Hi Temps = Lead fouling

[Let'sgoflying!]

Somehow I totally missed this in my studies.
As the EGT rises, so does the risk of lead fouling?
Can anyone explain it? Ted?
see attached dia. from an unlabeled, undated "Lycoming Flyer" which I received this year. I think it is pretty recent.

 

[poadeleted20]

The risk of lead fouling is highest when combustion temps (and, consequently, EGT's) are lower, not higher. The reason is that leaded avgas also contains lead-scavenging agents which are there to "grab" the free lead and carry it out the exhaust. Those agents are thermally-activated, and work best at higher combustion temps. So, the higher your EGT's, the less likely you are to have lead fouling, and that's why the situation most conducive to lead fouling is low power and full-rich mixture, like you have during taxi and past the abeam position in the traffic pattern. It's also why Lycoming makes recommendations for (among other things) pre-shutdown lead scavenging runs. See Lycoming Service 185B for those recommendations, and remember that they apply equally to engines originally designed for 91/96 octane avgas like the 180HP O-360's and 160HP O-320's.

 

[Tom-D]

The risk of lead fouling is highest when combustion temps (and, consequently, EGT's) are lower, not higher. The reason is that leaded avgas also contains lead-scavenging agents which are there to "grab" the free lead and carry it out the exhaust. Those agents are thermally-activated, and work best at higher combustion temps. So, the higher your EGT's, the less likely you are to have lead fouling, and that's why the situation most conducive to lead fouling is low power and full-rich mixture, like you have during taxi and past the abeam position in the traffic pattern. It's also why Lycoming makes recommendations for (among other things) pre-shutdown lead scavenging runs. See Lycoming Service 185B for those recommendations, and remember that they apply equally to engines originally designed for 91/96 octane avgas like the 180HP O-360's and 160HP O-320's.

Have you noticed the date on your reference?

You should talk to your new Lycoming Tech reps.. they do not agree with it.

The lead scavenging agent you refer to is called "lead bromide" it is nothing more than an agent to prevent the lead from adhering to any surface, so, it simply rolls into a ball and lodges in a crevice, (think spark plug) or gets scavenged into the oil, and ends up caked on a valve guide.

 

[Tom-D]

OBTW every one read all you can about 100VLL, the new fuel that was certified recently. up to 39% less lead but still able to meet the requirements of 100LL, still the same color, smell and usage.

 

[poadeleted20]

Have you noticed the date on your reference?

You should talk to your new Lycoming Tech reps.. they do not agree with it.

The lead scavenging agent you refer to is called "lead bromide" it is nothing more than an agent to prevent the lead from adhering to any surface, so, it simply rolls into a ball and lodges in a crevice, (think spark plug) or gets scavenged into the oil, and ends up caked on a valve guide.

Your post is contrary to what Lycoming tells me, including the current revision of the O-360 Operator's Manual. I'm sure Ted will be along to sort it all out.

 

[poadeleted20]

OBTW every one read all you can about 100VLL, the new fuel that was certified recently. up to 39% less lead but still able to meet the requirements of 100LL, still the same color, smell and usage.

Maybe so, but it still has lead, and can thus foul both your engine and the environment. Non-starter, that, even if the FAA lets you use it in your engine.

 

[Doggtyred]

OBTW every one read all you can about 100VLL, the new fuel that was certified recently. up to 39% less lead but still able to meet the requirements of 100LL, still the same color, smell and usage.

Some others have said this regarding 100VLL:
A more accurate description is that 100LL had a finite limit of lead it could contain. Most avgas refined and sold today had much less lead than the limit. The new 100VLL standard actually certifies a new max limit that is lower than 100LL and reflects what is actually being sold.

 

[Cap'n Jack]

OBTW every one read all you can about 100VLL, the new fuel that was certified recently. up to 39% less lead but still able to meet the requirements of 100LL, still the same color, smell and usage.

Like Dave said, pretty much the same stuff we've been using for some time now. They just "formalized" the blend.

 

[Tom-D]

Your post is contrary to what Lycoming tells me, including the current revision of the O-360 Operator's Manual. I'm sure Ted will be along to sort it all out.

