[Diy_efi] Re: Burning Aluminium etc.

[gary]

> 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.

Actual 'real time' testing has shown otherwise.  With due respect to
you Phil, it would appear, this 'theory' is outdated.  Not only are
there different 'levels' of detonation, but the familiar description of
'instantaneous explosion' is no longer appears valid.

In regards to preignition and detonation, either can result in the other.

GAS

----- Original Message ----- 
From: "Phil Lamovie" <phil at injec.com>
To: <diy_efi at diy-efi.org>
Sent: Monday, April 18, 2005 5:00 AM
Subject: [Diy_efi] Re: Burning Aluminium etc.


> 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.
>
> Regards,
>
> Phil