Investigation into mid-air engine failures yet to yield answers as pilots fear for their safety

[onetrack]

@ Mike Borgelt -

 

In the 1920's TEL was regarded as quantum leap in fuel additives. When your spark plug fires, it ignites a flame front which travels through the combustion chamber, burning the petrol/air mixture.

 

TEL makes the flame front travel more slowly, and also less turbulently. Lead virtually eliminated engine knock. Overnight, compression ratios jumped from 4:1 to 7:1, and the modern high-output engine was born.

 

But TEL has even more benefits. When it burns, TEL turns into a tan-coloured layer of lead oxide, which covers the valves and the combustion chamber.

 

The valve heads hammer against the valve seats, several thousand times a minute. The lead oxide acts as a cushioning agent, and protects the valve head and the valve seats.

 

The lead oxide is also a lubricating agent. This lubricating action also reduces wear in the valve guides.

 

 

[Mike Borgelt]

In the 1920's TEL was regarded as quantum leap in fuel additives. When your spark plug fires, it ignites a flame front which travels through the combustion chamber, burning the petrol/air mixture.TEL makes the flame front travel more slowly, and also less turbulently. Lead virtually eliminated engine knock. Overnight, compression ratios jumped from 4:1 to 7:1, and the modern high-output engine was born.

But TEL has even more benefits. When it burns, TEL turns into a tan-coloured layer of lead oxide, which covers the valves and the combustion chamber.

 

The valve heads hammer against the valve seats, several thousand times a minute. The lead oxide acts as a cushioning agent, and protects the valve head and the valve seats.

 

The lead oxide is also a lubricating agent. This lubricating action also reduces wear in the valve guides.

Source?

 

 

[facthunter]

I don't believe the lead has any effect on valve guide wear, at all.. This IS an oft repeated furphy. The guides don't get anywhere near hot enough for it to become liquid which is what must happen before it does anything. good. Neither does the Rotax 912 head anywhere. That's why using avgas 100LL has not been recommended, with the Rotax. I've run millions of KM's on gas powered vehicles, serviced and repaired many others and the non hardened heads do wear valve seat rapidly without lead.. Recessing is too great at even 100,000 kms. sometimes . Some engines were never suitable at all for LPG use, even good quality otherwise ones.. Hardened valve seats came out co-incident with unleaded being introduced. Accumulation of lead deposits is a problem and a bromide compound has to be added to clear them from the engine. This causes the white surface on the inside of some exhaust pipes on aircraft. Plugs also foul particularly the lower ones on "flat" engines with lead deposits running 100 LL. Nev

 

 

[onetrack]

@ Mike Borgelt -

 

https://www.springer.com/cda/content/document/cda_downloaddocument/9789400778832-c1.pdf?SGWID=0-0-45-1443209-p176304584

 

 

[Downunder]

Rotax's, running water cooled heads probably don't get up to the temps of air cooled heads and my guess is deposits are less likely to be burned off and so accumulate.

 

The gearbox and clutch arrangement don't like to be contaminated with lead deposits also.....hence more frequent gbox inspections/overhauls.

 

 

[Mike Borgelt]

@mike -

https://www.springer.com/cda/content/document/cda_downloaddocument/9789400778832-c1.pdf?SGWID=0-0-45-1443209-p176304584

 

This bit?

"Anti-valve seat recession additives The lead additive (TEL), in addition to its primary purpose of increasing octane number, also provides a critical wear-reducing function by depositing a thin protective layer of lead salts on valve seat surface. Without this protection, exhaust valve seats wear or recede into the cylinder head. After banning of use of TEL in 1990s, the problem of wear appeared. The problem of valve seat recession is overcome by the use of chemicals based on potassium, phosphorous and manganese salts. The combusted metal salts act as a protective lubricant and prevent the direct metal-to-metal contact that would otherwise cause high wear. "

 

Not specifically referring to aircraft and in fact seems to refer to cars and the removal of lead from car fuel.

 

You also need to explain the Swedish experience with aircraft engines I referred to:

"Sweden pioneered with unleaded grade 80(octane) in 1981. This fuel was also used by the air-force. In year 1991 our second generation unleaded AVGAS grade 91/96 was launched. This fuel is still used in Sweden and also elsewhere. In Sweden regularly about 80 % of the piston powered fleet is using this fuel, which after 25+ years has flown for millions of flight hours in thousands of aircraft and in any weather /technical condition. Removing lead from an engine improves life time of the valvesystem. An engine using 100 LL may have 2000 hours for TBO. The same engine using our unleaded grade 91/96 UL usually runs 3000 hours between TBO"

 

Maybe the Hjelmco fuel has added potassium, phosphorous and manganese salts? Seems it is the lead salts or other compounds being deposited does the protecting. Kind of hard to argue against the Swedish experience.

 

Here's Richard Feynman in scientific method:

If you've never heard of him you should look him up.

[facthunter]

Some of these additives really play up with plug insulators shorting.. Metal salts are good conductors of electricity. Nev

 

 

[Mike Borgelt]

Only time I've had plugs short it was due to metal balls of lead.

 

 

[onetrack]

Well, if the valve seat protection from lead oxide deposits, from leaded fuel, are a major furphy, and not true, perhaps you who all know better, had better inform SAE and the oil companies - who just happen to produce the fuels.

 

https://www.penriteoil.com.au/assets/tech_pdfs/Valve%20Seat%20Recession%20April%202015.pdf

 

Investigation of the Mechanism of Exhaust Valve Seat Wear in Engines Run on Unleaded Gasoline on JSTOR

 

Yes, the last lot of technical information does relate to automotive engines - but they were run at WOT for in excess of 10 hrs. This is equivalent to aircraft engine requirements.

