[Diy_efi] Timing Advance Curve?

[Bill Washington]

Gents,
    From previous knowledge and reading all the posts my understanding 
is as follows:
1. Knock or ping is caused by detonation.
2. detonation by name and observed resulting damage is an explosion of 
part of the air/fuel mixture before the flame front from the spark plug 
reaches it in the cylinder.
3. Octane rating of a fuel relates to Knock resistance rather than any 
other parameter.
4. Increasing the advance results in the flame front further increasing 
the pressure while the piston is still rising, and this can result in an 
explosion if/when the  unburnt mixture(composition) in a part of the 
cylinder reaches the critical pressure, temperature for the particular 
fuel's Octane rating to self ignite (explode).
5. Pre-ignition is uncontrolled ignition of the fuel/air mixture by a 
hot spot (glowing carbon etc) prior to application of the spark (IE 
uncontrolled excessive advance) and can therefore result in Knock/ping.
6 Knock can be exacerbated by a non-uniform air/fuel mix throughout the 
cylinder, resulting in some sections of the mix that are more prone to 
explode. (IE they will self -ignite at a lower pressure/temperature)

Through the 80's and early 90's I had a Peugeot 504 - (engine = 1.9l, 
naturally aspirated, push rod, Hemi cross flow head, central spark plug, 
wet sleeve, dual throat carburated, with water injection - jet added at 
the venturi just above the throttle butterfly) Factory specified 
advance(at idle) was 8 degrees, without the water injection ping 
occurred at about 10 degrees advance, but with the water injection it 
occurred at about 18degrees advance. I ran about 16-17degrees advance. 
The distributor also applied the standard further mechanical and vacuum 
advance. Water consumption was about  4l water per 60l of fuel highway 
driving, about 1/2l water per 60l of fuel city driving. The cylinder 
head and pistons remained perfectly clean over 400,000 km travelled in 
that time. Fuel used was 96 Octane leaded.

Regards
Bill W

>--__--__--
>
>Message: 2
From: "Hugh Keir" <hugh at sol.co.uk>
>To: <diy_efi at diy-efi.org>
>Subject: Re: [Diy_efi] Timing Advance Curve?
>Date: Sun, 22 Dec 2002 13:18:29 -0000
>Reply-To: diy_efi at diy-efi.org
>
>Mike,
>
>My comment was partly based on some stuff I read ages ago mostly on aviation
>fuel and gave a history of fuel design from 1st world war onwards, there
>have been some very informative replies since then covering race fuel which
>have made me wonder about the absolute validity of my post.
>
>With reference to pump gas, please explian why it is normal to run more
>advanced ignition timing on a high octane fuel, it suggests to me
>that the process of igniting and burning the fuel is slower than with the
>low octane offering.
>
>If I can find the article or any other information I will post it.
>
>Hugh
>
>
>  
>



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