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Avgas quality concerns ... helicopters

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Avgas quality concerns ... helicopters

Old 5th Oct 2018, 00:33
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Originally Posted by Bend alot View Post
Removing the lead in the fuel to C441's gives the same engine problems in the north, from what I hear Eddie.
That is good to hear, I was starting to think it is an operator problem
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Old 6th Oct 2018, 11:05
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Chemistry of things like fuel have benefits and penalties in achieving a target such as a "octane rating"

They are not tabled as such as they are by products of a requirement of the fuel.

Changing any part of the chemistry can keep the same "octane rating" and other performance items like say burn speed.

But can have massive changes on other things due to chemistry change - say more acidic for example, that brings on corrosion in humid conditions on valve faces that accelerates wear.

A single atom can change things dramatically.

Lead seems to have effects on cooling and lubrication in certain applications as a by product.
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Old 7th Oct 2018, 08:56
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Folks,
Cessna 441 --- leaded fuel, am I missing something here, or has somebody been re-engining Conquests??
Tootle pip!!
PS: Years ago now, but persistent engine/fuel system problems due fuel quality is why Qantas Eastern got rid of Titans, with a policy decision of no more petrol burners. As we found out later the problem was EDA.
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Old 7th Oct 2018, 10:02
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Originally Posted by LeadSled View Post
Folks,
Cessna 441 --- leaded fuel, am I missing something here, or has somebody been re-engining Conquests??
Tootle pip!!
PS: Years ago now, but persistent engine/fuel system problems due fuel quality is why Qantas Eastern got rid of Titans, with a policy decision of no more petrol burners. As we found out later the problem was EDA.
Yep you missed passed comments on a C441 fuel issue witnessed by a poster (here) on another thread that we still await to hear about its fuel issue from the ATSB.

The lack of lead allowed a massive fungal growth in the fuel tanks!!
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Old 7th Oct 2018, 10:53
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Originally Posted by Connedrod View Post
Once again not quite true. Whist the boundary layer protects the top of the piston detenation will at the extreme will and can blow down the side and top of the piston.
This is kind of true but not really very illuminating. Knock/detonation excites the resonant frequencies of the gas in the combustion chamber causing the gas to oscillate back and forth in varying patterns at the fundamental and higher order harmonic frequencies. There are many different modes to this oscillating pattern but the pressure wave that is generated needs an associated gas velocity to make it happen so yes, when a pressure peak arrives to one side of the piston crown the gas will be stuffed down the side of the ring land - that's what makes the pressure happen. It's the velocity of the gas that disturbs the boundary layer and causes the increased heat transfer rates associated with symptoms of higher CHTs.

The higher the knock pressure amplitude the faster the gas has to move so heavy knock is associated with high local gas velocities and thus high heat transfer. The local pressure of the wave against the combustion chamber can also fatigue the material (which at higher temperatures also has a lower tensile strength and therefore fatigue strength) causing pitting associated with knock damage.
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Old 8th Oct 2018, 04:56
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Originally Posted by Bend alot View Post
Yep you missed passed comments on a C441 fuel issue witnessed by a poster (here) on another thread that we still await to hear about its fuel issue from the ATSB.

The lack of lead allowed a massive fungal growth in the fuel tanks!!
?? So the Conquest was burning Avgas 100LL (which I assume is an alternative fuel) instead of Jet A. Why would you do that, except when Jet A is not available?
Or am I still missing something ---- how did piston engine problems possibly consequent on a change to Avgas 100LL constituents rope in Conquests??
Tootle pip!!
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Old 8th Oct 2018, 05:22
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Leadie, the smart asses are commenting on a Conquest that had both motors stop due to lack of fuel. You're not missing anything.
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Old 8th Oct 2018, 09:33
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megan - more the comments of an eye witness of the 441 that make me question a posters comments and knowledge.


"There was no fuel uplifted on the highway. Unless of course there is a secret squirrel method of doing this."
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Old 8th Oct 2018, 10:11
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Originally Posted by megan View Post
Leadie, the smart asses are commenting on a Conquest that had both motors stop due to lack of fuel. You're not missing anything.
Megan,
This gives a whole new meaning to "thread drift".
Tootle pip!!
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Old 8th Oct 2018, 11:17
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Originally Posted by Bend alot View Post
Chemistry of things like fuel have benefits and penalties in achieving a target such as a "octane rating"

They are not tabled as such as they are by products of a requirement of the fuel.

Changing any part of the chemistry can keep the same "octane rating" and other performance items like say burn speed.

But can have massive changes on other things due to chemistry change - say more acidic for example, that brings on corrosion in humid conditions on valve faces that accelerates wear.

A single atom can change things dramatically.

Lead seems to have effects on cooling and lubrication in certain applications as a by product.

Back on track back here - it is very hard to post as a "new here member" when not new member waffle a bit and need to be reminded that even if they "eye witness" they can be wrong and at times admit they are.

