Accuracy of A/F Calculation from Exhaust Gas Composition of SI Engines

The accuracy of real-time A/F measurement at engine test benches has been improved with a modified equation to calculate A/F from exhaust gas composition. In addition to CO, CO₂, total hydrocarbon (THC) and O₂, the proposed equation includes NO and NO₂ concentration as variables. In an attempt to improve the accuracy of the assumed constants in the equation, experiments have been conducted using automotive exhaust H₂O and H₂ analyzers. The accuracy of the proposed equation was proven through experiments and it was also found useful for precise evaluation of three-way catalyst or oxygen sensor characteristics.