Last winter was cold and long. We had problems with the diesel from our company gas station.
So what do we need to keep in mind for this winter?
Blockage of the fuel filter by paraffin crystals
The next winter is bound to come and with it sometimes an unpleasant surprise for many diesel drivers. Trucking companies and other large commercial users always buy diesel at the lowest price possible. Therefore, when temperatures start to drop, there may still be intermediate products or even pure summer diesel in the tank. Even private passenger cars that are not driven much may still have fuel in the tank that does not yet meet the low-temperature requirements placed on winter diesel according to DIN EN 590. The start attempt on a cold morning can then quickly turn into a false start. Starting at a temperature below approx. +3 °C, paraffin crystals form in the diesel. These snowflake-like crystals restrict the flowability of the fuel. As a result, it "thickens" to such an extent that it can no longer be conveyed through the line or the fuel filter to the injection pump. Despite a slightly different composition of the basic fuel of summer and winter diesel, certain additives (so-called WASA - Wax Anti-Settling Additives) must also be added in winter for flowability. They prevent the paraffin crystals from agglomerating and growing larger, which can lead to a blockage of the fuel filter.
"In the past", instead of additives, gasoline was mixed in (up to 30% depending on the outside temperature!) to maintain flowability. This is something you must never do again under any circumstances! Modern common rail injection systems are lubricated by the fuel. Therefore, the fuel must have a certain lubricity ready, which would be severely disturbed by the addition of gasoline.
The standards (DIN EN 590 for diesel, DIN EN 14214 for biodiesel) define the CFPP test, which describes fuel behavior at low temperatures. The Cold Filter Plugging Point, CFPP for short (EN 116), is used to check whether the fuel can still be pumped through a defined filter (symbolizing the normal fuel filter) at the required temperatures. It should be noted that the method determines the cold suitability in the laboratory. This means that the measured value in the vehicle is not exactly the same, but can be much worse than determined. It is therefore possible that fuel that has a CFPP of -20°C nevertheless causes problems on the vehicle at an outside temperature as low as -10°C. This is due to several reasons: the fuel filters installed in the vehicle typically have a much finer mesh size than the filter in the laboratory process. Also, the fuel in the vehicle is in a cooling phase significantly longer than in the laboratory process (a few hours overnight vs. a few minutes in the lab), because like any crystallization, the formation of wax crystals is a function of time. It is even possible that two vehicles with diesel refueled at the same pump behave differently. While one vehicle runs perfectly at -28 degrees, nothing works on another type with the same fuel. The reason for this is that the electrical fuel filter heating system is designed differently for the vehicles.
If you want to be on the safe side, you can switch to the so-called premium diesel grades, whose extreme cold resistance is advertised by the manufacturers. However, this security also comes at a higher price at the gas station.
More "lenient" regulations apply to heating oil, some of which is used in stationary diesel engines for power generation. Here, in DIN 51603-1 (extra light heating oil), the cold suitability is linked to the cloud point. In contrast to the fuel standard DIN EN 590, the standard does not specify which cold suitability corresponds to which season. However, a CFPP above -10 °C is not permissible according to the standard. The lower suitability for cold temperatures compared to diesel fuel for vehicles results from different requirements; for example, the heating oil only has to remain pumpable within the logistics chain. Larger wire cross-sections and more powerful pumps are also in use there. The end customer typically stores the heating in frost-free premises (e.g. oil cellar).
The cold suitability of fatty acid methyl esters (FAME) or biodiesel according to DIN EN 14214, which are used as diesel substitutes or added to diesel, is also tested with the CFPP.
However, a distinction is made between whether the biodiesel is to be used as a blending component in mineral fuels and whether pure biodiesel (so-called B100) is to be used as a fuel or heating oil.
The biodiesel blend component for diesel fuel may have a lower cold weather suitability than the final product (diesel) has at the corresponding time of year. The adjustment of the low-temperature suitability of the end product is therefore carried out via the mineral component.
In the DIN EN 14214 standard, pure biodiesel (FAME) has the same requirements for low-temperature suitability as its mineral counterpart in DIN EN 590. In addition, the monoglyceride content is limited depending on the season. These compounds are responsible for the occurrence of filter blockages due to thickening, especially in biodiesel.
In the corresponding standards for diesel and biodiesel fuels (B100), the requirements for cold behavior are regulated in the national annex. The following applies to Germany: