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Posted for "Fred Moreno" <[EMAIL PROTECTED]>:
Earlier this week I went to the EAA Regional Meeting with Tom Poberezny and
EAA staff at the Hiller Museum at San Carlos Airport. It was mostly an
update on EAA activities and questions and answers. The most interesting
part to me was the response to a question about 100LL which was given by an
EAA staff member that follows the issue closely. Here are the high points
from his response and to subsequently questions I asked him afterward. I
have added in square brackets [ ...] some of my comments based on research
over the last few days, both on the web, and in some engine test books.
* Tetraethyl lead (TEL) is produced in only one plant in the world in the
UK. The firm operating this plant [Octel. Inc.] bought the plant in East
Germany and shut it down. [Confirmed.] The plant in Chechnya is unlikely
to resume production anytime soon.
* The last corners of the world using leaded motor gas will cease doing so
this year thus completing the worldwide removal of leaded fuel from the
motor gas pool.
* Demand for TEL is dropping 15% per year.
* 100 LL will be phased out between 2005 and 2010. The regular production
of TEL will cease in 2005 and 100 LL after that date will use stored
supplies of TEL. [I found the Octel web site and sent an e-mail asking for
confirmation.]
* Usage of 100LL is dropping rapidly. The large engine piston fleet is
being retired in favor of turbine engines in corporate and commuter use,
and old freighters like DC-6's are also being retired due to lack of spare
parts for big round engines.
* About 70% of the general aviation fleet can use 82UL.
* FBOs only want to stock one type of fuel because of the cost of
equipment and inventory. So they stock what everyone can use -100LL.
* Only seven refineries in the U.S. can produce 100LL, while every
refinery in the US (about 400) is capable of producing 82 UL today, if it
chooses.
* Cessna's approach has been to use low compression engines capable of
using 82UL for lower horsepower applications, and rely on new diesel
engines for higher powers for future larger aircraft.
* Diesel engine progress has been poor because aero diesel engines must
use jet fuel. Jet has a much lower cetane rating than diesel fuel. This
leads to higher peak pressures in the engine (somewhat like knock)
resulting in heavy engines, [confirmed in Taylor's classic text book] and
so far they will probably be too heavy for use in current
aircraft. Additives can raise the cetane rating of Jet fuel, but the cost
adder is unacceptable to turbine engine operators. So a high cetane jet
fuel blend would have to be separately produced and stocked. But recall
from above that FBOs only want to stock one fuel for piston engines.
* 100 LL is actually about 102-104 octane (motor method), and this high
level is needed because of high possible cylinder head temperatures (in
some cases combined with high manifold pressures in turbo'ed units) in air
cooled engines. Certification requires that these must operate up to red
line CHT without detonation when full rich.
EPA and the regulators are not trying to ban leaded avgas because the
industry is working on the problem. However, it will be effectively banned
sometime after 2005 as the demand drops and price reaches such high levels
that it is effectively no longer available.
* [Refineries can make high octane unleaded fuel, but at prohibitive
prices. Unocal has a limited number of outlets for racers in the Los
Angeles area, but fuel costs are typically $5-6 per gallon without taxes
since these are not road fuels.]
* Every 20F drop in cylinder head temperature reduces the engine octane
requirement by approximately 2 points.
Smaller four cylinder engines in the 160 to 180 HP class can use 82 UL today.
* There will be an unleaded Avgas produced to replace 100 LL, but it will
not be as high octane as 100 LL. It will probably be a low vapor pressure
formulation that will be around 94 octane tailored to meet technical and
cost requirements. [Auto gas is rated with an anti-knock index AKI, the
average of the motor method octane and the research method octane,
R+M/2. Motor method octane is typically 5 points higher than research
method, and corresponds closely to aviation octane. So 96 aviation octane
is probably around 96.5 AKI, quite a bit higher than 92 premium auto
fuel. And it will probably be more expensive.]
* Consequently, larger engines, 200 HP and up, 500 cubic inches and up,
and turbocharged engines have an uncertain future past 2005 as 100 LL
supplies dry up and the price skyrockets.
* Liquid cooled engines can operate with much lower octane because of
lower combustion chamber temperatures. Lowering head temperatures from
400F to 200F can reduce the motor octane rating as much as 10 points, down
to 92-94 octane. [However, details of combustion chamber design can also
be important.]
* In the opinion of the EAA representative, the only solution is "modern
engines, liquid cooled, with electronically controlled fuel injection and
ignition systems such as those that have been demonstrated to run
[efficiently] on 92 octane auto fuel today."
I conclude from this that the long term future of Continental TSIO-550's in
Lancairs and TSIO-540 Lycoming engines in Malibus is dim indeed. UNLESS the
engine manufacturers produce retrofit packages for the existing fleet of
engines. Perhaps these would be derived form current FADEC systems, for
example, and take the control of the mixture and propeller away from the
pilot to avoid detonation. However, the recertification problems in all
the different air frames would seem to be immense.
Are current generation certified turbocharged high performance piston
engine airplanes endangered species?
Eric your comments and insights appreciated.
Fred Moreno
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