularly suitable for the cooling of an ICE.

A promising solution for the Combined Heat and Power (CHP) micro production is certainly represented by Organic Rankine Cycle (ORC)-based power units. In the domestic appliances with electrical power range of the units below 1 kW, the reduced dimensions of the components represent a critical aspect as well as the need to guarantee a high reliability. When the hot source is represented by solar energy, the optimization of the electricity production keeping insured the thermal energy availability represents an aspect which invites to a proper management of the unit. Solar-based ORC-recovery units frequently work in off-design conditions due to the variability of the hot source and to the Domestic Hot Water (DHW) requirements. For this reason, the design and the selection of the components should be carefully performed. The expander is commonly retained the key component of the unit being the one that mainly affects the behaviour. For the mentioned power ranges, the volumetric expander is the best technological option and, among those available, Sliding Rotary Vane Expander (SVRE) are gaining a sensible interest. At off design conditions, according to permeability theory, the expander intake pressure linearly varies with mass flow rate of the Working Fluid (WF) which is the most suitable and easiest parameter to be changed. This modifies the performances of the unit, both from a thermodynamic and technological point of view. In this paper, the speed variation of the expander is considered as control parameter to restore design expander intake pressure. In order to assess a strategy for the speed variation of the expander, in this paper a comprehensive model of the SVRE is presented when it operates in a solar-driven ORC-based unit. The model is physically based and recovers and widens the permeability theory developed by the authors in previous works. An experimental ORC-based unit was fully instrumented and operated, coupled with a reservoir, usually present when flat plate solar collectors are used, which store the thermal energy which fulfils thermal energy requests and feeds the generating unit. The model was widely validated with the experimental data properly conceived for the purpose. In the unit the expander speed was varied and, thanks to the permeability theory, the relationships between WF flowrate variations, inlet expander pressure and expander speed variation were investigated. The potentiality of a control strategy of the expander revolution speed of the expander was fixed as well as a deeper understanding of the SVRE behaviour and relationships between operating variables. In particular, it was observed that varying the speed from 1000 RPM up to 2000 RPM, the expander behaviour was optimized ensuring proper working condition matching with a (30–100 g/s) flowrate range.

Abstract Engine thermal management is a promising option to reduce fuel consumption and harmful emissions of Internal Combustion Engines. This is particularly suitable to support the transition towards a carbon-neutral transportation sector, considering that the role of combustion engines is expected to persist in the near and medium future. In this study, a prototype pump electrically actuated was compared to a mechanical pump of a downsized gasoline engine that propels a real vehicle. In the first phase of the analysis, the cooling circuit was tested from a hydraulic point of view on all its branches using an engine mounted on a bench equal to that working on the vehicle. The hydraulic circuit was fully characterized via pressure transducers and flow meters in all branches for different thermostat lifts, representing different coolant temperatures. On the same bench, the OEM pump and an electrically actuated one, suitably redesigned on an operating point more representative of the real operating conditions, were tested. A vehicle propelled with the same tested engine (having a conventional mechanically actuated pump) was run on the road following three different driving cycles. The engine revolution speeds were registered, as well as the temperature of the cooling fluid. The electric and mechanical pumps were compared using the performance maps previously obtained. The electric pump speed was set to deliver the same coolant flow rate as the OEM pump, following the same sequence of thermostat lifts. The results show that a 60 % average reduction of the pump energy consumption is possible, leading to an average specific CO2 emission reduction of 1 g/km. This result is even more relevant during urban driving, with emission savings hitting 2.5 g/km.

Abstract The current work presents a thermodynamic analysis of a Trilateral Flash Cycle (TFC) system for low grade heat to power conversion applications. Novel aspects of the research are the usage of rotary positive displacement expanders as prime movers of the TFC system as well as the reference to working fluids and their mixtures at the state of the art. In particular, the role of a correct built-in volume ratio of the expander with respect to the pressure ratio of the thermodynamic cycle is emphasized. In fact, a mismatching of these two quantities would lead to an isochoric expansion process which, in turn, might negatively affect the overall power recovery. With reference to a transcritical CO 2 stream at 100°C as heat source for the TFC system, parametric and screening studies were carried out using different expander built-in volume ratios and working fluids respectively. Among the fluids analyzed, results showed that pure substances such as R1234ze(E) and propane would provide a greater specific work but, on the other hand, would require built-in volume ratios (8 and 14) that are beyond the capabilities of rotary positive displacement expanders (5). The addition of CO 2 to the afore mentioned working fluids would ease the mismatching issue but, at the same time, would reduce the specific power output. Regarding the built-in volume ratio analysis, it was found that optimal values change in accordance to the working fluid and refer to an expansion process with a slight isochoric phase.