Evaluating Different Strategies to Minimize cold-start Emissions from Gasoline Engines in steady-state and Transient Regimes.

Exhaust car emissions increase significantly at particular gasoline engine driving cycle such as cold-start when the three-way catalyst has not reached its light-off temperature. More efficient technologies are needed to reduce these extra emissions. This study focuses on comparing two strategies to lower cold-start pollutants on a commercial monolithic catalyst: (i) a high content of PGMs (Pd and Rh) loading with a variable concentration distribution along the catalyst, called zone-coating, was investigated in order to take advantages of an in situ pre-heating due to exothermic oxidation processes. And (ii) the use of external device for heating the monolith with the aim to shorten the laps of time to reach the required temperature for their conversion. Both approaches were compared below 300 °C in terms of NO, CO and hydrocarbons conversions as well as N2O formation with respect to homogeneously wash-coated catalyst. For evaluation, complex exhaust gas compositions were considered at different steady-state air-to-fuel λ ratios and high frequency transient lean/rich regime to mimic real operation in gasoline engine exhaust. Results show that a pre-heating of the catalyst at 300 °C is necessary to avoid completely N2O formation from NO reduction with CO. Remarkably higher NO and CH4 conversions were observed during transient regime rather than steady-state lean, rich or stoichiometric conditions at 200 and 300 °C. [ABSTRACT FROM AUTHOR]