So I will say the safety in certain aircraft has been reduced. Hot maybe humid and a reduction in lead can be a factor for this - lead was not added for cooling or anti wear on exhaust valves but it seems to have an effect when reduced - why I don't know. How is aircraft safety regulated in Australia?

Not Shell!
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Old 8th Oct 2018, 14:18
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Originally Posted by rutan around View Post
A.E.F.R says:


Really? If the lead salt deposit you're talking about is lead oxybromide how does it deposit on those mating surfaces? Lead oxybromide melts at 703.4*F. The engine exhaust is between 750*F and 1,650*F so it is in liquid form. The exhaust gas exits through the open valve at better than 600 km/h The valve head is heated to close to the exhaust gas temperature. Under those conditions I don't think anything would stick to to mating surfaces.

The most convincing argument for me that it is an old wives tale that lead is a lubricant and /or cushion is the result when natural gas or propane gas is used in internal combustion engines instead of leaded fuel. The engines last just as long if not longer and there is not an atom of lead in either gas.
I find it very strange that you think that. There is plenty of evidence that engines run on LPG need hardened valve seats and those that don't have them are likely to suffer valve seat recession and valve burning.
I first came across this in the early 1970s. My fiance's father had an almost brand new Leyland Mini van that he had professionally converted to LPG. Within weeks it began misfiring. The company who carried out the LPG conversion wouldn't take responsibility. I was asked to take a look. I removed the cylinder head and the valves and seats were already showing damage. The A series engine was one of those that had the seats cut directly in the cast iron head; it became a well known problem in later years on that type and on some other engines.

Valve Seat Recession Explained

Earlier this year I had to have a new exhaust valve seat fitted to a single cylinder motorcycle engine (Royal Enfield) because it had recessed; the valve was also damaged beyond further use. The only explanation I can think of is that the seat was too soft to be used on unleaded fuel; the exact type was never officially imported to my country (Indian home market bike) and it's possible the fuel formulation is different.

I can't explain the molecular effects because I'm not a chemist but I certainly do know what I've experienced first hand.
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Old 8th Oct 2018, 19:15
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Originally Posted by rutan around View Post
The most convincing argument for me that it is an old wives tale that lead is a lubricant and /or cushion is the result when natural gas or propane gas is used in internal combustion engines instead of leaded fuel. The engines last just as long if not longer and there is not an atom of lead in either gas.

Originally Posted by rutan around View Post
What Lead Balloon said.
The cylinders and valves are not hurt by natural gas or propane because their octane rating is above 100
Originally Posted by Lead Balloon View Post
As has already been explained, ‘unleaded’ propane or natural gas didn’t cause valve recession.

Actually, Valve seat recession is a significant, well known and well documented problem with piston engines converted to petroleum gas fuel. You folks probably ought to stop using that as your "most convincing argument" as 30 seconds with Google shows that it's not true.
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Old 8th Oct 2018, 20:46
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Nobody said that valve seat recession wasn’t a problem.

What we said was that the cause of the problem was not the absence of lead.

What we said was that the cause of the problem was heavy detonation and high CHT that resulted from putting lower octane fuel in engines designed for higher octane fuel.

You should spend 30 seconds actually reading what we said.

Last edited by Lead Balloon; 8th Oct 2018 at 20:57.
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Old 8th Oct 2018, 21:50
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Originally Posted by Lead Balloon View Post
Nobody said that valve seat recession wasn’t a problem.

What we said was that the cause of the problem was not the absence of lead.

What we said was that the cause of the problem was heavy detonation and high CHT that resulted from putting lower octane fuel in engines designed for higher octane fuel.

You should spend 30 seconds actually reading what we said.
You probably ought to refrain from saying "nobody" and "we" because the other guy very clearly was claiming that valve recession is not a problem in PG fuel engines. (Which is quite demonstrably not true) I will quote again, his precise words, as you appeared to miss it the first time I quoted them:
Originally Posted by rutan around View Post
The most convincing argument for me that it is an old wives tale that lead is a lubricant and /or cushion is the result when natural gas or propane gas is used in internal combustion engines instead of leaded fuel. The engines last just as long if not longer and there is not an atom of lead in either gas.
Now, I will concede that your own repeated references to valve recession in PG fueled engines, in the same discussion, were a little more ambiguous, and that when you said:
Originally Posted by Lead Balloon View Post
As has already been explained, ‘unleaded’ propane or natural gas didn’t cause valve recession.
that it could have been just a poor choice of words, that you didn't really mean that valve seat recession is not a problem in PG fueled engines, and you didn't intend to interject that as a means of demonstrating that the lead itself had no direct affect on valve recession, but it certainly appears that way to me. If I misunderstood your purpose for making those statements, I am now left wondering what your point was for those statements? If you now agree that valve seat recession was a problem in PG engines, as it was in the first unleaded gas engines (pre-hardened valve seats) then you must also agree that it doesn't prove that lead was not the factor which prevented valve seat recession? So, what is your purpose of referring to it repeatedly in the discussion?
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Old 8th Oct 2018, 22:32
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It could be that lead forms some sort of intermetalic layer on the valve and seat that has a protective effect, but we don't know that. the real question to ask is how has the fuel composition changed because the change HAS to be the cause of the damage, no matter the octane rating or performance characteristics.
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Old 8th Oct 2018, 22:48
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What was the octane rating of the “PG fuel” to which you referred, A Squared? I certainly agree that if it wasn’t sufficient for the engines in which it was used, it too would cause detonation and higher CHT and valve seat recession, thus proving (again) that it wasn’t the absence of lead that caused the recession.

