Good day everyone
Here's the latest on a thread from mid-November:
Begin forwarded message:
From: William R. Bayne <[EMAIL PROTECTED]>
Date: December 1, 2004 11:42:01 AM CST
To: W Atkinson
Subject: Re: [COUPERS-TECH] Mixture/EGT
Good Morning Sir,
Everyone on the coupe list benefitted from your most welcome input. Thank you.
It took me until today to get (apparent) of what I said below. Per Marc Hutcheson of AOPA:
"I found the information you were
seeking in regards to the lead content of aviation fuels.
73 grade does not have any lead. 72 is the natural gas limit. Fuels of
higher octane are treated with lead to increase their volatility. Since 73
is only one step up from 72, nothing is added.
80/87 has 0.5 grams of lead per gallon, while 100LL has 2 grams of lead per
gallon.
Marc C. Hutcheson
Aviation Technical Specialist
Aviation Services Department
800-872-2672 (USA-AOPA)"
Perhaps we have inadvertently tried to address two different problems simultaneously.
The first problem is excessive lead fouling running 100LL in low compression engines not designed with it in mind.
A second problem is that if, as you say, "100LL actually puts less stress on the engine than unleaded Mogas",
we need more information as to how and why, and how best to mitigate any effect on engine reliability or longevity.
Could you also elaborate on the following requests by others?
"What would you recommend for leaning procedures for C-75/C-85 engines? C-90/O-200 engines?
"What do you think about adding Marvel Mystery Oil to 110 LL (4 oz per 10 gals has been recommended)?"
Regards,
William R. Bayne
--
Begin forwarded message:
From: Walter Atkinson
Date: December 1, 2004 1:34:12 PM CST
To: "William R. Bayne" <[EMAIL PROTECTED]>
Subject: Re: [COUPERS-TECH] Mixture/EGT
Fuels of higher octane are treated with lead to increase their volatility.
Interesting concept. I was unaware of that aspect and will research that issue. Lead is put in the fuel to address two operational issues. It lengthens the latency period of the organization of the flame front and makes the peak internal cylinder pressure occur at a later point in the combustion cycle. This lowers the stress on the head. The other major benefit is the resistance to auto-ignition, or detonation.
The first problem is excessive lead fouling running 100LL in low compression engines not designed with it in mind.
Aggressive ground leaning will address this difficulty in almost all applications.
A second problem is that if, as you say, "100LL actually puts less stress on the engine than unleaded Mogas",
we need more information as to how and why, and how best to mitigate any effect on engine reliability or longevity.
I addressed that in the above response about the latency period of the fuel and the effect it has on the peak pressure pulse. That said, if the timing was set for the unleaded fuel as a design parameter, that should not be a serious issue of concern in the smaller engines.
Could you also elaborate on the following requests by others?
"What would you recommend for leaning procedures for C-75/C-85 engines? C-90/O-200 engines?
The smaller engines seem to do fine with ROP mixtures but in many cases without carb heat, cannot be made to balance the F:A ratios. In those engines where the F:A ratios can be balanced through the knowledgeable use of carb heat, they will run smoothly LOP EGT. That results in a much lower fuel consumption and lower cylinder head temperatures.
"What do you think about adding Marvel Mystery Oil to 110 LL (4 oz per 10 gals has been recommended)?"
Adding MMO will lower the octane rating. Probably not by very much. It has been claimed by some that MMO has an anecdotal benefit in engines run ROP to help keep the rings from sticking. I am unaware of any real research which proves or disproves this.
Walter Atkinson
Advanced Pilot Seminars
