Comparison between Pressure- and Ion-Current-Based Closed-Loop Combustion Control Performance

Combustion control is key for achieving maximum efficiency in internal combustion engines. For SI (spark-ignition) engines, knocking combustions occurrence can be controlled using a protective closed-loop control system, but additional information, such as combustion angular phase, is needed to minimize brake-specific fuel consumption in the entire engine operating range. The proposed solution is a closed-loop Spark Advance (SA) controller based on pre-defined combustion phase targets, able to react to excessive knocking levels. Pressure- and ion-current-based combustion closed-loop control are compared in the article, by implementing both solutions in Model-In-the-Loop environment and then in real time. Both controllers are characterized by an aggressive strategy, which pursues the optimal combustion angular phase, and by a protective action governed by measured knocking levels. Experimental tests carried out at the engine test bench demonstrate the possibility of using the ionization current signal as the main input to a closed-loop combustion controller, both in knock-free and knock-limited conditions: the considered indicators (mean values and standard deviation of the controlled variables) to estimate the controller performance while using the pressure or the ionization current signal are comparable, confirming the robustness of the ion signal for control purposes.