Active regeneration experiments were performed on a production
diesel aftertreatment system containing a diesel oxidation catalyst
and catalyzed particulate filter (CPF) using blends of soy-based
biodiesel. The effects of biodiesel on particulate matter oxidation
rates in the filter were explored. These experiments are a
continuation of the work performed by Chilumukuru et al., in SAE
Technical Paper No. 2009-01-1474, which studied the active
regeneration characteristics of the same aftertreatment system
using ultra-low sulfur diesel fuel.
Experiments were conducted using a 10.8 L 2002 Cummins ISM
heavy-duty diesel engine. Particulate matter loading of the filter
was performed at the rated engine speed of 2100 rpm and 20% of the
full engine load of 1120 Nm. At this engine speed and load the
passive oxidation rate is low. The 17 L CPF was loaded to a
particulate matter level of 2.2 g/L. Active regeneration was then
performed using fuel dosing in the exhaust, which was oxidized at
75-80% conversion efficiency in the diesel oxidation catalyst.
Temperatures from 475°C to 550°C at the inlet of the CPF were
examined. Experiments were performed using ultra-low sulfur diesel,
5 and 20% biodiesel blends in order to determine the particulate
matter oxidation dependence upon biofuel percentage and to compare
with the previous results with ultra-low sulfur diesel. A method
was developed to produce more accurate measures of the particulate
matter loading in the CPF and improve the estimation of the thermal
oxidation rate during active regeneration. In addition to the
particulate matter mass, measured parameters included pressure
drop, filtration efficiency, particle size distribution, and
gaseous emissions.
Results with 20% biodiesel show a reaction rate five times
higher in the particulate filter for active regeneration as
compared to ultra-low sulfur diesel. For example, for a CPF inlet
temperature of 525°C, 19.6 minutes was required to oxidize 70% of
the particulate matter with ultra-low sulfur diesel, as compared to
9.8 minutes with 5% biodiesel and 3.4 minutes with 20% biodiesel at
the same conditions. This, combined with the lower particulate
matter production from biodiesel blends, shows a significant
benefit from the use of biodiesel in terms of minimizing the fuel
needed to actively regenerate the particulate filter. Regenerations
are not required as often, and due to the higher reactivity, more
particulate matter is oxidized per gallon of dosing fuel at lower
temperatures.