Unleaded fuel proponent Lyondell/Basell says it expects the FAA to finish testing its UL100E by the end of September of this year. The company says the agency has done detonation testing of its UL100E fuel in six models of Continental IO-550 engines to identify “the optimal timing advance for UL100E in the IO-550-A, -B, -C, -D, -E, -F, and -L series of engines.” The testing was done as part of the Piston Aircraft Fuel Initiative evaluation of the fuel at the William J. Hughes Technical Center for Advanced Aerospace in Atlantic City and is a key milestone in assessing the fuel as a possible unleaded replacement for 100LL. In a statement to AvBrief, the company said it’s also making progress with an ASTM specification for its fuel and is about to start testing it in a turbocharged Cessna T-206 Turbo Stationair, and when all of the data is in it will rule on its suitability for high-performance engines. “The FAA will use the PAFI test results to define the eligible fleet and outline any operational and/or engine modifications required for a small portion of the fleet via a Special Airworthiness Information Bulletin (SAIB),” the statement said.
Lyondell/Basell declined to elaborate on the detonation testing, but it has been open about the possibility that some large-bore engines may need paperwork or even mechanical changes to be authorized for its use. “Generally, to prevent detonation, the ignition timing (the moment the spark starts the fuel to burn in the cylinder) can be retarded. That gives the fuel less time to burn before the piston reaches the top of the combustion chamber and starts down. That retarded timing reduces peak cylinder pressures and reduces the likelihood that the fuel-air “charge” will self-ignite (auto-ignite) which results in detonation. However, delaying the spark also reduces power output and engine efficiency resulting in increased fuel consumption for the same horsepower. In addition, the delayed spark will cause the exhaust gas temperatures and the critical turbine inlet temperatures (TIT) for turbocharged engines to increase (an earlier version of this story included incorrect information on that point). Delaying the spark can also increase fuel consumption and reduce power output and can lead to overheating. The net effect can be derating the engine and its certified horsepower rating, potentially affecting takeoff, climb, and cruise performance. Lyondell/Basell said it would leave it to the FAA to announce what, if any, impacts its test results will have on the high-performance engines.
As for the ASTM process, the company said the organization has published a specification for fuels that use ethers as octane boosters. “This is the first ASTM specification for UL100E, the unleaded aviation gasoline co-developed by LyondellBasell and VP Racing,” the company said. The company can now make its case for approval by ASTM under that specification. ASTM approval is a requirement of the PAFI process. UL100E is the only fuel left in that testing, which, if successful, will potentially lead to FAA “fleet approval” of the fuel. The other two candidate fuels, GAMI’s G100UL and Swift Fuels’ 100R, are both using the Supplementary Type Certificate (STC) process for FAA certification. G100UL has STC approval for all certified aircraft engines but is still waiting for approval for helicopters. It is not pursuing an ASTM specification. Swift has STCs for the R- and S-model Cessna 172s and recently earned an ASTM production specification for its fuel.
Another key component of the process is determining compatibility with the various materials the fuel will come in to contact with in the aircraft. Lyondell/Basell says the materials testing was done by aircraft manufacturers Van’s Aircraft, Piper Aircraft, Textron, and Cirrus. The full text of Lyondell/Basell’s statement is below.
As a technical matter, retarding ignition timing by 3-5 degrees on a Lycoming will not significantly affect performance. The practice has been employed in various models of the 200 HP IO-360 series for many years as a way of lowering CHTs. However, that may not be the case with other engines. Retarded timing generates higher EGTs, more combustion chamber deposits, and can reduce rated power by a margin greater than the standard Lycoming (+ -) 5%. What impact it has on engines with electronic (variable) ignition timing will need to be vetted, as will engines fitted with high compression pistons or operate with unusually low or high RPMs.
I applaud Lyondell’s efforts, but transition to any unleaded fuel for all air-cooled aircraft engines will not be led by Occam’s Razor nor are detonation limits the only concerns.
For all the complaining about ancient technology, the standard Lycoming or Continental aircraft engine is a marvel of engineering compromise. Until those ancient designs fade to the dust from which they were forged, this will still be a complicated issue.
