Message-Id: <5.1.0.14.2.20020427173226.0294ca90@lancaironline.net>
Date: Sat, 27 Apr 2002 17:32:33 -0400
To: lml@lancaironline.net
From: Epijk@aol.com (by way of marv@lancaironline.net)
Subject: Re: Fuel Grade List
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In a message dated 3/27/2002  at 7:34:17 AM Pacific Standard Time, 
wdodson@bak.rr.com writes:

<<<...In todays' mail I recieved Lycoming Service Instruction No. 
1070M.  It deals
with aviation gasoline fuel and octane ratings adequate for Lycoming
engines.  It is not a pretty sight when one reads between the lines.  What I
see is the demise of aviation gasoline as we know it...>>>

Walter:
I was browsing through the LML postings I have saved, and ran across this 
one from a month ago, to which I had intended to respond, but just forgot.

Your observations about the imminent demise of 100LL and the problems it 
will cause for operators of high-output air-cooled engines are indeed 
correct, and could become a significant problem for domestic operators 
sooner than we might wish.

The requirement for fuel with lead content of 100 "LowLead" (which contains 
four times the TEL of the highest-octane autogas ever available, 
Sunoco-260) is established by the certification requirements for detonation 
margin in the worst case (kind of like a sustained hot-day climb out of 
Death Valley {or Phoenix} at Vx).

Detonation margin is affected by a variety of factors, including inlet air 
temperature, peak cylinder pressure, rate of temperature rise, peak and 
mean combustion chamber surface temperatures, etc.

One of the major factors is chamber surface temperature, which, for a given 
heat input (power) is closely related to the heat rejection capability of 
the cylinder head system. Clearly, the heat rejection is most severely 
limited during max power operation in min-cooling situations (the hot-day 
climb at Vx).

The detonation margins can be improved by a variety of methods, one of 
which is to use fuel having a very high effective octane rating (detonation 
resistance). But if it is necessary to operate a given engine on a fuel 
with reduced detonation resistance (93 autogas compared to 100LL, for 
example), one of the most straightforward methods to avoid engine damage is 
to limit the maximum allowable manifold pressure (ie: derate the engine). 
That maximum MAP is established by careful testing in a tightly-controlled 
environment.

That derating method could be used to recertify existing aircraft engines 
for use with a lower-octane fuel. It MIGHT not be a terrible problem for 
your aircraft, but consider the implications on a typical cabin-class 
"light" twin (C-340, C-421, Piper P-Navajo, Aero-Commander 685, for 
example) in which:

(a) the air-cooled engines are turbocharged to very high power outputs 
(severely challenging the structural as well as heat-rejection capacities 
of the engine) and
(b) the ability of those aircraft to achieve the required minimum 
single-engine climb rate at gross weight depends on the engines producing 
the power at which they were certified.

A reduction of that certified maximum power (by mandated derating) could 
easily transfer many of those (and other) aircraft into the (limited 
usefulness) category of "full-fuel, zero-person" aircraft.

<<<...In North America we are probably safe for some years to come ...>>>

Maybe, maybe not. There's more info on this subject at:

       http://www.epi-eng.com/ac-v8.htm

Jack Kane
EPI, inc.