Some Fuelish Thoughts

The fuel situation is attracting lots of attention again and generating ample discussion around the aviation blogs and boards. It looks like there is a consensus forming that the EPA and FAA are serious about establishing a definite sunset for 100LL aviation gasoline. And so, the hand-wringing and finger-pointing over how we got here, and what will be the impact of 100LL's demise and what will happen next?

Reportedly, EPA officials are saying that a notice of proposed rulemaking (NPRM) could be seen as early as October 2010, with a targeted phase-out date of 2017. If that's accurate, an additional seven years grace doesn't seem too bad, especially considering the length of time that we've enjoyed the protected status of AvGas as the only lead containing motor fuel available in the US. But we really do have to get serious about figuring out what's next.

The piston-powered segment of general aviation is at a fork in the road. One path involves developing one or more alternate lead-free 100 octane fuels. The other path requires development of power-plant modifications to allow all of the fleet to function with fuel providing significantly less than 100 octane performance.

This is somewhat like the chicken and the pig discussing the ham-and-eggs breakfast, where the chicken is interested and the pig is involved. Some engines will run just fine on lower octane fuels. Like the chicken, their owners get to watch all this with mild interest. But N631S and I find ourselves in the role of the pig, since our O-470-U engine has an 8.5:1 compression ratio and an aggressive timing specification. It's unlikely to be happy with much less than 100 octane.

This point was made pretty emphatically by TCM's chief engineer, Bill Brogdan, in an AvWeb podcast wherein he describes Continental's testing of legacy engines on reduced octane fuels. They've been surprised to find that the worst performers are not the fire-breathing turbocharged engines but rather, the high-compression normally-aspirated powerplants. Like my O-470-U. Hmmm...

TCM seems to feel that the only thing close to a "sure bet", if 100LL is indeed going away, is a 94 octane lead-free fuel (94UL) that is essentially 100LL with the lead taken out. They are working on ways to keep the legacy fleet flying on that fuel. Unfortunately, their answer for the normally-aspirated engines seems to be to reduce the compression ratio. This is major surgery (essentially a "top overhaul" with add-ons and lots of $$$$) and would entail a significant reduction in horsepower. It's not a pleasant prospect.

The folks over at Textron-Lycoming are of the opinion that it's really important to develop a 100 octane solution and they are much taken with the G100UL fuel being proffered by the clever folks at GAMI (George Braly and friends). In February, General Aviation News offered a good summary article describing the G100UL project. By all reports, the fuel performs nicely as a substitute for 100LL and, very importantly, can be mixed with 100LL in any proportion without unpleasant consequences. This is a vital consideration for any transition between fuels.

Another alternative, which I blogged about last September, is SwiftFuel from Swift Enterprises (Dr. John Rusek's venture) in Indiana. Like G100UL, SwiftFuel seems to perform nicely as a 100LL replacement and seems fully compatible with the current leaded fuel.

Both of these lead-free alternatives are undergoing continued testing. Both are beginning the lengthy and difficult ASTM certification process. In addition, George Braly is trying to convince the FAA to allow certification of G100UL for certain airframe and engine combinations under the STC process. The FAA is reported to be unenthusiastic with respect to this option.

Either or both of these alternative fuels may represent viable options for life after 100LL. The economics of both are still subject to investigation. One or the other may fall by the wayside; one or the other may prove to be just what the doctor ordered.

If both fuels turn out to be technically and economically viable, it's worth remembering that SwiftFuel is not a petroleum product. As a bio-fuel, it may help general aviation to move in a "greener" direction, a benefit that G100UL would not offer.

But what if neither fuel works out - whether for technical or economic reasons? What do I do with N631S in 2017 (or whenever)? Should I panic now, or wait a few years?

John Frank, who heads up the Cessna Pilots Association (CPA), is one of the "wise old heads" in General Aviation. He's been looking bemusedly at the stir about the 100LL issue and suggests that we all calm down. John points out that a workable solution to this issue has been around for about 70 years. In a message to CPA members, John tells us that:

It is called Anti-Detonation Injection (ADI). It was developed before World War II and was used on some fighter and cargo aircraft well into the 1950s. Basically at high power settings a water/methanol solution is injected into the induction system. The injection of this fluid cools the fuel charge, and increases the density thus permitting more fuel to enter the cylinder. As the water/methanol solution vaporizes it absorbs heat which further reduces the combustion temperature and the amount of heat transferred to the cylinder head. The alcohol in the fuel charge burns but is more resistant to detonation than even 100LL avgas.

Is ADI the perfect solution to the problem of lower octane unleaded fuels in our aircraft engines? No, of course not. There is an expense and an added system to the aircraft that must be operated and maintained. A fuel that is a direct replacement for 100LL would probably be the perfect solution, but so far that has not appeared.

Is ADI the best solution available? Maybe yes, maybe no. Probably depends on what fuel the industry can develop between now and when 100LL is no longer available.

The point is that ADI is a workable solution of proven technology that can be made to function on just about any aircraft/engine combination. So to those in the industry who are running around shouting "The sky is falling, woe is us." I say "Get a Grip." There is a workable solution and it has been there all the time.

That sounds like a good Plan B to me (Plan A being development of a viable 100 octane lead-free fuel). I'm going to calm down and go flying!