Use of biodiesel can lower the balance point temperature in diesel particulate filters (DPF) compared to Ultra Low Sulfur Diesel, and can cause a measurable increase in the regeneration rate of the DPF, according to data from the first phase of a study by the National Renewable Energy Laboratory and Cummins presented at DEER 2006.
The balance point temperature (BPT) is the temperature of the DPF at which the amount of soot that is accumulating in the filter equals the amount that is oxidizing off. If the BPT is lower than the general exhaust temperature, then no active regeneration is needed to clear the filter. Conversely, if the BPT is higher than the general exhaust temperature, active regeneration of the filter—an artificial, higher temperature burn—is necessary.
The researchers found that the BPT was lower by 45° C for a B20 blend and by 112° C for B100, compared to ULSD fuel. They also found that the measurable increase in regeneration rate of the DPF was not accompanied by significant differences in NOx emissions, which suggests that inherent differences in soot reactivity are primarily responsible for the observed differences in BPT and regeneration rate.
The team characterized the soot from the various fuels by a variety of methodologies, and found that use of biodiesel produces a much more disordered soot structure containing higher levels of oxygen, and that the soot for biodiesel fuels is much more reactive in oxygen than diesel soot.
By not only validating the compatibility of biodiesel blends with advancing aftertreatment technology but by also showing a benefit, this work paves the way for wider adoption of biodiesel blends in on-road heavy-duty diesels. Such vehicles are required by the 2007 particulate emissions standards to use DPF technology.
This first phase of the study was using steady-state conditions, and a 2002 engine certified to 2004 emissions levels. The second phase will move to a 2007-compliant engine and aftertreatment system, and test under transient conditions.