Simulation of charged species flow and ion current detection for knock sensing in gasoline engines with active pre-chamber

Recently, it has been wildly recognized that active pre- chamber has a significant effect on extending the lean burn limit of gasoline engines. Ion current signals in the combustion is also considered as a promising approach to the engine knock detection. In this study, the feasibility of employing ion current in an active pre- chamber for combustion diagnosis was analyzed by three-dimensional numerical simulation on a single- cylinder engine equipped with active pre-chamber. The flow characteristics of charged species (NO⁺, H3O⁺ and electrons) in the main chamber and pre-chamber under knock conditions are investigated at different engine speeds, intake pressures and ignition timings. The results show that the ion current can theoretically be used for the knock detection of the active pre- chamber. The peak value of the electron or H3O⁺ mass fraction caused by knocking backflow can be used as knock indication peak. Intake pressure is the most critical factor affecting the intensity of knocking backflow. The electron knock indication peak can be significantly increased by 193.99% when the engine speed downed from 3000 r/min to 1500 r/min; increased by 53.26%, when the intake pressure is increased from 0.1 MPa to 0.2 MPa. Only increased by 23.8%, when ignition timing adjusted. Therefore, under a low speed and a high load condition, the knock is more likely to occur and be detected by the ion current in the active pre-chamber. And the knock indication peak is not only influenced by knock intensity, but also by the flow induced by, for example, piston motion.