Autogas for GA
My studies of fuel are a couple of years old now, but I did a lot of work on it for the worlds #2 car manufacturer. This included interviewing the head fuel technologists at a number of the oil companies. At the time BP only made 98 at Kwinana, but things might have moved on.
While BP may supply Caltex in QLD my point is that its not exclusive and if the spot market is favourable it will be substituted with Singaporean fuel. Also BP supply California with fuel from time to time depending on US supply and exchange rate, so there are times when BP does not have any excess capacity to supply other brands.
For my money, I only buy BP, Shell or Mobil and only from high volume sites. I also frequently have to supply fuel specifications to clients and my experience is that BP, Shell & Mobil have the most easily accessible specification sheets and have accessible fuel technologists when I require specific clarification. In the past we have also conducted batch testing of commercially available fuel from a variety of service station sites. As I noted earlier, the quality between different service station can be significantly different.
Having said that, the United 98 octane is very good and the guys next door get more power on engines on the dyne than the BP racing fuel. But, it contains ethanol, so its neither suitable for aircraft or any of my cars.
Regarding aircraft valves, I cannot disagree more. Get an old aircraft pot and take it to a race engine guy or cylinder head modification guy and ask what they think. The valve seat profile (ie seat angle and the contours leading to and from the seat) is very old fashioned. The UN paper talks to this, which is why I included it.
This is what Continental say:
I forget the timing, but at least Continental made a change to its valve seat material a few years ago. Car engines started moved to hardened seats and modified valve profiles in the late sixties / seventies, but it really got going in the late eighties when catalytic converters became mandatory, which is why the reports such as the 2012 UN one don't report problems moving to unleaded fuel, as I said I included it because of its very nice explanation of seat design. Aircraft engines started changing seat materials sometime after 2000. The problem is that many GA aircraft can have engines with over 20 years calendar life and therefore are in the pre-hardened seat era.
The FAA AVGAS transition committee is concerned about valve recession of replacement fuels and deems testing of this as required.
Peterson Aviation (who hold 20,000 MOGAS STC's) and who are probably the major proponent of unleaded fuel say:
This Swedish paper agrees
https://gupea.ub.gu.se/bitstream/207...gunwpe0019.pdf
This paper by Barlow:
says:
The previous papers are based on the Swedish experience which was the first country to phase out leaded fuel in the 1980's. The paper by Barlow documents real world engine wear examples from removing lead which include valve seat wear, valve burning and turbocharger wear. I hadn't read this before, but apparently lead forms a protective coating on the turbocharger impeller.
Here's another one
http://www2.isye.gatech.edu/~vthomas...ation_lead.pdf
While BP may supply Caltex in QLD my point is that its not exclusive and if the spot market is favourable it will be substituted with Singaporean fuel. Also BP supply California with fuel from time to time depending on US supply and exchange rate, so there are times when BP does not have any excess capacity to supply other brands.
For my money, I only buy BP, Shell or Mobil and only from high volume sites. I also frequently have to supply fuel specifications to clients and my experience is that BP, Shell & Mobil have the most easily accessible specification sheets and have accessible fuel technologists when I require specific clarification. In the past we have also conducted batch testing of commercially available fuel from a variety of service station sites. As I noted earlier, the quality between different service station can be significantly different.
Having said that, the United 98 octane is very good and the guys next door get more power on engines on the dyne than the BP racing fuel. But, it contains ethanol, so its neither suitable for aircraft or any of my cars.
Regarding aircraft valves, I cannot disagree more. Get an old aircraft pot and take it to a race engine guy or cylinder head modification guy and ask what they think. The valve seat profile (ie seat angle and the contours leading to and from the seat) is very old fashioned. The UN paper talks to this, which is why I included it.
This is what Continental say:
In such fuels, the lead acts as a lubricant, coating the contact areas between the valve, guide, and seat. The use of unleaded auto fuels with engines designed for leaded fuels can result in excessive exhaust valve seat wear due to the lack of lead. The result can be remarkable, with cylinder performance deteriorating to unacceptable levels in under 10 hours.
