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All road fuels are subject to strict quality controls and are vital to maintain standards and provide authorities with the ability to assess safety risks and environmental pollution. In europe, for example regular mineral diesel is subject to the EN 590 standard. In 1997 the European Committee for Standardization (CEN) was tasked with developing a uniform standard for Fatty Acid Methyl Ester (FAME). The result was the EN 14214 specification. Click here for more information about biodiesel standards

The standard was introduced in 2004 and applies to all EU member states.

Specification: 860-900 kg/m3 at 15°C

Biodiesels generally have higher densities than mineral diesel (EN 590 820-845 kg/m3 at 15°C)

Density increases with a decrease in hydrocarbon chain length and with degree of unsaturation of the molecules. This can impact on fuel consumption as fuel introduced into the combustion chamber is determined volumetrically.

The Viscosity of neat vegetable oils are many times higher than biodiesel and diesel and their use in unmodified engines can lead to serious problems. The increased viscosity results in poor atomization and incomplete combustion which leads to coking of injector tips. This results in engine power loss.

Biodiesel still has higher viscosity than mineral diesel (3.50-5.00mm2/s at 40°C vs 2.00-4.50 mm2/s)

Viscosity decreases with unsaturation but increases markedly with contamination by mono, di or tri glycerides.

Specification: ≥120°C for FAME (>55°C for EN 590 Diesel)

Pure rapeseed methyl ester has a flash point value of up to 170°C. This parameter is affected by residual
components within the fuel that are combustible, for example methanol.

Sulphur emissions are harmful to human health. High sulphur fuels cause greater engine wear and in particular shorten the life span of catalytic converters.

Specification is <10ppm Sulphur

Biodiesel derived from pure Rapeseed oil will contain virtually no Sulphur, however biodiesel derived from animal sources may contain significant quantities.

Specification: minimum Cetane number of 51

This serves as a measure of ignition quality. This is the most pronounced change from vegetable oil to the transesterified product. Fuels with low cetane numbers show an increase in emissions due to incomplete combustion. Biodiesel derived from saturated oils (such as palm oil & tallow) tend to have the highest cetane numbers but tend to have inferior cold flow characteristics.

Specification: maximum of 0.02% (m/m)

Ash describes the amount of inorganic contaminants, such as catalyst residues, remaining within the fuel. Ash is related to engine deposits left from combustion.

Specification: maximum 500 ppm

Biodiesel is hygroscopic it can absorb atmospheric moisture or pick up water in storage. Consequently there can be problems meeting the specification. At around 1500 ppm the solubility limit is reached and the water bottoms out. Free water promotes biological growth as well as breaking down biodiesel into fatty acids.

Total contamination is defined as the insoluble material retained after the filtration of a heated sample over a standardized 0.8μm filter.

The limit is 24 ppm

Biodiesel samples with high quantities of insoluble materials tend to cause fuel filter and injector blockages. High concentrations of soap stock are often associated with high total contamination.

This related to the likelihood to cause corrosion to copper, zinc and bronze parts of an engine.

A polished metallic strip is heated at 50°C for 3 hours, washed and compared to standard strips.

Corrosion is likely to be caused by free acids or sulphur compounds. However biodiesel gives consistently good results in this area and is unlikely to fail (in part due to the low sulphur content).

The Oxidative stability specification is defined as a minimum Rancimat induction period of six hours.

Essentially a fuel is heated at 110°C in a constant air stream and the formation of volatile organic acids is detected. This property relates to the overall storage stability of the fuel. Higher degrees of unsaturated biodiesel molecules tends to decrease oxidative stability. Natural antioxidants are present in many biodiesels that are carried over from the parent oil such as tocopherols or carotenoids. Oxidation stability can be improved with the addition of antioxidant additives.

Acid value is a measure of mineral acids and free fatty acids contained in a fuel sample. It is expressed in mg KOH required to neutralize 1g of FAME.

High fuel acidity is linked with corrosion and engine deposits.

Iodine number is a measure of unsaturation (i.e. number of double bonds) within the biodiesel molecules.

It is expressed as the grams Iodine required to react with 100g of FAME sample.

High Iodine value is related to polymerization of fuels, leading to injector fouling. It is also linked to poor storage stability.

Specification minimum 96.5% ester (m/m)

This is measured using gas chromatography and is restricted to esters falling within the C14-C24 range. It is ultimately a test for reaction conversion i.e. yield
Linolenic and polyunsaturated esters are controlled as they have been shown to
display a disproportionately strong effect on oxidative stability.

The methanol content must not exceed 0.20% (m/m)

Methanol can be removed from FAME by washing or distillation.

High methanol contents pose safety risks due to the very low flash point of methanol. Methanol is also toxic, and the presence of excess methanol may also effect the fuel in terms of material combatibility.

There is a limit on the mono, di, and triglycerides of no more than 0.80%, 0.20% and 0.20% respectively.

Total glycerol is the sum of the bound and free glycerol and must not exceed 0.25%

Failing to meet this specification implies low conversion to ester and can lead to deposit formation on injectors and valves.

Sodium and Potassium are limited to a combined 5ppm maximum

Attributable to the presence of catalyst and can lead to residual ash deposition in the engine.

Calcium and Magnesium are limited to a combined 5ppm maximum

These may arise from the addition of hard water in the washing process. Calcium and Magnesium soaps have been linked to injector pump sticking.

The phosphorous limit is 10 ppm and normally arise from phospholipids within the starting material.

High phosphorus fuels are suspected of destroying catalysts and increasing emissions.