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 and gas hourly space velocity, 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 O2 from the catalyst, yielding free surface sites. As for the formation of secondary products the optimal frequency for maximum pollutant conversion does not always correspond minimal N2O and NH3 emissions. The variation of split cycle reveals the enhancement of C3H8 and NO conversion after lean-rich and rich-lean switches and C3H6 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.