Lean of Peak

[RV7ator]

All,

This thread is a spin-off from a question asked of me on another thread, response put here because it involves LOP ops with a carburetored Lyc.

Comment was that Lycoming says it can't be done. I'm not surprised. Lyc doesn't think anything can be done until someone else shows them so. That's why ECI and Superior are eating their lunch in the experimental market.

Now to the point. Yes, I do run my carburetored O-360 lean of peak, mostly. That's because only cylinders 2 and 3 are LOP; 1 and 4 are slightly ROP. So I am taking some liberty with the pure definition of LOP wherein all cylinders are LOP. If I were to lean more to make all LOP, I lose way too much power.

What helps me is that the Superior sump I had Aerosport Power install has internal contouring to help even the fuel distribution. Lycoming's design looks more like a septic tank and drain field. Even distribution is the key and it's fuel injection's big (potentially) improvement over carburetors. With a set of GAMI injectors, very smooth LOP operations is the norm. Such a FI system would be many thousands of dollars initially and still more life cycle cost than a carburetor.

Also, I wouldn't even attempt LOP no matter the type of fuel system unless the engine was equipped with all-cylinder CHT/EGT monitoring.

So, I have many more dollars for fuel, and I get a wee bit of a massage to boot. Just how smooth a particular carbed engine runs when you screw down the mixture is an individual experience. I've flown behind carbs and injectors. Some of each type have been smooth as a baby's bottom, while others will remove your fillings. There's a lot of cross-over between the two regarding economy and smoothness. The RV and a 172 I've been operating the same for 2,000 hours work just fine L (mostly) OP.

John Siebold
Boise, ID

 

[penguin]

GAMIs on Lycomings

John,

My experience is broadly in line with yours. I can't get my current carbed O-320 to run smoothly LOP, probably because of the Lyc sump. Completely agree with the value of all cylinder monitors.

The only other point is that I am skeptical of the benefits of GAMIs on (all)Lycomings. On older Continentals the benefit is clear, but Lycs suffer from a different problem (mostly). They generally don't steal much fuel from other cylinders, but older injectors may not be well balanced, due to wear an manufacturing inaccuracies. So on a new Lyc fitted with either Precision or Airflow injectors I'm not sure that GAMIs will be any better as the they are all made to similar tolerances. On a older Lyc fitted with a Bendix system there may be some value in swapping to GAMIs. In any event a GAMI lean test is very useful in figuring out what is going on.

Pete

 

[gmcjetpilot]

Well not exactly

All, This thread is a spin-off from a question asked of me on another thread, response put here because it involves LOP ops with a carburetored Lyc.

Comment was that Lycoming says it can't be done. I'm not surprised. Lyc doesn't think anything can be done until someone else shows them so. That's why ECI and Superior are eating their lunch in the experimental market. John Siebold. Boise, ID

John I am the one that asked the question. I have heard of LOP with a FI engine but not a carb. I am not saying you can't do it, but I am not sure how useful it is and if may be you could be doing more harm than good. The FI engines that run "true" LOP have all cylinders within a few degrees EGT and are at least 40F LOP. I am not sure what advantage two cylinders at 20F LOP are doing. Also what are the other cylinders doing? Are they at peak, 10F ROP? Higher EGT, higher temps. I don't like to run hottest cylinder closer than 75F ROP. I have a Carb and can't get LOP operations. If I had FI, I would try for the 40F LOP operations.

Here is someone who ran lean of peak and paid the price:
http://www.eaa49.av.org/techart/hakes08.htm
(There is a correlation to short cylinder life and leaning, which Lycoming has documented. They see more cylinders (die early) as price of fuel goes up.)


Lycoming does say LOP is not practical or possible due to uneven mixture distribution with carbs. If you are running two cylinders lean of peak and two rich you will have different power on the cylinders you would expect rough running. From my experience, when I lean a carb Lycoming, as soon as the first Jug hits lean peak EGT or just past, the engine starts to get rough, since the other cylinders are still rich and making more power. What happens past peak EGT is the power curve drops very quickly. ROP (by 50F) you don't have as much roughness with small difference in mixture / fuel distribution, because the power curve on the rich side is flat compared to the lean side, which drops quickly with mixture. The first cylinder hitting LOP will produce less power and the uneven power pulse, which is unpleasant.

Also 20F LOP, you are running is very close to peak which is not a great place to live. What are your other two cylinders doing? Peak? This might be a bad thing to do to your engine. (?) There are many reasons this is not a good idea. For long life on a Carb engine, Lycoming does not recommend an exact EGT but for Econ operations, lean for smooth operation ROP, which is about 50F ROP. I read somewhere they (Lycoming) recommend not less than 75F ROP for ECON. Running anywhere near peak (lean or rich) I don't think is a great for the engine and will not be as smooth. For best power Lycoming recommends 100-150F ROP.

If you can't run true LOP where every cylinder is 40 LOP, smoothly, I think you should run ROP, where all cylinders are about 50F ROP or more. Fuel is used to cool the engine. LOP uses the fact that you are so lean you are making less heat (and power) and there is no chance of detonation. This also means you will fly slower. Of course always never lean above 75% power. Some feel that fuel lubricates the engine and I can't say yes or no.

Superiors sump: I know they claim their sump has better features. They do look nice: http://www.superiorairparts.com/pieceParts_Sumps.asp

May be your set up is ideal. However Lycoming or Clone, they all have the same carb and will always produce some mis-matched fuel distribution well beyond the +/-0F EGT spread required for true LOP operations. The problem is the induction is not a steady state thing. Induction happens in pulses. Fuel/air backs up in the plenum and induction tubes. There is variation in each cylinder, compression and exhaust. Typical cross over exhaust are really not ideal at all. In fact the tube length between pairs is large. This exhaust difference affects the induction.

