The soot buildup in the DPFs must be periodically removed in a passive or active way. If it is not removed according to the manufacturers’ recommendations it will plug and cause serious engine damage.

The most common passive regeneration devices burn off the soot at high temperatures during normal engine operation and are found mostly on vehicle engines that are normally operating at high RPM’s (i.e. long haul highway trucks).

Active regeneration devices are considered for engines that are in idle and/or low rpm’s for a considerable time during their operational lifetime (construction equipment, garbage hauling trucks). These types of DPF’s require that the engine be placed in a high rpm mode for a lengthy period of time (30 minutes or more) to attain temperatures sufficient to burn off the soot build-up. Obviously this creates an added expense not only in fuel and operator costs but also down time during the work day.

Passive devices are expensive but they have long lifetimes paralleling that of the engine itself and require little servicing if they are properly maintained.

The Active designs however are another story. Since they are constantly building up soot and require considerable operator scrutiny and maintenance, their lifetime can be much shorter and add considerable expense to any business using them.

Filter designers are constantly experimenting with ‘new’ designs and interior substrate materials to extend the time between required regeneration. Another alternative to improving the regeneration process may be the recently CARB-approved fuel additive, Viscon. Some of its customers are reporting positive effects (extended time between regenerations). This would be easy to explain, as Viscon (according to the CARB testing reports) decreases PM emissions by more than 25% by improving the fuel itself (making it a more uniformed blend). As it accomplishes that PRIOR to the combustion, it simply decreases the PM load received by the DPF and subsequently extends the operational time between required regeneration periods.

www.worktruckonline.com/Article/Print/Story/2008/01/What-Fleet-Managers-Should-Know-About-Diesel-Particulate-Filters.aspx

www.msha.gov/nioshmnmfilterselectionguide/mnm_dpf_explanations.pdf

Fuel additives can chemically provide some of this efficiency but the negative tradeoffs just aren’t acceptable in today’s world.

Cleaner Diesel Fuel Additive – How might this be done?

A review of the literature provides some clues.

A pure low molecular weight (1-2 million) hydrocarbon polymer, polyisobutylene, is currently used in many industrial processes to exert a viscoelastic effect where other hydrocarbons in the mix are made to relax and thus improve the outcome. The details have been extensively studied and this viscoelasctic effect on hydrocarbons has also been shown to improve their combustion in fuels.
The details have been reported and we can look at them in the next entry. For now… check this reference material on viscoelastic effects.