All Soot Deposits Are Not Created Equal: Variations on a Theme of Peclet Number

Mansour  Masoudi, Delphi

It’s been widely reported that backpressure of wall-flow filters is not an accurate representation of the quantity of soot deposit in the filter.  It is shown here that this is due to the soot deposit microstructure changing according to exhaust flow conditions through the filter, namely flow rate and flow temperature.  The exact deposition condition and hence soot microstructure depend on mass transfer Peclet number, a ratio of transport by convection vs. diffusion.  Details and examples are provided, along with results from both light-duty and heavy-duty engine soot emission studies through filters.  Applications of these findings in regeneration control are also demonstrated.