Effects of biodiesel blends on particulate matter oxidation in a catalyzed particulate filter during active regeneration
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. Copyright © 2010 SAE International.