“Generally, to prevent detonation, the timing (the moment the spark starts to burn fuel in the cylinder) is retarded to give the fuel more time to thoroughly burn in the cylinder.”
Retarding ignition moves the point of peak pressure further past TDC. Doing so also lowers the peak pressure since the combustion occurs in a larger space. As the other commenter says, this increases EGT and lowers power output.
Higher EGTs could be an issue for turbo inlet temps.
Reduced takeoff and climb performance… how this plays out will be interesting. Increased TO FF may be required. Some aircraft may not be able to reach the required FF without other changes.
Electronic ignition with the ability to advance based on MP and RPM will help most alt altitude.
Reminder: The mission was to find an unleaded fuel that can replace 100LL.
If we wanted to derate the engine, we could use auto fuel all along.
Retarding the timing is the worst way to accommodate octane deficiency. Retarding the timing 5 degrees reduces max power significantly and more so on higher CR engines. Worse than that, the power loss in LOP operation is far greater. It also causes even more deposits and higher EGTs.
A much better way to derate the engine for lower octane fuel is to lower the manifold pressure (and advance the timing accordingly). The timing should always be at an optimum based on MAP or BMEP, AFR, RPM and inlet temp.
To retard the timing using magnetos is bad joke: Any ignition device driven from the accessory case, using points and a distributor has a total timing fluctuation of 3-5 degrees when in good shape. For this reason distributor ignitions on cars went away some 30 years ago. Direct crankshaft position sensing must be used for ignition to achieve precise timing to meet emissions (on cars) and to do valid octane requirement research.
Optimum ignition energy and timing can reduce the octane requirement 1-2 points.
Good Luck!
KS
Correct. The idea of retarding timing is cowpucky.
Obviously not much thought about 2nd and 3rd order effects by simply issuing a Special Airworthiness Information Bulletin (SAIB) to wave a magic wand to allow for reduced engine performance. A SAIB is not going to fix the performance tables in your POH, only the TC holder can do that. At least the STC route has a legal basis for someone other than the Mfg/TC holder to make those changes. Is the FAA just going to authorize a blanket increase (add 10%/20%) in TO distance to the book number as the legal solution? Same for POH list of fuel types allowed, is the FAA going to legally declare UL100E as equivalent to 100LL for regulatory purposes.
My helo has a derating table printed right on the headliner if unleaded gas is used (and, of course, POH elements as well). Perhaps this will be required for other aircraft as well.
I’m old enough to remember being knocked out at the dentist with Ether. How many of us have been in aircraft whose interiors smell like AVGAS? Does that give you warm fuzzies if the new chemistry has the tendency to put you to sleep? Say nothing of the carcinogenic effects. What good idea fairy let this organic chemistry monstrosity come to be? Say nothing of it not being a drop in with the derating of motors. The whole situation is astounding in its ignoring everything about the pilot who has to deal with this nightmare fuel (quite literally).
Horse hooey. ETBE based fuels were evaluated for 4.5 years by Textron/FAA and for the past 7 years by the FAA, numerous OEMs, and pilots. None have reported CNS effects from exposure to UL100E or fuels with even higher levels of ETBE.
The ether you inhaled was diethyl ether, not ETBE. Different chemical, metabolic pathway, and CNS effects.
Maybe you should focus on the materials compatibility issues of your fuel instead of spreading misinformation about ours?
“Straightshooter” – – my name is George Braly. I work with GAMI and have been flying aircraft with high octane unleaded fuels for the last 15 years.
Could you share with the readers who you are and which company you are with?
Naptime,
About a year ago, I was in a conference room with about a dozen people. There were small 100 ml sample jars of one of the ETBE based fuel chemistries and several others.
An older guy with some chemistry background, picked up the sample jar of the ETBE based fuel and opened the lid and then “wafted” their hand across the top of the jar back and forth toward their face to smell the fuel and compare it to the jars of 100LL and G100UL they had just evaluated.
There was a middle aged woman sitting 4 feet across the table. Rather quickly, she suddenly pushed back from the table and stated (exclaimed ? ) loudly – – “Put the lid back on! That is nauseating and starting to make me dizzy…” Then she got up and left the room.
******