From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Subject: Re: Low sulphur fuel - OK for bikes???
Date: Fri, 10 Nov 2000 17:53:01 GMT
firstname.lastname@example.org (Ivan Reid) wrote:
>Andy Bonwick <email@example.com> wrote in <....>:
>>...., firstname.lastname@example.org (Ivan Reid) wrote:
>><snip the question>
>>> Why wouldn't it be? They've just taken a pollutant out of the mix
>>>so that they can dump it at an earlier stage than when you spread it
>>>around in your exhaust fumes...
>>Out of curiosity, are they taking the additional sulphur out before
>>refining, or during?
Suphur/sulfur is present in most crude oils, ranging from small, stinky,
molecules like the mercaptans ( also deliberately added to reticulated
natural gas to detect leaks ), to very large molecules that remain in the
solid black residues after distillation.
Recognising that a *.uk group is included, I should note that the
agreed international spelling of sulphur in chemistry journals
is now sulfur, so I'll use that.
The volatile sulfur compounds, such as sulfur dioxide, hydrogen
sulfide, etc. may be removed at the well head - as they may increase
corrosion of the oil and gas pipelines and storage tanks. The
remaining sulfur compounds dissolved in the oil usually remain there
until the refinery processes the oil.
Simply, the refining process involves distilling the oil into
several fractions that are mixed to produce products of increasing
molecular size with the desired properties.
Liquidied Gases ( boiling below ambient temp; Sulfur < 0.01%)
Gasoline/Petrol ( boiling between 30 - 220C; Sulfur 0.005 - 0.05% )
Kerosine ( boiling between 150 - 250C; Sulfur 0.01 - 0.2% )
Diesel ( boiling 220 - 400C; sulfur 0.05 - 0.5% )
Lubricating oil base grades ( vacuum distilled - 350C+ )
Residual Oils ( thick, blank gunge; sulfur 1 - 5% )
Along the way in the refinery, the sulfur compounds are extracted
from fractions and usually the organic parts ( carbon and hydrogen )
are recycled, and sulfur is separated as elemental sulfur. Note
that sulfur does burn and produce energy ( but unfortunately also
produces sulfur oxides that are pollutants resulting in sulfuric
acid ) - so most large residual oil burners ( eg power stations )
will have scrubbers on their exhaust. Note that nitrogen compounds
in the heavier fractions will produce nitric oxides, as may lean
burning of low nitrogen-containing fuels - because the higher temp.
of lean combustion dissociates nitrogen from the air.
In general, as we worry more about pollution, we put sophisticated
scrubbers, catalysts etc. on exhausts, and sulfur often inhibits the
performance of emission devices intended to reduce hydrocarbon or
other pollutants. One way to improve emissions is to further reduce
the sulfur content - so emission devices aren't affected.
The sulfur removal is usually more expensive the lower you want to
go, and the regulators usually also bundle other compositional
changes ( such as narrowing the permitted boiling range to make
engines less polluting, or removing known toxins ( benzene, PNAs)
or catalyst poisons ( lead ). Often a new "low sulfur" fuel
also has other compositional changes.
[ begin Flame Bait ]
I suspect that the UK regulations lag behind the US because UK
bikes dripped more hydrocarbons onto the road compared to what
dissapeared out the exhaust, if my experience of Ariel and BSA
bikies was any guide.
[ end Flame Bait ]
Refining "clean fuels" can produce fuels that still have the important
performance criteria ( octane number for gasoline/petrol; cetane
number for diesel ), but which have other properties changed
( rubber seals swell or shrink differently ).
The general trend for gasoline is that the low-sulfur fuels also
have lower aromatic and olefinic hydrocarbons, and also have
a narrower boiling range - especially if engines have moved from
carburettors to fuel injection - as in the USA.
In general, assuming the engine is OK to run on unleaded ( no
exhaust valve seat recession ), it will cope OK with low sulfur
fuels, as the oil companies are now fairly careful to ensure that
composition changes don't affect heritage fleets. If the new fuel
is also lower volatility, it may make cold-starting more difficult
on older engines with carbs. Not certain about the UK situation, but
many countries are lowering the volatility to reduce evaporative
emissions ( the emissions that evaporate from carb bowls, fuel tanks,
storage tanks ).
I suspect any new fuel in the UK will mimic European fuels, and thus
bike and auto makers will have introduced the newer types of
fuel lines and seals ( that are resistant to most of the newer fuel
additives, such as oxygenates ), in the 1980s and 1990s.
Note that it's usually elastomers ( seals ) that are most affected
by the compositional changes in cleaner fuels. From the above, you
can see diesel has relatively high sulfur content, and moves to
reduce sulfur and particulate emissions in California resulted in
a well-publicised spate of seal failures in large, expensive, truck
If your eyes haven't glazed over, and you want more chemical
detail, read the Gasoline FAQ in the rec.autos hierarchy at one
of the Usenet FAQ sites ( eg www.faqs.org ).