Hi;
This is closely related to the recent alternative fuel thread, but perhaps separate enough to ask on its own. So I will.
I'd like to build a homebuilt plane. My plan would be to buy a used Continental 0200, C90-12F or similar. These typically run on 100LL.
I talked at length to an engine man, Don Swords of "Don's Dream Machines" in Georgia. I really don't know aviation engines, but this man has worked on them for "ever." He seems to know every nut, bolt and spec about these engines, so for the moment (humour me) let's assume he's the real deal.
He mentioned that auto gas in Continentals is bad. If I recall his words correctly, auto gas burns fast, in about 10 degrees of crankshaft rotation. Ignition for a C90 occurs at 18 degrees before Top Dead Center, meaning all the avgas is burned and max pressure is reached several degrees before TDC. This will come as little surprise to those who know that TEL is added to Avgas to reduce/delay/eliminate pre-ignition, and save your pistons from getting hammered. At least that's my understanding of its reason for being added to avgas.
Don mentioned that 100LL actually burns slowly, and takes around 28 degrees of crankshaft movement before it's burned up (presumably at high or cruise RPM). That means that the piston reaches TDC, and the gas is still burning, maximizing pressure just after TDC, and still imparting work onto the piston as it starts its journey downward. No pre-ignition. Also, the lead, I have read, assists in lubrication of valvetrain components.
So here it is: If this is true (please feel free to tell me how many of my specs are wrong) what will replace 100LL??? Does it make any sense for me to buy a used C90, or will there suddenly be a useless glut of them on the used market if a 100LL ban happens soon? I'm thinking micro about a macro problem, but what relatively inexpensive used 100 HP engine would you buy if the Continental/Lycoming world might be coming to an end?? Is this unlikely, the 100LL ban, I mean?
And while we're on this, and I'm only a greenhorn in terms of understanding engines and fuels, what properties are desired in an avgas? Slow burning? Cool burning? Hot burning? High pressure, non-toxic, etc.,....
Thanks. Hope you've got some steam left in you after my small novel.
Cheers, Tom.
This is closely related to the recent alternative fuel thread, but perhaps separate enough to ask on its own. So I will.
I'd like to build a homebuilt plane. My plan would be to buy a used Continental 0200, C90-12F or similar. These typically run on 100LL.
I talked at length to an engine man, Don Swords of "Don's Dream Machines" in Georgia. I really don't know aviation engines, but this man has worked on them for "ever." He seems to know every nut, bolt and spec about these engines, so for the moment (humour me) let's assume he's the real deal.
He mentioned that auto gas in Continentals is bad. If I recall his words correctly, auto gas burns fast, in about 10 degrees of crankshaft rotation. Ignition for a C90 occurs at 18 degrees before Top Dead Center, meaning all the avgas is burned and max pressure is reached several degrees before TDC. This will come as little surprise to those who know that TEL is added to Avgas to reduce/delay/eliminate pre-ignition, and save your pistons from getting hammered. At least that's my understanding of its reason for being added to avgas.
Don mentioned that 100LL actually burns slowly, and takes around 28 degrees of crankshaft movement before it's burned up (presumably at high or cruise RPM). That means that the piston reaches TDC, and the gas is still burning, maximizing pressure just after TDC, and still imparting work onto the piston as it starts its journey downward. No pre-ignition. Also, the lead, I have read, assists in lubrication of valvetrain components.
So here it is: If this is true (please feel free to tell me how many of my specs are wrong) what will replace 100LL??? Does it make any sense for me to buy a used C90, or will there suddenly be a useless glut of them on the used market if a 100LL ban happens soon? I'm thinking micro about a macro problem, but what relatively inexpensive used 100 HP engine would you buy if the Continental/Lycoming world might be coming to an end?? Is this unlikely, the 100LL ban, I mean?
And while we're on this, and I'm only a greenhorn in terms of understanding engines and fuels, what properties are desired in an avgas? Slow burning? Cool burning? Hot burning? High pressure, non-toxic, etc.,....
Thanks. Hope you've got some steam left in you after my small novel.
Cheers, Tom.
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