The farming community is able to purchase rebated fuel – ‘red diesel’ – for agricultural use. However not all fuels are of equal quality and users should take care that the fuel they buy is fit for purpose and is stored in appropriate conditions.


A recent development is as from April 2015 a new marker is included to assist combat duty fraud whereby unauthorised parties obtain ‘red’ fuel and remove the marker dye to re-sell rebated fuel at non-rebated prices. The new marker is a chemical additive which is included in minute quantities but which will enable the authorities to identify rebated fuel. To the farmer user this change should of itself have no direct consequence but it does raise the issue of appropriate fuel quality.


On-road diesel fuel complies with a standard EN 590:2013. Ideally this should be the quality purchased but off-road fuel is sometimes offered to standard BS 2869:2011. These standards are not identical and vary mainly with regard to density and to Cetane number. The more dense the fuel the greater power; however, denser fuel is more difficult to atomise during injection.

The Cetane number is a measure of the combustion quality of the fuel and the BS standard is lower at 45 than the EN at 51. A Cetane number as low as 46 will significantly delay the start of ignition beyond what is desired. This will lead to incomplete combustion of the fuel and therefore allow the build-up of carbon on internal engine components. Hydrocarbon, carbon monoxide and nitrous oxide emissions will also increase.


Using low quality fuel in modern engines can cause many problems from premature blocking of fuel filters to poor running and increased fuel consumption. Various approved fuel treatments are available from franchised dealers to counter any deficiencies.


Since 1 Jan 2011 fuel companies have had to supply Sulphur-Free Diesel  ( ‘SDF’ with a maximum 10 ppm sulphur) for use by Non-Road Mobile Machinery, including tractors. Other fuel grades remain available and it is important that users should assure themselves of the quality obtained. The reason for this concern is that higher sulphur levels in the fuel will lead to more contamination in the engine. For Stage IIIB engines and above, high sulphur levels can damage the exhaust treatment system.


It is highly recommended that customers ask their suppliers to confirm the quality of fuel they are offering and to satisfy themselves that it is accordance with the manufacturers’ advice as given in the operator’s manual or other material.


Good practice with regard to storing and handling diesel fuel is more important than ever. Bulk tanks and bowsers must be in good condition and in-line filters should be installed to provide an additional level of protection. The potential inclusion of bio-fuels of up to 7% raises the concern of water contamination and build-up of bacterial growth. The role of the fuel filter has been elevated and users should monitor regularly.