The FAA AVGAS transition committee is concerned about valve recession of replacement fuels and deems testing of this as required.
Peterson Aviation (who hold 20,000 MOGAS STC's) and who are probably the major proponent of unleaded fuel say:
However, lead has also been found to protect valves and seats against valve seat recession.
https://gupea.ub.gu.se/bitstream/207...gunwpe0019.pdf
The crucial
question is therefore whether or not a car with soft valve-seats can use unleaded gasoline.
This matter has been under heavy investigation. It seems to be a matter of interpretation since
conclusions differ between studies, the results are coinciding. One fact that
researchers, oil companies, and vehicle salesmen agree upon is that only 0.05g lead per liter is sufficient to prevent VSR (McArragher et.al., 1994).
question is therefore whether or not a car with soft valve-seats can use unleaded gasoline.
This matter has been under heavy investigation. It seems to be a matter of interpretation since
conclusions differ between studies, the results are coinciding. One fact that
researchers, oil companies, and vehicle salesmen agree upon is that only 0.05g lead per liter is sufficient to prevent VSR (McArragher et.al., 1994).
says:
"The lead compounds, oxide and sulphate mixtures resulting from combustion proved to be the most effective lubricant for cast iron or unhardened valve seats ever produced. here is also another less well documented but none-the-less crucial benefit, ie the lubrication of the bottom of the valve guide...."
Here's another one
http://www2.isye.gatech.edu/~vthomas...ation_lead.pdf
A secondary role of lead additives is lubrication of the exhaust valves.
The most extensive study of the car maintenance consequences of using unleaded gasoline in cars designed for leaded gasoline was a 5-year study of 64 matched pairs of cars (62).
cylinder heads were replaced more often on the cars using
unleaded gasoline,because of excessive valve-seat wear
unleaded gasoline,because of excessive valve-seat wear
Laboratory studies confirm that under prolonged, severe driving conditions,valve-seat recession will occur if unleaded gasoline is used in engines without hardened valve seats
And from Shell itself
AVGAS Facts and Future - Shell Global
AVGAS Facts and Future - Shell Global
s 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 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.
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 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.
Join Date: Jul 2007
Location: in the classroom of life
Age: 55
Posts: 6,864
Likes: 0
Received 1 Like
on
1 Post
So explain why when the radial piston ag guys started using ULP (to save a $$) and started having valve issues in their old design heads, they then did nothing but change the timing.....and their problems went away.
No lead....less in fact as it would have worn away, and still the problems went away with timing changes.
The same thing for many cars.
In any case.......in GA aircraft it is a moot point.
No lead....less in fact as it would have worn away, and still the problems went away with timing changes.
The same thing for many cars.
In any case.......in GA aircraft it is a moot point.
No lead....less in fact as it would have worn away, and still the problems went away with timing changes.
Mogas also has other additives to replace the lubricating properties of lead to some degree. It is not without lubricating properties entirely. I haven't paid a lot of attention to it, but I think Potassium is one and MTBE may be another - although it is controversial, and I suspect that the industry may have moved to something new. I forget what was behind Shell's move from Optimax to V-Power, but involved a wholesale change to the fuel's chemistry.
Join Date: Jul 2011
Location: Sarnia, ON
Posts: 89
Likes: 0
Received 0 Likes
on
0 Posts
Swift fuel ATSM approval
Having said that, I just checked the type certificate for the Victa and it states "Fuel: 80/87 minimum grade aviation fuel." and nowhere does it nominate which standard that fuel must conform to.
Seems no reason it can't use 100SF or G100UL now. They are both aviation fuels and both have octanes greater than 80/87. If I was stupid enough to ask CASA they would say no, but might be better to seek forgiveness than ask permission.
Join Date: Jul 2007
Location: in the classroom of life
Age: 55
Posts: 6,864
Likes: 0
Received 1 Like
on
1 Post
What does the POH say about fuel or in section 2? 
Just because it says 80/87 that is not the end of it. The ASTM is an industry standard and in no way reflects a FAA approved fuel. ASTM is irrelevant in terms of its aviation approved status.
