Schlagwort-Archive: fuel

FAA approves unleaded fuel for piston fleet

The FAA signed on September 1 supplemental type certificates that allow General Aviation Modifications Inc.’s 100-octane unleaded fuel (G100UL) to be used in every general aviation spark-ignition engine and every airframe powered by those engines. The move was hailed by the industry as a major step in the transition to an unleaded GA future. The FAA’s approval of the use of G100UL fuel in all piston aircraft satisfies a longstanding goal of finding a solution that can be used for the entire GA piston fleet.

“I’m proud of GAMI, the industry team, and the FAA for persevering over the long term and getting a fuel that the FAA has recognized as a viable alternative to low lead,” AOPA President Mark Baker said. “It’s vital that we find solutions to what has been plaguing general aviation since the seventies. It’s certainly the biggest issue I have dealt with in my time at AOPA. This is a big deal,” Baker added, “but there is a lot of work yet to be done.”

In 2021 the FAA approved STCs for GAMI covering a smaller number of Cessna 172 engines and airframes, and then expanded the approved model lists (AML) to include essentially all lower-compression engine and airframe combinations. Though that was seen as an encouraging step forward in the yearslong path to supply unleaded aviation fuel to the piston aircraft fleet, the STCs did not include aircraft needing the higher-octane fuel that accounts for 60 to 70 per cent of avgas consumption. This latest announcement by the FAA addresses the needs of those higher-compression engines.

GAMI cofounder George Braly said, “This is a big day for the industry. It means that for a lot of our general aviation communities, and especially for a high fraction on the West Coast, relief is on the way. And it means that our industry will be able to go into the future and prosper, and provide the essential infrastructure for this country for everything from Angel Flights to critical training of our future airline pilots.” Braly thanked AOPA and the GA community for their support through this long process. “Without it we couldn’t have gotten this done,” he said. Braly has said that Ann Arbor, Michigan-based fuel supplier Avfuel is standing by to manage the logistics and distribution of G100UL, and said he is open to partnerships. “Our arrangement is that any qualified refiner or blender of existing aviation fuels will be eligible to produce and sell it subject to the quality assurance requirements that the FAA has approved,” he said.

When will G100UL reach airports and aircraft tanks?
The timing for when G100UL will reach airports is still uncertain. “It’s going to take a while to manage the infrastructure” including manufacturing and distribution, Braly said. The supply chain “is still a very wounded infrastructure and that’s not going to make the process any easier, but we have a handle on how to do this, and with the support of the major players I think we can do that. It’s going to be limited, to begin with, but it can be ramped up rapidly,” he said. Baker said it’s important to get any fuels approved for use in the California market as soon as practical, in light of the fact that some municipalities have prematurely banned the sale of leaded avgas and threatened a safe and smart transition to unleaded fuel. “It is a politically charged issue there, and this will help keep our airports open with fuel that works with all aircraft.” AOPA will also purchase a number of unleaded fuels to use in its fleet of piston aircraft used for GA travel and flight training, showing members it has full confidence in FAA approval pathways and processes.

What will G100UL cost?
While the cost of the fuel has not been determined, Braly said the small-batch production process that will initially earmark the arrival of G100UL at airports means that the fuel will cost slightly more than leaded avgas. “Small volume batches cost money,” he said. “Until we can get [production] revved up that we’re making millions of gallons at a time, there will be an incremental [additional] cost,” he said. “It’s not going to be unreasonable,” he said. “Pilots in America will not be paying what they’re paying for avgas in Europe today.” And while they may pay a little more at the pump, owners can expect to see engines that operate more efficiently. “I think the days of cleaning spark plugs every 50 hours are going to be behind us for good,” Braly said.

Swift Fuels Inc., an Indiana-based company, has received FAA approval for its 94-octane unleaded fuel and has expanded its distribution, particularly to the West Coast. Swift Fuels’ 94-octane fuel meets some, but not all, of the demand of aircraft with low-compression engines. The company is developing a 100R unleaded fuel with more than 10 per cent renewable content. In addition, two fuel candidates are currently in the Piston Aviation Fuels Initiative testing process. AOPA continues to encourage all fuel manufacturers to follow through with their own formulations, Baker said. “We’d like to see several fuels available that all work together and blend together. Competition is always a good thing for the markets.” Source: ‘AOPA‘.

Application for Use of UL 91/94

Continental, a subsidiary of Continental Aerospace Technologies Holding Limited, announced its efforts today to expand the use of alternative fuels in select lower compression avgas engines. Continental® has submitted a formal application to the FAA, that if approved, would authorize the use of unleaded aviation gasoline in over 100 popular engine models including select O-200s, IO-360s, O-470s, and IO-470s. As the industry searches for a long-term fuel solution, Continental® considers 91UL and 94UL fuel as a transitional step in a long-term strategy to reach more sustainable aviation.

With the pending approval of this application, Continental® strives to enable aviators the opportunity to select a greener alternative. “While Continental offers Jet-A engines that utilize readily available heavy fuels, the majority of Continental aviators are flying behind an engine fueled by a lead avgas like 100LL,” said Dr David Dörner, Vice President of Global Research and Development. “If we want the future generations of aviators to enjoy the beauty of flight, it is imperative that the industry collaboratively evaluate alternatives and identify viable solutions. Unfortunately, not everyone has access to quality fuels, but by expanding fuel sources, aviators can choose to fly while being more environmentally responsible.”

