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Flash-boiling of fuel sprays occurs when a super-heated fuel is discharged into an environment whose pressure is lower than the saturation pressure of the fuel and can dramatically alter spray formation due to complex two-phase flow effects and rapid droplet vaporization. In gasoline direct injection (GDI) engines, typically, it occurs during the injection process when high fuel temperatures make its saturation pressures higher than the in-cylinder one. Flash boiling significantly affects the spray structure and fuel-air mixture formation, with, potentially, if spray collapse is avoided, positive consequences for the engine performance and pollutant emissions. Hence, this paper developed a modelling approach based on the coupling of Eulerian multi-phase and Eulerian-Lagrangian simulations to reproduce flash boiling sprays physics. It allows a comprehensive description of the flash-boiling phenomena that begins within the injector’s ducts and continues outside, where a particular mechanism for primary breakup occurs. Experimental data of the Engine Combustion Network (ECN) Spray G injector, covering various operating conditions, were exploited to assess the reliability of the numerical technique adopted. The validation was performed taking into account various parameters such as axial liquid and vapour penetrations, droplet size and images regarding the near-nozzle zone. The numerical model achieves a pretty good level of agreement with the experimental data and, in particular, it is sensitive to the spray behaviour in the different operating conditions.

The numerical reconstruction of the liquid jet generated by a multi-hole injector, operating in flash-boiling conditions, has been developed by means of a Eulerian- Lagrangian CFD code and validated thanks to experimental data collected with schlieren and Mie scattering imaging techniques. The model has been tested with different injection parameters in order to recreate various possible engine thermodynamic conditions. The work carried out is framed in the growing interest present around the gasoline direct-injection systems (GDI). Such technology has been recognized as an effective way to achieve better engine performance and reduced pollutant emissions. High-pressure injectors operating in flashing conditions are demonstrating many advantages in the applications for GDI engines providing a better fuel atomization, a better mixing with the air, a consequent more efficient combustion and, finally, reduced tailpipe emissions.

Paper proposes the design of a novel hydrogen-fueled hybrid power unit for zero-emission city transit bus applications. In particular, the powertrain consists of an electric drive fed by a hybrid power unit composed of a functional coupling of a high power density Flywheel Energy Storage System (FESS) and a high energy density hydrogen Fuel Cell (FC).The objective of the study is to design an HPU with an operation that can better follow the dynamics of the road power demand, optimize energy efficiency and reduce the power of the FESS.For this purpose, the FC power unit is partitioned in a certain number of stacks: each of those is on-off operated around its best-efficiency operating point; power transients are covered by the FESS bench. The control strategy of the hybrid power unit is based on the state of charge of the FESS. The performances of the vehicle on a reference mission were simulated through a modular and parametric approach: each part of the model was separately calibrated and validated by experimental data from literature.Simulation results highlight that the proposed hybrid power unit and control strategy make it possible to obtain an overall power output for the FC stacks which better follows road power demands (if compared to more traditional FC power units) increasing the system energy efficiency. In addition, the proposed control strategy allows a relevant downsizing of the FESS to be achieved.

The ever more stringent vehicle emissions rules lead gasoline engine research and development toward usage of direct injection systems. This technology is already present in commercial vehicles, but still there are many aspects that can be improved and need a deepening. For this reason, it was considered important to provide a review of the latest research topics, sorting them as if we are following the ideal fuel droplet life, beginning from the injection and ending after the combustion reaction, making available to researchers a tool to understand the state of the art of gasoline direct injection’s research and technologies. In a previous work (Part 1), spray breakup, the first and crucial process that occurs when the fuel is injected within the combustion chamber, was extensively treated. In this work, a broad review of research on the mixture formation process, on combustion and on pollutants emissions is carried out.

