It looks like VW will support 5% bio in the fuel...summary below...it also discusses oil dilution from bio
full article here:
full article here:
Meeting the 2007 regulations requires the incorporation of diesel particulate filters to trap soot. To avoid filter plugging, however, the accumulated soot needs to be burned offâ€”a plugged filter will cause high backpressure and operational issues. Many original engine manufacturers (OEMs) use a regeneration scheme in which fuel is introduced late in combustion to create an exothermic reaction downstream in the filter, which burns off the soot. The resulting ash from regeneration of the filter can collect for hundreds of thousands of miles.
Volkswagen is using post-injection for regeneration and according to Stuart Johnson with the Engineering and Environmental Office of Volkswagen Group of America, the issue of oil dilution from biodiesel is a real concern for the automakers. â€œWe can tolerate up to 50 percent fuel mix in the oil but no more,â€ he said at the 2008 National Biodiesel Conference.
Volkswagen tests using B5 and post-injection showed 45 percent oil dilution after 10,000 miles, but surprisingly no engine damage was evident upon inspection. â€œUsing B10 at 10,000 miles surpasses that 50 percent thresholdâ€”and that is unacceptable,â€ Johnson said. â€œWe want longer oil change intervals as a car company, so itâ€™s hard for us to talk about this.â€ The implications are that increased fuel dilution due to biodiesel blends could lead to premature engine wear if oil changes are not done more often.
Senior technical advisor for Cummins Inc., Howard Fang, explains to Biodiesel Magazine exactly how this inordinate accumulation of biodiesel in the crankcase oil takes place.
Cummins has done extensive work to characterize biodieselâ€™s effects on engines, performance and exhaust. â€œBiodiesel definitely promotes fuel dilution,â€ Fang says.
Post-injection of fuel into the cylinders is intended to vaporize in the cylinder but not combust, exiting then through the exhaust valves and traveling downstream where the introduction of the unburned fuel to the catalyst creates an exothermic reaction incinerating the collected soot. Inevitably the heavier fractions of fuel will not vaporize during post-injection and in liquid form can adhere to the cylinder walls. Through the slapping motion of the pistons and oil rings, the unburned fuel from post-injection can make its way through the tight, hot quarters between the piston, rings and cylinder walls. The fuel accumulates in the crankcase and dilutes the oil, which is a major concern regarding engine wear and longevity.
â€œUsing post-injection you will generally see elevated levels of fuel dilution regardless of what fuel youâ€™re using,â€ Sappok says. Because biodiesel has a higher distillation temperature and boiling point, when itâ€™s present in the post-injected fuel it tends to dilute the oil on a level disproportionate to its blend ratio in the fuel. Fang says this is just now becoming understood.
Through his work at Cummins, Fang has developed a new algorithm to predict the amount of fuel dilution when running on various blend ratios of biodiesel. â€œThe conventional way to derive the calibration to estimate the amount of fuel oil dilution is completely wrong,â€ Fang tells Biodiesel Magazine. This conventional approach to determining biodieselâ€™s dilution effects on oil when implemented in a lab suggests mixing 5 percent of B20 in fresh oil, then 10 percent B20, and so on to create a calibration curve through analytical means such as infrared (IR) or gas chromatography (GC), the results from which can then be used to predict unknowns using the slope created by those data points. â€œWe cannot use this way to quantify the fuel dilution from biodiesel in the oil,â€ Fang asserts. â€œThe problem is in all IR, GCâ€”any analytical technique reallyâ€”you assume the concentration is B20 but because ultra-low sulfur diesel (ULSD) is easier to vaporize, the concentration of biodiesel on the cylinder walls is higher than 20 percent, maybe way higher.â€ In fact, Fang has developed a method to more precisely measure this and found that post-injected B20 can lead to as much as 40 percent methyl ester accumulation on the cylinder walls.
Fangâ€™s new method to determine this uses what he calls an oil tracerâ€”a component that is stable, not subject to decomposition or easy oxidation and is compatible with additives. â€œWe monitor the tracer concentration and quantify the decrease and correlate it to a certain fuel percentage and estimate the fuel dilution,â€ Fang explains. There are many different compounds suitable as oil tracers, but Cummins has been using pentaerythritol ester (PE). â€œItâ€™s a very common oil component used for aviation oil, so itâ€™s very compatible with oil,â€ he says. The GC or IR signal of PE is far different from the oil and additive signatures so the amount of the tracer can be easily quantified.
Sappok ran across a different analytical problem: Inordinately high oxidation readings gained from fresh oil and fresh biodiesel mixed. It is his conclusion that the ester peak interfered with the oil oxidation spectra.
At MIT, Sappok is interested in how trace contaminants resident in biodieselâ€”even that which is within the ASTM specâ€”may cause trouble downstream. Calcium and magnesium are limited to 5 parts per million (ppm) in D 6751, the B100 spec. Sappok says 1 ppm of trace metals in the fuel can equate to as much as 1,000 ppm of the same material in the engine oil. â€œOil consumption is about a thousand times less than engine fuel consumption,â€ Sappok says, which is where his calculation comes from. According to him, even biodiesel within the trace metals specification can lead to inordinate concentrations of potentially damaging metallic ash loading in the DPF. Sappokâ€™s concern is that ash from trace metals in biodiesel may either contribute to ash buildup in DPFs, facilitate a gradual deactivation of the catalyst used in regeneration, or both. Ongoing research conducted by Sappok will lead to a better understanding of how sodium and potassium ash specifically affect aftertreatment systems. â€œThereâ€™s not been a lot of work on this yet,â€ he says.
Fang doesnâ€™t buy this argument about trace metals in biodiesel, and the 1:1,000 ratio of contaminants present in the fuel versus that which ends up in the oil. â€œWeâ€™ve never seen that ash can cause trouble for the DPF,â€ Fang says. â€œIf the regeneration scheme is good, the ash is not an issue. â€¦ The MIT estimates are too high from my point of view.â€ Even though for years biodiesel has been heralded as a lubricity additive helping keep fuel system components like the moving parts inside fuel injection systems operating smoothly, the bitter irony here is that, when post-injected, it tends to dilute engine oil and interacts with additives and increases the possibility of engine wear. Much work remains developing viscosity improving, anti-wear, dispersant and detergent additive packages in which adverse reactions with biodiesel are significantly reduced.