Correlation of Air Fuel Ratio with Ionization Signal Metrics in a Multicylinder Spark Ignited Engine

This investigation analyzes and characterizes the ionization signals in correlation to individual AFR values obtained from wide-band electrochemical oxygen sensors located in the exhaust runners of each cylinder. Experimental studies for this research were conducted on a 2.0L inline 4 cylinder spark ignited engine with dual independent variable cam phasing and an intake charge motion control valve. Nineteen metrics characterizing the ionization signal were determined on an individual cylinder and cycle basis. Linear and quadratic regression analysis was performed between the ionization metrics and the AFR values for the four cylinders. The results show that a number of good correlations exist between select ionization signal metrics and AFR values on individual cylinder basis. However when all four cylinders are combined, the correlations deteriorate reducing the accuracy in which AFR estimates can be made. Additionally, it is shown that various independent factors such as engine speed and load, in-cylinder charge motion, ignition timing, dilution, and type of fuel caused additional variation in the correlations.