In-Cylinder Measurement of Combustion Characteristics Using Ionization Sensors

This paper documents the results of an engine dynamometer study into the use of in-cylinder ionization probes on a 1.6L EFI engine. The objective of the investigation was to determine if there is sufficient correlation between ionization probe information and other combustion parameters to allow use of the ionization probe as a sensing element as part of a direct feedback control system to control engine air-fuel ratio and/or spark timing. Specific emphasis was placed on determining performance at lean air-fuel ratios with the goal of controlling the engine near the lean limit of operation. Use of the spark plug as an ionization sensor was also investigated.