As far as Superior and ECI eating Lycoming's lunch, it is from the fact they cost $4,000 to $5,000 less, and less to do with better fuel distribution. It may be more sales hype. Lycomings, ECI and Superior all make about the same power. Carbs have inherent design and limits based on the law of physics, which all the engines share. However tuned intake, tuned cylinders, tuned exhaust and exact fuel distribution (FI) no doubt can improve fuel economy.

Carbs are not bad or terrible, but to run LOP you have to have very precise fuel distribution which no carb on any brand engine can produce. I have an O-360 and it is great. Carbs are simple, reliable, don't require high-pressure pumps and of course are many thousands cheaper. Also those who have FI usually don't have the desire to mess with there fuel system to optimize it for LOP operations. Also LOP operations means slower speed. Fuel savings is from the fact you are making less power. Less power less speed. So even if the Carb engine is using a little more fuel it is making more power ROP. There is no free lunch. If you want to save fuel in a carb engine fly higher for less % power or pull the throttle back**.

**(Pulling the throttle back is one of the worst things to do from a lean stand point, because the butterfly causes a restriction and biases the fuel towards the front or back, so fly high with WOT for best lean condition. That is why 7,000-8,000 feet is the best altitude to fly because it is the lowest altitude that you can fly with WOT and at or less than 75%, which is highest power allowed you can lean at. The higher the better, as power decreases the FF is reduced. Somewhere 12,000'-14,000' (gross weight) is the limit for a good trade off in speed and fuel economy. Above 12,500' will require O2. All this assumes a ZERO wind condition. If you are flying low and want to lean you must throttle back below 75% power, but because of the "pumping loss" and increased fuel distribution difference from the partially closed butterfly it will not be as good as WOT.)

Here is a good explanation of Carb and FI.
http://www.lycoming.textron.com/mai...cations/keyReprints/general/fuelInjector.html

It is just the way it is, carb?s can?t be run (practically speaking) LOP, except for your engine. How you are getting acceptably smooth operations? I don't know but it is pretty good trick with a Carb. True LOP operations require FI and matched injectors. The savings you are getting from two cylinders running LOP 20F may be very little? Have you measured the fuel burn difference? To get any big gain you need all Jugs at 40F LOP. From what I have hears on a little Lycoming the best you can hope for with FI (running LOP) vs Carb is about 0.6-0.8 gal/hr, which is great, with the fuel prices as such. The pay back time is much less than it use to be. FI not running in LOP operations, typical ROP operations in cruise, will still be better than a Carb, but the difference is very small when compared to LOP operation (like 0.1-0.2 gal/hr). LOP operation is a kind of new thing in GA, especially for small engines. With large high HP engines the savings are greater, and with the multi cylinders, the big engines tend to run smoother even if the mixture is slightly off. Some FI Lycoming (4-cylinders) can not run LOP well, even with injector work.

I also agree GAMI injectors are sales hype and that the Airflow performance has very well matched injectors and will fine tune them. As far as Bendix (now Precision Aeromotive) I don't know.

John, I suggest calling Superior and asking them if it's cool to run 20F LOP for engine health. I would love to know what kind of fuel savings you are getting. G

Here are good articles:
www.lycoming.textron.com/support/publications/keyReprints/operation/leaningEngines.html
http://www.lycoming.textron.com/support/engineOperationTips/SSP700A.pdf

 

[wlull]

Running LOP

The best thing about GAMI is all the information and testing they have done. I admit I run a big bore Continental with FI. Still building my Lycoming hauler! So this post is alittle off center. I read the above posts and the articles they sighted and just felt compelled to relate my experience.

When I purchased my plane the IO470 had 1100 hours and had seen about 20 hours use in the last five years. I had read everything I could find on running these engines and opted to try the GAMI way even though I didn't have there injectors. I put 700 hours on that engine over three years before going to overhaul. Because it had set so long it used oil ( about a qt every five hours) but the compression readings never changed. How I ran it is as follows: Always ran 65% or less. Always ran at peak or alittle LOP. The thing is GAMI says you can't hurt the engine at any mixture setting if you run 65% or less and my experience seemed to follow this.

After rebuilding the engine (with GAMIs) and ECI cyls. I follow the same procedure except now I run at least 50 LOP down low and at peak up high. I have over 500 hours to date and contrary to conventional wisdom my compressions have remained 76-78/80 on all six cyls. and I use a qt of oil every 25 - 35 hours ( I do have an air/oil separator).

On the very rare occasion that I run 75% or above I run 125% ROP. I have read several places that running 75% or higher from 25 LOP to 75 ROP is an engine eater. So I just don't do it.

Also another CW no no I do all the time is lean to a EGT temp on all climbs (1100 summer and 1150 winter).

This all works for me, how everone else manages their engine is up to them. I say do your own research and decide what is right for you.

The best to all and I'm sorry for my rambling!
Bill

 

[RV7ator]

Lean is Mean

Oy, G, I've an airplane to build, so my response is a bit terse.

Many of your points are good, but old news to me, and some are plain wrong. And to really light your fire, I run my carbed 360 LOP on mogas!

The executive summary of our exchange so far is: It's all relative, EGTs that is (New Agers go away).

The guy who trashed his engine in the EAA link was running 100LL. Poor devil; it killed his engine. He was following Lyc recommendations about which there is a substantial body of evidence against/challenging/refuting many Lyc recommendations. For starters, search around AVweb for articles/columns by Jim Deakin about where to run your engine. Similar, but far less researched and referenced, are occasional fluff pieces in AOPA and other slicks.

Lyc has a lawyer problem. It's why ECI and Superior are encroaching on them, technically for lack of Lyc innovation, and financially because Lyc has a burdensome overhead buying their peace from clueless juries. You can be sure Lyc will never come out with some manner of operation different then they've always prescribed, lest some shark sue them for being wrong in the first place and that's why Uncle Willy CFIT'd.

