Fuel storage
Since the Fuel Quality Directive was implemented into UK law
on 14 January 2011 there has been considerable confusion as to
whether this means that recreational boat users will now be using
biodiesel. In fact the only requirement placed on the recreational
boating community on 14 January was that they must use sulphur
free fuel if their craft do not normally operate at sea.
The confusion arose because the fuel supply industry indicated
that it would meet its legal requirements by supplying sulphur
free road transport diesel (EN590) which by law can contain anything
up to 7% biodiesel by volume.
What impact does biodiesel have?
It is difficult to know just how much of a problem biodiesel
is in these small volumes; we have it on good authority that road
diesel is the only fuel available in most European marinas and
this does not appear to have caused the problems that some have
anticipated. In fact there are a number of boaters who actually
prefer to run their boat engines on road transport diesel as they
feel that it is cleaner and burns better.
Increased care over storage
If you suspect that your fuel contains biodiesel or indeed you
have chosen to use EN590, increased care is needed in its storage.
Due to their hygroscopic nature, biodiesel blends can contain
more water than ‘normal’ diesel which can result in
accelerated corrosion, sediment formation, and filter blocking.
All of this can be controlled by good housekeeping and fuel management.
Biodiesel blends more susceptible to biological attack
All diesel is contaminated with water to some extent, either
because it is suspended in the fuel itself or it gets into fuel
tanks through faulty seals and vent pipes and from condensation
caused by changes in ambient temperature. The latter is a particular
problem in common rail diesel injector systems. Because biodiesel
is hygroscopic, it exacerbates the problem and biodiesel blends
are more susceptible to biological attack by micro-organisms.
Aerobic micro-organisms that consume hydrocarbons, such as fungi,
bacteria and yeast, usually grow at the interface between fuel
and water in fuel tanks. Anaerobic species can actively grow on
tank sides.
Bacterial growth
Bacterial growth can result in the blockage of fuel pipes and
filters and increase the problems of corrosion. Prolonged use
of contaminated fuel may result in damage to engines.
Bacterial growth can be prevented by eliminating water from fuel
tanks and conducting regular checks to ensure that tanks remain
free of water.
Where a bacterial growth outbreak has occurred, this can be addressed
either by emptying and cleaning the tanks, or by tackling the
outbreak with biocide additives and filtering.
Deposits
Biodiesel is a better solvent than ‘normal’ diesel.
As a result it may pick up deposits already in fuel systems and
in fuel tanks.
To prevent those deposits from blocking filters, a one-time replacement
of storage tank and off-road equipment fuel filters, outside the
regular service interval, after 2 to 3 tank throughputs of biodiesel
is recommended.
In addition, fuel seals in sight gauges on older fuel storage
tanks may be incompatible with sulphur free diesel, irrespective
of whether it contains biodiesel, and may require replacing. Users
should examine seals and if there are signs of leakage, they will
need a one-off replacement of these seals.
Oxidation
The oxidation stability of biodiesel is poorer than that of ‘normal’
diesel. Over time oxidation can precipitate solids with the potential
to block filters in fuel distribution systems. To minimise the
likelihood of this occurring, it is recommended that users take
particular care to ensure a fuel turnover period of once every
6 months and, in any event, no longer than once every 12 months.
Biodiesel blends have a higher Cold Filter Plug Point (CFPP)
than ‘normal’ diesel which means it may not flow as
well (a phenomenon known as ‘waxing’) in cold weather
or stop altogether. However, the fuels made available to the latest
standards (BS EN 2869:2010) include additives to prevent waxing
and maintain oxidisation stability.
Current advice based on good practice recommends that:
Fuel in any tank is turned over regularly,
at least every 6 months and certainly no more than 12 months.
When in use, tanks are kept as full as possible,
to reduce condensation, however this must be balance against the
amount you use and how long a tankful is likely to last you.
Water must be drained off regularly (although
it is rarely possible to remove it all) in order to discourage
MBC. Consideration should be given to modifying the drain facilities
to make them more effective.
Seals and components in the fuel system are
inspected and, where necessary, replaced.
Strainers and filters are checked and cleaned
more regularly.
It is understood that this is easier said than done. Smaller
marinas and boatyards may only have one supply tank and may not
sell enough fuel to turn it over regularly particularly in the
winter months.
Many recreational craft are laid up over the winter with full
tanks for 6 months or more in some cases. A balance must therefore
be struck between the amount of fuel bought and the amount of
fuel you use.
Where possible you should try to buy diesel that does not have
biodiesel in it. But remember that the problems described here
also affect ‘normal’ diesel as well, albeit to a lesser
extent.
If you are concerned about biodiesel and whether there is something
nasty in your tank, test kits are now available, which can identify
whether contamination is present and its severity. These have
been demonstrated to give quick and accurate results on-site.