The objective proposed by the EU to drastically reduce vehicular CO2 emission for the years up to 2030 requires an increase of propulsion systems’ efficiency, and accordingly, the improvement their technology. Hybrid electric vehicles could have a chance of achieving this, by recovering energy during braking phases, running in pure electric mode and allowing the internal combustion engine to operate under better efficiency conditions, while maintaining traditionally expected vehicle performances (mileage, weight, available on-board volume, etc.). The energy storage systems for hybrid electric vehicles (HEVs) have different requirements than those designed for Battery Electric Vehicles (BEVs); high specific power is normally the most critical issue. Using Li-ion Batteries (LiBs) in the designing of on-board Energy Storage Systems (ESS) based only on power specifications gives an ESS with an energy capacity which is sufficient for vehicle requirements. The highest specific power LiBs are therefore chosen among those technologically available. All this leads to an ESS design that is strongly stressed over time, because current output is very high and very rapidly varies, during both traction and regeneration phases. The resulting efficiency of the ESS is correspondingly lowered, and LiBs lifetime can be relevantly affected. Such a problem can be overcome by adopting hybrid storage systems, coupling LiBs and UltraCapacitors (UCs); by properly dimensioning and controlling the ESS’ components, in fact, the current output of the batteries can be reduced and smoothed, using UCs during transients. In this paper, a simulation model, calibrated and validated on an engine testbed, has been used to evaluate the performances of a hybrid storage HEV microcar under different operative conditions (driving cycles, environment temperature and ESS State of Charge). Results show that the hybridization of the powertrain may reduce fuel consumption by up to 27%, while LiBs lifetime may be more than doubled.

The paper deals with the performance assessment of a small scale cogeneration system for building applications, featuring an Organic Rankine Cycle-based plant bottoming a solar collector array for combined heat and electricity generation. A sliding vanes rotary expander and a water cooled condenser are employed in the recovery section. A comprehensive MATLAB® model accounts for the dynamic of each component, as both a stand-alone device and a plant-integrated unit: a parametric study is presented and an off-design analysis is performed to properly assess the performances of both the heat exchanger and the expander. Heat availability to the ORC heat exchanger is evaluated, based on solar availability, thermal losses in the pipes and plant requirements, in terms of operating temperature and pressures, having the collection area, the mass flowrate for the fluid in the solar collector branch and the fluid type in the recovery section as main variables. Due to the need for DHW production, a storage unit for hot water is present, upstream the recovery branch: dependently on the ability the fluid at the collector outlet has to meet the ORC requirements for proper operation (about 110°C), the ORC evaporator is fed and the recovery section enabled. Both continuous and unsteady operation underwent an in-depth analysis, as well as the benefits associated with different discharge times for the storage unit: dependently on whether the electrical output or the thermal one need to be maximized, a different control logic for the whole system comes out (e.g. either a flash or a progressive tank discharge). The virtual platform allowed the setting-up of a pilot plant, for direct performance assessment and model validation.

Among the wide technological opportunities to reduce CO2 emissions in the transportation sector, Waste Heat Recovery (WHR), done by Organic Rankine Cycle (ORC) power units, was subject of a great scientific interest. However, several complications apply for an on-board operation and management, which reduce its real benefit in terms of net fuel consumption reduction. Weight increase, encumbrances, engine backpressure, intrinsic off design operating conditions are all negative aspects which should be still solved. In this paper, the interest is focused on the limiting factors of an ORC-based unit operating on board: engine backpressure due to Heat Recovery Vapor Generator (HRVG) presence, surface of the condenser and additional weight. All these aspects behave as limiting factors of the WHR. Considering the mechanical power produced by the unit as a desired input value, the paper discusses the HRVG and condenser sizing as a function of engine backpressure, weight increase and vehicle frontal area required by the condenser. The engine considered was an IVECO F1C turbocharged diesel engine and the reference vehicle was a light duty one. Experimental data have been used for gas temperature and flow rates. The paper considers also the possible presence of an internal regeneration within the ORC which increases plant efficiency (reducing the dimensions of the HRVG and condenser) but introduces an additional heat exchanger. A correlation between weight of the heat exchangers and condenser frontal area as a function of the mechanical power recovered has been presented, without and with the regeneration stage.