Where you and I diverge mainly is ROP. +75 or so is the WORST place to be, so I read often outside of Lyc, and completely contrary to your assertion. You can't hurt an engine LOP, but you can ROP. When my #2 and 3 are LOP, the others are near peak. CHTs are wonderful, which speaks more to proper air cooling than whether the EGTs are 25 or 50 degrees one way or the other.

Ambients play a big roll. Most of my flying anywhere requires MEAs above 9k or else I'll hit mountains within 30 minutes. Lean 'till the engine stops; you can't hurt it at 9 or higher. Yes, higher is key to economy. If you have to throttle the engine to get 75% or less you do get higher pumping losses and the airplane's draggier down lower.

Pulling the throttle back a bit can be GOOD. It's common practice on carbed 182s because it does cause extra swirling, therefore better mixing and distribution. I've had a GEM in my 172 for 9 years. The effect is noticeable as stated, the rpm loss undetectable on the mechanical tach. The 172 has a detented mixture control. I would be able to better tune the mixture if it were a vernier, since the detents are either richer or leaner than I would like to set per the GEM. But a vernier control would require an STC (none exist) or 337. So much for the criticallity of mixture as viewed by Cessna and the FAA. The manual says lean till rough, enrich till smooth. Without a GEM and vernier you can't do otherwise.

What does "ZERO wind conditions" have to do with running an engine? I think I get your drift in that you might want higher power when bucking a headwind. But I could really run with this one and start a thread about the dreaded downwind turn.

In sum, it is relative. Your engine may vary, and I think we've learned more in recent years than Lyc will admit. Get a GEM, fly high, use mogas!, and run LOP. Or ROP if that feels good; Mother Lycoming says it's all right.

John Siebold

 

[dlloyd3]

Most of the good stuff has already been said. Anyone curious about running their engine LOP really should read all those articles by John Deakin on AvWeb. After reading his stuff, I am scared to run ROP.
Balanced fuel flows on an injected engine is generally better than fuel air distribution in a carburated engine. But this is only one factor in making an engine run smoothly. Both intake and exhaust manifolds of varying lengths and restrictions complicate matters. Fluid dynamics are never stable due to opening and closing valves. Change some variables like RPM or air density, gosh, it's a wonder these things don't shake right off their mounts.
In the last issue of Flying, Richard Collins again poo poos LOP operation during a demonstration of a Lancair Columbia 400 saying it wasn't smooth as operating ROP. Fuel flow was down three or four gallons but not worth the slightly rough running engine. Couldn't get his GAMI injected P210 to run smooth either.
I have been running the IO550 in my spam can many years LOP. Two engines went well past TBO with not one cylinder problem. Another reman engine ate it's way through 8 exhaust valves in 1550 hours (see what John Deakin says about this). Some engines have been smooth LOP, others not so. I run WOT all the time above 5000 feet. Usually cruise at 7-9000. The only time the present engine (675 smoh by Superior, with GAMIs) runs rough is when I attempt to burn less than 12.5gph. This is so at higher density altitudes and 2500 rpm or at lower altitudes and rpm. Typical fuel flow is 13.5. Same conditions but ROP would be 16.5, and cylinder head temps would be 40 to 50 degrees hotter.
Everyone should investigate on their own how their engine performs at various fuel flows. Set up cruise flight, record temperatures at incrementally lower fuel flows. Doing this will demonstrate the absolute hottest CHT's that can be produced occur at 40 degrees ROP. Richer or leaner mixtures will produce lower CHT's. You pays your money and makes your choice.

 

[gmcjetpilot]

Interesting, but apple sauce

RV7ator, John Siebold wrote: The guy who trashed his engine in the EAA link was running 100LL. Poor devil; it killed his engine. He was following Lyc recommendations about which there is a substantial body of evidence against/challenging/refuting many Lyc recommendations. For starters, search around AVweb for articles/columns by Jim Deakin about where to run your engine. Similar, but far less researched and referenced, are occasional fluff pieces in AOPA and other slicks.
I have read his articles. He he got a free set of injectors and wrote an article. I am sure they are great for large Continental. Most LOP operations that work are on 6 cylinder engines. Small Lycomings are going to get less advantage from LOP operations. INJECTORS: You know an injector is, a very simple piece of brass with a hole in it, that squirts fuel into the intake port near the valve. There are no secrets. Squirt Squirt. It is like the TV info-commercial and the "Fuel Tornado 2000" or "Fuel Magic-Magnets" you put on your car or truck's fuel system to improve HP and fuel economy. Once you pay all that money you have to prove it works to justify it (I never bought one BTW). You drive your car with more care to show it works.

FI systems for the Lycoming, like Airflow performance, come with well tuned injectors out the box. They will custom tune/ flight test your injectors on your plane for $300. There is more to it than just the injector. You not only have to match your injectors, but your whole engine. If your exhaust is imbalanced, have a weak jug or two, injectors are not going to do it all. You can always try for LOP operations, but your mileage may vary (pun intended). 4 bangers, FI or not, are not as good as 6-cyl in LOP operations.

