Unleaded Avgas Update

[BenNabors]

Originally Posted by swjohnsey

It would be interesting to study how the military on both sides dealt with varying octane in aircraft during WWII. Octane ranged from 87 for the Germans to 150 for the allies.

The average life span was only 150 hours before they were shot down.

[sailvi767]

Originally Posted by BenNabors

The average life span was only 150 hours before they were shot down.

A majority were lost in training! 150 hours might be high.

[rv6ejguy]

It's pretty easy to obtain higher octane than 100LL exhibits by using aromatics however the specific gravity of these is generally around 17% higher than gasoline so if you put much in, fuel weight increases which will put you outside the spec. You need to find some other compound to spike octane rating without the extra weight.

Aromatics have known health impacts as well so you are trading the effects of TEL for other potential harms. If they just want to ban TEL, fine, but why trade X damage for Y damage, using aromatics?

[Avanza]

Just ad ethanol and you will incease resistance to knock.
I have run a standard IO-360, 180 hp for more than 10 years on 5% ethanol.
All fuel lines, mechanical pump is insulated/ vented.
Fuel servo is mounted about 10" from oil pan.
Engine is clean inside, you can still see the criss cross marks in the cylinders.
Mogas has 5 % ethanol here in Sweden and it woks fine.
Only thing I have noticed, on hot summer days >80F climbing to 10,000 ft
one will se reduced fuel pressure for the first 30 min of the flight.
I think that fuel standards may be different depending where you live.
Reducing fuel temperature also works to reduce risk for engine knocking.

[rv6ejguy]

Adding 5% ethanol has a minimal impact on improving octane rating.

[moosepileit]

Different countries and states in the US have different, even seasonal vapor pressures for emission control vs. ease of starting in cold weather or due to high elevations or both.

I hope an AVGAS fix of zero ethanol MOGAS will have not only acceptable octane and density but also a standard, very acceptable vapor pressure to keep vapor lock equal or near enough to 100LL.

I'd be fine with a few points denser, once octane is enough to operate without detonation or preignition margins being compromised. It also must flow properly- not vapor lock.

[rv6ejguy]

I think it's safe to say that vapor pressure of any drop in avgas replacement fuel will be an important spec to meet along with all the others. With STCs, which already exist for using mogas in certain aircraft, some fuel system changes or warnings may be required to comply, due to vapor pressure differences.

[N427EF]

Pure Ethanol has a higher octane number than gasoline (100 Octane)
Ethanol is an effective octane booster and engine cleaner, available and currently the accepted standard to achieve octane levels for motor gasoline.
According to General Aviation News, 91 octane E10 Mogas has 3%-5% more BTUs/gallon than 100LL.

I'd be fine with a few points denser, once octane is enough to operate without detonation or preignition margins being compromised. It also must flow properly- not vapor lock.

You can boost Octane levels to over 100 with ethanol and detonation is not a concern.( Preignition is not octane related)
Vapor lock can be eliminated by properly designing a fuel system.

Lead (TEL) is the accepted devil to boost 100LL to its required octane rating.
Its toxicity is now widely exploited by overzealous environmentalists and it is high time we accept something in its place.
Especially all of us in the experimental category who have the privilege of experimenting ought to be a little more adventurous with our freedoms

[rv6ejguy]

E10 Mogas won't meet the vapor pressure or detonation resistance criteria of current 100LL ASTM specs as a drop in 100LL replacement, though it's been proven to work fine on Experimental installations with proper fuel system design and careful attention to ignition timing, IAT and CHT limits.

[N427EF]

E10 Mogas won't meet the vapor pressure or detonation resistance criteria of current 100LL ASTM specs as a drop in 100LL replacement

I am not proposing a "drop in" replacement, just a solution for most of us who operate 8:5 to 1 Lycs. You really don't need 100 octane to operate that engine.