An Algorithm for Calculating the Air/Fuel Ratio from Exhaust Emissions

A confusing number of equations have been developed and published for calculating the air/fuel ratio of an operating engine from the composition of its exhaust gasses. These methods make varying use of the information available from the gas concentration measurements, but they all are based on the same chemistry of combustion. The method described here is a single algorithm that duplicates the results of all the well known published equations and can adapt to different measurement circumstances, such as when an oxygen measurement is not available or if the gas sampling point is moved to after the catalyst. Data are presented to demonstrate the equivalence of the algorithm and equation evaluations.