Fri, 13 Nov 1998 14:39:53 +0100 - Message No. 4456
From: Vladimir Stehlik

Subject: Neverending story ...


Hi all,

I would like to add something to the neverending story about lead in the
fuel, or in the engine of an @. Hope that this can help to end these
discusions ...

The text that follows was found in my text book that I used during my
studies at the universtity and it's official learning text of future
engine designers in our school, but maybe that some words are not so
officially translated (I did the translation), because I don't know all
the special words - I'm not an chemician.

Note: Pb stands for LEAD; all the name of the chemical compositions are
just rewriten from czech with english accent, I don't have chemical
dictionary, but if possible I'm writing its chemical formula, hope it
will be understanable


-->
... in the past, when it was needed the 'octane number' - ON (the number
that follows the name of the fuel, like SUPER 98, and says something
about its ideality and therefore its performance, my note) was increased
by small amount of chemical components, so called 'antidetonators'. The
one that was used mostly is 'tetra-ethyl-of_lead' Pb(C2H5)4,
alternatively 'tetra-methyl-of_lead' Pb(CH3)4 ...
(then you need to add something to take that Pb from the burning space -
where it creates some oxygen-compositions, that stays here - this work
is done by f.e. 'di-brom-methane' C2H2Br2, 'di-chlorine-ethan' C2H5Cl2
etc. - my explanation, shortening the article)

... except of toxicity, Pb in the fuel (all the time we are speaking
about fuel for the @, not diesel, my note :-) ) in greater amounts (more
than 0.04 g/dm3) forbids removing other components from the exhaust
gases and their transmutation on the catalytic converter (cat), because
it closes pores on the cat's surface ... (hope that this is well known
info about Pb and cat, my note).

To decrease toxicity of fuel and exhaust gases, the amount of Pb in the
fuel was decreasing (in CZ from 0.65 g/dm3 to 0.15 g/dm3 in the 1991),
while ON was kept by change of chemical constitution of the fuel. The
most effective is greater amount of aromatic compositions - but their
emisions in the non-burned form are also dangerous - by the proper
chemical process on the raw oil it is also possible to increase amount
of iso-alkanes and it's possible to add oxygen-compositions, from which
the mostly used is METYL-TERC-BUTHYL-ETHER (MTBE).

Thus was allowed production of unleaded fuels (in fact they are fuels
with less than 0.013 g/dm3 of Pb), for cats not dangerous. Fuels with a
minimum amount of Pb are still needed for failure-free operation of
older engines with cast-iron engine's heads without inserted valve's
saddles, because of their protection from deposition of burning
products, which have lubricating and anticorrosive effect (it's not the
@'s case, my note).

<--

bibliography : Combustion engines I, Prof.Ing. Jan Macek, DrSc., Ing.
Bohuslav Suk,CSc., CVUT Praha 1994 - university text book
- if there is an interest I can make a copy and send you this part of
the book (in czech) or add some bibliography

_UNOFFICIALY_ translated by me ... UFFF ;-)), chemical english is
terrible !


Here is my conclusion from what I understood (I'm not specialized in
engine's design, my studies were about car's design, but we had to learn
something about engines) :

there some emisions from the engine using leaded fuel and some from
unleaded fuel, they differs 'the same way as these two fuels itself',
all the main emisions (COx, NOx, solid parts etc.) are the same, there
is no remarkable influence on the engine itself, unless you have older
engine (as specified above) or cat - then you have to use proper fuel
and not any other. In all other cases it does not matter, and you should
follow the instructions given you by the producer of your engine - and
it's for @ _UNLEADED_ fuel.

So I guess there is no reason to discuss this once again and again and
...

Please stop it.

Bye for now

Vlada




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