The European standard for biodiesel EN 14214 defines the maximum and minimum limits for each of the tests – these limits are set to protect the end user so that the engine will perform and no damage is caused. Roughly, the tests can be broken down into two types – those highlighting deficiencies that will cause immediate problems; and those where deficiencies in the fuel will cause long term problems. The latter is of special regard in how the warranty will apply to vehicles using biodiesel.

Tests that affect performance in the short term

Density Biofuels generally have a higher density -this will affect the volume of oil delivered into the combustion chamber.

Viscosity Biodiesel tends to be significantly more viscous than mineral oil – this can lead to poor atomisation and incomplete combustion which leads to coking of injector tips.

Flash Point Flash Point measures the temperature at which enough vapour is being given off to cause an explosion when it comes into contact with a flame. Generally biodiesel has a relatively high flash point compared to mineral oil. But sometimes methanol carries over from the production process and makes the biofuel hazardous.

Sulphur Sulphur emissions are harmful to human health, high sulphur fuels cause engine wear and shorten the life of catalysts. Biodiesel from rape seed oil contains virtually no sulphur; however, if animal fat is the source the sulphur can be high.

Carbon Residue This is the material left after the evaporation and burning of the fuel. If it is too high, deposit can occur on injector tips and the combustion chamber.

Cetane Number This is a measure of the ignition quality of the oil – fuels with low cetane numbers tend to give increased emissions due to incomplete combustion.

Sulphated Ash This measures the amount of contaminants such as catalyst residues remaining within the fuel. Ash is related to engine deposits on combustion.

Water Content Water is a constant problem both for producers and users. Excess water promotes bacterial growth and encourages the reversal of biodiesel into free fatty acids.

Total Contamination This measures the insoluble material; if the values are high the solids will cause filter and injector blockages.

Copper Stripe Corrosion This measures the likelihood to cause corrosion to copper, silver and bronze parts – the general culprit tends to be free acids or sulphur compounds.

Oxidation Stability The oxidation stability measures the ability of the oil to resist oxidation – this is important in the overall storage ability of the oil. The higher the degree of unsaturation (double bonds) within the biodiesel, the lower the oxidation stability. Stability can be improved with the addition of antioxidants.

Acid Value Acid value or total acid number is a measure of mineral acids and free fatty acids in a fuel – both are linked to corrosion and engine deposits.

Iodine Value Iodine number is a measurement of total unsaturation (double bonds) within the biodiesel product. A high iodine value in a fuel can lead to polymerisation and injector fouling.

Ester Content Ester content measures the degree of reaction conversion in the manufacture of biodiesel. Linolenic and polyunsaturated esters have to be controlled because of the strong negative effect on oxidation stability.

Methanol Content The methanol has a low flash point which causes a safety risk and it is also a health hazard.

Glycerides These must be kept low as they are a measurement of low conversion yield – high results can lead to deposits on valves and injectors.

Group I & II Metals Sodium, Potassium, Calcium and Magnesium arise from the addition of catalysts and can lead to high ash levels in the engine.