AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Electric Field Directed Self-Assembly and Fragmentation of Dendritic Soot Structures as a Means for Amplifying Soot Detection
DAVID BILBY, David Kubinski, Matti Maricq, Ford Motor Company
Abstract Number: 18 Working Group: Aerosol Physics
Abstract The native charge on combustion generated soot allows for effective particle capture in an electrostatic trap. The deposited soot grows into surface-attached dendritic structures whose features depend upon electric field strength. For instance, the height of the dendritic structures is curtailed when the van der Waals adhesion force is overpowered by the electric force. Dendrites which would otherwise grow above this force-balance limited height instead undergo fracture. Upon fracture, dendrite fragments carry charge from one electrode to another in the electrostatic trap. The current delivered by the dendrite fragments is about 1000 times larger than the native soot charge current, thereby amplifying the effect of soot deposition. We present scanning mobility particle sizer evidence of soot capture and of large, highly charged soot fragments exiting the trap. Using transparent traps, we show micrographs with evidence of soot dendrite growth and fragmentation. We also use current measurements on electrostatic traps in order to investigate the influence of flow and electric field on the dendrite fragmentation mechanism. Finally, we describe the dendrite growth and fragmentation using a kinetic model and are able to reproduce our experimental observations of trap current. This work provides a self-consistent explanation of how soot dendrite fragmentation can be used to amplify the current signal measured via electrostatically captured soot. Furthermore, this amplification mechanism could potentially provide the basis for a cheap, robust On-Board Diagnostics sensor for particulate filter monitoring in vehicle applications.