Winter diesel fuel

Testing the cold start capability of an engine after three days in a cold chamber. (car maker facilities in the UK, 1945)

Winter diesel fuel (also known as winter diesel or winterized diesel (AE)) 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^[1]) 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.^[2]

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.^[3] 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.^[4] 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 gas 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.^[4]

Blending

In North America, gas stations offer two types of diesel fuel - according to ASTM D975^[5] these are named No.1 and No.2 fuel. No.1 fuel (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.^[6]

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 ignite the gasoline early on possibly destroying the injectors.

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.^[4][7]

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, Croatia, 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.^[8] 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.

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).^[9] 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).

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.^[10]

Austria

Winter diesel is required to have a CFPP below -20 °C in winter and in the transitional period below -15 °C.^[11] Some premium diesel offers include CFPP guarantees beyond that (OMV MaxxMotion CFPP -35 °C,^[12][13] Aral/BP Ultimate Diesel CFPP -24 °C / -30 °C^[14])

Belgium

Belgium has taken over the European standard in NBN EN 590. Winter diesel must at least meet the CFPP -15 °C characteristic by law.^[15] 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.^[16] 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^[17]

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.^[18] Additionally there is a common Třída 2 class diesel offered as skiing regions require arctic diesel for the equipment (e.g. snow groomers).

Denmark

Diesel fuel is governed by the Danish DS EN 590 standard.^[19] It denotes three periods for diesel fuel for Winter (Vinter), Fall (Efterår) and Summer (Sommer)^[20] - further values are given the actual results of diesel fuel offered at Shell und Statoil stations in Denmark.^[21][22]

Finland

Analysis rules follow the EN 590.^[20]

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.^[23]

Germany

The time frame and minimum characteristics are prespribed in DIN EN 590. Some premium diesel characterisations include a CFPP value that extends the winter diesel value by some degrees.(OMV MaxxMotion CFPP -35 °C,^[12][13] Aral/BP Ultimate Diesel CFPP -24 °C / -30 °C^[14])

Netherlands

The Netherlands has taken over the German DIN standard - a separate standard was not created as most fuel supply for gas stations is organised cross border for example at Shell.

Norway

Norway has taken over the European standard into its national NS-EN 590 standard. In the mid winter period the standard diesel fuel must meet the arctic winter diesel class 2 conditions (Vinterdiesel Arktisk Grad 2).^[24] The time frames may be extended in some regions by about +/- 14 days.^[24]

Poland

The legal minimum time frames are usually extended by gas stations by a few weeks and in very cold winter conditions gas stations will switch to arctic winter diesel with a CFPP of -32 °C, in some regions even requiring arctic diesel atr -40 °C.^[25] Some premium diesel offers have a better CFPP irrespective of the actual weather conditions (BP Ultimate Diesel CFPP -30 °C all-seasons,^[26] Statoil DieselGold/SupraDiesel CFPP -40 °C in winter^[27])

Russia

The regulations in Russia refer to the GOST 305-82 «Топливо дизельное. Технические условия» (diesel fuel. technical requirements). The standard defines three climatic types of diesel fuel:

Spain

Analysis rules follow the EN 590.^[20]

Switzerland

Although the Swiss standard SN EN 590 has specifications for both summer and winter diesel the market only offers a single diesel type throughout the year ("Ganzjahresdiesel") that will meet the winter characteristics during all seasons.^[13][28][29] Some premium diesel characterisations include a CFPP value that extends the winter diesel value by some degrees. (OMV MaxxMotion CFPP -35 °C,^[12][13] Aral/BP Ultimate Diesel CFPP -24 °C / -30 °C,^[14] Agrola Diesel cleanline CFPP -30 °C ^[30])

United Kingdom

The United Kingdom differentiates diesel fuel into Summer and Winter Fuel according to BS EN 590^[31] and BS EN14214 (biodiesel).^[32][33] The same numbers are used in the Republic of Ireland. Distribution of winter biodiesel in the United Kingdom starts in November and ends in March.^[31]

United States

In the United States there is no legislation on a fixed time frame when winter diesel must meet a specific temperature characteristic. The ASTM D 975 standard does not specify the cold flow requirements of diesel fuel. Instead, it suggests that the cloud point be no more than 6°C higher than the 10th percentile minimum ambient temperature for the month the fuel will be used. The 10th percentile temperature corresponds to the minimum temperature that would be reached no more than 3 days out of 30 for the month (decile). The ASTM D 975 contains overview maps that show the expected tenth percentile temperature for every month for each state.^[34]

Using these guidelines gas stations offer "winter ready diesel" for sale to the Motorist - there are two ways to achieve this:

• winter blend - the gas station has blended the No.2 diesel with No.1(kerosene) by some percentage.
• winterized diesel - the No.2 diesel has been treated with additives by the diesel supplier.

As the treatment with additives (1:40000^[35]) is a cheaper way to enhance No.2 fuel in winter, most stations offer winterized diesel in cold weather conditions. In regions with colder weather, most gas stations offer No.1 fuel at the same pump allowing drivers to decide for themselves on a winter blend.

See also

• Dieselisation

References