Prediction of emission performance of a Pd/CeZrAl-three-way catalyst during warmup and start-stop modes in a next-generation plug-in hybrid electric vehicle

Abstract

Designing next-generation three-way catalyst (TWC) emission aftertreatment systems (EATS) requires an accurate model to predict dynamic performance during cold-start and warm-up, which generate significant emissions. Low catalyst activation temperatures during multiple start-stop modes in hybrid and plug-in hybrid electric vehicles (PHEVs) further complicate the EATS design. This work develops a dynamic Pd/CeO₂-ZrO₂-Al₂O₃ TWC model to predict conversion rates and degradation factors for fresh and aged catalysts. A surface adsorption/desorption reaction TWC model is proposed that considers platinum group metal (S1 PGM), three-phase boundary (S2 TPB), and fast and slow oxygen storage capacities (Fast OSC S3, Slow OSC S4). The kinetic reaction rate constants are parameterized using synthetic gas reactor tests. Dynamic inlet conditions and experimental data (temperature, flow rate, gas composition) are measured in a next-generation PHEV during the low-speed phase (0–650 s) of the Worldwide Harmonized Light Vehicles Test Cycle (WLTC), which represents the warmup and 10 start-stop modes. The TWC is aged at 900°C for 40 h, and the vehicle test includes a 6 h soaking, following the suggested test guidelines. By incorporating degradation reactions and optimized kinetic rate constants, the dynamic conversion rates of CO, NO, and total hydrocarbons (THC) during warmup and multiple start–stop modes were reasonably reproduced, thereby confirming the model’s validity. Analysis of transient catalyst surface histories suggests that frequent engine start–stop operations lead to excessive oxygen supply at the three-phase boundary (TPB), thereby inhibiting the purification reactions. Furthermore, catalyst degradation reduces active site density, resulting in lower reaction rates and poorer purification performance.