When did they tell it to you, the 2 reps at AWO flyin this year were avid believers in running LOP and using as little lead as you can.

high power setting simply allows high rates of flow thru the combustion chamber to get as much lead out as possible before shut down, but it really doesn't work because most operators will not do the lean burn prior to shut down, so the lead stays there with or with out the lead bromide additive.

believing other wise is denying the problem exists, yet we still have fouled plugs and stuck valves.

the only answer is less lead to start with thus 100VLL, comes to find out the industry has been over dosing the fuel with lead for years, due to old beliefs that more is better.

Remember when 100LL came out the industry still had large radials in service, and the 100LL was to replace all fuels including 100/130 and 115/145. so more was better, but not any more so the FAA authorized a 39% reduction of the TEL in 100VLL

 

[Cap'n Jack]

the only answer is less lead to start with thus 100VLL, comes to find out the industry has been over dosing the fuel with lead for years, due to old beliefs that more is better.

Remember when 100LL came out the industry still had large radials in service, and the 100LL was to replace all fuels including 100/130 and 115/145. so more was better, but not any more so the FAA authorized a 39% reduction of the TEL in 100VLL

The industry has been putting less lead in the fuel, not overdosing.

FAA survey data has shown that the lead content can vary by up to 39% from the maximum lead value listed in the specification while still meeting the MON minimum requirement. Consequently, and most importantly, grade 100VLL has the same minimum octane rating and will provide the same level of anti-knock performance as 100LL and 100 avgas grades.​

As for "authorizing" a 39% reduction, the actual reduction is only 19% in the maximum lead content.

Grade 100VLL is identical to 100LL in all aspects, except that the maximum lead content is reduced by about 19%.​

Ref: http://www.eaa.org/autofuel/saibs/100_VLL_avgas_SAIB_NE-11-55_9-14-2011.pdf

 

[Tom-D]

Maybe so, but it still has lead, and can thus foul both your engine and the environment. Non-starter, that, even if the FAA lets you use it in your engine.

Well that's a no brainer.....

up to 39% less lead has to be an improvement, Does it mean we will get 39% more life out of our engines? don't know, but it is a start. I know that every engine certified on 80/87 will be better off on 100VLL.

 

[Let'sgoflying!]

So is the chart wrong or not, threadwanderers?

 

[Tom-D]

So is the chart wrong or not, threadwanderers?

I think the chart is simply some bodies opinion. Because I have never seen proof that lead bromide even works.

 

[Cap'n Jack]

So is the chart wrong or not, threadwanderers?

I do note the temperature scales is in degrees F; Lead bromide vaporizes at 916° C which is ~1,681° F yet they seem to have the fouling from lead bromide at ~900° F? Looks like they may have used the wrong temperature scale?

 

[ronnieh]

A little clarification. The agent that is blended into leaded (TEL) gasoline is ethylene dibromide or EDB. EDB combines with lead oxide to form lead bromide. The lead bromide is a white powder that melts at 373 deg C and boils at 916 deg C. The amount of TEL added to gasoline is dependent on the amount of anti knock property desired. The lead also acts as a lubricant and "cushions" the valve to valve seat contact. This is the reason hardened valve seats began being installed in auto engine heads when leaded fuel was phased out.

 

[Let'sgoflying!]

I think the chart is simply some bodies opinion.

When I used to run my engine slobbering rich I would see all that build-up in my plugs. Once I started running leaner and hotter that went away.

Would anyone conclude it was the amount of fuel or some other factor causing the build-up, or is it the temperature it was run at?



(please, please lets not segue into 'is lead a lubricant' please!)

 

[poadeleted20]

When I used to run my engine slobbering rich I would see all that build-up in my plugs. Once I started running leaner and hotter that went away.

Would anyone conclude it was the amount of fuel or some other factor causing the build-up, or is it the temperature it was run at?

I would say leaning/increased temps based on years of experience before and after learning this, and it's consistent with the Lycoming Engine Operator's manuals for the O-235/320/360 engines and Lycoming SL 185B. If anyone can find anything in writing from Lycoming disavowing those publications, I'd like to see it.