Lyc has a lawyer problem. It's why ECI and Superior are encroaching on them, technically for lack of Lyc innovation, and financially because Lyc has a burdensome overhead buying their peace from clueless juries. You can be sure Lyc will never come out with some manner of operation different then they've always prescribed, lest some shark sue them for being wrong in the first place and that's why Uncle Willy CFIT'd.
I don't have any Textron Lycoming stocks, but I believe them more than I believe AvWeb who is writing about how great a product is. The company the invented the modern horizontal piston aircraft engines, making them for +60 years and has ten's of thousands of hours of test stand and flight test hours can't be too dumb. Law, Lawyers and legal issues a side, LOP is not a given, slam dunk, sure thing, works for all engines, installations and method of fuel metering (Carb, FI). Engines have been run well lean of peak for almost 70 years. They (engineers) know all about it. NACA (now NASA) did research in the 1940's on LOP operations with all kind of engines. Lycoming has done the same studies, this is old news. Lycoming does not say it can't be done, just it is not practical for small carbureted engines. You are not correct saying Lycoming will never change procedures. Lycoming calls for LOP operations on the Piper Malibu, with a large 350HP FI and turbo engine: http://www.avweb.com/news/usedacft/182792-1.html , Why? It is worth it. What fuel savings do you think you are getting, really, on a MPG basis with a little 160-180 hp engine. I never read how much fuel LOP is saving over ROP and what the TAS is. I personally doubt you can get worth while LOP ops with a Carb, but I am ready to be amazed. I have heard of moving the butter-fly (slightly) to get better fuel distribution bias (front to back), but never tried it. Still it is apple sauce.

Where you and I diverge mainly is ROP. +75 or so is the WORST place to be, so I read often outside of Lyc, and completely contrary to your assertion. You can't hurt an engine LOP, but you can ROP. When my #2 and 3 are LOP, the others are near peak. CHTs are wonderful, which speaks more to proper air cooling than whether the EGTs are 25 or 50 degrees one way or the other.
Again LOP, if you can achieve smooth operations, than go for it. However most find it is not practical. As far as running on the ROP side and damage, that is not true. As long as you are below 75% power and the CHT and Oil Temp are acceptable you are safe. Lycoming recommends ROP and smooth operations for ECON. They don't specify an exact EGT but it is around 50F to 75F ROP. They recommend 100F-150F for best power. This is cool with Lycoming. No one is saying run at peak EGT. I understand how LOP works and why it should not damage your engine, you are making less power and therefore making less heat. No extra fuel is available to cool the engine, but it is not needed. All this LOP stuff is good if you can get smooth operations, and all cylinders are LOP by 40F-50F. Even than, fuel saving on a small 4-cyl Lycoming is smaller than on a large Continental or 350HP Lycoming. LOP airspeed is slower than ROP operations. You are burning less fuel but you are making less HP and therefore going slower. To save fuel fly higher (as long as there is favorable winds or winds are not too adverse). Otherwise PULL the throttle back (way back) and you will save way more fuel than all the monkey motions to get true LOP operations.

I don't think Lycoming is lying about finding more cylinder damage with lean operations. I agree if done carefully, with full engine instruments, LOP Ops can be safe. However the 2 jugs at 20F LOP with the other two near peak on the rich side does not sound good. That is why carbs should not operate LOP, the 50F EGT spread is too much. LOP needs all EGTs to be close.

Ambient play a big roll. Most of my flying anywhere requires MEAs above 9k or else I'll hit mountains within 30 minutes. Lean 'till the engine stops; you can't hurt it at 9 or higher. Yes, higher is key to economy. If you have to throttle the engine to get 75% or less you do get higher pumping losses and the airplane's draggier down lower.
I agree hitting a mountain is bad. Leaning till it stops is bad technique, but to each his own.

Pulling the throttle back a bit can be GOOD. It's common practice on carbed 182s because it does cause extra swirling, therefore better mixing and distribution. I've had a GEM in my 172 for 9 years. The effect is noticeable as stated, the rpm loss undetectable on the mechanical tach. The 172 has a detented mixture control. I would be able to better tune the mixture if it were a vernier, since the detents are either richer or leaner than I would like to set per the GEM. But a vernier control would require an STC (none exist) or 337. So much for the criticallity of mixture as viewed by Cessna and the FAA. The manual says lean till rough, enrich till smooth. Without a GEM and vernier you can't do otherwise.
Yes full instruments like GEM are great. However most C-172 are LUCKY to have one EGT, if that. I have about 150 hours in C-182's, most giving dual instruction. I did not know about this trick 15 years ago, so I never tried it. I was happy if the pilot checking out got the cowl flaps. I do know how to clear carb ice with a back fire in a C-182.

What does "ZERO wind conditions" have to do with running an engine? I think I get your drift in that you might want higher power when bucking a headwind. But I could really run with this one and start a thread about the dreaded downwind turn.
It has nothing to do with leaning; it has everything to do with flight planning. Winds aloft affect range and ground speed. (Yes I hope) From a pure performance stand point "zero winds" are used to compare performance (apples). No matter how efficient your airframe and engine is at high altitudes, when faced with 50 kt head winds at 8,500' and little winds down low, say at 2,000', you would be better flying at high power (not leaned) and lower altitude, terrain permitting. Right? (Tail wind fly slower, head wind fly faster) Using LOP operations means going slower and more exposure (time in) the head wind. You may have lower fuel flow with LOP but more fuel burn, miles per gal, for the trip and take longer. I never tried much LOP operations because none of the planes I have fly or have flown can do it. I would love to hear real actual numbers on fuel burn and speed at LOP and than ROP.


In sum, it is relative. Your engine may vary, and I think we've learned more in recent years than Lyc will admit. Get a GEM, fly high, use mogas!, and run LOP. Or ROP if that feels good; Mother Lycoming says it's all right.
I have a GRT EIS4000 engine monitor. I would never use MOGAS, it is only $1.00 less if you even can get it. To me that it is not worth it. Although that is a total different debate. However there have been so many accidents from autogas users I would not risk it.

I am not saying LOP is not good or can't work; I don't think Lycoming says that either, but everything has to be right (near perfect) to get the advantage, large engines (6 cylinders) have more to gain and carbs are just not able to produce fuel distribution that will allow consistent LOP operations. As far as damage from LOP, if done well, not a problem. If not done well it can cause grief. I am sure that is where Lycomings experience comes in. They know that in the field pilots may screw it up.

