FARGO, N.D. — Biodiesel is, as the name implies, a biological product. It’s susceptible to many of the same problems as other biological organisms — things like bacterial infections.
Think about it. Corn, soybean, canola and any other organic substances entering biodiesel refineries are biological. They remain in an organic state, just like cooking oil, so they must be treated with greater care than fossil fuel until you burn them in your diesel engine.
Higher percentages of biofuel in the diesel blend means more bacterial problems. A B20 is more delicate than some of the older B2 biodiesel blends.
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Typically, the organic portion of a B10 blend is more than 50 percent soybean oil, corn is nearly 20 percent and it’s about the same for canola. The balance is animal fat and waste cooking oil.
Microbial contamination has become a greater problem since ultra low sulfur diesel (ULSD) came on the scene in 2006. Before that, high sulfur content controlled the bacteria. The problem in a tank where microbes thrive is the line where water in the bottom meets the lighter diesel on top.
This critical line occurs in any diesel tank, from the smallest yard tractor to the largest bulk storage facility, says Eric Lawson, biodiesel specialist working with MegCorp Fuel Consulting in Minnesota.
Lawson was demonstrating to farmers at Fargo’s Big Iron trade show what happens in various biodiesel scenarios. In one glass beaker, there was a distinct separation between water and the B10 biodiesel, with all the water settling to the bottom. Although the tainted biodiesel had only been in the beaker for one week, microbial growth was visible to the naked eye.
“Biodiesel is more stable today than back in 2006, when the blend was only two percent biological. But even with that small percentage, we had real problems because of too much glycerin,” recalls Lawson, explaining that glycerin is byproduct of the biological oil. It creates problems because of its waxy characteristic.
“When they eliminated sulfur in 2006, they eliminated the antimicrobial control agent. You might have had two or three inches of old water setting in the bottom of your tank for 15 years, but the sulfur prevented microbes from growing. When we took away the sulfur, that’s when we started seeing bacterial problems in biodiesel.”
Lawson says microbes require water, oxygen and warmth. In the winter, water at the bottom of diesel tanks is frozen, preventing microbial action. Prior to Tier 4 emission regulation changes, farm implements did a significant amount of work in cooler temperatures in early spring and late fall, so the microbes had some degree of warmth to foster growth. Microbes were more prevalent if you ran your implements in hot weather.
But now, under Tier 4 criteria, hot diesel is returned to the tank whenever the engine is running — summer, winter, spring or fall. Microbes love it.
“Bacteria get into the pump and into the injectors. We usually trace the problem back to the service tank. Of course, from there it can get into a lot of engines.”
Lawson says he doesn’t see this microbial problem nearly as much in vehicles that keep running. Semi-truck tractors used on highways top up with fuel, burn it, then top up again. Farm implements work long days for a few weeks, then go into storage — a perfect scenario for microbes.
The stability of ULSD lasts for six months to a year. That means combines in particular are susceptible to fuel problems. With marginally stable fuels, even your tractors and sprayers might have problems after just six months of storage.
“The message is that we can’t take fuel for granted anymore. We never used to require stabilizing additives. Today they’re essential. The other consideration is the quality of fuel you buy.
Lawson said if a sample taken from the bottom of the tank is bright and clear there shouldn’t be any problem.
“But if you find water and cloudy fuel, then you know you’ll have an issue somewhere down the road. You’ll need to add a universally soluble biocide.”
In changing filters, if you find a fine black sediment, it’s probably oxidation. This is caused by hot fuel returning to the tank, creating something like coking of the fuel.
Parafin occurs naturally in No. 2 diesel fuel when the temperature is at or below the cloud point. The Filter Manufacturers Council says the cloud point is the temperature at which paraffin begins to form cloudy wax crystals. These wax crystals flow with the fuel and coat the filter element. This quickly reduces the fuel flow and starves the engine.
Typical cloud point temperatures range from -28 C to -7 C. They may occasionally be as high as 4.4 C. Kerosene and No. 1 diesel contain very little paraffin, and therefore have cloud points and pour points near -40 C.
MegCorp says fuel filters can occasionally be plugged with a brown grease that’s similar to Vaseline, indicating one of three possible conditions. The biodiesel may not meet the criteria of ASTM D6751. Water absorbing filters hold the water on the filter media, thus attracting monoglycerides. Sediment on the filter can also attract monoglycerides. Melting the monoglycerides off the filter requires temperatures in excess of 65.5 C.
Sediment is one of the easiest problems to spot. It’s characterized by a filter plugged with rust, tank scale and other foreign particles in the folds. Sediment also attracts glycerin, which degrades the fuel and causes further plugging. This condition may require a major cleanout of the implement tanks.
MegCorp recommends changing all filters going into winter and adding stabilizers to all diesel vehicles and storage tanks.
