AV8ORJWC
Joined: 13 Jul 2006
Posts: 1149
Location: Aurora, Oregon "Home of VANS"
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 Posted: Thu Sep 21, 2006 9:40 am Post subject: [LML] Re: Backfires LOP |
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This snippet of a post from the guys of GAMI has value to the issue of cylinder heat temperatures. It also touches on LOP operations, low r.p.m. idle times, lead deposits and longevity of exhaust header tubes (not to be confused with exhaust valve guides and sodium filled valves). The question for the day, what role does the lead additive in 100LL play in detonation when you run high CHT or high compression pistons. Take it away Monty -.
John - #600
Do not Archive
From: Lancair Mailing List [mailto:lml(at)lancaironline.net] On Behalf Of Walter Atkinson
Sent: Thursday, September 21, 2006 8:27 AM
To: Lancair Mailing List
Subject: [LML] Re: Backfires LOP
Jim:
**I believe that the ROP has excess fuel which should cool the burn and just maybe leave MORE lead on the valve stem than while LOP.**
1) The excess fuel really does not cool the burn. What happens is that the excess fuel delays the burn RATE, which delays the peak pressure, which lowers the pressure against the thermal boundary layer and decreases the number of BTUs that are transferred into the metal.
2) I garner from your statement that you think lead in the fuel helps lubricate the valves. This is another OWT. Lead as it exists during and after the combustion event is a salt of bromide. (Bromide is added to the fuel to scavenge the lead so it leaves the combustion chamber, rather than leave deposits. Since the temp of combustion is around 3800 dF and the lead salt melts at 1308dF, it leaves the combustion chamber as a gas.) In any case, salts are abrasive. Abrasives make really poor lubricants. Lead does nothing to lubricate the valves. Nothing.
Walter
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