Bypass oil filtration technology, which was introduced to the trucking industry in the 1930s, has been positioned mainly as a way for fleets to extend engine oil life and oil drain intervals.
However, oil filtration is now getting a fresh look as fleets search for ways to maintain current oil drain intervals and boost protection of engine components from the side effects of EGR emissions-reduction technology.
“Bypass filtration has always aimed to achieve two things: control soot levels and reduce abrasive wear by removing a much higher percentage of the smaller wear-causing particles than a full-flow oil filter is capable of addressing,” explains Brent Birch, laboratory manager for Champion Labs, maker of the Luber Finer Zgard bypass filtration system.
“First of all, soot particulates are abrasive and contribute to engine component wear. It also thickens the oil, reducing its lubrication properties,” he says. “With EGR, transporting, cooling, and then reintroducing part of the exhaust stream back into the engine to reduce emissions also can increase soot in the oil. So bypass filtration is…positioned to help remove that extra soot and thus preserve and potentially extend the protective qualities of the engine oil.”
Then there is the issue of acidic corrosion, a situation that can be exacerbated by the nature of EGR, Birch says. “EGR engines operate at a much higher heat level [20 to 30 degrees higher than pre-'02 diesels], yet you are also cooling down exhaust gas and re-introducing it into the engine,” he notes. “That allows for more water condensation to form, which combines with the sulfur dioxide compounds created as a byproduct of diesel fuel combustion. Sulfur dioxide combines with water to form sulfurous acid, which combines with oxygen to form an even stronger sulfuric acid, which is very corrosive.” Sulfuric acid can also increase engine wear, so with big bore diesel overhauls costing upwards of $3,000 per cylinder, it's not hard to see why fleets using EGR engines are looking for ways to minimize the conditions which could lead to increased component wear, Birch says.
“Our Zgard bypass filter, for example, contains extra Zinc to help support the engine oil's TBN [total base number] in order to reduce the potential for acid formation,” he says. “However, this may become less of a problem as we move to ultra-low-sulfur diesel fuels in 2006.”
Birch points out, however, that the real value of bypass oil filtration for EGR engine users is the reduction in oil soot levels. Champion Labs worked with an outside firm to test its bypass system with a fleet using Mack EGR engines, with the desired oil change interval pegged at a soot level of 3%.
Using just the standard full-flow oil filter required an oil change at 150 hours because the soot loading level reached 3%, Birch notes. When a bypass filtration system was added, the fleet's engine oil didn't reach the 3% level until 300 hours.
“The key is that a bypass filtration system has a much tighter filtration media, so it can remove much smaller soot particles without interfering with the oil flow rate within the engine,” Birch explains.
High soot levels can also deplete the additives lubrication makers put into engine oil, which help enhance the oil's ability to combat engine wear. Sometimes, just a 1/2% extra higher level of soot can start depleting additives, he adds.
In 2007, the next generation of low-emission engines will be in operation, perhaps bringing new challenges to oil filtration systems. Not only will new aftertreatment systems make an appearance, but the very composition of engine oil may change.
“From the lubrication side, oil additive packages may be completely different than what's used today,” says Birch. “Though there will be far less sulfur in the fuel, there will be some, so we will still be dealing with the sulfuric acid formation issue. Other corrosive compounds-such as nitric and organic acids — could also be formed So particulate filtration will still be key in 2007. We see bypass filtration serving as a backstop, if you will, to help protect the oil additive packages as well.”