I have a O-360A1A and I am happy to throttle back to 2250 rpm (Hartzell limit)/ 20" map and back through town at 175 mph and 7.5 gal/hr. If I want to really fly slow and save gas, 20-squared, 168 mph @ 6.5 gal/hr. G

Here is a Avweb article I agree with on the subject:
http://www.avweb.com/news/reviews/182501-1.html

 

[rv7 2003]

I have used gamis on a 540 lycoming and they work very well indeed. IMHO it was money well spent, even thogh I feel they were pushing thr price.
AVWEB has many good articles on LOP. I think the authors name was Deakin .

 

[RV7ator]

Sinatra

Well, G, what have we?

You're O.K. with LOP, but not with a carb.

Just because an engine is carbed, however, doesn't exclude an airplane from the club. Mine are carbed, they're smooth enough with even enough burns to allow LOP, maybe not on every cylinder, but I've realized benefits from doing so (lower temps, lower fuel bills). The engines remain in a steady state of health. I've fiddled with the 172 extensively over 2000 hours. One year I leaned by the book, lean til rough, enrich till smooth: 7.5 gph. The next year, I ran LOP as best I could: 7.2 gph. Since LOP is, indeed, slower, the mpg is only slightly in favor of LOP. I've only 130 hours on the RV, but regularly achieve 7.2 gph LOP (By the Hobbs, it's 7.0; I've adjusted for rolling around on the ground). It burns a lot more down low, just like a 360 should, and it's always ROP.

I use LOP. And I've got carburetors! Just like so many other aspects of airplane operation, you need to know what you're doing.

I'm done. See you at the gas pump.

John

"Sinatra"? I did it my way.

 

[akarmy]

I have heard of moving the butter-fly (slightly) to get better fuel distribution bias (front to back), but never tried it.

Not going to touch the rest of this interesting discussion... but on the subject of moving the butter-fly.

My Aerosport 0-320 D2A will run nice and smooth between 2300-2400 and 2500 and above. At those RPM's the leaned EGT spread is 25deg. But put the throttle at 2450 and the EGT spread goes to 250deg and it starts running rough! From that condition if you pull the throttle slightly back you can feel a bit more power from the engine as the EGT's level. In talking to Bart about it he indicated that this was normal for Carbed engines to have certian conditions that would create these uneven burns.

 

[osxuser]

From running the stock O-360 A1A in our Cardinal, I do the same this as the orginal poster. Get up to 8-10K feet, pull the mixture until it starts running rough, then bring it back up a couple of clicks. Usually ends up running about peak. Got it down to 7.5GPH though .

 

[cobra]

Why dont you guys get together and demand a decent fuel injection system from your beloved Lycomming- one that sets an accurate fuel/air mixture based on sensors and real-time conditions like every automotive manufacturer has offered for at least a decade now?

I can't help but think this type of discussion is a great reason to consider alterntive power sources, or at least, some consideration of working out a conversion setup. I really question how accurate fuel/air ratio can be adjusted based on listening to the engine thru earphones in a noisy cockpit and relying on EGT alone. There are too many variables that constantly change, and the range of safety gets pretty damned narrow with an air cooled motor running lean under power.

 

[gmcjetpilot]

No thanks

Why dont you guys get together and demand a decent fuel injection system from your beloved Lycomming- one that sets an accurate fuel/air mixture based on sensors and real-time conditions like every automotive manufacturer has offered for at least a decade now?

There are too many variables that constantly change, and the range of safety gets pretty damned narrow with an air cooled motor running lean under power.

If you are talking about car engines, they still don't match a dedicated aircraft engine in reliability, power to weight, economy and ease of installation. (Car motor = water pump, water hoses, radiator, electronic fuel injection, electronic ignition, dual electric fuel pump, fuel return lines = more stuff to break = pull over to the curb)

The reason you don't want electronic fuel injection is because it requires electricity, and when that dies your engine dies, BAD IDEA. With this we would be no better than auto engines and their needlessly complicated systems. Mechanical systems are much more reliable and independent from electrical power.

There are NOT many variables in an airplane engine at a constant RPM, constant power and torque. Unlike a car engine going from idle to max power and back to idle, up and down hills, not to mention emission requirements, aircraft engines operate 90% of the time in a narrow power band. What is required on a car is not needed or desired on an aircraft. G

Aircraft = light , simple, reliable and powerful (at low RPM)
Car = not so light, not so simple, reliable (?) and powerful if you REV it for the moon (reduction drive needed , another system to fail and added weight)

 

[cobra]

George,
Good points for sure. My experience with most solid state electronics is that once they they pass a short initial inspection period, they last and perform indefinately as long as they are not overheated, and tend to be lighter than their mechanical counterparts. I feel that a backup battery is sufficient to provide emergency backup power if needed. Mechanical controls are more prone to wear, lose calibration easily, have far more problems with part and cable breakage, and will fail if not lubricated or become dirty, so there are problems either way.

The last time I checked, fuel/air mixtures are influenced by any temperature, air density (moisture content), and/or pressure (altitude or power setting) change; carbs are prone to icing and vapor lock. I believe were discussing fine tuning at near-ideal lean mixtures however. To assure optimum accuracy and best performance/economy under all conditions, electronic instrumentation, with sensors and feedback loops are needed.

The only place I disagree with your comments is that I feel that the consistency and reliablity improvements provided by water cooling is well worth any weight difference. The weight differences are insignificant in some apps as you know (e.g., Wankel rotaries).

