Winter diesel fuel (also known as winter diesel, alpine diesel, or winterised diesel) refers to diesel fuel enhanced to prevent it from gelling in cold weather conditions. In general it is achieved by treatment with additives that change the low temperature characteristics of the fuel.

Operation Diesel fuel is prone to waxing or gelling in cold weather; both are terms for the solidification of diesel oil into a partially crystalline state. Below the cloud point the fuel begins to develop solid wax particles giving it a cloudy appearance. The presence of solidified waxes thickens the oil and clogs fuel filters and injectors in engines. The crystals build up in the fuel line (especially in fuel filters) until the engine is starved of fuel, causing it to stop running.

The cold filter plugging point (CFPP) is based on a standardized test that indicates the rate at which diesel fuel will flow through a standardized filtration device in a specified length of time when cooled under certain conditions. Similarly the "Low Temperature Flow Test" (ASTM D4539) indicates the winter performance of diesel with improver additives. Note that both the CFPP and LTFT temperature is some degrees above the pour point temperature at which diesel fuel loses its fluid character and that pumps would stop operating.

There are a number of solutions available which allow diesel engines to continue to operate in cold weather conditions. Once the diesel motor is started it may continue to operate at temperatures below the CFPP – most engines have a spill return system, by which any excess fuel from the injector pump and injectors is returned to the fuel tank. When the engine has warmed, returning warm fuel should prevent gelling in the tank.

Fuel Preheater Low-output electric heaters in fuel tanks and around fuel lines are a way to extend the fluid characteristics of diesel fuel. This is a standard equipment in vehicles that operate in arctic weather conditions.

As the fuel filter is the first point to become clogged up, most diesel motor cars are equipped with a filter heater. This allows summer diesel with a CFPP of –7 °C to be operated safely in –20 °C weather conditions. The fluid characteristics of winter diesel are also extended allowing a diesel type of CFPP –15 °C to be operated safely in –24 °C weather conditions.Betriebshandbuch Golf 4 TDI, Ausgabe 2001, Volkswagen AG, Abschnitt „Winterbetrieb", Zitat: Das Fahrzeug ist mit einer Filter-Vorwärmanlage ausgerüstet. Die Kraftstoffanlage wird dadurch bei Verwendung von Winterdiesel, der bis –15°C kältebeständig ist, bis etwa –24°C betriebssicher. [...] Krafstoffzusätze (Fließverbesserer), Benzin und ähnliche Mittel dürfen dem Dieselkraftstoff nicht beigemischt werden. Note that a filter heater cannot melt wax particles in the feed system so that fuel supply can be problematic at cold start.

Additives Retail stores offer a number of additives that will lower the CFPP of diesel oil. These will only be effective when added above the Cloud Point as the additive needs to mix well with the diesel oil – ideally the additive should be added at the fuel station when the fuel is still warm from the storage tanks.

The additives will not prevent the diesel from developing wax particles but these are hindered from melding together to form larger wax flakes that can clog up the fuel filter. In comparison with blending diesel fuel with lighter fuel (that has a lower CFPP) the usage of additives is cheaper and gas stations in cold regions offer diesel fuel with additives at no extra cost (see below). If the gas station offers winterized diesel you should not add additional additives – the fluid characteristics may deteriorate due to incompatible additives and the CFPP enhancement may be reversed.

Blending In North America, gas stations offer two types of diesel fuel – according to ASTM D975 these are named No. 1 and No. 2 fuel. No. 1 fuel (similar to kerosene) has a natural CFPP of -40 °C but it is more expensive than No. 2 fuel. Adding No. 1 fuel will lower the CFPP of No. 2 fuel – adding 10% will lower the CFPP temperature by about 5 degrees.

