An innovative, ION current-based, knock intensity index for gasoline engines

In response to increasingly stringent global regulations aimed at significantly reducing CO2 emissions, improving the efficiency of internal combustion engines has become a primary objective in powertrain research. Furthermore, the need to extend the engine operating range under stoichiometric conditions and to accommodate alternative fuels, such as e-fuels, makes the implementation of an on-board knock control system almost essential, particularly in high-performance gasoline engines. The main objective of this work is to derive knock-related information from a sensor other than in-cylinder pressure transducers, which are typically used in test bench applications but still present cost and reliability limitations for on-board use. To address this challenge, the paper presents the conceptualization and application of a knock intensity index based on ionization current measurements. Following an extensive literature review and a physical analysis of the combustion chamber’s natural frequencies sensed through both in-cylinder pressure and ionization current signals, a new index, named IonInt , has been developed. The IonInt index combines band-pass filtering, signal integration, and a weighted summation to generate an original metric that outperforms the previously adopted ionization current-based index across all evaluated engine operating points. The results demonstrate that the knock detection capability of ionization current-based indexes is significantly improved, tending toward the performance of traditional pressure-based indexes. Future work will focus on implementing the proposed index in an on-board closed-loop control system, with the goal of enhancing engine performance while reducing fuel consumption and CO2 emissions.