Impact of operation parameters and lambda input signal during lambda-dithering of three-way catalysts for low-temperature performance enhancement

A synthetic exhaust gas bench was dynamically operated to investigate the impact of temperature, amplitude, split cycle, mean lambda, gas hourly space velocity, and oxygen storage capacity on average pollutant conversion and product selectivity of three-way catalysts in periodic operation. As temperature and amplitude increase and oxygen storage capacity decreases, the optimal frequency for maximum pollutant conversion increases. This is consistent with faster desorption of CO and O$_2$ from the catalyst, yielding free surface sites. Regarding the formation of secondary products, the optimal frequency for maximum pollutant conversion does not always correspond to minimal N$_2$O and NH$_3$ emissions. The split cycle variation reveals the enhancement of C$_3$H$_8$ and NO conversion after both lean-rich and rich-lean switches and C$_3$H$_6$ and CO conversion after rich-lean switches at the optimal frequency. As periodic operation does not affect existing engine settings or operating conditions, it is a cost-effective control strategy for meeting future emission limits.