Technological and commercial development of vehicles specifically conceived for urban use would certainly be a crucial aspect in making mobility sustainable in urban contexts thanks to their limited in size and low fuel consumption and emissions. Hybrid drive trains are particularly suited to this purpose: If properly designed, very small-sized thermal engines can give all the energy and power required for the application, also making pure electric driving possible when required. The authors are involved since a decade in proposing new low-cost solutions to address this market sector. Market itself explored these possibilities and nowadays offers some BEV solutions in this market share, but it is still lacking in proposing solutions for a parallel full hybrid drive. The main reason must be searched in the complexity of normally applied parallel-hybrid propulsion systems which is not compatible with the limited costs of the application. Taking the lead from these considerations, the authors here propose a simple concept for a parallel-hybrid kit for quadricycles called Hybrid Power Pack (HPP) which is now installed and under long-range testing on a running vehicle and is available for full characterization and optimization. The HPP was used to equip a small city car to obtain a low-price parallel-hybrid propulsion system concept. The HPP is fully described in the paper and a model of its main parts is presented, devoted to HPP control design. The model was calibrated on the application and its effectiveness was demonstrated through a proper experimental activity. Results show that the most promising configuration is that with the EM mounted on the secondary shaft of the centrifugal CVT controlled with a Discrete State machine algorithm. This configuration is now under construction at the ENEA labs: Experimental results on vehicle running in real condition will be presented soon.

The paper copes with a transcritical CO2 refrigeration plant: R744 (CO2) is an economic and natural refrigerant with a negligible impact on the environment and with good thermodynamic and safety properties compared to synthetic ones, and it is a sustainable alternative in commercial refrigeration of retail food. A specific 18 kWt test bench is available and under testing in the lab of the University of L’Aquila. Experimental tests were performed at different external temperatures between 8 °C and 33 °C: first results showed that COP (Coefficient Of Performance) decreases when external temperature grows up. Experimental data made it possible to calibrate a mathematical model of the test rig, useful to evaluate the effect of the possible introduction of new technologies: variation of receiver pressure, intercooled two-stage compression and expander in place of the high pressure throttling valve. All these technologies may be useful to improve plant efficiency and to promote new “green” installations in warmer climates, where food conservation standard in terms of goods cold-chain are increasingly demanding, especially considering EU and Global goals on HFC reduction targets (e.g. EU F-gas regulation - 2014 and Kigali amendment to the Montreal Protocol - 2016).

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.

The paper presents the development of an experimental research facility based on a transcritical single stage vapour compression refrigeration cycle with CO2 as the working fluid. The experimental setup includes instrumentation and controls which enable tests in a broad range of operating conditions. The measurements presented refer to external temperatures between 21.0°C and 33.5°C; in this latter operating point, energy and exergy analysis allowed the breakdown of irreversibilities. In particular, the gas cooler contributes to the 42.6% of the total exergy losses while the share due to the high-pressure expansion valve is 27.2%. In order to improve the performance of the refrigeration system, a theoretical model was developed including an ejector as the replacement of the expansion valve. The results show that the Coefficient of Performance (COP) is strongly dependent on the entrainment ratio; a value of greater than 0.6 seem to lead to higher COP values, even at low external temperatures. EPTA S.p.A.

In this work we evaluate the changes in energy demand and resulting air pollutant emissions from the introduction of Battery Electric Buses into the public transport fleet operating in Rome. Our approach to evaluation is based on the adoption of geo-referenced open-data set, published in GTFS format by the Rome's public transport agency, that contains detailed information about transit stops, routes and service schedules of the bus lines. We use an electric bus simulation tool to obtain specific energy consumption models based on real driving cycles. The findings of this study indicate noticeable reductions in the primary energy consumption and the emissions of both GHG gases and toxic local air pollutants such as NOx and PM. © 2017 IEEE.

Paper deals with an extensive experimental activity carried out in Italy by ENEA Research Lab on Low impact vehicles and by the Energy engineering group of the University of L'Aquila about the energy efficiency of quick vehicle battery charging using a DC CHAdeMO compliant recharging 50 kW infrastructure. Both the charger and the vehicle (a Nissan Leaf) battery were fully monitored to gather detailed information about their behaviour at different power loads. The performances of the battery pack equipping the vehicle have also been monitored and evaluated through an extensive campaign, both on typical urban and extra-urban uses, and on vehicle rolling test bench.

