thermal crack damage. A surface microphone coupled directly to the filter sub-
strate through a hole in the can and intumescent matting measures brick vibration,
while a background detector measures exhaust pipe and canning vibration events
in order to discriminate metallic thermal expansion. Vibration and internal ther-
mocouple data is presented from exothermic regenerations for several different
filters loaded with soot on a commercial Diesel Particulate Generator with standard
Diesel fuel and fuel treated with a catalytic additive. The extension of the tech-
nique to testing on a vehicle is demonstrated. (2) A relatively simple, post-test
evaluation which involves reverse aspiration of DPF test parts with a cold Diesel
soot aerosol generated with compressed air. The technique can locate DPF cells
where the soot aerosol is not filtered though the substrate between the inlet and
outlet channels. The deposition of soot on the substrate is shown to be an indicator
of internal damage and, together with simple optical microscopy, can help to
identify failure mechanisms. The paper presents examples of the above techniques
to examine thermal damage to Silicon Carbide and Aluminium Titanate DPFs
which have been subject to ‘worst case’ regenerations.
Keywords DPF
Crack
SML
DPG
Diesel
1 Introduction
The regeneration of heavily loaded Diesel Particulate Filters (DPF) parts can cause
thermal damage to DPF substrates due to the high thermal gradients associated
with the exothermic oxidation of the deposited soot.
The threshold of thermal damage depends on the physical properties of the DPF
material used—including: thermal conductivity, heat capacity, material strength
(fracture toughness K
Ic
), Coefficient of Thermal Expansion (CTE), Young’s
modulus (E), melting point/maximum application temperature. Further, the
application of a catalytic coating to the DPF or addition of a fuel borne catalyst can
significantly affect the threshold of exothermic reaction.
Most wall flow DPFs fall into two categories as follows:
Monolith These have a single brick construction and are usually made from
Cordierite.
Segmented For vehicle applications, these are typically made from individual
segments which are cemented together. They are usually made from
Silicon Carbide.
The differences in the physical and thermal properties of these filter types leads
to significant differences in thermal damage resistance (usually associated with
loaded regeneration).
610 T. Hands and Q. Li