For some diesel motors it is also possible to add even lighter fuels like gasoline to extend the CFPP characteristics. Some car makers were recommending adding up to 20% gasoline to permit operation in cold weather (at the price of higher consumption) and it had been common practice in Europe where No. 1 fuel is not offered at gas stations. Since the 1990s car makers began selling only direct injection diesel engines – these will not withstand any gasoline portions in the fuel as the high pressure in the injection device will not withstand any loss of lubrication from fuel oil without doing damage to the injectors. High pressure fuel pumps depend on diesel fuel for lubrication and the addition of gasoline will cause adverse wear and eventual failure of the pump.

Car makers selling common rail or Unit Injector diesel engines prohibit the dilution of diesel fuel with either gasoline or kerosene as it may destroy the injection device.

Winter fuel classes Due to improvements in fuel technology with additives, waxing rarely occurs in any but the coldest weather. In regions with a cold climate, the standard diesel fuel at fuel stations is required to meet certain CFPP characteristics. In Europe this is governed by the EN 590 standard which had originally been created to describe the validation of low-sulphur diesel – its national variants came to include earlier legislation on diesel characteristics in winter conditions. EN 590 statutory regulations exist in all countries of the European Union, as well as Iceland, Norway and Switzerland.

Winter diesel For the "temperate" climatic zones, the EN 590 standard defines six classes from A to F. In Central and Western Europe, the winter diesel (Winterdiesel, diesel d'hiver) must meet Class F conditions at least from the beginning of December to the end of February. During a transitional period (mostly October and April), a lower class must be met.

Tests in the Alpine regions have shown that the diesel fuel offered at gas stations extends the law requirements by some degrees, showing a CFPP of −27 °C in all samples.Test der Temperaturbeständigkeit von Winterdiesel The CloudPoint is not specified in EN 590 although DIN 51603 for heating oil specifies a CloudPoint below +1 °C for CFPP −10 °C. Current additives allow a CFPP of −20 °C to be based on diesel fuel with a CloudPoint of −7 °C.

Class A Class B Class C Class D Class E Class F CFPP value +5 °C 0 °C −5 °C −10 °C −15 °C −20 °C CloudPoint (not specified in EN 590)

Arctic diesel For the "arctic" climatic zones, the EN 590 standard defines five classes from 0 to 4. In Scandinavian countries, the winter diesel (Vinterdiesel) must meet Class 2 conditions. Some refiners offer both standard winter diesel and arctic winter diesel in parallel, commonly differentiated as Winter Diesel (Winterdiesel, diesel d'hiver) and Arctic Diesel (Polardiesel, diesel polaires). The low cloud point (CP) of EN 590 ensures that wax particles do not precipitate to the bottom of the tank upon standing because daytime temperatures might melt them together. Properties beyond Class 4 would require a kerosene type fuel with a low cetane number (at least 45 in EN 590).

Class 0 Class 1 Class 2 Class 3 Class 4 CFPP value −20 °C −26 °C −32 °C −38 °C −44 °C CloudPoint −10 °C −16 °C −22 °C −28 °C −34 °C

Road diesel requirements by country

Australia The Australian Standard for Automotive Diesel AS 3570 specifies maximum limits for cloud point based on the 12 calendar months and the different climatic regions in Australia. The Standard lists 12 climatic regions and the limits range from −3 °C to 15 °C. Ordinarily, Australian automotive diesel fuels on average have a cold filter plugging point value that is about 2 °C below the cloud point. The Standard also lists particular locations where fuel problems may possibly occur because of cold weather conditions.

