GA prepares for unleaded future

unleaded fuel has a few problems at the moment as I understand it.

Ethanol is incompatible with the hoses seals, gaskets, and other parts in current engines.

The unleaded gas you get at the pump from day to day doesn't even come close to the uniformity you get in a load of Avgas. Autogas varies widely from the accepted standards, ends up mixed with other things sometimes, and the QC in general isn't very good.

The "octane" ratings of aviation fuels are based on actual testing in real engines. Automotive fuel octane is based on averages of how that formulation "should" perform. Also, the scales are different. 100 octane avgas is roughly equivalent to 105 octane auto gas.

Last but not least, because of the variance in auto fuels they tend to vapor lock more easily than avgas.

All of these things are surmountable, it'll happen eventually.
 
drunkenbeagle said:
I think Jet-A burning diesels are more likely to happen first. Lycoming and Continental will probably decide that is more profitable to design and certify those ;)
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You have to find a suitable replacement for what's already out there if you want it to work. So far Jet A and Diesels aren't that. You'll see those more often to be sure, but a viable replacement is absolutely necessary.
 
trafficinsight said:
Ethanol is incompatible with the hoses seals, gaskets, and other parts in current engines.
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It also needs a fuel heater for cold operations, however it can work on any mixture 100ll to ethanol. The plus to ethanol is an increase in performance, a major downside is that you lose fuel efficiency.

I flew a loaded C-152 running on ethanol in the TX summer and was amazed at the kind of performance we got out of it. You can get around 15% more hp on ethanol(I forget the exact number, I'd have to dig through my books to find it). Also, we ran a 95% ethanol 5% water mixture and got better performance than a 100% ethanol mixture. I know it sounds weird, but if I wasn't the one churning out the data for my prof I wouldn't have believed it.
 
Ajax BU said:
It also needs a fuel heater for cold operations, however it can work on any mixture 100ll to ethanol. The plus to ethanol is an increase in performance, a major downside is that you lose fuel efficiency.

I flew a loaded C-152 running on ethanol in the TX summer and was amazed at the kind of performance we got out of it. You can get around 15% more hp on ethanol(I forget the exact number, I'd have to dig through my books to find it). Also, we ran a 95% ethanol 5% water mixture and got better performance than a 100% ethanol mixture. I know it sounds weird, but if I wasn't the one churning out the data for my prof I wouldn't have believed it.
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Right until the end I was like :eek:...

Did your research get published?
 
The need for lead in engines that need it is twofold: octane enhancement, and as a cushion for the valves. TEL is a fabulous octane booster, however, it's entirely possible to produce a 100 octane (or higher) fuel without TEL. Older engines that do not have hardened valve seats do require the lead as a cushion to avoid seat degradation.

100LL has significantly less less than the older AvGas formulations did, however it is still significantly higher in lead content than leaded car fuel ever was.

Whether or not you need 100 Octane fuel depends not on the overall HP rating of the engine, but on the level of performance of that engine (mainly the compression ratio and/or amount of boost via forced induction, typically a turbocharger in aviation engines), typically measured in HP/liter or HP/ cubic inch.

Aviation fuel Octane ratings are published via the Motor Octane Method (MON), whereas pump gas ratings are published via the Motor Octane Method/ Research Octane Method (RON) average (R+M/2). The MON is always 7-10 points lower than the RON, and is a much better measurement of how a fuel performs. Due to this difference of scales, AvGas as measured on the R+M/2 scale is actually about 104-105, whereas Premium Unleaded (typically rated 91-93 R+M/2) is roughly 87-90 MON.

Converting the bulk of the piston fleet to an unleaded, pure gasoline fuel is no big deal at all, as most of the engines do not need the lead (either for octane enhancement or for its cushioning effect). However, the engines that do need lead really need it, and without it will not last very long.

In search of a replacement for 100LL the key is that we do not want alcohol in the fuel, and we want a highly regulated and standardized fuel (of which pump gas is neither).

The need for an unleaded fuel really should be a push to get piston aviation technology out of the 1930s.

The smell of AvGas is very similar to auto racing fuel, and is not caused by the TEL. It is simply high quality, highly aromatic, real gasoline (as opposed to the junk we call gasoline at the car pump).

In the big picture, I'm not sure how much more development we're going to see for gasoline fueled piston engines, as diesel powerplants (that can burn Jet-A) have a much brighter future.
 
trafficinsight said:
Right until the end I was like :eek:...

Did your research get published?
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Well it wasn't really my research, I was just in his upper level calculus class at the time. It was my professors thing. He started on this ethanol thing years ago, and did a transatlantic trip on ethanol in 1989.

We converted all of our planes to ethanol and did air pollution sampling all over. He has done an incredible amount of research and had tons of things published about his work.

I know the video quality is poor but this is an interesting video about his transatlantic trip:

http://www.youtube.com/watch?v=fR1kJ2z3zxM

And on an unrelated note, the 2nd pilot on the trip--his wife, makes the best brushetta ever. I know that has nothing to do with flying, but it is probably the reason that bread was ever invented.
 
Ajax BU said:
It also needs a fuel heater for cold operations, however it can work on any mixture 100ll to ethanol. The plus to ethanol is an increase in performance, a major downside is that you lose fuel efficiency.
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Very true, but the loss of efficiency is a huge problem for an airplane. In addition, on anything but a new aircraft, designed for alcohol based fuels, the conversion is much more complicated, as the entire fuel system needs to be made alcohol friendly.
 
