Exhaust Emission Based Air-Fuel Ratio Model (I): Literature Reviews and Modelling

This paper presents three different methods for obtaining equivalence ratio/air-fuel ratio from the internal combustion engines. Emphasis is placed on reviewing several important air-fuel ratio models based upon the analysis of gaseous emission constituents in the exhaust of the engines as alternate to that obtained conventionally from fuel and air flow rate consumptions of the engines.

A thorough analysis of all the factors that may affect the accuracy of fuel-air equivalence ratio is conducted which include the ambient conditions such as temperature and humidity, the assumed water gas reaction constant and the inclusion of oxides of nitrogen constituent in the model. A comprehensive model based upon chemical reaction of air-fuel mixture is proposed with flexible inputs of fuel type and the above factors in addition to the volume concentration inputs of carbon monoxide, carbon dioxide, oxygen and unburnt hydrocarbons.

Results show that four essential exhaust gas emission concentrations viz carbon dioxide, carbon monoxide, oxygen and hydrocarbons are adequate for obtaining an accurate equivalence ratio provided that the fuel type and the range of parameters that may affect the accuracy of air-fuel ratio are properly defined.