Lyondell/Basel-VP Racing says tests on a high-compression (8.5:1) I0-550-D show the engine will make its normal takeoff horsepower using its UL100E unleaded fuel even though the engine timing needs to be retarded 3° to meet detonation margins. The company unveiled the data at the annual National Warbirds Operator Conference Feb. 8 in Virginia Beach. The presentation is covered in a video prepared by A&P Michael Luvara as part of his fuel compatibility series. Lyondell/Basell-VP Racing has been candid that high-output engines using its fuels will need operating adjustments, but the tests apparently show the changes don’t significantly affect performance on this engine, which is in widespread use. Spokesman Andrew Findlay told the meeting that there are “no discernible takeoff power changes to the Continental I0-550-D at takeoff power with 3° of ignition timing retard” when compared to using 100LL at the normal timing setting of 22° before top dead center.
The testing was done at the FAA’s William Hughes Technical Center in New Jersey, where UL100E is undergoing testing in the Piston Aviation Fuels Initiative (PAFI) program. The fuel is one of three being considered as a replacement for 100LL to eliminate lead exhaust emissions by 2030. Swift Fuels’ 100R and GAMI’s G100UL are also in the running but are not in the PAFI program. G100UL has already received STC approval for all certified aircraft, while Swift is looking to expand its STC approval from two models of fuel-injected Cessna 172s. According to the PAFI testing, the engine with normal timing (22° BTDC) using 100LL made 294 takeoff horsepower while the same engine, with the timing set at 19° BTDC and using UL100E, made 295 takeoff hp. The unleaded fuel caused a 2% increase in exhaust gas temperatures to 1,456° Fahrenheit. The fuel is also being tested in a DC-6 in Alaska, a Cirrus SR-22, and a Canadian Harvard warbird, the equivalent of a U.S. T-6.
Swift Fuels 100R is now being tested head to head against 100LL in an Allison V12 engine in a comprehensive set of evaluations being done by STRIX Aero. “STRIX uses sophisticated engine monitoring equipment to evaluate operating performance of the engine to compare 100R to 100LL,” said the presentation given by STRIX’s Cory Miller. Results from those tests are expected in two to three months. There was no mention in Luvara’s video of G100UL at the meeting. The balance of Luvara’s video deals with a recap of his fuel testing efforts over the past year and some new compatibility testing on rubber components. The video is below.
An earlier version of this story misstated the timing settings. They have been corrected. Sorry for the error.
I applaud the unleaded effort here but I’m concerned that conventional magnetos and standard shop practices may be too imprecise to ensure accurate ignition timing for the fuel used. Traditional mag timing tools are clumsy, archaic, and subject to multiple errors. Compounding the problem, magneto wear and tear will drift internal timing, thus affecting ignition timing to the engine. Finding a 3-degree drift, or more, is not unusual.
Electronic ignition and a more accurate measure of timing indication would certainly help and may be needed for operating extremes, but engine detonation is a messy business. Margins against such events must not be compromised if flight safety is valued above the goal of integrating unleaded avgas to General Aviation.
You are correct, in tightly controlled conditions the results can be excellent. But in the real world, less detonation resistance/less margin for error will rear its ugly head. The good news here is a typical wear method for magnetos is wear on the points cam follower (the rubbing block lubricated by a felt pad) leading to later opening and retarded timing.
Also of note, the Continental IO550 is not a true high compression engine, with lower compression than many Lycoming engines and the IO550-D is well known for strong detonation margins. This is due to excellent cooling properties, combustion chamber design and modest compression ratios.
I’d rather see testing done on typical high compression Lycoming parallel and angle valve engines.
Adding TEL to the fuel slows the flame front in the combustion chamber. That is what increasing the octane value does and that is why it was added. Take it out and you have a lower octane, faster burning fuel, requiring a timing change if you want to maintain the same HP.
Nothing new here!
KS
“I’d rather see testing done on typical high compression Lycoming parallel and angle valve engines.”
Agreed. Successful testing of high-output, turbocharged angle- and parallel-valve Lycoming engines would, by default, find the remainder of the flat-engine fleet to be eligible for the fuel. Large bore radial engines and highly-boosted liquid cooled variants each have unique operating qualities that will require modification or altered output limitations beyond simple timing adjustments.
I’m glad to see the positive results here. From my race car engine dyno days, it was always obvious that when using higher octane fuels, more timing was required to maintain output. So it is no surprise that a reduction in timing results in the same HP when the fuel used has different/faster burn characteristics. For example, many non high performance auto engines do not make more HP on premium 93 octane vs. regular 87 octane. Even with the knock sensors allowing full ign timing.