Patrick said:
In the big picture, I'm not sure how much more development we're going to see for gasoline fueled piston engines, as diesel powerplants (that can burn Jet-A) have a much brighter future.
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I disagree, I think that unless you can get new airplane prices down to reasonable levels then it'll take many years for that to happen... and even then Jet A is not panacea. The diesel 172 stats were dismal.
 
trafficinsight said:
I disagree, I think that unless you can get new airplane prices down to reasonable levels then it'll take many years for that to happen... and even then Jet A is not panacea. The diesel 172 stats were dismal.
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A light airplane is an absolutely perfect application for a diesel- low RPM, high torque, and relatively constant load. There is always going to be a lower BSFC (Brake Specific Fuel Consumption) for a diesel than for an Otto (gasoline) cycle engine. This is good, as it means less fuel burn for the same amount of power.

Until someone can figure out a way to cut the cost of a turbine engine down to under $50K, or some other form of powerplant becomes viable, piston is where it's at for a small aircraft, and diesel makes a heck of a lot more sense than gasoline, especially since the available gasoline engines we have to choose from are still using 1930s technology.

The problem with the Thielert converted 172 was an overall lack of power, since the engine simply did not put out enough. This equates to the wrong choice of diesel engine, not to be confused with a blanket statement that "diesel is bad."

However, you are correct, in that it will never be an attractive proposition to hang a diesel (or any kind of new engine) onto an older aircraft (and "older" in this case could mean 5 years), and thus yes, we do need a replacement for 100LL to fuel the remaining piston fleet.
 
Patrick said:
A light airplane is an absolutely perfect application for a diesel- low RPM, high torque, and relatively constant load. There is always going to be a lower BSFC (Brake Specific Fuel Consumption) for a diesel than for an Otto (gasoline) cycle engine. This is good, as it means less fuel burn for the same amount of power.

Until someone can figure out a way to cut the cost of a turbine engine down to under $50K, or some other form of powerplant becomes viable, piston is where it's at for a small aircraft, and diesel makes a heck of a lot more sense than gasoline, especially since the available gasoline engines we have to choose from are still using 1930s technology.

The problem with the Thielert converted 172 was an overall lack of power, since the engine simply did not put out enough. This equates to the wrong choice of diesel engine, not to be confused with a blanket statement that "diesel is bad."

However, you are correct, in that it will never be an attractive proposition to hang a diesel (or any kind of new engine) onto an older aircraft (and "older" in this case could mean 5 years), and thus yes, we do need a replacement for 100LL to fuel the remaining piston fleet.
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I wasn't implying that diesel is bad but that the engine they used was heavier, underpowered, largely untested, ran hot, and Jet A is heavier so you had a 172 you could only put 2 people in as long as they were both FAA standard or under and had no baggage, and it was the only engine available at the time. Then Thielert got into trouble and the support dried up.

All I'm saying is that pinning everything on Jet A right now, in my opinion, is not a good idea. Seems like you agree! ;)
 
Patrick said:
A light airplane is an absolutely perfect application for a diesel- low RPM, high torque, and relatively constant load. There is always going to be a lower BSFC (Brake Specific Fuel Consumption) for a diesel than for an Otto (gasoline) cycle engine. This is good, as it means less fuel burn for the same amount of power.
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I agree with everything after this paragraph. IMHO, diesl is the wrong choice for a piston aircraft simply because of the process diesel uses to cumbust. A lack of pressure will cause a diesel to become silent, i.e. altitude. In a diesel engine the sheer amont of pressure in the cumbustion chamber is what is lighting off the fuel. It is timed to enter the cyl. the same way the spark it timed to burn gasoline. So when you get a diesel at altitude, and the turbo takes a powder nap, the engine is prone to stalling. I think this is one of the reasons that diesels have not caught on in the piston fleet, along with weight concerns, because a diesel can not be built as light as a gasoline engine to contain the amount of pressures present in a diesel engine, i.e. the underpowered 172 you have quoted. It was a matter of finding an engine in that airplane that would still leave the airplane within acceptible CG limits. And the lack of power was not due to the engine itself, it was more of finding something that would fit, and deal with everything else later.

Most diesels will simply not run reliably on the amount of pressure above around 13,000 feet without turbocharging, and some won't start, or re-start above those altitudes. And while the majority of small pistons fly well below those altitudes, what are we to do with the airplanes that don't. Like said in the previous paragraph, it is a good idea, but it should go no farther than that, an idea. I spent more than a few years fixing auto's and trucks, and the last 4 was spent working mostly on diesels (Cummings). Knowing what I know about them makes me not want to fly anything diesel powered with wings.

The EPA is dooing nothing other than stron arming GA because we are considered "The little guy" of aviation. I am for the replacemnt of the lead in our fuel, as long as a drop in replacement is found. The amount of carbon and other chemicals found in the current blend of fuel is more harmfull than the amount of lead. Whats going to happen to all of the foriegn airplanes that come to the states that have not been converted to run on our special blend if it requires a modification? The EPA is an national organization. If we decide to change our fuel, it needs to be a world wide change, not just a local change. The implacations of just changing it here in the US would have an impact much more than some of our government think.

If it's not a drop in solution, than it's just not a good idea. And the current levels of lead are within the new "acceptible" limits. Refrence the EPA's study of the air and soil quality from around Santa Monica airport.


P.S. No spell check installed on this computer, please excuse my mistakes:drool:
 
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