 

[rv6ejguy]

If you are talking about car engines, they still don't match a dedicated aircraft engine in reliability, power to weight, economy and ease of installation. (Car motor = water pump, water hoses, radiator, electronic fuel injection, electronic ignition, dual electric fuel pump, fuel return lines = more stuff to break = pull over to the curb)

The reason you don't want electronic fuel injection is because it requires electricity, and when that dies your engine dies, BAD IDEA. With this we would be no better than auto engines and their needlessly complicated systems. Mechanical systems are much more reliable and independent from electrical power.

There are NOT many variables in an airplane engine at a constant RPM, constant power and torque. Unlike a car engine going from idle to max power and back to idle, up and down hills, not to mention emission requirements, aircraft engines operate 90% of the time in a narrow power band. What is required on a car is not needed or desired on an aircraft. G

Aircraft = light , simple, reliable and powerful (at low RPM)
Car = not so light, not so simple, reliable (?) and powerful if you REV it for the moon (reduction drive needed , another system to fail and added weight)

You'd have a hard time convicing a lot of people that a Lyc is more reliable than a Toyota, Lexus, Honda, Subaru etc. I don't see crankshafts breaking on them just as a for instance. There is NO WAY that aircraft magnetos are more reliable than modern distributorless auto ignitions. There are no moving or wearing parts in these. I can't remember the last time I had a rad hose or water pump fail on even some 20+ year old crap I drive in the winter with original parts. EFI has proven to be way more reliable than carbs with no maintenance. Again using the example of some old Toyota EFI cars I have had, all with the ORIGINAL injectors, pumps, ECUs, regs, rails, O-rings and filters totaling well over 400,000 miles. Never even touched these.

While you may not embrace FADECs or EFI in general on aircraft, many people are. The Eggenfellner Subes have demonstrated tremendous reliability so far considering the learning curve. Several are now well over 1000 flight hours and most high time users report no problems, almost nil oil use, almost no maintenance in that time. One customer has our EFI on a Suzuki V6 powered Titan P51 replica, runs and sounds great, burns NO oil in 85 hours between changes of synthetic oil. He was an old school carb and magneto guy who had great reservations at first about EFI. Now he is totally converted and would never go back.

Most installations are equipped with either dual batteries and/or dual alternators so this idea of electrical power dying is really a non-issue unless you are 2 hours out over the ocean or something. Personally I would not fly any single engine plane out this far anyway, carbs, EFI, magnetos or not.

Yes, auto engines will be heavier but they will do most other parts of the mission equally well or better than a Lycoming for less $ in the long run. Through various forums and groups, auto engine users are sharing info on fuel and electrical system designs to increase the relliability of the supporting systems even more, making conversions easier and safer for the others who follow.

As far as EFI applied to Lycomings and Continentals, we have done this as well with great success. LOP no problem with EGT spread at 20-30F between hottest and coldest cylinders and 15-20% reduction in fuel flows at the same TAS on several different airframes. One C-85 showed a 25% reduction in fuel flow using EFI over the carb. This shows how poor the carb and manifold designs are are some aircraft engines. Another friend has a new Lyc clone with the "improved sump/intake". EGT spread is still 180-200F so it is no better than the factory Lyc sump. A wealth of real world flying EFI and FADEC experience shows tangible gains are possible with this technology over carbs and magnetos.

 

[Vince Koehn]

Efi Io-390

I want a electronic fuel injected Lycoming IO-390 in my next RV. I would not bat a eye to fly behind electronic fuel injection. I have a good friend who is a ASE Master Auto Tech and he is amazed at how the Lycoming engines are so 18th century. All be it they are a good proven engine, no argument there. But I think aircraft engines certainly could use a little sprucing up and I can't wait until electronic fuel injection....until then I am happy with my carb.

 

[f1rocket]

I sense a thread steal coming on!

 

[gmcjetpilot]

U R Right

I sense a thread steal coming on!

HaHaHa HaHaHa Good one G

George,
The last time I checked, fuel/air mixtures are influenced by any temperature, air density (moisture content), and/or pressure (altitude or power setting) change; (That is what the RED KNOB is for); carbs are prone to icing and vapor lock (AT THE SAME TIME ) . I believe were discussing fine-tuning at near-ideal lean mixtures however. To assure optimum accuracy and best performance/economy under all conditions, electronic instrumentation, with sensors and feedback loops are needed.(AGAIN RED KNOB + PILOT BRAIN + EGT MONITOR = PRECISION manual CONTROL. It is not hard to lean an engine with Mr. Mixture cont'l.)

The only place I disagree with your comment is that I feel that the consistency and reliability improvements provided by water cooling is well worth any weight difference. The weight differences are insignificant in some apps as you know, e.g., Wankel rotaries. (U R RIGHT, WATER COOLING IS SUPERIOR TO AIR COOLING, WHEN I GO WATER COOLING IT WILL BE A V-8 or V12 IN A P-51 REPLICA, LIKE A THIUNDER MUSTANG )

You'd have a hard time convicing a lot of people......(I would not even try)

While you may not embrace FADECs or EFI in general on aircraft, many people are..... Several are now well over 1000 flight hours and most high time users report no problems.......... (I am sure and glad to hear it)

Most installations are equipped with either dual batteries and/or dual alternators....... (True, more power to you )

Yes, auto engines will be heavier but they will do most other parts of the mission equally well or better than a Lycoming for less $ in the long run. (I don't know what the "mission" is, but for an overall aircraft engine, you can't get more simple and reliable than a Lycoming.)

