The research on two-stroke engines has been focused lately on the development of direct injection systems for reducing the emissions of hydrocarbons by minimizing the fuel short-circuiting. Low temperature combustion (LTC) may be the next step to further improve emissions and fuel consumption; however, LTC requires unconventional ignition systems. Jet ignition, i.e., the use of prechambers to accelerate the combustion process, turned out to be an effective way to perform LTC. The present work aims at proving the feasibility of adopting passive prechambers in a high-pressure, direct injection, two-stroke engine through non-reactive computational fluid dynamics analyses. The goal of the analysis is the evaluation of the prechamber performance in terms of both scavenging efficiency of burnt gases and fuel/air mixture formation inside the prechamber volume itself, in order to guarantee the mixture ignitability. Two prechamber geometries, featuring different aspect ratios and orifice numbers, were investigated. The analyses were replicated for two different locations of the injection and for three operating conditions of the engine in terms of revolution speed and load. Upon examination of the results, the effectiveness of both prechambers was found to be strongly dependent on the injection setup.

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.

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.

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.