 

[poadeleted20]

Ron my question was an either/or so I can't tell which side you are taking. Thanks.

Fixed it.

 

[Ted]

Gee, I go spend a bunch of hours flying a couple of Continentals around lean of peak all weekend (well, some of them were rich of peak) and look what happens...

That is the first I've seen of that graph, and I have no idea of its accuracy, or how it was devised. What I also have no idea of are the conditions as inputs they used to get that. So, with that in mind...

Remember that when you're running leaned out as opposed to rich, you have less lead that goes through the engine. For example, in the Aztec I fly at about 10.5 gph a side LOP instead of standard 14 ROP. Well, that right there is 25% lower fuel burn, which means 25% less lead. So logically, I'd expect that you'd foul your plugs less (and I do, when compared to my friend on the field with an Aztec who runs ROP). Perhaps they did some study that found with the same amount of lead and different EGTs, hotter will produce more fouling, all else equal. Whatever it is, I'm sure it was done before I was born.

From an operational perspective, I would not change anything about my operation from that graph. Dave notes correctly that if you run your engine leaner, you foul your plugs less (again, less lead). If you have a plug fouled on the ground, the running the engine hard and leaning it out method will work for cleaning it in most cases. However, I wouldn't do post-flight scavenging runs. That just puts a bunch more heat into the engine and cooks your cylinders. The only time I'll run an engine on the ground longer than it takes me to taxi to parking is on a turbocharged engine as prescribed.

Actually, sometimes when I note one fouled plug not firing (out of the 24) if it's stubborn in wanting to get cleaned on the ground, I'll just take off. The temperatures and pressures from takeoff power end up cleaning it off, and it's firing probably by the time the wheels are nestled in their wells. An in-flight mag check confirms this once I'm happily situated in cruise.

 

[Let'sgoflying!]

Thanks Ted, btw here is the source. Hope I don't torque off Lycoming by publishing it, heck I got it on the net somewhere.

(Their page 17, pdf page 11)

 

[Tom-D]

I would say leaning/increased temps based on years of experience before and after learning this, and it's consistent with the Lycoming Engine Operator's manuals for the O-235/320/360 engines and Lycoming SL 185B. If anyone can find anything in writing from Lycoming disavowing those publications, I'd like to see it.

Leaning reduces the amount of lead used, which is a larger factor than temps.

If the temp was the answer to lead fouling we would already have solved the problem. because we all run power setting above that required for lead scavenging. yet we still have fouled plugs, that require cleaning.

Running at LOP is the same temps as ROP, but a lot less lead is being used. Thus every thing stays cleaner longer.

 

[poadeleted20]

Leaning reduces the amount of lead used, which is a larger factor than temps.

Not by the evidence. I get reductions of like 10-15% in fuel flow by leaning in cruise, and almost unmeasurable on taxi, yet the leading is reudced by at least half, probably 75%, and maybe 90% (subjectively measured by examining plugs).

If the temp was the answer to lead fouling we would already have solved the problem. because we all run power setting above that required for lead scavenging. yet we still have fouled plugs, that require cleaning.

If we ran at full power all the time, that might matter. But we don't do that on the ground or in the traffic pattern, and that's where the majority of lead fouling occurs. If you can't reach the necessary temp with throttle, you have to do it with mixture.

 

[Tom-D]

Not by the evidence. I get reductions of like 10-15% in fuel flow by leaning in cruise, and almost unmeasurable on taxi, yet the leading is reudced by at least half, probably 75%, and maybe 90% (subjectively measured by examining plugs).

Are you leaning all the way to LOP ? are you leaning at all power settings? remember any throttle change is a mixture change.

If we ran at full power all the time, that might matter. But we don't do that on the ground or in the traffic pattern, and that's where the majority of lead fouling occurs. If you can't reach the necessary temp with throttle, you have to do it with mixture.

It is a well known fact from the days of Lindbergh that the farther you can fly on a gallon of fuel the better off you are, both in maintenance and fuel economy.
Deckins has been preaching this for a long time. and has writen many times you do not have to be in the red box to get lead scavenging, you only must be above 900+ C as quoted above. it doesn't require full power to do that.

