Bad Bio Diesel Fuel Can Cause Problems

Posted 11/12/2009
By Jim Newkirk

With the focus on environmental responsibility and people watching their budgets, consumers nationwide have become much more interested in bio fuels. Most of us are very familiar with the 10 percent ethanol blends as well as the E85 fuels in use around the country. Consumers may be tempted to use cheaper grades and different blends of fuel to save some cash. As technicians, we've all experienced vehicles with "bad gas" and the resultant driveability problems. We'll start seeing more issues as consumers start to fill non flex fuel vehicles with E85 to save a few dollars.

"For diesel-powered vehicles, the problem of incorrect fuel use is becoming even more prevalent as people look at using bio diesel sources to fuel their diesel vehicles.”

For diesel-powered vehicles, the problem of incorrect fuel use is becoming even more prevalent as people look at using bio diesel sources to fuel their diesel vehicles. While use of commercially prepared bio diesel fuels is a good thing, use of improperly prepared or blended bio diesel can cause driveability issues, just as on the gasoline vehicles mentioned above.

Let's take a look at bio diesel fuels and some of the issues that technicians are encountering when these fuels are used improperly. The common commercial bio diesel blends available to the consumer are generally rated from B2 to B20 bio diesel. The number indicates the percentage of bio fuel that is blended with standard diesel fuel. So as an example, a B10 bio diesel fuel is a 10 percent bio to diesel blend while a B20 bio diesel fuel is a 20 percent bio to diesel blend.

So what exactly is the "bio" part of bio diesel? Bio diesel is made from renewable feedstock sources such as plant matter (examples: soybean oil, canola oil, palm oil) or animal fats (examples: tallow, recycled cooking oils, fryer grease). In either case, the biomass used to produce the fuel must be properly processed. Chemically, biomass fuels are made up of triglycerides of fatty acids (that's the stuff that clogs your arteries when you eat too much pizza!) and this is not something we want running through a diesel injection system.

When processing the biomass to make bio fuel, a chemical process known as "transesterification" is performed. In transesterification, the biomass is reacted with alcohols (usually methanol but other alcohols could be used as well) and a catalyst. This produces a bio diesel fuel (chemically a fatty acid methyl ester) similar to standard diesel fuel and glycerin (the bad stuff we don't want in the fuel). Separate out the glycerin and you have a clean bio diesel fuel.

As technicians, you will encounter diesel vehicles that have had a bio diesel fuel system retrofit kit installed with separate fuel tanks and valves allowing use of either bio or regular diesel fuel at the flip of a switch. You will also encounter customers who simply pour bio diesel directly into the vehicle fuel tank. Now, as long as the customers in question are using properly prepared and blended bio diesel, there should be no problems ... right? Wrong.

Let's look at why. Most automotive manufacturers recommend bio diesel blends of 5 percent or less (B5 bio diesel) and the bio fuel used to create this blend must adhere to the American Society for Testing and Materials (ASTM) D-6751 standard of fuel quality. There is some risk associated with running a diesel engine on bio diesel fuels that exceed the manufacturer's specified fuel blend requirements and the risk of running a vehicle on improperly processed bio diesel fuel is greater still.

For example, Volkswagen recommends bio diesel mixtures of no greater than 5 percent be used in their vehicles. While a diesel will run on up to 100 percent bio diesel, problems can occur due to improper fuel blending and preparation and concentration of bio diesel. The ASTM D-6751 standard provides for maximum permissible levels of free glycerin contained in the bio diesel fuel. If excess free glycerins are present, deposit formation in the vehicle fuel system is likely to occur with detrimental results.

The situation becomes even more grim if an unprocessed bio diesel fuel (such as vegetable oils or fry grease) or mixtures of processed bio diesel fuels (such as those distilled in a non-commercial process) in excess of the manufacturer's mixture recommendation is used. The eventual accumulation of fatty deposits can cause fuel system failures ranging from misfire issues to clogged filters, pumps and injectors. In worst-case scenarios, actual failure of components is possible.

In 100 percent blends of bio diesel that meet the ASTM D-6751 standard for fuel quality, the bio diesel fuel will fall below the requirements of free glycerin and total glycerin content (0.020 free glycerin or 0.240 total glycerin expressed as a percentage of total fuel mass). Excess glycerin content can cause deposit formation, leading to fuel system clogging and also can contribute to poor cold weather running and startability issues.

The key point to remember is that a properly prepared and blended bio diesel fuel meeting the ASTM D-6751 standard and used in the manufacturer's called-for blend percentages should not cause any issues. On the other hand, running your car on fryer oil filtered through a strainer may sound like a great way to save money, but in the long run improperly prepared bio diesel can cost a customer in damaged equipment and repairs.

Jim Newkirk is the Identifix European team leader. He is ASE master with L1 and Bosch BSC certified.

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