Effect of Biodiesel Blends on Diesel Particulate Filter Performance

Tests of ultra-low sulfur diesel blended with soy-biodiesel at 5% and 20% were conducted using a 2002 model year Cummins ISB engine (with exhaust gas recirculation) that had been retrofitted with a passively regenerated catalyzed diesel particulate filter (DPF). Results show that on average, the DPF balance point temperature (BPT) is 45°C and 112°C lower for B20 blends and neat biodiesel, respectively, than for 2007 certification diesel fuel. Biodiesel causes a measurable increase in regeneration rate at a fixed steady-state condition, even at the 5% blending level. The data show no significant differences in NO_x emissions for these fuels at the steady-state regeneration conditions, suggesting that differences in soot reactivity are responsible for the observed differences in BPT and regeneration rate. Soot from the various fuels was characterized by determining the fuel and lubricant fractions of the soluble organic fraction, elemental and organic carbon content, amorphous carbon/graphitic carbon ratio by Raman spectroscopy, carbon/oxygen ratio by energy dispersive x-ray analysis, and reactivity in oxygen by TGA. Results indicate a much more disordered soot structure, containing higher levels of oxygen as biodiesel is blended into the diesel fuel. The soot produced from biodiesel and blends is much more reactive in oxygen than diesel soot. It is concluded that the lower balance point temperature and higher DPF regeneration rates for biodiesel containing fuels are observed because the soot generated from these blends is more reactive.