Air-Fuel Control to Reduce Emissions, II. Engine-Catalyst Characterization Under Cyclic Conditions

An experimental program was carried out to investigate the effect of changing the frequency and amplitude of air-fuel fluctuation on catalyst performance. From experimental data, physical characteristics that relate the catalyst performance between the cyclic and static air-fuel conditions were identified, and a frequency domain model is established for the catalyst to allow prediction of its system performance based on its intrinsic properties. By utilizing the concept of air-fuel maldistribution in characterizing the engine exhaust and treating it in frequency domain, this catalyst model can be used to simplify the prediction of emission performance when the engine exhaust air-fuel is known, and optimized strategies for air-fuel control can be derived.