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Universal Exhaust Gas Oxygen (UEGO) sensors are widely used in engine exhaust streams to measure the recently burned air-fuel (A/F) mixture ratio. UEGO sensors are also frequently used to characterize transient A/F behavior during throttle or fuel variations. This study experimentally compares a UEGO exhaust based sensor response to that obtained from an in-cylinder Fast Flame Ionization Detector (FFID) during engine transients. UEGO sensor transient response time is seen as a limitation to the type of transient measurement that can be accurately characterized. A brief comparison of conventional transient fuel x-τ model parameters based upon the different measurement techniques shows that the transient fuel compensation calibration can be a function of measurement technique and method.

Cranking and startup fuel control has become increasingly important due to ever tightening emission requirements. Additionally, engine-off strategies during idle will require substantially more engine startup events with the associated need for very clean starts. Thus, knowledge of an engine's Air-Fuel Ratio (AFR) during its early cycles is necessary in order to optimize cranking and startup fueling. This paper examines and compares two methods of measuring an engine's AFR during engine startup (approximately the first second of operation); an in-cylinder technique using a Fast Flame Ionization Detector (FFID) and the conventional exhaust based Universal Exhaust Gas Oxygen (UEGO) sensor method. Engine starts using a Ford Zetec engine were performed at three different temperatures (0, 20 and 90 C) as well as different initial engine starting positions.