Investigation of air-fuel ratio control using ionic current signal

摘要

The objective of this paper is to investigate the control of air-fuel ratio (AFR) using an ionic current signal. Experimental measurements have been carried out to study the characteristics of the ionic current signal near ignition poles in a constant-volume combustion bomb. The ionic signal is characterized by a front flame and post flame during combustion. The intensity of the ionic signal strongly depends on the AFR at the time of combustion. The maximum values in both the front flame and the post flame will occur at close to the stoichiometric value. Furthermore, minimum values of the durations from ignition to two peaks will also occur where the AFR is close to the stoichiometric value. From this observation of the ion signal characteristics, a feedback control of AFR in a closed loop is proposed and the algorithm is outlined for detecting whether the mixture is in the lean or the rich combustion condition. Then control logic is given based on the information on lean or rich combustion. A unique condition of combustion around stoichiometry is also discussed. It has been shown that the developed control algorithm covers the entire combustion region: lean, rich, and stoichiometric.