This illustration shows how an anti-gel can keep fuel in a liquid state. Both test tubes were chilled to the same frigid temperature.
Choosing the right biodiesel
In winter, lack of fuel flow is one of the most troublesome issues for truckers, and the bottleneck in the system that makes the flow stop is the fuel filters. Filters work on an extremely fine level, so any tendency for the fuel to form wax crystals or anything similar will block good filters and stop the truck in its tracks.
“All diesel fuel has waxy components that form crystals as temperature drops,” says Cyclo’s marketing manager, Laura Smith. “When temperature drops further, crystals form a lattice network, thereby thickening diesel fuel and eventually leading to gelling.”
Unlike diesel, biodiesel doesn’t contain paraffin wax, but it has its own set of cold-weather problems. “It still gels in cold temperature because lowering the ambient temperature causes the viscosity of the biodiesel to increase,” says Erik Bjornstad, who is in charge of technical sales at Bell Performance. “Between the two phases in the fuel, you have multiple mechanisms causing gelling and thickening of the fuel blend, leading to filter plugging.”
Cold filter plug point, or CFPP, is an essential piece of data truckers need to know about their fuel in winter, because it represents the temperature at which they can expect fuel problems to begin. The refiner generally provides pour point, cloud point and CFPP data for their blend, and the trucker can find out that information from the fuel wholesaler, says Matthew Cohen, general manager of Solpower and a consultant to StarBrite, an additive manufacturer.
Biodiesel fuel’s CFPP differs from diesel’s because, says Dave Slade, technical representative at Renewable Energy Group, a biodiesel refiner, “it consists of something called ‘methyl-esters,’ which normally solidify at 25-30 degrees F. That’s the biggest issue, as diesel fuel gels at a much lower temperature.”
He says biodiesel may also contain small amounts of mono-glycerides, which are converted to methyl-esters as they are refined. Since no chemical process is perfect, there are always small amounts that don’t get converted, he says. Problems most often occur when the mono-glyceride level is too high or you have “excess water” in the fuel, Slade says.
The best refiners remove nearly all the mono-glycerides, but poor-quality biodiesel contains much higher amounts, and these are often responsible for the gelling troubles you’ve heard about. The small amounts that the best fuel retains “stay in solution,” which means the fuel remains liquid, Slade reports. This normally prevents trouble.
Cohen says, “Most data suggest that B2 to B5 (2 percent to 5 percent biodiesel) will behave similarly to pure diesel fuel, and any filtration problems are generally related to fuel quality and cleanliness rather than its actual CFPP.”
How do you find the best refiners? The National Biodiesel Board has been encouraging refiners to adapt their production processes to the BQ-9000 standard for some time. BQ-9000 not only determines that the process uses the best refining methods, but guarantees that its performance is monitored constantly and problems are corrected immediately. You can also ask if the fuel meets the ASTM 6751 specification.
Another factor in CFPP is the raw material used to make the fuel, regardless of the refining process. “B100 made from soy will typically have a cloud point of 30-32 degrees Fahrenheit and reach its CFPP at 28 degrees,” Cohen says. B100 made from palm oil or animal fats, he adds, might have much higher levels of both saturated and unsaturated fats and a CFPP approaching 60 degrees. Cloud points for some oils can be even higher.
“Depending on what feedstock is in the blend,” Cohen says, “B20 can have a range of increased sensitivity to cold from +5 to +20 degrees. If a typical diesel fuel is good to 12-14 degrees, using a B20 blend can take the fuel’s cold weather serviceability up to 17-34 degrees F” – a hot day during a Midwestern winter.
Interestingly, some engine manufacturers actually prohibit the use of bio