TCM Tackles the Fuel Problem

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During Continental's press conference summarizing its fuel research into a replacement for 100LL, I had the odd feeling of waking up from a bad dream. As we reported this week, Continental's idea is that maybe the industry can get by on a fuel called 94UL—essentially 100LL minus the lead. They've embarked upon a series of tests to find out if the supposition will fly, so to speak.

The bad dream part is that for nearly three decades we've been writing stories about the difficult struggle to find an octane enhancer as good as lead and now here comes TCM to say, well, never mind. It reminds me of that classic headline about World War I: "Archduke Found Alive; War a Mistake."

I'm happy to see Continental take on this research and happier still to see them talking about it. The engine companies have tackled this critical problem only in fits and starts and Continental's last run at the problem, its PowerLink FADEC, has been met with disinterest in the market.

Nonetheless, I think Continental is going to have its hands full proving that 94UL has sufficient octane to keep high-power turbocharged engines from detonating under worse-case conditions. Previous efforts at running lower octane fuels in such engines haven't been encouraging. The problem is that in that tiny slice of the envelope that represents high power, high temperatures and high altitude, cylinder head temps head for the mid-400s. In a perfect world, if the factory got the baffling right and if it stays right after a few years of mediocre maintenance, maybe the cylinders will stay cool enough. I'll believe it when I see it.

There are various ways to address the lack of octane. One is to throw more fuel at the engine—the old gas-is-cheaper-than-valves approach. Another is to throw more air at it, in the form of faster climbs or lean-of-peak operation or both. Retarding the timing a few degrees can also help. All of these exact a performance penalty and Continental concedes the point. It also concedes that the 94UL solution won't necessarily require FADEC, an encouraging nod to market reality.

Even if it turns out that 94UL won't work for turbocharged engines—or at least all turbocharged engines—it would be nice to have it available. For the vast majority of airplanes, it has more than enough octane.

Comments (14)

I know that some experimentation was done years ago with ethanol, but have seen nothing about the recent use of auto gas with 10% or 85% ethanol in av engines. Given it's ability to improve octane, it seems like a reasonable possibility. Or?

Posted by: Richard Van Pelt | April 1, 2009 5:42 PM    Report this comment

Richard Van Pelt. I believe the reason ethanol isn't used in aviation is it readily absorbs water, leading to, at best leading to accelerated corrosion of fuel system parts, at worst ice forming in the induction system resulting in a substantial loss in power. Do correct me if I'm wrong!

Posted by: Duncan Clement | April 2, 2009 5:42 AM    Report this comment

Duncan, my company in South Africa has done more than 3 years research into straight ethanol as an aviation fuel and is in the process of having it approved locally.

Ethanol is not corrosive, but some of the impurities found in distilled ethanol are. Water in the fuel is far less of a problem than water in your avgas.

The only downside is the lower energy content which results in about 15% less range. The difficulties of hard starting in cold weather have been solved.

Posted by: Chris Martinus | April 2, 2009 6:35 AM    Report this comment

Some bright spark at TCM must have said: "Lets generate a little business by encouraging people to blow the heads off of their cylinders with lower octane fuel..."

Seriously, I expect that TCM's tests were done with new engines with balanced injectors, calibrated fuel controllers, perfect engine baffles and exhaust systems, and magnetos timed to a tenth of a degree.

It is unrealistic to expect that engines in the field will accept lower octane fuel, especially those that have had average maintenance, or have the usual differentials in fuel flows to each cylinder (carbureted or injected).

Even for normally aspirated engines the margin for detonation is small. I fly my IO-520 pretty carefully, but I don't have GAMI injectors (yet). Look carefully, and you can see that there has been evidence of occasional detonation in the cylinders that tend to run lean.

Using over-rich mixtures to avoid detonation will generate more carbon deposits on valve stems and exacerbate an already difficult problem with TCM valve guides.

What will TCM say when the problems triggered by 94 octane land on their doorstep?

It’s good that they are testing but it’s going to take a little more than just testing in one aircraft. A FADEC might not be required, but expect a lot of restrictions.

I wonder what Lycoming is saying in their shop? Unless they join the party, it won't happen. These are the same people that have had their heads in the sand concerning LOP operations.

Posted by: David MacRae | April 2, 2009 8:01 AM    Report this comment

Paul Bertorelli, >>Even if it turns out that 94UL won't work for turbocharged engines—or at least all turbocharged engines—it would be nice to have it available. For the vast majority of airplanes, it has more than enough octane.

Then would two different grades of avgas need to be avaiable? When we went to 100LL, didn't the economics say it would be to expensive in dollars and the logistics to have more than one grade of fuel? Using 94UL may be a step backwards at least in economics not to mention the damage it may cause to higher compression engines. At least with 100LL we had one fuel that (sort of) fit all.

Posted by: GREGORY MORTON | April 2, 2009 10:19 AM    Report this comment

Have there been any REAL studies done as to the effects of using alcohol as an octane booster? A nice idea might be to operate a high performance twin with one engine running current 100LL and the other an alcohol blend. After 2000 hours or so some meaningful evaluation might be achievable.

