[Diy_efi] Re: Burning Aluminium etc.

[niche at iinet.net.au]

Havent been on this list for a while as my LAN had port forwarding
problems anyway, for what its worth...

Aluminium will burn (oxidise) in the solid state and very quickly,
if fact its almost impossible to have aluminium without an oxide
layer,

Eg:

Take a sheet of aluminium, immerse it in kerosene and whilst you
keep in under the surface of the kero, rub off the oxide layer with
steel wool...

Wait till it cools down and everything is settled, then lift it out of
the kero into air and it will get damn hot very quickly as the surface
layer oxidises - yes BURNS...

So anything which removes the surface oxide layer (sapphire) will
cause the metal to burn... The oxidation wont continue because the
underlying metal removes heat very well and the oxide layer is almost
totally impervious to oxygen passage - well until you scratch it or
cause the layer to be lifted.

Its very dangerous to have molten aluminium, if you jostle it enough
exposing a large surface area to air you could have an explosion,
so be wary that aluminium in the solid state can burn...


Regards from


Mike Massen
Perth, Western Australia
VL Commodore Fuse Rail that wont warp or melt !
http://niche.iinet.net.au



At 06:00 PM 18/04/05, you wrote:


>Hi Guys,
>
>While I have seen and created my very own "low windage pistons"
>I have not seen any data that would confirm that "combustion" of
>the Aluminium (Aluminum) has taken place.
>
>Of course all that is required is a set of scales. Perhaps someone
>who has a partially ventilated set might do the experiment and help
>enlighten the list.
>
>A quick check of the "blue bible" gives the boiling point of pure Al
>as 2467 Degrees C at STP. As no combustion could occur prior to
>vaporization I would posit that what is occurring is melting as a result
>of the pressure created during a detonation or two.
>
>(Bosch Automotive Handbook ISBN 1-56091-918-3)
>
>
>Here things get murkier.
>
>>>> "Almost all the failures we see probably start with
>>>> preignition, which is far more devastating to an
>>>> engine than detonation.  If fact, we believe that most
>>>> of these engines would make TBO, running 100% of the
>>>> time in "light" detonation."
>
>There is a very large difference between the nature of the two
>events. Pre ignition is mostly caused by spark plug tip anomalies
>such as "glowing" due to incorrect heat range or having deposits
>on the tip that are acting as glow plugs.
>
>Occasionally a bad exhaust valve seat to valve contact can also
>produce the local hot spot required
>
>The subsequent combustion is indeed combustion in a normal sense.
>It starts at the spark plug tip or other glowing spot and radiates
>outward as best it can.
>
>Though it may be earlier  than intended and may cause the very
>familiar knocking or pinging noises (piston thrust face reversal syndrome)
>it will most often cause no more that skirt cracking on the thrust side
>as well as all the by products of too much advance.
>
>Detonation is on the other hand an extremely violent and unforgiving
>condition. It is the result of spontaneous combustion of the air fuel
>mixture. There is no flame front to be seen as it occurs everywhere
>at the same time. The pressure rise traces are vertical and the first
>sound you hear  is usually the front timing seal being blown out or
>some other blow through related failure.
>
>That is not to say that the only way to hole a piston is through
>detonation but it is still the easiest and the best.
>
>You could of course do something silly like run your engine at
>80 to 90% of full load, the rpm at 90 to 100% of max. with the fuel
>leaned off to Lambda 1.1 and the spark over advanced just right
>and the ring tension a little low and the ring grooves full of carbon
>build up to get the pistons crown to overheat to the point of liquefaction.
>
>Of course giving the operator (pilot) a manual air/fuel mixture control
>and reassuring them that Lambda A/F (not sure why this is the A/F
>target under these conditions) is denoted by peak exhaust temps
>may lead directly to the impact site.
>
>YMMV....
>
>Hope this helps,
>
>Regards,
>
>Phil
>
>
>
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