Fuel-to-Air Ratio Stimulation Suitability for Pollutant Emissions Reduction under Transient Driving Conditions

Fuel-to-air ratio stimulation, also called λ cycling or λ modulation, is a natural consequence of controlling fuel-to-air ratio in closed-loop with a switch-type λ-sensor. Nowadays, wideband λ-sensors are broadly extended and fuel-to-air ratio stimulation is an additional option that can or not be implemented in the control strategies to improve TWC conversion efficiency through the increase of the catalyst activity. The present work focus on the suitability of applying fuel-to-air ratio stimulation in a turbocharged GDI engine equipped with a close-coupled TWC. In particular, the influence of the main parameters such as stimulation amplitude and frequency on tailpipe emissions at steady-state conditions is assessed. The potential of λ cycling in order to reduce pollutant emissions in the face of fuel-to-air ratio disturbances has also been evaluated. Results show how a proper λ modulation decreases NOx emissions at lean conditions. However, at rich conditions CO emissions increases when fuel-to-air ratio stimulation is imposed.