Through various forums and groups, auto engine users are sharing info on fuel and electrical system designs to increase the relliability of the supporting systems even more, making conversions easier and safer for the others who follow. (This is good thing)

As far as EFI applied to Lycomings and Continentals, we have done this as well with great success. LOP no problem with EGT spread at 20-30F between hottest and coldest cylinders and 15-20% reduction in fuel flows at the same TAS on several different airframes. One C-85 showed a 25% reduction in fuel flow using EFI over the carb. This shows how poor the carb and manifold designs are are some aircraft engines. (That would be interesting, but huge piston faces, slow RPM are very differnt that tiny pistons and high RPM. A EIFI would be cool conversion if you could get LOP, but with "tuning" a mecahnical FI can do that. I can't see going as fast on less fuel, at least using LOP, the power curve says: LOP = Less power = slower)

Another friend has a new Lyc clone with the "improved sump/intake". EGT spread is still 180-200F so it is no better than the factory Lyc sump. A wealth of real world flying EFI and FADEC experience shows tangible gains are possible with this technology over carbs and magnetos. (180-200F spread, get your money back or your shot gun, he got screwed, that is crazy and not indicative of normal operations with a stock mechanical FI or Carb for that matter.)

G

 

[osxuser]

You'd have a hard time convicing a lot of people that a Lyc is more reliable than a Toyota, Lexus, Honda, Subaru etc. I don't see crankshafts breaking on them just as a for instance. There is NO WAY that aircraft magnetos are more reliable than modern distributorless auto ignitions. There are no moving or wearing parts in these. I can't remember the last time I had a rad hose or water pump fail on even some 20+ year old crap I drive in the winter with original parts. EFI has proven to be way more reliable than carbs with no maintenance. Again using the example of some old Toyota EFI cars I have had, all with the ORIGINAL injectors, pumps, ECUs, regs, rails, O-rings and filters totaling well over 400,000 miles. Never even touched these.

But that doesn't mean it's a good idea. I ain't going to fly behind a watercooled engine with 20+ year old hose. Just because it still works doesn't mean it's prudent. There is NO doubt that a properly run Lyc will out run, and out last any auto conversion on the market today, while still being lighter, producing the same or more power, and similer fuel burns. I know a guy with a Comanche that has 2700hr's on his 260, still going. We have a 35-year since Factory New O-360A1A, never been overhauled at about 1500Hr's still going strong. There is simply no argueing the proven reliablity. At 2000hr's going 120Kt's, your figure the Lyc's got you 240,000 Nautical Miles. At 200MPH, it's getting you 400,000 Statue miles. Another interesting figure, is your 3000 mile oil change in your car, going 60mph is about 50 hr's of operation. Do we see a trend here? The service periods for these engines, even in their completely different applications, are nearly identical, as is their expected service life. The car engine doesn't even really do better in it's native application!

While you may not embrace FADECs or EFI in general on aircraft, many people are. The Eggenfellner Subes have demonstrated tremendous reliability so far considering the learning curve. Several are now well over 1000 flight hours and most high time users report no problems, almost nil oil use, almost no maintenance in that time. One customer has our EFI on a Suzuki V6 powered Titan P51 replica, runs and sounds great, burns NO oil in 85 hours between changes of synthetic oil. He was an old school carb and magneto guy who had great reservations at first about EFI. Now he is totally converted and would never go back.

I have no arguement against Electronic FI, EI or FADEC. But I do think it belongs on an aircraft engine, not a car conversion. The economics just don't work out in anyone's favor. I'd like to do GAMI's PRISM system on the lyc I'm planing to rebuild for the -7. http://www.gami.com/prism.html

Maybe a different EI, but the prism system uses real-time parameters, instead of maps.

 

[cobra]

Osxuser

There is NO doubt that a properly run Lyc will out run, and out last any auto conversion on the market today, while still being lighter, producing the same or more power, and similer fuel burns.

You have been brainwashed.

The Mazda Renesis and 20Bs are lighter (abt 350 lbs firewall forward), significantly more powerful (230/300+HP), far more durable (no measurable wear > 2000 hrs), cheaper to buy ($2500-8000), maintain, and overhaul (<1000), and the fuel burn is very close to comparable HP Lycs.

 

[f1rocket]

The Mazda Renesis and 20Bs are lighter (abt 350 lbs firewall forward), significantly more powerful (230/300+HP), far more durable (no measurable wear > 2000 hrs), cheaper to buy ($2500-8000), maintain, and overhaul (<1000), and the fuel burn is very close to comparable HP Lycs.

Then why isn't everyone flying with one of these running out front??? Don't respond, I already know the answer.

 

[rv6ejguy]

I'm not flying with 20 year old hoses on my aircraft, I simply state that most modern auto engine whether installed in aircraft or cars require almost no maintenance in their entire lifespan. Platinum plugs are going 100,000 miles, synthetic oil change intervals exceed 15,000 miles, no ignition parts to service, EFI has proven to be virtually maintenance free for decades of use. Not sure where this idea comes from that aircraft engines require less maintenance?

I don't dispute that a carbed Lycoming does the job, I just got to fly a friend's 7A/ Lyc and was pretty impressed actually but all this stuff put forth about cars engines not lasting as long as aircraft engines even in an aircraft installation is nonsense and every time I've asked someone to provide evidence to back up this claim, all I hear is silence or conjecture. Teardowns of some Subes now with 600 -1500 hours show no measurable wear on anything, perfect compression, no oil use. There is no doubt that 2000 hours will be no problem for these engines and more likely in excess of 3000 hours will be the norm between overhauls. For about $5500, you get a complete NEW factory longblock if you don't want to overhaul yourself. For about $650 you can grind valves and seats and get gaskets, rings, bearings, belts etc. and DIY. Sorry, I just don't see Lyc or Lyc parts cheaper than this. With the tight tolerances of liquid cooled engines and superior oils like Mobil 1, combined with similar piston speeds and 5 or 7 main bearings, forged cranks and rods, die cast block etc., the Sube has design and metallugy to be superior and has proven to be very bulletproof. They are so over designed that running at 4500 rpm is nothing. There are several basically stock bottom ends running over 900 hp. Try that for even 5 seconds on a 3 main bearing Lyc!

