Biodiesel and Cold Weather meet in Minnesota

Biodiesel and Cold Weather meet in Minnesota

The Minnesota Department of Agriculture recently released (February 15, 2009) a report to the legislature regarding the states mandated biodiesel program and the cold weather issues it has caused.

Starting in September 2005 Minnesota required that virtually all diesel fuel sold in the state contain at least 2% biodiesel. This level is supposed to be raised to 5% in 2009, 10% in 2012, and finally 20% in 2015.

This report by the Governors “Biodiesel Task Force” created in 2003 shows that there a number of significant problems with using biodiesel blends, particularly in areas subject to long periods of cold weather.

Some of the issues noted in the report:

· Discussion indicated at least fifteen cases of unusual filter plugging in commercial trucks this winter for which the cause had not been determined. Discussion of possible causes included engine manufacturers’ reduction of truck filter sizes (from 10 to15 microns down to 2 to 5 microns), paraffin from diesel, glycerin from biodiesel, water contamination, biotic contamination as a result of ultra-low sulfur diesel levels plus water contamination, and vehicle designs in which the fuel filter is located away from the engine.

· Discussion that existing cold flow test procedures are not sufficiently predictive of the
cold temperature performance of diesel fuel with or without biodiesel. ASTM International and other organizations at a national level must develop new test methods that are more predictive of the cold weather performance of diesel fuel and biodiesel blends.

· Variations in seasonal availability of fuel were also discussed, specifically routine shortages of diesel fuel at terminals in the fall leading to the practice of bulk plants and fleets buying and storing fuel in the late summer for use in the fall and early winter months when shortages of diesel are anticipated. Such stockpiling of B10 or higher could result in problems in above ground tanks.

· The suggestion was made that the Task Force discussions should freely address the availability and quality of all winter fuel in the state instead of being confined only to biodiesel. Given recent changes in the diesel industry, including biodiesel, low-sulfur diesel fuel and smaller fuel filter pore diameters, a wide range of issues regarding equipment and diesel fuel with and without biodiesel must be addressed.

Laboratory testing has indicated that blending with number one (#1) diesel at 50/50 rate produces results similar to treating with additives but the #1 fuel is at a far higher cost.

There is also a concern over whether the current testing (e.g. Cold Point (CP), Cold Filter Plug Point (CFPP), Pour Point (PP), Low Temperature Flow Test (LTFT)) done to assess cold weather operability characteristics of diesel fuel are adequate for testing biodiesel blends.

Unfortunately this discussion has been complicated by many factors including the change from Low Sulfur (LSD) to Ultra-Low Sulfur diesel (ULSD), that diesel fuel changes seasonally, the fact that biodiesel derived from different base oils have far different characteristics, that transportation and storage affect quality, and that materials will tend to precipitate out of biodiesel when it cold for extended periods of time.

To read the complete Minnesota Report to the Legislature please click here: Report to the Legislature February 2009

Please post your comments, questions, ideas, and thoughts.

Diesel Doctor

Copyright 2009© - William Richards

Diesel Fuel Mileage Decrease in Winter

Why Diesel Fuel Economy Drops in the Winter

Diesel fuel, particularly in the northern tier states changes rather significantly from season to season. In the cold weather months generally starting in September or October refiners begin to alter the chemical composition of diesel fuels to improve cold weather operability characteristics to meet ASTM, Pipeline Operator, and Customer requirements and specifications.

Refiners talk about the components that come out of the refining process as “streams”. In a typical refinery today there can be over 180 “streams” coming from the refining of crude oil. The addition of lighter product streams are known by names such as “aromatic chemicals”, “naptha’s”,” kerosene’s” and others to #2 diesel (whether Ultra-Low Sulfur Diesel (S-15) or Low Sulfur Diesel (S-500)) will lower (improve) the Cloud Point (CP), Cold Filter Plug Point (CFPP) commonly referred to as the gel point, and Pour Point (PP) depending on how much of those components are added to the base fuel. Refiners have a lot of latitude in determining how much of and what components are used to make these improvements.

The issue from a fleet operators standpoint is that these changes lower energy (Btu) content of the fuel. It is normal for fuel economy to decrease from one to as much as five percent seasonally. This decrease can be further exacerbated by fuel racks and or distributors further cutting with kerosene to try and improve cold weather operability. The normal energy content of #2 ULSD ranges between 138,000 and 140,000 Btu’s, kerosene is much lower ranging between 130,000 and 135,000 Btu’s, whereas gasoline is about 124,000 Btu’s per gallon.

As you can see the more lighter components added to fuel, the lower the energy content. Note: ULSD has 1%-3% lower Btu content than the LSD. This is primarily due to reduction in wax content in ULSD.

So if you put all of this together in a time line, you can see that you begin using additive to improve cold weather performance at the same time the refiners are blending the fuel in a way that reduces Btu content which lowers your fuel economy, then in the spring you stop using additive at the same time the refiners are going to a “summer” blend which increases the Btu content and so your mileage goes up.

Other cold weather considerations are more idle time, slower transit speeds, more time in traffic, and even driving through snow all, of which can have a significant negative impact on fuel usage.