Study of Cycle-By-Cycle Air-to-Fuel Ratio Determined from the Exhaust Gas Composition and a Novel Fast Response Device Based on a Wide Band Lambda Sensor

This paper describes cyclic Air/Fuel ratio (AFR) measurements carried out with a novel device (fUEGO) based on a production Universal Exhaust Gas Oxygen sensor, but modified to give an improved frequency response. The results are compared to AFR calculated from a fast CO/CO₂ analyser and a fast response flame ionization detector (FID).

The direct comparison of the two different methods for determining the cyclic AFR reveals that the electrochemical device is in reasonable agreement with the more complex carbon balance method and can provide reliable cyclic AFR measurements with a reduced requirement for equipment and data post processing. The fUEGO however is sensitive to elevated levels of uHC's (unburned hydrocarbons) during misfires or partial burns and readings during such situations usually show deviations compared to the carbon balance method.

The frequency response of the fUEGO is in the 6 - 12 milliseconds region, depending on the step size of the AFR step, and although this is slower than the fast CO/CO₂ analyser and the fast FID, cyclic resolution is possible up to high engine speeds.