An exhaust emissions based air-fuel ratio calculation for internal combustion engines

This paper describes a method for accurate determination of air-fuel ratio based upon exhaust gas emissions analysis as an alternative to the conventional direct air and fuel flowrates measurement. A thorough analysis of all the possible parameters that may affect the accuracy of air-fuel ratio is conducted which includes the instrument error, ambient conditions, the assumed water-gas shift reaction constant, the humidity of the atmospheric air and the inclusion of oxides of nitrogen in the air-fuel ratio model. Results show that four essential exhaust gas emission concentrations, namely carbon dioxide, carbon monoxide, oxygen and hydrocarbons, are adequate for obtaining an accurate air-fuel ratio provided that the fuel type and the range of parameters that may affect the accuracy of air-fuel ratio are properly defined.