It is being touted as part of the answer to dependence on foreign crude oil. Farmers are enthusiastic about biodiesel as it provides additional sources of revenue for them. Original equipment manufacturers, however, are more cautious about blending biodiesel and conventional fuel for their vehicles. Many, including Detroit Diesel, John Deere, Navistar, Mercedes and Volvo/Mack, prefer that biodiesel be no more than 5 percent of the blend (B5) fueling most of their equipment.

Over the past two years, some questions have been raised about biodiesel performance in engine operations. Fuel dilution is one well-known problem area. The bio component in biodiesel blends has a higher boiling point than traditional diesel fuels, making biodiesel more likely to be in the blowby gases which get past an engines piston rings and into the crankcase. Once there, its higher pour-point characteristics can create some real problems in low-temperature operations.

In our August 2007 issue, I wrote about possible engine oil issues that might arise from the use of biodiesel blends, including fuel dilution, deposits and corrosion problems. That same year, Infineum ran a Caterpillar 1N engine test with engine oils artificially spiked to have fuel-dilution levels of 5 percent biodiesel; this resulted in failing test results due to ring deposits.

Fresh Insights

We now have more insight into how biodiesel can challenge engine oils. In early 2008, a series of industry standard engine tests were run on biodiesel blends using engine test reference oils, with the objective of determining if there are any effects on lubricant performance from the use of B20 fuel. The tests were undertaken by the National Biodiesel Board and the Engine Manufacturers Association, and the results were presented by the Columbus, Ohio-based industry consultant David Stehouwer to last Junes ASTM Heavy Duty Engine Oil Classification Panel meeting, in Vancouver, Canada.

The experimental design called for running the Cummins ISB, Caterpillar C-13 and Mack T-12 engine tests. The oil tested was Reference Oil 831, which meets the current API CJ-4 heavy-duty engine oil specification. The only change was in the fuel used: Normally, an industry standard test uses reference fuel that meets specific properties. Those properties include boiling range, sulfur content, energy content and chemical composition (paraffinic, naphthenic, aromatic content). This series of tests used a blend of standard diesel fuel and biodiesel meeting ASTM D6751, with the biodiesel set at 20 percent of the blend.

As many readers know, the three engine tests are all part of the API CJ-4 specification.

The Cat C-13 is a 500-hour test using a Caterpillar C-13 engine with all-steel pistons, operated at 1,800 rpm and 1,200 grams per minute fuel rate. It evaluates the performance of crankcase lubricants with regard to piston deposits and oil consumption.

The Mack T-12 is a 300-hour test using a prototype E-Tech engine with a variable geometry turbocharger and production EGR cooling heat exchangers to simulate 2007 engine operation, but with increased exhaust gas recirculation rates. Test objectives are to evaluate the performance of crankcase lubricants with regard to cylinder liner, ring and bearing wear.

The Cummins ISB is a 350-hour test using a Cummins ISB engine, and evaluates a crankcase lubricants ability to reduce camshaft lobe and sliding cam follower wear. After an initial 100 hours of steady-state operation at 1,600 rpm to accumulate 4 percent soot in the oil, the engine is operated for 250 hours on a 28-second cycle simulating front-end loader operation.

Mixed Results

The Cummins ISB test showed that there was no adverse effect on cam and tappet wear when using B20 fuel compared to laboratory reference runs. Engine operational data also showed that the test was well within normal parameters. Used oil data showed that Total Base Number (TBN) loss was in the upper range of results. (TBN indicates the oils base reserve, needed to combat acids that can degrade the fluid.) The oils Total Acid Number (TAN) increased beyond the normal range, and viscosity increase was significantly higher.

The Cat C-13 engine results showed that top groove and top land carbon deposits were well within acceptability range and fell on top of reference run data. However, second-ring top carbon deposits were at the very top limit of acceptability, and above reference results. Oil consumption was a bit elevated but within acceptance limits. Two cold stuck rings were reported but not the one with the highest carbon level. This test also had cold stuck rings on other test runs. Used oil analysis showed TBN losses near the mean, with relatively high viscosity increase and TAN increase as well as oxidation levels which were significantly higher.

The Mack T-12 engine results showed cylinder liner and ring wear weight losses were well within acceptance levels and were similar to other reference runs. Oil consumption was also well controlled. Top groove and top land carbon were similar to other oils tested on PC-10 fuel. Lead content in the used oil was above acceptance limits, as well as lead increase per 50 hours. Viscosity increase was in the lower part of the range and TBN loss was near the mean, while TAN increase and oxidation were significantly higher.