© 2014 The Authors. Alternative vehicle powertrains (hybrid, hydrogen, electric) are a right answer to the emissions problem in very congested urban areas. The most effective alternative choice is surely represented by fuel cell vehicles. The design and optimization of this kind of powertrain can take a great benefit from mathematical models which include auxiliary management and control strategies of the energy fluxes: the use of a virtual platform limits the expensive and time-consuming experimental activity. The Authors present a lumped parameter mathematical model of a hybrid vehicle fed by a fuel cell pack. The propulsion system (fuel cell and battery) is accurately designed according to energy balancing. The mechanical power is given by an electric machine, whose behavior as alternator allows the energy recovery during braking. This aspect is treated with particular care (inside the overall vehicle and powertrain modeling). Vehicle's stability and safety has been also verified before recovering energy, re-modulating the braking action. Hi-CEPS EC project “Highly integrated combustion electric propulsion system”; Italian national project “MECCANO – Industria 2015

This paper reports the results of experimental tests performed at ENEA (Italian National Agency for New Technologies, Environment and Sustainable Development) in its "Casaccia" Energy Research Center to evaluate the energetic and environmental performances of a Heavy-Duty Compressed Natural Gas (HD CNG) engine fuelled with a hydrogen-methane blend of 15% in volume. A lean burn Mercedes 906 LAG engine has been optimized properly calibrating ECU engine maps regarding both ignition advance and air to fuel ratio (AFR). It was therefore possible to correct ignition advance to take into account the faster combustion speed given by the hydrogen content of the fuel mixture. Equivalence ratio (Lambda) has instead been modified in order to minimize the NOx emissions. All the tests were performed on a steady engine test-bed focusing the attention on the most important parts of the engine maps. The target of the activity was the reduction of energy consumption and CO2 emissions, still catching targets on pollutant emissions to getting the homologation of the engine in the same environmental category of the original one. Experimental results showed a reduction of CO2 variable with the ignition advance: decreasing the ignition advance timing the advantages are reduced. A reduction of CO2 of about 9% can be observed, for the same overall levels of pollutant emissions. After the calibration procedure the engine has been object of formal EU homologation and is running on a city bus since the start of 2013. Results about the on-road experimental campaign (which will last 150.000 km) will be published in future. Copyright © 2013 SAE International.

This chapter discusses hydrogen-methane blends for use in the transportation industry. The use of fossil fuels in hydrogen production may limit the advantages of this technology. However, a more sustainable approach is being developed in the use of renewable sources to supply energy for electrolysis. An energetic and environmental assessment of hydro-methane is necessary to determine its sustainability, and the information collected must be used to drive technological choices. © 2014 Woodhead Publishing Limited All rights reserved.

Last decade enthusiasm about hydrogen-based economy on FC has partially been lost and spotlight is now back on using pure hydrogen or hydrogen mixtures in ICE. Pure hydrogen use in spark ignition (SI) ICE requires a dedicated engine design to optimize the high speed flame and the high pressure and temperature inside the combustion chamber. But, on the other end, may lead to high exhaust emissions of nitrogen oxides NOx. Moreover, hydrogen fueled vehicles also suffer of a very low mileage due to the very low energy density of the fuel, since hydrogen as a compressed gas at 200 atmospheres and ambient temperature has around 5% of the energy of gasoline of the same volume. All these motivations, together with the now capillary diffusion of natural gas (NG) distribution for residential and transportation purposes (especially in Europe) is making more and more interesting the option of H2 using as an additive to natural gas: NG powered vehicles, in fact, reached a very high maturity with high reliability and environmental performances. In recent years experimentations were conducted in many laboratories and research centers to verify the positive effects of hydrogen when blended with natural gas. The maturity achieved by H2–NG mixtures is also stated by commercialized gas which is available in USA with the registered trademark of Hythane® (a mixture of 20% H2–80% NG in volume). In this paper the hydro-methane option is fully outlined, a complete energy analysis and environmental sustainability is realized, considering all the main possible options available in mixture production and final use.