 

[Ted]

Thanks Ted, btw here is the source. Hope I don't torque off Lycoming by publishing it, heck I got it on the net somewhere.

Pretty sure the Lycoming flyer is available for download off their website. There is some good information there.

It is a well known fact from the days of Lindbergh that the farther you can fly on a gallon of fuel the better off you are, both in maintenance and fuel economy.

That is variable, in part depending on how fast you're trying to go with your engine(s). If you want to go as fast as your plane can possibly go and want a best power mixture, you are probably best running off a bit richer to keep your heads cooler (depending on the plane). I have friends who run their planes that way with high reliability. Yes, more fouled plugs, but so long as the CHTs are in a happy range, they won't be changing cylinders frequently. Personally, I run LOP because I'm happy to sacrifice a bit of speed for the lot of fuel savings, and I think most of us are of a similar mindset. But it is a tradeoff. LOP or ROP, you can get high reliability if done right. Done wrong, you're going to have low reliability.

 

[poadeleted20]

Are you leaning all the way to LOP ? are you leaning at all power settings? remember any throttle change is a mixture change.

I usually lean to peak EGT. I find that LOP creates more rougness than I like in the carbureted engines I've owned. And yes, I'm leaning all the time except for takeoff at lower altitudes where full rich is essential for CHT control.

 

[Tom-D]

I usually lean to peak EGT. I find that LOP creates more rougness than I like in the carbureted engines I've owned. And yes, I'm leaning all the time except for takeoff at lower altitudes where full rich is essential for CHT control.

When you are doing every thing right, 100VLL should be even better for you, AS a matter of fact, we would be better off with no lead, in this respect, but we are not there yet.

I do not agree that rich is essential for CHT control. because the same temps can be achieved on the LOP side of the curve. with less lead being introduced to the engine.

 

[poadeleted20]

When you are doing every thing right, 100VLL should be even better for you, AS a matter of fact, we would be better off with no lead, in this respect, but we are not there yet.

No argument that 100VLL would be better, but not so much that the industry is going to spend the money to dump 100LL and switch to 100VLL when we are so close to 100UL which, when certified, will result in an end to 100AL (100 any-lead).

 

[Tom-D]

No argument that 100VLL would be better, but not so much that the industry is going to spend the money to dump 100LL and switch to 100VLL when we are so close to 100UL which, when certified, will result in an end to 100AL (100 any-lead).

TEL is expensive, the less the industry uses the more the profit margine, I believe we will see it quicker than you think.

 

[Skylane81E]

When you are doing every thing right, 100VLL should be even better for you, AS a matter of fact, we would be better off with no lead, in this respect, but we are not there yet.

I do not agree that rich is essential for CHT control. because the same temps can be achieved on the LOP side of the curve. with less lead being introduced to the engine.

True but on T/O I want all the ponys the plane can give me so a peak power mixutre is what I'm after. Once I'm cruising I go as lean as my ****-poor-induction O-470 will let me

 

[Tom-D]

True but on T/O I want all the ponys the plane can give me so a peak power mixture is what I'm after. Once I'm cruising I go as lean as my ****-poor-induction O-470 will let me

What you speak of as "peak power" is known as "best power" and is smack dab in the middle of the "Red box Dekins preaches about, and is the cause of the big bore Continental cylinder failure.

 

[Skylane81E]

True, and that's why we have the "economiser" valve in the carb. When actually using all my 230 hp I'm content to use the power enricment features.

now as the power useage falls off so does my mixture setting.

 

[Ted]

What you speak of as "peak power" is known as "best power" and is smack dab in the middle of the "Red box Dekins preaches about, and is the cause of the big bore Continental cylinder failure.

But as you keep on adding fuel, your power drops off a lot slower than when you subtract it on the LOP side.

If we were running engines designed to stay LOP all the time, including takeoff, then we'd get whatever power they made there and be happy with it.

Even Deakin runs at full power, full rich on takeoff. In his book he preaches how great it is that they do that on all the old warbirds he flies.

