Modeling on a Three-Way Catalyst Used in Series Hybrid Electric Vehicles Focusing on Its Catalytic Behavior at Cold Start

Exhaust gas from series hybrid electric vehicle (SHEV) engines has characteristics different from those of conventional gasoline and parallel HEVs because there is a trend of iterated intermittent steady-state engine operation at a specific high-efficiency point and engine stop. A catalyst model that can reproduce the purification performance of a close-coupled three-way catalyst against the distinctive emissions of SHEVs was previously developed; however, improving the estimation accuracy in the period from a cold start to the completion of the light-off process remains challenging. To overcome this issue, the redox behavior of Rh was investigated in this study. After transient mode tests, the catalyst surface was oxidized due to exposure to high temperatures and an oxidative atmosphere for some time, causing activation deterioration. The activation promoted through light-off from the deteriorated state at cold start was modeled by introducing a rate equation with Arrhenius form to express the activation process. The completed model reproduced the performance trend in lean and rich iteration tests in a model gas experiment and achieved favorable estimation accuracy in worldwide light-duty test cycle mode calculation.