Browse Publications Technical Papers 2019-01-1291
2019-04-02

Fuel-to-air ratio stimulation suitability for pollutant emissions reduction under transient driving conditions 2019-01-1291

Traditionally, fuel-to-air ratio (FAR) stimulation, also called lambda cycling or lambda modulation, was a natural consequence of controlling the fuel-to-air ratio in closed loop with a switch-type lambda sensor. Thus, its possible impact on three-way catalyst (TWC) performances was widely addressed in literature. However, nowadays wideband lambda sensors are widely extended, thereby, FAR stimulation is an additional option that can be (or not) implemented for control purposes. Most previous works concerning the effect of stimulation on TWC performance use to be carried out in laboratory reactors or in test benches with engines that cannot be considered representative of the current state of the art, particularly regarding gasoline direct injection systems. Moreover, these studies focus mostly on catalyst conversion efficiency instead of pollutant emissions at TWC outlet, therefore, the superimposed impact of FAR stimulation on exhaust gas composition and TWC performance are not been accounted for. In present work, after assessing the influence that the most relevant parameters such as amplitude, frequency, mass air flow, temperature or time-average FAR have over pollutant emissions in a state-of-the-art turbocharged and gasoline direct injection engine (GDI) at steady conditions, the authors focus on the suitability of applying FAR stimulation under the most relevant driving conditions, such as catalyst purging after injection cut off as well as FAR disturbance rejection.

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