Modeling on a Three-Way Catalyst Used in Series Hybrid Electric Vehicles Considering Its Specific Engine Operation Attribute

Abstract

With the worldwide strengthening of environmental regulations for automobiles in recent years, series hybrid electric vehicles (SHEVs) have been developed as a promising system that can satisfy both fuel efficiency and power performance. The exhaust gas from SHEV engines is distinctive and different from those of conventional gasoline and parallel hybrid electric vehicles because there is a tendency for repeated intermittent steady-state engine operation at a specific high-efficiency point and engine stop. Consequently, this study aimed at constructing a catalyst model that can reproduce the purification performance on a close-coupled three-way catalyst (cc-TWC) against the distinctive emissions of SHEVs. The emission properties of a commercially produced SHEV were investigated through transient mode tests on a chassis dynamometer. This revealed that the exhaust conditions turn dynamically from lean to rich to stoichiometric over a short period every time the engine restarts, and this behavior is repeated dozens of times per worldwide light-duty test cycle mode procedure. Subsequently, a one-dimensional (1-D) numerical simulation model for the cc-TWC was developed, following model gas experiments under several conditions spanning from lean to rich, to determine the catalyst properties in detail. Emission purification behaviors at the engine restart were reproduced by improving the TWC model to express the reaction rate variation and air excess ratio fluctuation.

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

“…As this study follows from our previous work, we refer the reader to ref or the Supporting Information (Figures S1–S3 and Tables S1–S4) for brief descriptions of the tested SHEV, vehicle test conditions and results, and specifications of the catalyst employed for the vehicle tests.…”

“…In our previous study, , the reaction site on PGM was defined as solely PGM without separating Pd and Rh for simplification of the kinetic parameter fitting and calculation load reduction. The TWC model was built as a 1-D surface reaction model that does not include gas diffusion in the catalyst layer.…”

“…The reaction scheme is described in Table and is based on the global reaction model used in the previous study, where 12 chemical species (O 2 , N 2 , CO 2 , H 2 O, CO, CH 4 , C 3 H 6 , C 3 H 8 , H 2 , NO, NH 3 , and N 2 O) were involved. In a double-layer model comprising Pd and Rh layers with different values of the kinetic parameters for each layer, the calculation becomes considerably more complicated, with twice the number of reaction rate equations.…”

“…The former is suitable for expressing actual phenomena more precisely, , whereas the latter, which generally has a lighter calculation load and higher robustness for calculation stability, tends to have been preferred more in recent studies due to increasing needs for performance simulation in transient mode. − Limiting the scope to SHEVs, many investigations have focused on power control systems and fuel economy, whereas those focusing on emissions are scarce. Therefore, in our previous studies, we performed a vehicle test on a commercially produced SHEV and investigated the attributes of the engine emission. , Then, in terms of close-coupled TWCs (cc-TWCs), a numerical 1-D model that can achieve favorable reproducibility for light-off test results under a wide range of λ conditions, including amounts of byproducts (such as NH 3 and N 2 O), was built by introducing kinetic parameter control (KPC) along with λ. KPC is a control method that involves switching rate constants along with λ by providing two or three sets of kinetic parameters and λ threshold values to switch them for each global reaction. Essentially, although the rate constant must be immutable, it is nearly impossible to express the whole purification mechanism of TWCs with approximately 30 global reactions because they have not been elucidated sufficiently.…”

Modeling the Catalytic Performance of Coated Gasoline Particulate Filters under Various Operating Conditions

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