Giovanni Vichi

Modeling and predicting the long-term performance of Li-ion batteries is crucial for the effective design and efficient operation of integrated energy systems. In this paper, we introduce a comprehensive semi-empirical model for Li-ion cells, capturing electrothermal and aging features. This model replicates the evolution of cell voltage, capacity, and internal resistance, in relation to the cell actual operating conditions, and estimates the ongoing degradation in capacity and internal resistance due to the battery use. Thus, the model articulates into two sub-models, an electrothermal one, describing the battery voltage, and an aging one, computing the ongoing degradation. We first propose an approach to identify the parameters of both sub-models. Then, we validate the identification procedure and the accuracy of the electrothermal and aging models through an experimental campaign, also comprising two real cycle load tests at different temperatures, in which real measurements collected from real Li-ion cells are used. The overall model demonstrates good performances in simulating battery characteristics and forecasting degradation. The results show a Mean Absolute Percentage Error (MAPE) lower than 1% for battery voltage and capacity, and a maximum absolute error on internal resistance that is on par with the most up-to-date empirical models. The proposed approach is therefore well-suited for implementation in system modeling, and can be employed as an informative tool for enhancing battery design and operational strategies.

Real-time estimation of the in-cylinder pressure of combustion engines is crucial to detect failures and improve the performance of the engine control system. A new estimation scheme is proposed based on the Extended Kalman Filter, which exploits measurements of the engine rotational speed provided by a standard phonic wheel sensor. The main novelty lies in a parameterization of the combustion pressure, which is generated by averaging experimental data collected in different operating points. The proposed approach is validated on real data from a turbocharged compression ignition engine, including both nominal and off-nominal working conditions. The experimental results show that the proposed technique accurately reconstructs the pressure profile, featuring a fit performance index exceeding 90% most of the time. Moreover, it can track changes in the engine operating conditions as well as detect the presence of cylinder-to-cylinder variations.

In order to ensure a high level of performance and to comply with the increasingly severe limitations in terms of fuel consumption and pollution emissions, modern diesel engines need continuous monitoring of their operating conditions by their control units. With particular focus on turbocharged engines, which are presently the standard in a large number of applications, the use of the average and the instantaneous turbocharger speeds is thought to represent a valuable feedback of the engine behavior, especially for the identification of the cylinder-to-cylinder injection variations. The correct operation of the injectors and control of the injected fuel quantity allow the controller to ensure the right combustion process and maintain engine performance. In the present study, two different techniques are presented to fit this scope. The techniques are discussed and experimentally validated, leading to the definition of an integrated control strategy, which features the main benefits of the two, and is able to correctly detect the cylinder-to-cylinder injection variation and, consequently, properly correct the injection in each cylinder in order to balance the engine behavior. In addition, the possibility of detecting misfiring events was assessed.

Recent innovations in engine control and diagnostics are providing room for development of innovative combustion approaches (e.g., low-temperature combustion) able to minimize the creation of pollutants. To ensure the constant fulfillment of the prescribed thermodynamic conditions, however, a fast real-time monitoring of the in-cylinder pressure is needed. To this end, dynamic pressure sensors, flush-mounted on the cylinder head, are commonly used. With this approach, the measurement accuracy is high, but the durability is limited by the harsh working conditions. The installation on the cylinder head is also complex. The development of robust and effective indirect measurement systems could then represent the enabler of a further development of this technology. In the present study, an innovative methodology to measure the in-cylinder pressure has been conceived and extensively tested on a four-stroke single-cylinder engine. The proposed approach is based on the analysis of the mechanical stress on the engine studs by means of a piezoelectric strain washer. This solution allows the user for a rapid and cost-effective sensor installation, described in the paper along with the signal post-processing techniques. Results showed good accuracy and robustness of the methodology, making the results of practical use for engine control.