To summarize: Using a CJ-4 engine oil and B20 biodiesel fuel, wear data and all controlled piston and ring deposits for these tests were within acceptance limits, and low-temperature viscometrics were not an issue. Low-temperature viscosity on the used oils also appeared to be good. Only lead corrosion and T-12 oxidation were worse than acceptance limits. The non-rated engine parts appeared clean and free of sludge. There is a general trend towards higher TAN without a corresponding drop in TBN. Infrared analysis shows more oxidation and ester formation, but it isnt clear that these are associated with viscosity increases. The issue of fuel dilution was not addressed in this test program.

Follow the Fleet

Plenty of questions remain, of course. For the diesel engine oil marketer, the question is: Will my oil perform satisfactorily with biodiesel blends? If not, what do I have to do to assure that biodiesel blend users are protected?

For the OEM, the question is a bit easier: What oils can I recommend for my equipment that will be satisfactory for use with biodiesel blends?

For the oil user, its an easy question: Which oil can I use?

Fleet testing can begin to give us some of the answers. The National Renewable Energy Laboratory has begun a program to evaluate B20 in typical operations. Last July it reported results from three fleets, including St. Louis Metros buses, another bus fleet in Boulder, Colo., and the U.S. Postal Service (which already uses B20).

The St. Louis Metro trial was typical of the test protocols being run with B20. The trial monitored 15 40-foot, 2002 model-year transit buses, all equipped with Cummins ISM engines certified to 2004 emission standards. For a period of 12 months, eight of these buses operated exclusively on B20, and the rest operated exclusively on petroleum ultra-low-sulfur diesel. The B20 and ULSD study groups operated from different depots at St. Louis Metro, but their bus routes were matched for duty-cycle parity.

Heres what the in-use evaluations found:

1) The B20 buses exhibited 1.7 percent lower fuel economy than the ULSD study group.

2) Reliability was comparable between the two study groups.

3) There was no significant difference in total maintenance costs between the two groups.

4) Engine and fuel system maintenance costs were 35 percent higher for the B20 study group, but because of bus-to-bus variability in maintenance costs, its not significant.

5) The B20 study group had a higher incidence of fuel filter and fuel injector replacements. Analysis of B100 and B20 samples did not indicate poor fuel quality. No fuel injectors were retained for tear-down analysis to determine failure mode and cause.

6) Lube oil samples were collected over a wide range of mileage within the drain interval, and analysis indicates no harm and some potential benefits with B20 use – notably, soot and wear metals were lower. Viscosity, total base number and corrosive metals were generally less degraded by ULSD use, but these qualities were still in-grade for the B20 buses throughout the oil drain interval.

Up Next: Test Development

It doesnt appear that there is a serious problem with using biodiesel, based on these field trials. However, the engine test protocols and industry standards we have in place are for more severe applications and are designed to provide a fail-safe environment. It is important to be sure that test procedures either account for biodiesel blends, or that modified tests or limits are established for biodiesel blends.

As an example, some specialized tests already measure performance of engine oils in natural gas-fueled engines, including the Cummins CES 20074 specification, which requires a special engine test operating on natural gas as a major part of the approval criteria. There is no reason to believe that a specific test for biodiesel cannot also be developed – but by whom, and at what cost in time and dollars? No one wants another test, so perhaps an existing test can be used with modified limits. It will still take development time and cost, but maybe not as great as a first-intent test.

If a biodiesel engine test procedure is developed, it will be necessary to develop an industry category to define it. The API process is available for just that purpose. This would give oil users and OEMs the opportunity to clearly identify the oil that is right for use.

The oil supplier will have to supply the oil, and that is always an issue since another oil category adds to the complexity of manufacturing and marketing. Oil suppliers naturally want to have as few products as is reasonable in order to simplify logistics. However, with the complexities of todays marketplace, it isnt always possible to have your cake and eat it too.

We can solve the lubrication problems that exist with biodiesel. Theres no doubt that biodiesel has a place in the fuels marketplace, beginning with areas where conventional diesel fuel is too expensive, or is not in sufficient supply, or where a local option makes biodiesel preferred.

There are sufficient data to show that biodiesel will perform and that – given some precautions regarding handling and storage, such as heated tankage and control of bacterial attack – it will be a valuable addition to the worlds need for energy.