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.