AN EXHAUST EMISSIONS BASED AIR-FUEL RATIO CALCULATION FOR INTERNAL-COMBUSTION ENGINES

This paper describes a method for accurate determination of air-fuel r atio based upon exhaust gas emissions analysis as an alternative to th e conventional direct air and fuel flowrates measurement. A thorough a nalysis of all the possible parameters that may affect the accuracy of air-fuel ratio is conducted which includes the instrument error, ambi ent conditions, the assumed water-gas shift reaction constant, the hum idity of the atmospheric air and the inclusion of oxides of nitrogen i n the air-fuel ratio model. Results show that four essential exhaust g as emission concentrations, namely carbon dioxide, carbon monoxide, ox ygen and hydrocarbons, are adequate for obtaining an accurate air-fuel ratio provided that the fuel type and the range of parameters that ma y affect the accuracy of air-fuel ratio are properly defined.