 

Not specifically referring to aircraft and in fact seems to refer to cars and the removal of lead from car fuel

You're reading what you want to see in the quote. There is nothing in the quote that makes specific reference to car fuels. The rest of the article regularly refers to all fuels, including Avgas and Avtur.

 

 

[kaz3g]

And

 

Fault putting helicopters at risk of mid-air failure, federal regulator warns

 

Suggestion of similar problems in 100LL in USA.

 

Kaz

 

 

[kaz3g]

Well, if the valve seat protection from lead oxide deposits, from leaded fuel, are a major furphy, and not true, perhaps you who all know better, had better inform SAE and the oil companies - who just happen to produce the fuels.https://www.penriteoil.com.au/assets/tech_pdfs/Valve Seat Recession April 2015.pdf

 

Investigation of the Mechanism of Exhaust Valve Seat Wear in Engines Run on Unleaded Gasoline on JSTOR

 

.

Very interesting Abstract...I don’t have access to the whole article but it makes sense to my limited understanding and memory of racing fuels a long while ago.

 

Adding lead (TEL) increases octane rating without impacting fuel burn speed. So the fuel manufacturer can set a mix of fuel to achieve desired flame speed and then adjust octane up by as much as 20 octane numbers with the TEL. So first benefit is better combustion and no knocking.

 

As a secondary effect, TEL oxidises in the chamber to PbO, Pb SO4, and a bit of PbCl and PbBr all of which act on the valve seat and face to form a protective lubricant barrier reducing the erosion of the metal by the passage of hot exhaust gases.

 

When I was young, the lead content of all Mogas fuels was much higher than now and we used to pour in toluene (methyl benzene) to make the mix more potent. But we also added upper cylinder lubricant in the hope the valves would last a bit longer.

 

Kaz

 

 

[Mike Borgelt]

AndFault putting helicopters at risk of mid-air failure, federal regulator warns

 

Suggestion of similar problems in 100LL in USA.

 

Kaz

Where is the suggestion of problems in America in the linked article kaz? The federal regulator they talk about is CASA not the FAA.

 

Sounds like the NT fuel supply changed from 100/130 to 100LL and the problems began. There was a discussion on the BD-4 group a while ago and there were problems with old fuel tank sealant. Seems some of the older sealants had troubles with 100LL and no problems with 100/130. If 100 LL indeed has higher aromatic content this isn't all that surprising.

 

This is a pretty good survey of Avgas lead content etc.

 

Avgas - Wikipedia

 

onetrack, your earlier article referred to problems when the lead was removed from petrol. As Avgas has not, in most of the world, had the lead removed, it clearly refers to cars. As do your latest links. They are talking about PoS Ford or Holden motors or similar which run the valves in cast iron heads without valve seats (cheaper to make) which your later links also refer to. Lead in the petrol let the manufacturers get away with this.

 

Aircraft engines with aluminium heads have proper valve seats in the heads which may explain the Swedish aero engine experience with unleaded Avgas. Refer to the Wikipedia article on the Hjelmco fuel.

 

To sum up, yes, lead prevents valve seat erosion in engines running the valves in cast iron heads without hardened valve seats. With hardened valve seats it seems there is no problem, as attested by the Swedish unleaded Avgas experience.

 

"after 25+ years has flown for millions of flight hours in thousands of aircraft and in any weather /technical condition. Removing lead from an engine improves life time of the valve system. An engine using 100 LL may have 2000 hours for TBO. The same engine using our unleaded grade 91/96 UL usually runs 3000 hours between TBO"

 

In aero engines lead deposits can build up on valve stems leading to sticky valves which can lead to the valves burning as they don't seat properly. The contact between the valve seat and the valve conducts head away from the valve during combustion.

 

 

[Yenn]

Those RR military engines all had sodium filled valves as far as I recollect. I worked on them in the army, not airforce. We had the Meteor engine, which was an un supercharged version of the Merlin. Would run all day at 640hp, rev limited to 2550rpm. The only one I ever saw in trouble was in a centurion tank and when it came into the workshop we all thought it had been fitted with a diesel engine. Lifting the hatches revealed a Meteor, built by Jaguar car co. I never got to see what the gudgeon pins looked like, but they sure sounded loose.

 

 

[facthunter]

I specifically referred to valve GUIDES and gave the reasons why. TEL does help valve seats, but it's use was for power increase with reliability by allowing higher compression ratios to be used on hot running engines with out knocking occurring. Most largish cylinder aero engines used sodium cooled valves but with small stemmed valves it reduces stem strength and doesn't help as much as the sodium has to shake around to distribute the heat The valve is not filled. There's a space or the principle doesn't work. Nev

 

 

[kaz3g]

Don’t know Mike. Can’t find it, sorry.

 

But I did find this on the Viva website:

 

© Aviation Gasolines:

 

(i) Avgas 100 or Avgas 100LL: the latest version of either DEF STAN 91-90, ASTM D 910 or CAN CGSB 3.25.

 

(ii) Avgas 82UL: the latest version of ASTM D 6227

 

The reference (ii) interests me. I wonder if 82UL is being supplied to NT ? My sense is this would be higher in aromatics, like Mogas, and without lead, but I don’t know what the possible effects might be.

 

I also read a research report that compared two 0-320 engines running in identical circumstances for 150 hours, one on Mogas and one on Avgas, without detectable differences in VSR. Would have been more impressive if they had both run to TBO?

 

.

 

Kaz