Tim McDonald sees plenty of comparisons between biodiesel and the petroleum-based fuel that it is designed to replace.
“It works like diesel, pumps like diesel, stays like diesel and more or less acts like diesel,” says the scientist at Auburn University’s Centre for Bioenergy and Bioproducts. With the exception of NOx, the biodiesel offers lower emissions, is biodegradable and is famously “less toxic than salt.”
“We’re at an exciting time. We’re moving from strictly fossil fuels into a new era of renewable fuels,” he added during a recent presentation to the Technology and Maintenance Council (TMC). “What are the options? At least in trucking, there aren’t very many.”
Of course nothing is perfect. In the right quantities, salt and diesel fuel are both toxic to laboratory rats.
The biggest challenges to the trucking industry can emerge because of the varying quality of biodiesel. Different feed stocks can deliver viscosities that harm injectors. Higher boiling points can mean higher concentrations of fuel in the engine oil. The reactive chemical compounds can also transform into acids and engine deposits.
“We know we’re going to have more fuel building up in the engine oil,” notes Lilo Hurtado of ExxonMobil Lubricants and Specialties, referring to recent tests on fuel blends that contain between three and 10% biodiesel. “We’re trying to understand is there any impact on the rate at which the oil is going to degrade?
“When the stability goes south on us, the other side effect is it’s going to generate more organic acids,” he adds, noting how they will attack metals such as copper and lead that are used in cam followers, bushings and bearings. New piston deposits can also emerge.
They are the types of challenges that make it important to monitor suppliers of the fuel -requesting fuel made from soy and introducing some additional filters on the dispensing equipment.
“You need preventive maintenance on your fuel supply that is just as good as the rest of your vehicles,” noted Keith Bechtum of the Donaldson Company, recommending a four-micron filter between the storage tank and the vehicle.
The condition of the filters can also be used to identify a number of challenges with the fuel. If the supply is contaminated with water, the filter element will become swollen or frayed. The presence of a fine black sediment will indicate oxidation, and a slimy filter can indicate the presence of microbes.
The latter issue has become more of a problem since the introduction of Ultra Low Sulfur Diesel (ULSD). The sulfur, says Bechtum, also acted as a natural biocide. “If the source of the supply was running on the edge … this probably put them over the edge.”
The same issues can lead to challenges with fuel filters on the truck.
“Generally, all fuel filters used today are compatible with biodiesel blends up to B20,” he says, noting how a fuel/water separator and final fuel filter will meet most needs in fuel that is up to 20% biodiesel. (The plant-based fuel will hold about six times as much water as its petroleum-based counterparts).
The vast majority of plugged filters, meanwhile, can be traced to the quality of the fuel rather than cold weather. While the fuel will cloud at 13oC and form a gel at 0oC, that can be addressed with fuel heaters.
“Making sure they give you a consistent blend of fuel is probably more important than ever,” Bechtum observes, noting how he would hate to use a fuel with high cloud point in the extreme cold. “It’s pretty important to know what your fuel supplier is giving you.”
Indeed, a 10-degree spread in the cloud point can make a difference in cold weather.
Emerging challenges in an engine that uses biodiesel can be spotted through an oil analysis program. In addition to measuring the fuel dilution on every sample, Hurtado also recommends a gas chromatography to measure biodiesel fuel dilution, especially in equipment that faces severe service or high idling times. But maintenance managers will need to make a special request for this test since some labs will only test fuel dilution once there is a sign of low viscosity. And a measure of the oil’s Total Base Number will help to ensure that any increase in acids can be addressed.
“You don’t have to test every truck in the fleet,” Hurtado says. “You just have to make sure you’re taking a representative population.”
McDonald suggests that most of the issues will be cleared up as the biodiesel becomes more popular.
“We have 75 years or more experience in making petrochemical diesel and optimizing that fuel for the engines we run today,” he says. “We don’t have necessarily all that much experience with biodiesel. But it is coming.”