Re: COZY: Fuel Grade Requirements for Lycoming Engines


Izzy
 

As metallurgy has improved since the 1920’s the valve/conditioning justifications may no longer be relevant. And perhaps it was bullshit back then too! 

Hard to trust corporate backed profit driven “science”.

Izzy
(603)410-7277

On Jun 11, 2022, at 11:20, Paul Saccani <saccani@...> wrote:

Hardly zero evidence of lead bromides being significant in valve seat lubrication.  Take a gander at;

Godfrey, Douglas, and Richard L. Courtney. “Investigation of the Mechanism of Exhaust Valve Seat Wear in Engines Run on Unleaded Gasoline.” SAE Transactions, vol. 80, 1971, pp. 1449–54. 

That was the first paper to demonstrate and describe the mechanisms by which lead bromides reduced valve seat wear.  Reduced welding of valve to valve seat and so forth falls under tribology, but as it doesn’t involve fluid motion, it is not strictly lubrication, but most don’t make that distinction.  Still, the effects were significant and beneficial - which doesn’t negate the issue of valve sticking and so on.  As we know, there are detail changes to engine construction to improve durability with unleaded fuels, but there are also many old aero engines out there that have yet to incorporate these changes.

The next significant paper was;
Schoonveld, Gary A., Richard K. Riley, Stephen P. Thomas, and S. Schiff. “Exhaust Valve Recession with Low-Lead Gasolines.” SAE Transactions 95 (1986): 700–712. 

Which showed that reducing the lead content in leaded fuels led to a significant increase in valve seat recession and reduced engine durability.

 This paper from 2000 rounds up many factors relevant to the issues and demonstrated that other metallic additives could take the place of lead bromides in reducing exhaust valve seat recession;

Hutcheson, R., "Valve Seat Recession - An Independent Review of Existing Data," SAE Technical Paper 2000-01-2015, 2000,

Incidently, you missed out on the significant corrosion aspects of hydrobromic acid and aluminium bromide resulting from the use of bromide lead scavengers.  Lead bromide also directly attacks steel exhaust components.
 
Conversely, lead bromides also significantly *increased* valve seat recession on earlier engine designs were the valve seat was machined directly into cast iron heads rather than being an insert, mainly by corrosion.

Cheers,
Paul Saccani

On 11 Jun 2022, at 13:08, Marc J. Zeitlin <marc_zeitlin@...> wrote:


Izzy Briggs wrote:

None of those documents seem to address the questions of what will replace rhe function that lead provides for….

The lead was there to increase octane #'s - nothing else. It was a cheap way of doing that. Some folks claimed that it also lubricated valves, but there is zero evidence for that, and as we see, it causes a lot of other functional problems in engines that will go away when the lead does (stuck valves, etc.).

yes, octaine/compression is critical,  but if the lead was always optional, the  why have in the fuel? And if the lead was required, than what in the new fuels replaces that function?

There are other octane boosters, most of which are more expensive than lead. The lead was not optional - it was just the cheapest way of getting octane levels up, as long as you don't care about poisoning air, water, animals, plants and people, which we didn't for a long time. The octane boosting replacement chemicals are far less noxious (although not without issues).

Seems like some important details are  being ignored for the safe of good policy. 

Nothing is being ignored. That's one of the reasons it's taken so long to get replacements that meet all the requirements for high compression and turbo-charged engines, which are the ones that use about 2/3 of all 100LL.

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Marc J. Zeitlin                      marc_zeitlin@...
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