Lots of things to unpack here today. Thank you, Russ, you have done an excellent job of keeping us all appraised of both the progress and the lack of progress on this front. Equally valuable, you provide us all with a forum to jump in and set the world straight - even though the majority of us are not fuel chemists either (leaving the door open in case I am the only one who’s STEM education is on par with Russ).
I was not involved in aviation back when 100LL became the “go to” fuel, but my training back at the turn of the millennium made clear what clear, red, green, and blue fuels were, and to pay attention that what went into my tanks was what I expected. Based on this, I would assume that not seeing those fuels at every airport doesn’t mean they were legislated into oblivion, but simply became less economically viable over time. It seems we unilaterally agreed to reduce the lead content at some point (thus the low-lead moniker), but I suspect that this is the first time we are intentionally creating a one-size-fits-all unleaded fuel for GA as a whole.
We have had unleaded aviation fuels for quite some time, but 100LL has dominated ever since I can remember. That would suggest that in spite of spark plug fouling (and being quite toxic) TEL must have some redeeming quality that is difficult if not impossible to find in equal degree elsewhere. To my understanding, the magic is not simply that it prevents detonation at this high of an octane, but that it produces a very smooth and consistent burn front as the flame propagates through the cylinder which is relatively gentle on the engine considering evenly distributed acceleration and evenly distributed heat. Of equal importance, it achieves this with nothing more detrimental to the engine itself than yucky (industry term) lead build up on the spark plugs.
In the search for a replacement fuel, we have three requirements. The first two are simple and straight forward: (1) 100 octane, (2) no lead. The third requirement is a little less clear: “whatever you do to achieve the first two items, it can’t have any side effects that are bad or unexpected”. This includes (1) shouldn’t cost more, (2) don’t degrade or interact with seals, gaskets, hoses and the like, (3) don’t cause parts on my engine to wear, (4) don’t make concentrations of heat in my engine, (5) stay fresh in my tanks and my carb literally forever. And (6) at least 100 more things that I am not smart enough to foresee. We’ve been told that the new fuels are everything we would ever hope for, but we have learned in recent years to be skeptical of the “experts”.
Whatever the “industry” chooses to go with, I will be stuck with. My ship will happily run on low octane, unleaded fuels, but it has only ever had 100LL in its tanks because I fly coast to coast and airfields that offer anything other than 100 low lead are few and far between. When the new and improved wonder gas is officially adopted, it will completely replace 100LL, and it will likely replace the lower octane fuels as well. Call me a nervous Nelly, but I believe in the maxim “The monster you know is better than the monster you don’t know”. As much as I want unleaded fuel, what are we replacing the TEL with, and will that new something turn out to be a monster in it’s own right? Only time will tell, and I am a proponent of taking all the time we have been given.
I don’t believe that EAGLE’s purpose is simply to see one or two unleaded high octane fuels reach the market. The goal should be to shepherd in the best replacement fuel we are capable of developing. Right now, 100LL still dominates across the country, and the amount of alternative fuel sold thus far isn’t even enough to taxi our fleet of GA aircraft to the run-up area. We have a long ways to go.
I believe that ASTM certification is important. It isn’t that the ASTM people are all knowing and will pass judgement on the formulation. The ASTM process allows the industry stakeholders (fuel manufacturers, engine manufacturers, aircraft maintenance shops, owners and pilots) to participate in creating a consensus criteria for the fuel and its manufacture such that any supplier can then be held to a consistent standard for formulation, performance, purity, etc. GAMI will not be the sole manufacturer or supplier of the new fuel for long (assuming it goes that way), and we want to guarantee that every “brand” of Avgas is the same as every other in formulation and performance.
I am happy to see both alternative fuels finally being sold. We need more exposure to these fuels than what we have seen so far. The FAA has approved an STC for GAMI’s fuel which was tested to their satisfaction, but I am unclear on what that entails. AOPA flew a single aircraft with GAMI fuel in one of two engines for a year. A large flight school used unleaded 94 octane for an extended period of time and then opted to return to low lead. Beyond that, I know very little about just how suitable these fuels are in certificated engines, and much less in my non-certificated Jabiru engine. After a million gallons have been consumed (rather than 1,000), we will start hearing about different people’s experiences with less than ideal engines, less than ideal test beds, and less than ideal engine management.
We still have six years; we should use every one of them to continue to assess, tweak, improve and reassess before we get into bed with something that we will have to “like it or lump it” for a very long time after.