Sviluppo di una rondella piezoelettrica per la stima della pressione nel cilindro

In-cylinder pressure measurement allows for the obtainment of fundamental information for the reduction of pollutant emissions and for the control of the combustion process, especially in applications characterized by unstable combustion such as LTC (Low Temperature Combustion), where an on-board combustion monitoring system is required. The aim of this thesis was the development of a piezoelectric sensor installed under the spark plug, which would allow to perceive a variation of the forces acting on the surfaces of the piezoelectric material due to the pressure variations inside the cylinder, generating a measurable voltage signal. The most convenient solution has been developed, with the miniaturization of the sensor as much as possible without compromising its functionality. The tests carried out with the first prototypes showed a significant correlation with the reference pressure sensor but also showed issues affecting the accuracy of measurement. Such issues are most likely caused by thermic stress both of the assembly and the piezoelectric element, which lead to a non-linear transmission of forces and a variation of piezoelectric properties. For this reason, a new algorithm has been proposed, which is capable of compensating for potential errors in the evaluation of combustion indexes.