As a part of Continental’s commitment to the future of general aviation, Continental® prioritized this group of engine models to conduct an extensive review on the impacts of alternative fuels in lower compression ratio engines. This performance study, held in conjunction with Eliminate Aviation Gasoline Lead Emissions’ (EAGLE) initiative, verified that the select powerplants perform as designed with the lower octane fuels. Continental’s testing scope includes other engine models and anticipates additional approvals in the future. Remain up to date on this topic by reviewing the service documents corresponding to your engine model. Pilots and operators should use only certified fuels for each engine application to ensure optimal performance and safety. Source: ‘Continental’.

The Future of General Aviation Fuels

Currently, the two principal types of fuel used in Aviation are Avgas 100LL and Jet A-1; Jet A-1 for turbine engines and Avgas for spark ignition piston engines. If you are a general aviation pilot, the one you are probably more familiar with is Avgas and it is this which we will concentrate on here. As you may be aware, Avgas contains Tetra Ethyl Lead (TEL) – the additive which has recently been banned in automotive forecourt fuels in the European Union for environmental reasons. Although the total fuel volume used in aviation is less than 0.5% of that used in the automotive sector in Europe, there is considerable pressure from Environmental Lobbyists to remove or replace TEL in Avgas and produce an unleaded grade. To understand what is involved, we first need to look at what benefits TEL has. As you may know from the problems with Automotive fuels, Lead compounds from TEL form a protective layer on the valve seat and prevents the soft valve seats from eroding. Without TEL small areas of a soft metal valve seat will fuse to the valve and be ‘plucked’ from the face of the seat.

Once attached to the valve they form an abrasive surface which further damages the valve seat. This combination of actions is known as Valve Seat Recession (VSR) as the seat of the valve is worn away and recesses into the cylinder head. The solutions to this are to either use a VSR additive or fit hardened valve seats which are resistant to this action. VSR additives are now commonly used in Lead Replacement Petrol on automotive forecourts, however for several reasons they are not yet approved for use in aviation engines. This means that the only current method of preventing the Valve Seat Recession for aviation engines using unleaded fuels would be to fit hardened valve seats. This is common in new manufacture Avco Lycoming and Teledyne Continental engines, but some older engines would need modification.

The other more significant problem with unleaded fuels is that of Octane rating. Octane rating is a measure of how resistant a fuel is to detonation or “pinking”; the higher the Octane rating, the more the fuel/air mixture can be compressed without detonation happening. To make this clear, octane rating is not a measure of the amount of energy in the fuel but is a measure of its resistance to detonation. The advantage of higher octane fuels is that a higher compression ratio or supercharging ratio can be used, which then leads to a higher engine cycle efficiency, which in turn means more power output for a given fuel burn. However, to confuse things further, there are four principal ways to measure Octane rating, RON, MON, Lean Mixture and Rich Mixture ratings. Road fuels tend to be measured on a RON scale, for which unleaded fuels tend to be 95 – 98 RON but are only 85 – 87 MON. Avgas is measured on Lean Mixture (similar to MON) but also has a Rich Mixture Octane rating.

The Lean Mixture rating is 100 octane (15 octane higher than the comparable 85 MON for unleaded Mogas) but Avgas also has a Rich Mixture rating of 130 which allows higher supercharger boost pressures to be used without detonation occurring. This is particularly a problem when using high power settings at low altitudes, for example during take-off. As you can see TEL in Avgas makes a significant difference to the octane rating and without it, Octane ratings would be back down to 80 – 85 Lean Mixture – the level for road fuels – instead of 100 / 130. This is not a problem for most typical modern normally aspirated engines as their compression ratios are quite modest and detonation would not be a problem with 80 – 85 Lean Mixture Octane fuel. However, for those aeroplanes with supercharged or turbocharged engines, the use of low octane unleaded fuels would not be suitable. The only way to operate these turbo engines on current unleaded technology fuels would be to significantly reduce the boost pressure of the supercharging and massively de-rate the engines. This de-rating would be so severe that many of the engines would no longer be powerful enough for the aeroplane in question. Modern aviation unleaded fuels are currently being developed, such as 82UL in the United States. This is an 82 Octane Lean Mixture rating fuel and is approved for use in modern non-turbo Avco Lycomings engines amongst others. However, it is not yet available in Europe but also not everyone can use it – your aircraft manufacturer must raise an Aircraft Modification document to approve its use. Some new Cessnas are approved to use 82UL, but most aircraft types currently do not have the manufacturer’s approval. The potential quantity of Avgas piston-engined aircraft worldwide that could use this grade is estimated to be around 60%, although some of these would probably need fuel system modifications prior to approval.

To date, there are no additives available to replace TEL which increase the Octane rating – the additives used in automotive Lead Replacement Fuels only tackle the problem of valve seat recession and do not effect the Octane rating of the fuel. Therefore if Avgas 100LL were to disappear, the only other option currently available to owners with turbo or supercharged engines would be for the aircraft manufacturer to raise a modification to replace their engine with either a turboprop or diesel engine. This brings us to the other recent advance in General Aviation engines; the development by several engine manufacturers of diesel engine technology. Shell is involved with all of the major prospective aviation diesel engine manufacturers and is working closely on these projects. These engines potentially offer several significant advantages over Avgas engines. They return up to 30% better fuel economy, use Jet A-1 rather than Avgas, and have the potential to be retrofitted to many light aircraft, replacing their current Avgas type engines. The downside will be the cost of engine replacement and aircraft modification and whilst some applications may be able to take advantage of this technology, this will not be a solution for everyone. So in summary, Aviation engines present many unique challenges to the development of Avgas and as such, there is yet no firm date to replace Avgas 100LL, but there can be little doubt that eventually Leaded Avgas will be withdrawn from use. However, this does not seem likely until suitable fully developed alternatives are available; a situation that is likely to be several years into the future. Source: ‘Shell‘. Bild: ‘Continental‘.