Hybrid electric vehicles (HEVs) are worldwide recognized as one of the best and most immediate opportunities to solve the problems of fuel consumption, pollutant emissions and fossil fuels depletion, thanks to the high reliability of engines and the high efficiencies of motors. Moreover, as transport policy is becoming day by day stricter all over the world, moving people or goods efficiently and cheaply is the goal that all the main automobile manufacturers are trying to reach. In this context, the municipalities are performing their own action plans for public transport and the efforts in realizing high efficiency hybrid electric buses, could be supported by the local policies. For these reasons, the authors intend to propose an efficient control strategy for a hybrid electric bus, with a series architecture for the power-train. To this aim, an integrated approach realized by coupling a zero-dimensional model of the vehicle with a mono-dimensional model of the thermal engine to evaluate fuel consumption and find the most suitable control strategy for the engine (totally decoupled to the mission). A kinematic approach has been implemented. The power required to the motor is defined by knowing the speed and altitude profiles related to the path, while the power request for the engine is calculated by means of a first order filter, which properly cuts the power load of the motor. A sensitivity analysis has been performed in order to define the optimal operating strategy for the engine, to minimize the fuel consumption. Moreover, a control on the state of charge (SOC) has been implemented to assure a correct use of batteries and avoid damages. Copyright © 2011 SAE International.

This paper depicts in depth a series hybrid vehicle with a generation system based on an internal combustion engine coupled to a permanent magnets synchronous motor. A storage system with high power density, assured by the Ultracapacitors Unit (UC), is able to meet the driver peak power requests to run the vehicle and to store a part of energy from regenerative brakings as well. In this work, the vehicle energy management for a series hybrid electric vehicle is discussed with particular reference to the Generation Unit (GU) and the Electric Energy Storage (EES). The communication system is configured and remotely controlled by means of the Controller Area Network (CAN). For the purpose of obtaining the Internal Combustion Engine (ICE) better working efficiency a software supervisor has been developed to manage the GU. Further, first experimental results achieved for the prototype at roll test bench will be shown.

Cooling system design has a crucial role in defining engine performance and operational limits. Many further improvements can be obtained both in the precision in controlling temperatures of the various engine parts (especially during transient operation), and in the energy consumption of the system. Moreover, the warm-up transient can be relevantly reduced producing benefic effects on vehicle emissions and interior conditioning and comfort. Taking the lead by these considerations, the authors developed an integrated model of an engine cooling system, which is characterized by a complete modularity and permits the simulation of any possible design configuration. The model acts as a “virtual engine cooling system”: its coupling with simple ECU models permits an off-line evaluation of the efficiency of new control strategies, model-based too. In this work a novel model for the engine thermal behavior is proposed to be included in the described modeling architecture. The model so makes it possible permit the simulation of fully transient working conditions including those encountered during engine warm-up.

Cooling system design has a crucial role in defining engine performance, operational limits and thermal comfort. Many further improvements with respect to the actual situation can be obtained through a more accurate control of an-board thermal needs. To this new interest the definition of new technical specifications must follow. The technical literature, however, seems not fully satisfying this need, not focusing on the influence of these technical specifications on system design, reliability and costs. In this paper the authors present a contribution in this direction, showing the capabilities of an active intelligent management of the engine cooling system. This can be obtained through different control strategies, strongly diversified for their cost-performance ratio. The potentiality of a model-based controller has been also investigated and compared with the correspondent closed-loop controller.Copyright © 2004 by ASME

Fuel cells are widely accepted to be the alternative powertrain with the highest potential to compete with the internal combustion engine for a mean-long future sustainable prospective for passenger mobility: Proton Exchange Membrane Fuel Cells (PEMFC) seem to be the most promising technology. Anyway, the final goal is still far to be reached, since often the great potential advantages connected with fuel cells are not completely obtained, due to the difficulties encountered in component design and optimization. Moreover, H2 availability still appears to be one of the most important limitations. Taking the lead by these considerations the authors derived a physically consistent integrated mathematical model of a PEM propulsion system: the model is fully modular and is aimed both to gain a deeper insight of the complex chemical and thermo-fluid-dynamical processes involved, and to the development of control strategies for the propulsion system and all its auxiliaries.

In reciprocating IC engines, very precise predictions of the mass of air inducted are required in order to improve engine design. To achieve this goal, a deeper knowledge of the boundary conditions on intake and exhaust manifolds must be obtained. A set of very accurate experimental data is also needed to perform model validation. In this paper an experimental activity was performed on a pipe test-rig which guarantees high reproducibility of the fluid-dynamic transients. Based on the obtained data, the authors introduced two parameters, which are able to improve the precision of the dynamic models of the flow past valves and through sudden enlargements.