Technical
“The words ‘gas oil’ or ‘red diesel’ in themselves are generic terms that mean nothing and everything at the same time”
calorific value, increased corrosion rates and damaged filters
• a reduced cold-weather handling performance
• an increased incidence of microbiological growth - the ‘diesel bug’- leading to sludge problems, blocked filters and fuel starvation
• the promotion of ‘layering effects’ in bulk storage
• a much reduced fuel shelf life which can lead to sludge from fuel oxidation products
• increased deposit forming tendencies
This last point is critical as it can lead to restricted flow in the injection system, which in common-rail engines, where injection pressures are extremely high and spray patterns complex, can result in catastrophic failure of the injectors themselves.
In terms of vehicle performance and engine operability, it is probably the fuel’s cetane number (the measure of how readily diesel fuel burns under compression - in general terms, the higher the number the better) that is having the most profound effect. At a cetane number of 45, red diesel is below DERV by 6 points and engines expecting to burn DERV often struggle, with typical symptoms being power loss,
“We are out of step with the rest of Europe, which uses DERV produced to EN590”
120 PC FEBRUARY/MARCH 2012
intermittent idle, excessive smoking and general ‘rough running’.
Here, in the UK and Ireland, we are out of step with the rest of Europe, which uses DERV produced to EN590 with a minimum cetane number of 51 to power its off-road vehicles: given the constraints and expectations being placed on them, global engine manufacturers are reluctant to supply or calibrate engines just for the UK and Ireland.
What Is Being Delivered As Red Diesel?
Red diesel should be supplied according to BS2869:A2 gas oil, but recent evidence suggests that fuel distributors or end-users rarely see a detailed delivery note or a certificate of analysis to this effect, and much is taken at face value and on trust. The words ‘gas oil’ or ‘red diesel’ in themselves are generic terms that mean nothing and everything at the same time and, whilst it is not a legal requirement to provide a specification, without one the consumer is blind to what he is receiving.
Much is also made of the supply of ‘FAME-free fuel’ (i.e. containing no biodiesel). This is increasingly a tough claim to make. As has been explained, biodiesel can be included in both red diesel and DERV and, indeed, all road fuel should contain a minimum of 5%
renewable content by April 2013 under the Road Transport Fuel Obligation. It should be assumed, therefore, that biodiesel is present already throughout the UK’s diesel pool, at least by the effects of co-mingling, unless your supplier is prepared to put it in writing that it is not. Note also that some parts of Europe allow B20 fuel (20% biodiesel content), and the more often that fuel is moved around Europe and imported into the UK (as is increasingly the case), then the more likelihood of an increased bio-content in the UK diesel supply.
Another common claim is that red diesel is simply DERV with a red dye added, and you are getting ‘premium fuel’ at red diesel pricing. If you are lucky, this may be the case but, again, it can’t be assumed, and our recent evidence is that the UK’s refineries continue to produce two distinct products or are importing increasing quantities of low grade diesel for use as gas oil.
In summary, therefore, there is now huge potential for variability in the off-road bulk fuel, and fuel-quality related problems continue to emerge on a routine basis. In addition, it is difficult for consumers to discover what is being delivered. The Department for Transport’s ‘Fuel Quality Directive Gas Oil Requirements’ suggests that fuel stocks are turned over at least every six
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