Also of note, I use and trust VP fuels extensively with great results in high boost turbocharged race car engines, to Rotax 914s (Stemme motorglider 115HP turbocharged 4 cylinder) along with both 2 stroke and 4 stroke race motorcycles.
I fly a 200HP Lycoming IO360 powered Cessna 177RG. It has more compression 8.7 to 1, than the Continental in question, and the IO390 STC has even more compression at 8.9 to 1!. These engines are well known to mildly detonate with 100LL on cold days at full power. This is why Lycoming reduced timing from 25º to 20º, with a loss of 3HP. I suspect these engines will not tolerate substandard octane.
Nice update but raises questions like, regarding mag timing, what are we to do during the extended transition between fuels on XC flights? Will our EFBs show us which FBOs have 100LL vs UL100E? Do we just retard the mag timing to be safe and live with those concequences? How do I know if 3 deg matters for whatever engine I’m flying behind?
Good questions. Also, it seems to me that whatever fuel is chosen MUST work properly combined with 0-99% 100LL on all engines. The GAMI fuel apparently works. Do the others?
Something worthy of consideration: Swift’s original UL100 Trimethylbenzene/isopentane (low vapor pressure) mix provides a stunning octane buffer as high as 130 octane and is completely benign to aircraft components. However when using UL100 it is near impossible to start a cold engine below about 40ºF.
This one issue can be addressed with an addition to the existing magneto/electronic ign systems. Using surface gap sparkplugs on the bottom locations, and using a brutally powerful, turbine engine-like 12 Joules of energy to initially fire those plugs. This produces an explosive plasma kernel that will ignite anything. Remember, jet engines can light cold, non atomized kerosene at altitude, this ‘ain’t’ easy and the ign systems are well designed for this.
The addl system would use both existing mags, existing spark plug harness connectors and the timing settings. It would simply provide 12 Joules of high energy spark during start, tapering the Joule energy down during initial warmup and switching over to the magneto spark when the spark plug is warm (using a temp sensor). Brutally simple, needing only a 14V/28V connector, and fail safe, if it quits, the magnetos both still function.
Remember, the snap-snap you hear when turbine ign systems fire is the 12 Joules of energy firing a surface gap plug. It is enough to ignite a non contact, non atomized fuel mixture or flooded fuel mixture via Localized overpressure Strong UV emission, Ionized radicals and Turbulence at the plug face. It does the mixing and pressure work for you.
What does this ignition mod look like – can you point us to an example? I’m experimenting with an MSD 6A firing the rear plugs on a 360hp M14P radial (which I realize will run any unleaded fuel above 80 octane). However, this ignition mod system only puts out 135mJ… The engine uses a “shower of sparks” (common to flat engines too), that appears to output 200mJ. I can’t imagine the system that would be required for 12J of firing power for surface gap plugs, both during start and normal operations.
My two cents: Setting the timing different (and the fuel flow, which is also required) wouldn’t be too radical if this fuel was universally adopted. But if it’s one of three fuels adopted, how are we supposed to travel cross country using different fuels as available? This would NOT be cross-compatible, so I think the UL100E should just be a non-starter. Why continue to waste time on it when there are better alternatives that are cross compatible? G100UL is the most extensively tested unleaded fuel available, and the fact that it may expose a few bad seals that needed to be repaired anyway would cost far less to the avgas-burning fleet than resetting fuel injection and timing.
G100UL is doing far, FAR more damage than just a “few bad seals.” I think at this point it is pretty much out of the running as a 100LL replacement. See the latest test results on it from Michael Luvara: https://www.youtube.com/watch?v=bqFZbtR4pRc
For heavens sake, everybody knows at this point that G100UL is the one that works! Pay the inventor some money and roll out the new gas, and STOP TALKING about it!
Russ, The BTDC timing in the article needs clarification. Is stock BTDC timing 21º (in text) or 22º (in table)?
Interesting that the TSI0 550 version of this engine with its 7.5 to 1 compression ratio is approved for a used with Swift UL 94. One would wonder with these reduced ignition timings if the I0 540 version of this engine might also run on Swift UL 94.
Did you mean the Lycoming IO-540? If so, I’ve been wondering about this as well. My engine is a standard compression Lyc IO-540-D4A5 (one of Lyondell’s test engine models), and Lycoming’s Service Instruction 1070AB from April 8, 2020, Table 3 shows the approved unleaded fuels for this engine to include UL94, UL91, Hjelmco 91/96 and even 93 AKI and Super Plus MOGAS. The only listed fuel NOT approved is 91 AKI MOGAS. So, almost anything. Looks like it doesn’t even need 100. Interesting that they chose to test this one.