High specific fuel consumption and pollutant emissions are the main drawbacks of the small crankcase-scavenged two-stroke engine. The symmetrical port timing combined with a carburetor or an indirect injection system leads to a lower scavenging efficiency than a four-stroke engine and to the short-circuit of fresh air-fuel mixture. The use of fuel supply systems as the indirect injection and the carburetor is the standard solution for small two-stroke engine equipment, due to the necessity of reducing the complexity, weight, overall dimensions and costs.This paper presents the results of a detailed study on the application of an innovative Low Pressure Direct Injection system (LPDI) on an existing 300 cm3 cylinder formerly equipped with a carburetor. The proposed solution is characterized by two injectors working at 5 bar of injection pressure. The injection nozzles are located in the liner wall at the opposite side of the exhaust port, with the axes oriented towards the piston at the BDC (Bottom Dead Center). The injectors are positioned above all of the cylinder ports in order to have an injection timing independent from the ports timing. The only constraint to the injection timing is related to the piston motion, with great benefits in terms of short-circuit reduction in all of the engine operating conditions.Numerical and experimental activity was carried out in order to identify the best injector configuration and to assess the system performance. The results of the preliminary 3-D CFD study are here reported. The best positioning of the injectors was determined at the operating condition of maximum power by means of a sensitivity analysis of the circumferential position and spray orientation. The performance comparison was evaluated in terms of fuel short-circuit and spray vaporization. The optimized configuration was also verified at lower revolution speeds and partial loads showing a great potential for all of the working conditions. The experiments on a real prototype on the test bench confirmed the predictions showing significant improvements in comparison with the original configuration.

High specific fuel consumption and pollutant emissions are the main drawbacks of the small crankcase-scavenged two-stroke engine. The symmetrical port timing combined with a carburetor or an indirect injection system leads to a lower scavenging efficiency than a four-stroke engine and to the short-circuit of fresh air-fuel mixture. The use of fuel supply systems as the indirect injection and the carburetor is the standard solution for small two-stroke engine equipment, due to the necessity of reducing the complexity, weight, overall dimensions and costs.This paper presents the results of a detailed study on the application of an innovative Low Pressure Direct Injection system (LPDI) on an existing 300 cm3 cylinder formerly equipped with a carburetor. The proposed solution is characterized by two injectors working at 5 bar of injection pressure. The injection nozzles are located in the liner wall at the opposite side of the exhaust port, with the axes oriented towards the piston at the BDC (Bottom Dead Center). The injectors are positioned above all of the cylinder ports in order to have an injection timing independent from the ports timing. The only constraint to the injection timing is related to the piston motion, with great benefits in terms of short-circuit reduction in all of the engine operating conditions.Numerical and experimental activity was carried out in order to identify the best injector configuration and to assess the system performance. The results of the experimental study are reported here. Standard low cost components from the automotive market were used, without a significant increase of weight. The benefits of the innovative two-stroke LPDI engine were evaluated at the test bench and compared with the performance of the configurations equipped with the carburetor and the indirect injection system.Once the position of the injectors inside the cylinder was defined, the development of the system at the test bench was focused primarily on the definition of the best injection timing, also taking advantage of the numerical results of the CFD analysis.The experimental setup and the fine-tuning methodology are discussed in detail. The goal was to reach the best thermodynamic efficiency and the lowest pollutant emissions of the LPDI system while ensuring the same engine power with respect to the other two configurations, without increasing the manufacturing costs.

In the last years, the engineering in the automotive industry is revolutionized by the continuous research of solutions for the reduction of consumptions and pollutant emissions. On this topic maximum attention is paid by both the legislative bodies and the costumers. The more and more severe limitations in pollutant and CO2 emissions imposed by international standards and the increasing price of the fuel force the automotive research to more efficient and ecological engines.Commonly the standard approach for the definition of the engine parameters at the beginning of the design process is based on the wide-open throttle condition although, both in homologation cycles and in the daily usage of the scooters, the engines work mainly at partial load where the efficiency dramatically decreases.This aspect has recently become strongly relevant also for two wheeled vehicles especially for urban purpose. Within this context the authors developed an integrated numerical model, in MatLab Simulink ambient, in order to couple the engine simulation, performed by means of a 1D computer-aided engineering code, with the dynamic behaviour of the whole vehicle. The model allows to estimate, along an imposed time-velocity profile, the operating conditions, the performance and the consumption of the engine simulating its real functioning in the vehicle. This approach was used by the authors for improving the efficiency of a scooter engine in its real functioning conditions. In detail, the effects of a high compression ratio were evaluated and a dedicated spark advance strategy was carried out in order to take under control the maximum in-cylinder pressure and as a consequence the occurrence of knocking phenomena.The results, supported also by a dedicated experimental activity, show the benefits of this approach in the engine design.