+ Maximum permissible cloud points (AS 3570 –1998) Jan Feb Mar Apr May-Jul Aug Sep Oct Nov Dec CP  Locations 15 10 5 2  1 4 7 11 14 15 °CAUC   Australia – Central (NT/SA) 15 15 12 9  8 10 14 15 15 15 °CAUN   Australia – North (WA/NT/QLD) 9 5 2 0 −1 10 14 15 15 15 °CNSW   New South Wales 15 12 7 4 2 4 7 12 15 15 °CQC   Queensland – Central 15 15 11 7 6 8 11 15 15 15 °CQCN   Queensland – Central North 15 15 12 7 7 9 12 15 15 15 °CQFNE   Queensland – North East 11 7 3 0 -1 0 2 7 9 13 °CQS   Queensland – South 8 6 4 2 1 2 4 5 6 9 °CSAS   South Australia – South 3 1 −1 −2 −3 −3 −1 0 2 3 °CTAS   Tasmania 9 6 3 1 0 1 2 4 6 8 °CVIC   Victoria 15 15 9 6 5 7 11 15 15 15 °CWAC   Western Australia – Central 10 6 4 3 2 2 3 5 8 10 °CWAS   Western Australia – South

Austria Winter diesel is required to have a CFPP below –20 °C in winter and in the transitional period below –15 °C. Some premium diesel offers include CFPP guarantees beyond that (OMV MaxxMotion CFPP –35 °C, Aral/BP Ultimate Diesel CFPP –24 °C / –30 °C)

Designation CFPP value time frame Winterdiesel –20 °C 01.10. – 28.02. Übergangszeit –15 °C 01.03. – 31.03.

Belgium Belgium has adopted the European standard in NBN EN 590. Winter diesel must at least meet the CFPP –15 °C characteristic by law. At gas stations of the VanRaak group the winter diesel is offered at a CFPP –20 °C in the time frame from 1. November to 28. February, and in the transitional period in October the diesel fuel will meet CFPP –11 °C characteristics. At gas stations of the "power" group the winter time frame is extended thereby offering a CFPP –20 °C winter diesel from 15 October through 15 March

Designation CFPP value time frame EN 590 diesel d'hiver / winterdiesel –15 °C 01.11. – 28.02. Class E

Canada Canada has an overall arctic climate. The Canadian General Standards Board publishes maps of common low temperatures for each region so that oil companies can adapt the diesel fuel accordingly, which they do about ten times per year. This scheme is inherited from the US Standard ASTM D 975 covering winter diesel (see United States). Measurements have shown that diesel fuel has a Pour Point of –30 °C which is common for arctic diesel in the rest of the world.

Czech Republic The time frames and minimum requirements for Czech winter diesel (směsné motorové nafty) is regulated by ČSN EN 590 offering the same classes as the European standard. The diesel fuel must meet the Třída B, Třída D and Třída F classes throughout the year. Additionally there is a common Třída 2 class diesel offered as skiing regions require arctic diesel for the equipment (e.g. snow groomers).

designation CFPP value time frame Třída B 0 °C 15.04. – 30.09. Třída D –10 °C 01.10. – 15.11. Třída F –20 °C 16.11. – 28.02. Třída D –10 °C 01.03. – 14.04.

Denmark Diesel fuel is governed by the Danish DS EN 590 standard. It denotes three periods for diesel fuel for Winter (Vinter), Fall (Efterår) and Summer (Sommer) — further values are given the actual results of diesel fuel offered at Shell and Statoil stations in Denmark.

Designation CFPP value time frame real CFPP real CloudPoint Sommer –10 °C 01.04. – 30.09. –12 °C 0 °C Efterår –15 °C 01.10. – 30.11. –18 °C –7 °C Vinter –20 °C 01.12. – 31.03. –24 °C –10 °C

Estonia

In Estonia, the winter diesel standards confine to EVS-EN 590. Winter diesel fuel must confine to the arctic Klass 1 values.

period CFPP value Cloud point time frame winter period –26 °C –16 °C 01.12. – 29.02. rest of year –5 °C none 01.03. – 31.11.

Finland Analysis rules follow the EN 590.

period CFPP value time frame summer period –5 °C 01.04. – 31.10. winter period –26 °C 01.11. – 31.03. arctic variety –44 °C in some locations

France In France the required characteristics must meet EN 590 classes of B, E and F for summer diesel, winter diesel and winter blizzards respectively.