Investigation of Correlation Between Ion Current Signal and NOX Emissions in Controlled Auto-ignition Engine

NOX is one of the main compositions in the modern engine emissions and the reduction requirements of NOX have turned to be more stringent. To control NOX emissions better, the technologies of NOX sensors are forced to achieve much faster response and higher accuracy. In this paper, the correlation between ion current signals and NOX emissions has been investigated by both experiments and simulations based on a direct-injection controlled auto-ignition (CAI) engine, which could provide a novel method to detect NOX emissions within combustion cycle. The simulation results presented this positive correlation from the chemical kinetics point of view, which could also directly reflect the formation order of the chemical products and the influence of temperature on the rates of main ionization and NOX generated reactions. Furthermore, the distributions of both ions and NO products have been shown with the CFD results, to illustrate their in-cylinder space correlation. Combined with the simulation results, the experimental results not only validated the positive correlation with two different fuels, but also provided the evidences fitting linear function. Based on the results, the cycle-based NOX emissions were estimated.