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.
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.
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