100LL Avgas Operations vs 100/130

[exhaustgases]

Thank you, thank you, thank you.
I've been attacking the TEL valve face seat lubrication issue for years. Its a temperature thing not a lubrication thing. TEL makes the cylinder head cooler than unleaded fuel, a proven test in an aircooled auto engine. Cooler head means less micro welding, or high temp errosion of seats and faces. The article is wrong about saying this is not true. The whole reason for an anti-detonate is to slow and inhibit combustion to prevent detonation, killing a high peak combustion chamber temperature, thus a cooling effect.

[Ken]

The whole reason for an anti-detonate is to slow and inhibit combustion to prevent detonation, killing a high peak combustion chamber temperature, thus a cooling effect.

So, when avoiding detonation, isn't it correct to say that the results are somewhat predictable given a fuel's properties, an engine's compression ratio, and a chosen power setting? Since I can't change the fuel (currently 100LL) and I can't change the engine, all I can do is manage the throttle. (This assumes no mechanical issues, i.e. good mags, spark plugs, valves, etc) --Ken

[CAPFlyer]

Ken,

That's pretty much it. Some engines (like the Allison, Merlin, and Griffon) seem to be little affected by 100LL. Considering that they were built to run on 85 Octane as a main fuel, it's not surprising. However, some of the bigger radials (with their larger pistons and higher compression) were designed specifically for "Hy Test" (as it used to be called) fuels, so when you use lower grades, you have to adjust power to prevent detonation since their power was based off having that higher anti-detonation capability.

The interesting thing is that testing of some of the unleaded fuel replacements suggests that some of these power limitations may no longer be an issue. Anderson Airmotive did a test on one of the fuels with an R2800 and ran 100 hours at 115/145 power settings without any unusual issues in the subsequent teardown. (see: https://www.aopa.org/news-and-media/all ... ial-engine )

So, there is hope, but until then, just know what fuels your airplane's engine is rated for, what fuel your power settings were designed around.

[mike furline]

Slightly off topic for the OP's comparison, but some more light reading on octane.

http://www.wwiiaircraftperformance.org/ ... -fuel.html