FAA have to be dealt with first.
Trust me on that
In fact legally you need only one of the two approvals, and it sure ain't the 4 letter one.
Just because it says 80/87 that is not the end of it. The ASTM is an industry standard and in no way reflects a FAA approved fuel. ASTM is irrelevant in terms of its aviation approved status.
FAA have to be dealt with first.
Trust me on that
In fact legally you need only one of the two approvals, and it sure ain't the 4 letter one.
Join Date: Jul 2007
Location: in the classroom of life
Age: 55
Posts: 6,864
Likes: 0
Received 1 Like
on
1 Post
From George W Braly
When we look at this problem - - we boil down the issues to a set of design requirements for a workable replacement avgas for 100LL.
Design Requirements for a Functional Drop-In Replacement for 100LL Avgas:
1) Detonation - - same-same as 100LL;
2) Material compatibility - - close or same-same as 100LL;
3) Economics - - close to 100LL. Close means ? ~ about 10-15% premium or less;
4) Fungible. Has to be mixable in the FBO tanks and the wing tanks. Otherwise a transition to a new fuel becomes a logistical nightmare.
5) Producible. Has to be able to be made inside the fence of existing refineries. Nobody is going to spend 100’s of millions to build new production facilities. This requirement is related to item 3) above; and,
6) Transparent. Has to be transparent to the pilot, the engine, & the airframe when compared to 100LL.
Frankly - - we can do an assessment of five of those six requirements in two or three days of testing at our facility. The material compatibility testing takes longer, but even that is subject to some pretty straightforward assessments.
But then actually doing all of the formal certification work is challenging.
All of the testing todate continues to demonstrate that G100UL(R) avgas meets each of those six requirements.
Swift decided to pursue an ASTM specification - - hoping then that someone will decided to undertake the expensive and time consuming work to do all of the FAA certification testing to actually get the fuel approved to that it can be added to the limitations section of the engine and airframe type certificates, then legally flown in the aircraft.
GAMI has taken a different approach. We decided to do a parrallel process. We are doing the heavy lifting certification work with the FAA. At the same time we have the ASTM process moving forward. The data we generate for the FAA certification effort can be used for most or virtually all of the ASTM data package. But the ASTM data package does not get you an FAA certification.
We continue to make good progress with the FAA certification effort. At the same time, we continue to move the ASTM specification approval process forward.
Regards, George
Design Requirements for a Functional Drop-In Replacement for 100LL Avgas:
1) Detonation - - same-same as 100LL;
2) Material compatibility - - close or same-same as 100LL;
3) Economics - - close to 100LL. Close means ? ~ about 10-15% premium or less;
4) Fungible. Has to be mixable in the FBO tanks and the wing tanks. Otherwise a transition to a new fuel becomes a logistical nightmare.
5) Producible. Has to be able to be made inside the fence of existing refineries. Nobody is going to spend 100’s of millions to build new production facilities. This requirement is related to item 3) above; and,
6) Transparent. Has to be transparent to the pilot, the engine, & the airframe when compared to 100LL.
Frankly - - we can do an assessment of five of those six requirements in two or three days of testing at our facility. The material compatibility testing takes longer, but even that is subject to some pretty straightforward assessments.
But then actually doing all of the formal certification work is challenging.
All of the testing todate continues to demonstrate that G100UL(R) avgas meets each of those six requirements.
Swift decided to pursue an ASTM specification - - hoping then that someone will decided to undertake the expensive and time consuming work to do all of the FAA certification testing to actually get the fuel approved to that it can be added to the limitations section of the engine and airframe type certificates, then legally flown in the aircraft.
GAMI has taken a different approach. We decided to do a parrallel process. We are doing the heavy lifting certification work with the FAA. At the same time we have the ASTM process moving forward. The data we generate for the FAA certification effort can be used for most or virtually all of the ASTM data package. But the ASTM data package does not get you an FAA certification.
We continue to make good progress with the FAA certification effort. At the same time, we continue to move the ASTM specification approval process forward.
Regards, George
