Quote:
Originally Posted by fjasper
I don't know all the details, but they've been working on a lead-free fuel for aviation use for a long time. It's apparently a difficult technical problem, due to the various requirements of avgas.
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You pretty much nailed it fjasper.
The main reason that most general aviation engines require leaded fuel is for knock protection at the various air densities that the engines operate at, the constant high engine loads, and the varying fuel ratios used. Detonation is most likely to occur at low altitudes and high engine load, such as during takeoff and climbout, which are usually performed at full-throttle. This would be a very bad time for any loss of power or mechanical failure due to detonation. Constant-speed propellers and turbocharging further complicate matters by adding additional cylinder pressure at lower engine speeds, both on the ground and in the air. Vapor-lock in the fuel lines is also a problem remedied by the TEL additive.
The Piper Warriors we have at the airport for flight training have Lycoming O-320 160hp, 4 cylinder, naturally-aspirated engines, requiring 100LL. I haven't seen many planes that run 80/87, but if they did they would be out of luck, because all of the FBO's that I know of only carry 100LL and Jet-A, unless you want to land on a grass strip and buy some street-grade fuel from farmer Joe's 55 gal drum. It is interesting to note that even the 100LL engines only run a compression ratio of 9:1, while the 80/87 aviation engines run around 7:1, much lower than any automotive engine that I can think of.
The primary thing with aircraft is reliability. Any detonation in flight is a bad thing. Any possible factor that could adversely affect engine operation or cause engine damage is simply unacceptable in an aircraft, mainly for safety reasons. If somebody hammers the gas in their car and blows a piston in their engine due to detonation on the ground, they just pull over and get it towed to the nearest garage. In the air, engine failures are much more dangerous, which is why there are many built-in redundancies such as multiple magnetos and spark plugs, mechanical and electric fuel pumps, multiple power systems, etc. It's basically the fact that they have been very reliable running 100LL up to this point, and any change that might adversely affect engine performance is generally frowned upon without very scrutinous consideration and extensive testing. Let me tell you, when an engine starts acting up in flight, it gets your attention VERY fast.
100LL normally contains 1.2 to 2 grams of lead per gallon, while 100/130 can contain up to 4 grams per gallon, hence the designation "low-lead". Many aircraft are still produced to this day requiring 100LL or 100/130.
Okay, enough of my aviation babble, now back to your regularly scheduled programming...