That said, the people who fly the big old radial warbirds and assume that everything translates identically to our little engines is incorrect. They are similar, but there are still differences.

 

[Tom-D]

But as you keep on adding fuel, your power drops off a lot slower than when you subtract it on the LOP side.

If we were running engines designed to stay LOP all the time, including takeoff, then we'd get whatever power they made there and be happy with it.

Even Deakin runs at full power, full rich on takeoff. In his book he preaches how great it is that they do that on all the old warbirds he flies.

That said, the people who fly the big old radial warbirds and assume that everything translates identically to our little engines is incorrect. They are similar, but there are still differences.

you are right on 2 points,

the mixture / temp drops off much quicker on the LOP side of the curve.

I have never seen a flat engine with a 2 speed 2 stage mechanical super charger with a pressure injected carb, with automatic altitude compensating mixtures, that injects fuel at the first stage of the super charger. and ADI.

That is quite a big difference.

 

[Ted]

I have never seen a flat engine with a 2 speed 2 stage mechanical super charger with a pressure injected carb, with automatic altitude compensating mixtures, that injects fuel at the first stage of the super charger. and ADI.

That is quite a big difference.

That's exactly my point. So pointing to the old radials and saying "They did this, therefore we should, too" may work sometimes, but not always.

 

[gismo]

That is the first I've seen of that graph, and I have no idea of its accuracy, or how it was devised. What I also have no idea of are the conditions as inputs they used to get that. So, with that in mind...

Remember that when you're running leaned out as opposed to rich, you have less lead that goes through the engine. For example, in the Aztec I fly at about 10.5 gph a side LOP instead of standard 14 ROP. Well, that right there is 25% lower fuel burn, which means 25% less lead. So logically, I'd expect that you'd foul your plugs less (and I do, when compared to my friend on the field with an Aztec who runs ROP). Perhaps they did some study that found with the same amount of lead and different EGTs, hotter will produce more fouling, all else equal. Whatever it is, I'm sure it was done before I was born.

From an operational perspective, I would not change anything about my operation from that graph. Dave notes correctly that if you run your engine leaner, you foul your plugs less (again, less lead). If you have a plug fouled on the ground, the running the engine hard and leaning it out method will work for cleaning it in most cases. However, I wouldn't do post-flight scavenging runs. That just puts a bunch more heat into the engine and cooks your cylinders. The only time I'll run an engine on the ground longer than it takes me to taxi to parking is on a turbocharged engine as prescribed.

Some potentially relevant things not mentioned so far:

1) The peak temp of the burning gases in the cylinder are a lot hotter than the exhaust gases.

2) EGT is affected by things that have little to do with the combustion gas temps inside the cylinder such as probe placement, ignition timing, mixture, and RPM.

3) The temp of the spark plug insulator is considerably less than the peak combustion temp or EGT and is affected greatly by the CHT as well as the plug's heat range.

So any graph that proposes to identify a range of EGTs that corresponds to lead fouling of spark plugs would have to involve a specific combination of all those item (and likely more) to have any validity.

 

[Ted]

All good points, Lance, which is why I wonder about the details of that particular science experiment.

 

[Skylane81E]

all true, but lead fouling affects more than just spark plugs, they are just the weakest link that we see inoperative due to lead most often.

 

[Tom-D]

All good points, Lance, which is why I wonder about the details of that particular science experiment.

The points that Lance makes should make you wonder if the lead scavenging agent works at all. Because the combustion temps are always above the 900+ degree that is supposed to make it work. yet we still have lead fouling.

and that is my point, using less lead is more effective than temps in our attempt to avoid lead fouling.

 

[Ted]

and that is my point, using less lead is more effective than temps in our attempt to avoid lead fouling.

I don't think anyone disagrees with you. But leaded fuel is what we've got for the moment, so it'd be good for people to know how to be able to minimize its effects as long as we have to deal with it.

 

[Skylane81E]

I don't think anyone disagrees with you. But leaded fuel is what we've got for the moment, so it'd be good for people to know how to be able to minimize its effects as long as we have to deal with it.

Lean, aggressively.