Posted by: Frank Loeffler | April 3, 2009 9:20 AM    Report this comment

I'm surprised we are discussing this again, having just done this under the Swift Fuel topic. Frank, following is what I found out from that discussion. There are a lot of naysayers out there who say mogas containing ethanol wont/cant work in aviation and point to anecdotal references. There are also quite a number of guys flying homebuilts using mogas with ethanol successfully despite the contrary opinion that it cant work. It is a fact that neither of the current mogas STCs allow ethanol so the only aircraft that can legally use it currently are experimentals. It is a fact that ethanol will attack certain materials installed in certified aircraft. It is clear that this issue can be addressed by replacing components with compatible replacements as evidenced by millions of cars, but that would require addressing certification issues. It is totally unclear and a matter of opinion as to whether or not any of the other potential issues cited are real or are grossly overstated. I doubt mogas could successfully be used with high performance powerplants without going to electronic controls such as used in cars, but I think it would be possible for mogas to work in a variety of lower performance aircraft with some minor mechanical and operational changes, but that is just my opinion.

Posted by: Mike Wills | April 3, 2009 3:09 PM    Report this comment

It seems to me that if rotary engines were so good they would be widespread. Instead, they were a dismal failure in automobiles. Besides, I can't imagine the paperwork to get one certified in my C206.

Posted by: KEN JACKSON | April 3, 2009 5:23 PM    Report this comment

The rotary engine doesnt solve the fuel availability issue for all of the existing recips in the gen av fleet. And a rotary can detonate on inadequate fuel, improper timing, and a host of other issues as well, just like a recip. The rotary comes with its own set of problems - its just like everything else, there are pluses and minuses. No, I dont think this is the solution to this particular problem, although I do believe the rotary makes sense for aviation applications. I may be biased though since I fly a rotary powered RV-4.

Posted by: Mike Wills | April 3, 2009 7:01 PM    Report this comment

AVGAS 91/96 UL from Hjelmco Oil in Sweden
which has been available at 70 + airports in Sweden for 18 years occationally has 94+ MON and can easily be tailored to permanently have this octane number. So flying Teledyne Continental engines on AVGAS 94 UL is nothing new. It has been done in Sweden for decades. Hjelmco:s AVGAS 91/96 UL which is an ASTM D910 AVGAS without lead already has engine manufacturers approval covering > 90 % of the entire world GA piston fleet. Increasing the octane to about 95 MON has a potential to increase this number to about 95 % of the world piston GA fleet. However at the end it is a matter of cost. Will the 90 % of the world fleet pay 5 % extra for their fuel to cover 5 % more aircraft or will the 95 % of the world fleet pay 20 % extra for their fuel to cover a boutique fuel for the remaining 5 % that really need 100 LL?

AVGAS 91/96 UL should cover up to approx 280 HP on most existent engine configurations.
Does the GA community really need more HP?
There are other options such as rotary engines and turbines.
A small group can hold a large group hostage!
What,s the interest of the majority?

Posted by: Lars Hjelmberg Hjelmco Oil Sweden | April 6, 2009 3:35 PM    Report this comment

Seems to me that your suggestion is simply trading one boutique fuel for another. You sell this fuel, correct? This sounds like a sales pitch.

I still have not been convinced that there isnt a viable low cost alternative with a vast distribution network, being burned in millions of cars everyday. I have not heard or read a convincing argument that a large majority of today's gen av fleet could not be modified to burn mogas safely. I concede there would be significant certification issues. Where would you rather spend your money, bringing your aircraft into the 21st century or paying for a new boutique fuel?

Posted by: Mike Wills | April 6, 2009 4:14 PM    Report this comment

Someone help me out here. So when we no longer have 100LL and TCM/Lycoming/FAA has approved 94UL for those aircraft that can use it, what about those of us with hi-performance engines that require more octane even with FADEC? Wouldn't this then necessitate two fuel grades? After all these years with only 100LL available, (at least in the U.S.), I find it hard to believe that our economics would allow two different avgas grades or we’d still have 80 octane along with 100LL. It doesn’t add $ up. 94UL may work in some aircraft but 94UL won't work in aviation economics. Boutique fuel or not, we will eventually have only one fuel (fits all), containing only approved components in the U.S. or elsewhere and that fuel remains to be found and/or approved.

Posted by: GREGORY MORTON | April 6, 2009 7:10 PM    Report this comment

Mike Wills: How to bring an aircraft engine that needs 91 or 95 MON to operate on MOGAS that at maximum can give you 85-86 MON.
Yes- AVGAS of all sorts are boutique fuels - do you want to get rid of all AVGAS as fuel?
After 30 + years in the business in Scandinavia I have no plans to enter the US so it is no sales
pitch - but I can after inventing, certifying, producing, distributing, selling and flying on unleaded AVGAS for approx 30 years -- transfer to you a lot a experience which is not available in the US.

Posted by: Lars Hjelmberg Hjelmco Oil Sweden | April 7, 2009 3:43 AM    Report this comment

At the peak of the musclecar era in the late 60s we had 500+ HP cars, many of which had to run on 100+ octane premium to prevent detonation. Today you can buy a car off the showroom floor that will produce 500+ HP, have performance that the musclecar era guys could only dream about, and it will run just fine on 91UL containing 10% ethanol. The technology in those 60s era cars was advanced compared to what is offered in gen av airplanes today.

The arguments against mogas use strike me as very similar to the arguments against lean of peak operations. Many naysayers who claim LOP will destroy your engine (including both Lycoming and Continental I beleive), while others routinely do it causing no detrimental effects and saving considerable sums of money in the process.

I guess I should just be happy that I fly an experimental and can burn whatever I choose.

Posted by: Mike Wills | April 7, 2009 10:17 AM    Report this comment

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