Newsgroups: sci.chem
From: ahahma@polaris.utu.fi (Arno Hahma)
Subject: Re: Help: Tetra Ethyl Lead replacement wanted for model engines
Message-ID: <C400oy.3n@polaris.utu.fi>
Date: Tue, 16 Mar 1993 20:24:33 GMT

In article <1993Mar16.173644.17969@kth.se> olsson@plafys.plasma.kth.se writes:

>An interesting thing from a chemical viewpoint is that a knock enhancing
>substance like amyl nitrate (Also sold under the brand name 'Diesel
>Ignition Improver'.) is combined with a knock inhibitor like TEL to
>give a better result than just reducing the amyl nitrate. Are there

I would call that quite an innovation, indeed! The amyl nitrate does
enhance the ignitability by compression, but unfortunately it also
makes the mixture detonate easier. If the engine starts knocking, it
means you have a detonation in the cylinder ruining the engine
quickly.

The idea of adding TEL is that it inhibits the detonation, but does
not make the ignition any harder. If you mix a ignition enhancer with
a knock eliminating substance in the fuel, the fuel will still ignite
as before, but resist knocking despite of that. This is really an
advantage in the model plane diesels, that load all of the fuel into
the cylinder before ignition.

With real diesels you need no TEL, as you inject the fuel _after_ the
compression, not before it, in fact, it would be a bad idea to use TEL
in them.

As for a replacement, there are little suitable materials. You don't
want to use aromatics (very high octane) or MTBE, as you would need a
considerable percentage of them in the fuel. As a result, the fuel
would be diluted and become difficult to ignite by compression - the
engine would be hard to start. Besides, aromatics et. al. would soon
melt your engine, as they contain no oxygen and burn very hot compared
to ether.

Ferrocene has similar properties as TEL, but the iron deposits from
its compression might be too heavy. In common, compounds, that easily
decompose into free radicals tend to reduce knocking.

>Goran Olsson                                  Department of Plasma Physics

ArNO