General Air Fuel Ratio and EGR Definitions and their Calculation from Emissions

Many exhaust gas analyzers only calculate the Air Fuel Ratio (AF) based on equations derived for the special case of combustion without exhaust gas recirculation (EGR), and therefore do not represent the combustion AF during lean operation with EGR. Equations that are not subject to this limitation will be presented. Using these equations to provide measurements of the combustion AF and total inert EGR is encouraged as they relate more directly to what governs the combustion process.