Are Biodiesel Blends Viable?

Made from renewable feedstocks, biodiesel promises to supplement the limited supply of traditional petroleum-based diesel fuel. However, it is not meant to be a direct replacement. "Biodiesel is not intended to replace diesel fuel completely, and will not be the solution on its own," says Amber Thurlo Pearson, National Biodiesel Board.

One reason is capacity constraints. "Production capacity is increasing to the tune of just under 900 million gal. of pure biodiesel," says Pearson. "Our goal is currently '5 x 2015', or 5% of on-road diesel fuel needs being met by biodiesel by 2015. That would equate to about 2 billion gal. Our current production/consumption for 2006 was at 225 million gal."

Although still far from its long-term goal, biodiesel capacity is expanding at a rapid pace, tripling in both of the last two years. According to Pearson, there were 25 million gal. produced in 2004 and 75 million gal. produced in 2005.

Technical hurdles to biodiesel's adoption stem from differences in chemistry compared to petroleum-based diesel. "If we had started with biodiesel 70 years ago and we were transferring to petroleum diesel, we would be having some of the same conversations we are having today about biodiesel," says Don Borgman, director of industry relations - North America, Deere & Co.

These differences can be mitigated by using lower blend ratios of the fuels. The most common blend is B5, a mix of 5% biodiesel and 95% petroleum-based diesel. Likewise, B20 equals 20% biodiesel content, B30 equals 30% biodiesel and so on. B100 represents pure biodiesel.

"If you took 100% concentration of [any product], it will have some impact," says Borgman. "At 5% concentration, 95% of the impact is going to be mitigated."

This is why many manufacturers recommend starting with B2 and B5 blends. "We do that to try to mitigate some of the different characteristics. We want the public to get familiar with it on a more gradual scale and not have bad experiences," says Borgman. "What we are really trying to do is get people educated and make sure all of the compatibility issues are resolved. There are some different things we need to learn to run biodiesel."

Pearson also points out that no modifications are needed to engines to run B20 blends or below.

More testing required
Biodiesel can offer some important benefits. "Biodiesel increases the lubricity of the fuel, which can result in longer fuel pump and injector life," says Kris Stearns, fuel and coolant engineer, Caterpillar.

And test data going back nearly a decade indicates it is a safe fuel. "[Caterpillar] has done testing with biodiesel starting back in the mid-1990s," says Stearns. "We have shown that our engines run well on it. In particular, some of the older engine models can run very well on even B100. There really have not been any performance issues with it."

Most manufacturers approve the use of at least B5, with no impact on the warranty as long as the fuel complies with the ASTM D 6751 specification for biodiesel. On certain engine models, blends up to B30 have been approved.

The hurdle to widespread manufacturer approval of higher blends appears to be adequate testing time for the new electronic engines.

"We are in the process of validating the biodiesel percentage that will be allowed for use in our technologically advanced 2007 on-highway diesel engines," says Stearns.

"We really want to get some testing time with the electronic engines to make sure we didn't miss anything in the analysis," agrees Richard Hall, product planning and process improvement, Case Construction Equipment. "The mechanical portions of the fuel delivery systems are very common between mechanical and electronic engines. But the electronic engines have a lot more sensors that adjust fuel based on certain engine operating parameters. That's what we are trying to monitor."

Power output
B100 biodiesel contains less energy content than petroleum-based diesel. "Round figures, you get about 140,000 BTU out of a gallon of petroleum diesel and you get about 130,000 BTU out of a gallon of 'neat' biodiesel," says Borgman.