Implications of Engine Start-Stop on After-Treatment Operation 2011-01-1243
It is commonly accepted that future powertrains will be based to
a large extent on hybrid architectures, in order to optimize fuel
efficiency and reduce CO₂ emissions. Hybrid operation is typically
achieved with frequent engine start-and-stops during real-world as
well as during the legislated driving cycles. The cooling of the
exhaust system during engine stop may pose problems if the
substrate temperature drops below the light-off temperature.
Therefore, the design and thermal management of after-treatment
systems for hybrid applications should consider the 3-dimensional
heat transfer problem carefully. On the other hand, the
after-treatment system calculation in the concept design phase is
closely linked with engine calibration, taking into account the
hybridization strategy. Therefore, there is a strong need to couple
engine simulation with 3d aftertreatment predictions.
In this paper, we perform measurements in flow-through catalytic
substrates and wall-flow DPF systems to monitor the thermal losses
after engine shut-off. In parallel, we use an existing
3-dimensional modeling platform (axisuite®/Exothermia SA), which is
enhanced with a heat transfer submodel to account for free
convection and radiation from the front and rear substrate faces.
The model predictions are compared with experimental data under
various operating conditions.
The validated model is used to predict the performance of a
diesel after-treatment system of a hybrid vehicle application. The
performance of the after-treatment system in terms of DOC
conversion efficiency is studied in detail with the help of
3-dimensional modeling during engine start-stop operation. The
importance of heat losses is illustrated and the potential
implications for exhaust system thermal management are