PS: My apologies A Squared. I now realise the last bit of the last sentence does not necessarily follow logically.



Last edited by Lead Balloon; 9th Oct 2018 at 00:04.
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Old 9th Oct 2018, 07:20
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AEFR posted:
in the early 1970s. My fiance's father had an almost brand new Leyland Mini van that he had professionally converted to LPG. Within weeks it began misfiring. The company who carried out the LPG conversion wouldn't take responsibility. I was asked to take a look. I removed the cylinder head and the valves and seats were already showing damage.
I'm not disputing that valve recession was a problem. I am disputing why. In the 1970s LPG conversions were not very sophisticated .While I can't vouch for it's accuracy the article below is a possible explanation for your fiance's fathers Mini van problem.

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Old 9th Oct 2018, 08:19
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Originally Posted by Lead Balloon View Post
What was the octane rating of the “PG fuel” to which you referred, A Squared? I certainly agree that if it wasn’t sufficient for the engines in which it was used, it too would cause detonation and higher CHT and valve seat recession, thus proving (again) that it wasn’t the absence of lead that caused the recession
LPG is much higher octane than petrol. As a rule, lighter fuels are higher octane: diesel = low octane, gasoline = medium octane, gas = high octane. LPG could be as high as 115 octane. Engines designed to run exclusively on gas typically run higher compression ratios than petrol or dual fuel engines e.g. the EcoLPi Falcon had 12:1 compression ratio, the petrol version was 10.3:1.

It would be a strange sort of detonation that only damaged the exhaust valve with none of the other damage typical of detonation.
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Old 9th Oct 2018, 08:44
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Rutan,

No I don't think so. I've been building and tuning engines (and modifying the advance curves of Lucas distributors) for well over 40 years. My bedside bookshelf is full of engine tuning manuals from a whole range of authors. I also used to teach piston engine theory to RAF student pilots. I've never seen any evidence that a less than optimum ignition timing setting causes valve seat wear. If ignition timing were drastically incorrect, i.e. too far advanced, detonation would be the immediate result. If too little advance, the result is less than optimum engine performance. Generally speaking, a higher octane fuel can tolerate a more advanced ignition setting.

On the other hand there is a great deal of evidence that the removal of TEL from petrol for environmental reasons resulted in rapid valve seat recession on many older engines. Many of them had to be retro-fitted with good quality, hardened steel valve seats (as did my old design motorcycle engine a few months ago). LPG obviously contains no TEL.

AVGAS contains a relatively large amount of TEL, even the advertised "Low Lead" (LL) quality (a reduced amount compared to that from years gone by, but still about five times the amount that the old 4 star road fuel had). Some years ago I experimented with an unleaded / LL AVGAS mix in a very high compression competition engine I had built (it was quite common to do this). I researched this and was surprised to learn that I only needed about 1 gallon in 5 of unleaded to bring the octane rating up to the desired level. The engine loved it. What surprised me was that the colour of the inside of the tail pipe went from black to grey with just one tankful, as did the plug colour, just as in the old days of "proper" leaded fuel.

LPG naturally has a very good octane rating but is known to cause valve problems on some engines (see the list in the link below) because it is generally seen as a "dry" fuel. I have a brand, old stock Lucas distributor originally intended for an LPG engine (Land Rover) in my garage. I used to collect new old stock to dismantle them for parts or just use the bodies to build on. I stripped it down but I soon discovered that it has considerably more total advance (taking into account both mechanical and vacuum) than those required for any petrol engine I've come across.

Valve Seat Recession Explained

Here's another interesting link:
LPG Problems
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Old 9th Oct 2018, 09:59
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AEFR
If ignition timing were drastically incorrect, i.e. too far advanced, detonation would be the immediate result.
Not necessarily. If the octane rating of the fuel is high enough it won't detonate. However if the timing is too far advanced ie the fire is lit too early all the fuel will be burnt at or even before top dead centre. This means peak pressure occurs early and, at first, is doing negative work until the piston is past TDC and can begin to move down and do some useful work. The lengthy time (relatively) that peak pressure (and high heat) are in the cylinder's head transfers much more heat to the enclosing metal before the valve opens and dumps the exhaust gas and cooling can begin. It is the heat doing the damage.

How did you address the problem of different flame front speeds for the different fuels?
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