Abstract
An asymmetry in NO conversion efficiency is apparent during trans-stoichiometric air–fuel ratio steps over a three-way catalyst. After a lean-to-rich step, NO conversion becomes high very rapidly and asymptotes to a higher value, followed by a reduction to a high, but reduced level. Following a rich-to-lean step, conversion remains high for a period before gradually decreasing to the low level seen at steady lean operation. This dynamic response in NO conversion can be modelled by a three-way catalyst model which includes ceria reoxidation by way of NO dissociative adsorption. Five, periodic, different aspect triangular waveforms were tested to try to exploit the asymmetry by waveform shaping. No strong trends in average NO conversion efficiency resulted; however, some shapes seemed to give a better overall conversion.
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