As far as EGT spread goes in Lycs, I've talked to no less than 7 Lyc owners with carbed O-320/ O-360 engines fitted with 4 probe EGTs. All report EGT spreads of 180-200F. I think this is probably the norm but I'd welcome a survey here from others so equipped.

The mechanically injected IOs appear to be much better at 50-75F. The problem with such high EGT spreads and attempted LOP operation is that when the first one reaches peak, the other 3 cylinders may be operating at an AFR as rich as 12.7 to 1 according to our studies. This explains the roughness as each cylinder is producing different amounts of hp. With proper mixture distribution between cylinders possible with EFI or good mechanical injection, AFRs can be held within .2 rather than 2.0 of each other. Result is much smoother operation and the possibility of getting all cylinders to peak at nearly the same time. This avoids having the leanest cylinder encounter lean misfire while attempting to bring the other cylinders to peak. It should be noted that best power is made at around 13.5 to 1 AFR so having cylinders richer than this loses power and explains why fair reductions in fuel flows are possible with EFI without losing speed as you would with a poor carb setup.

 

[dan]

EGT spread

I keep hearing people talk about this "EGT spread" thing. It drives me nuts. The delta between EGT on cyl 1, 2, 3, 4 is essentially meaningless, right? I could see trying to get CHTs closer to each other...but EGT is just a relative indication of where the cylinder is on its mixture curve. Right? Am I wrong about this?

What is important is that the cylinders reach peak EGT at the same, or similar, fuel flows. It doesn't matter (imho) if cyl 1 peaks at 1480 and cyl 2 peaks at 1380, as long as they peak together (or as close to the same fuel flow as possible). There's enough variation in the way EGT probes are installed and oriented, you're gonna see some differences in EGTs from cylinder to cylinder.

Maybe there are some real engine experts out there who can tell me what the value of a "small EGT spread" is. I have yet to comprehend any value behind that!

I imagine there are all these pilots out there trying to "close the gap" with their EGTs and get them to be more in line with each other. And they may not be paying any attention to peak-vs-fuel flow.

CHTs, sure...get 'em close if you can. But "EGT spread" is irrelevant (imho).

Please correct me if I'm wrong! I don't want to run around with false assumptions.

)_( Dan
RV-7 N714D
http://www.rvproject.com

 

[cobra]

why isn't everyone flying with one of these running out front???


Yeah, Ive wondered the same thing .

The point was not which engine to use- that is a personal choice based on many factors (and I certainly support anyone who prefers Lycomming over something I personally believe to be improved technology).

The point is that there ARE other legitimate choices that have a lot to offer, particularly so when it pertains to fuel injection and value engineering. I was simply correcting an inaccurate stereotypical statement.

 

[rv6ejguy]

I keep hearing people talk about this "EGT spread" thing. It drives me nuts. The delta between EGT on cyl 1, 2, 3, 4 is essentially meaningless, right? I could see trying to get CHTs closer to each other...but EGT is just a relative indication of where the cylinder is on its mixture curve. Right? Am I wrong about this?

What is important is that the cylinders reach peak EGT at the same, or similar, fuel flows. It doesn't matter (imho) if cyl 1 peaks at 1480 and cyl 2 peaks at 1380, as long as they peak together (or as close to the same fuel flow as possible). There's enough variation in the way EGT probes are installed and oriented, you're gonna see some differences in EGTs from cylinder to cylinder.

Maybe there are some real engine experts out there who can tell me what the value of a "small EGT spread" is. I have yet to comprehend any value behind that!

I imagine there are all these pilots out there trying to "close the gap" with their EGTs and get them to be more in line with each other. And they may not be paying any attention to peak-vs-fuel flow.

CHTs, sure...get 'em close if you can. But "EGT spread" is irrelevant (imho).

Please correct me if I'm wrong! I don't want to run around with false assumptions.


)_( Dan
RV-7 N714D
http://www.rvproject.com

Ideally, all temps between cylinders should be as close as possible. With EGT monitors you can look at what temp each cylinder peaks at as well as it's relation to others when it peaks. Our testing has shown that in most engines the peak EGT is usually within 15-30F on all cylinders but when one peaks, there can be up to 200F difference in the one that peaks first vs. last. This is clearly indicative of wide cylinder to cylinder AFR variations. What do you suppose happens to the AFR in the 1st to peak cylinder as you continue to lean? The AFR might go from 14.7 (stoichiometric) to maybe 17 before the others reach 14.7 and peak EGT. Result? Lean misfire and very rough running on that cylinder. With EFI, we see all cylinders reach peak almost simultaneously, all cylinders are producing almost the same power and operation is very smooth.

 

[gmcjetpilot]

Good point

I keep hearing people talk about this "EGT spread" thing. It drives me nuts. The delta between EGT on cyl 1, 2, 3, 4 is essentially meaningless, right? [SNIP]

[SNIP]There's enough variation in the way EGT probes are installed and oriented, you're going to see some differences in EGTs from cylinder to cylinder. Dan

Good point Dan, EGT probes are hard to get installed exactly the same, and the value of EGT is not as important as peak EGT, CHT and Fuel Flow. I have seen a 100F difference from just variations on probe installation and the probe itself. Just mounting the probe a fraction of an inch further down the exhaust stack or on the opposite side of the bend will change the reading.

EFI no doubt can do better than manual/mechanical based on more sensors and computer microprocessor control. The real break thru is with a full FADEC, http://www.fadec.com/graphics/technical_diagram_big.jpg

Even better would be a true one lever FADEC (no prop control). The problem of course with FADEC is cost vs. benefit on an airplane. Call me crazy I love my big red knob. STOP THAT, NO you silly I am talking about my manual mixture control under my instrument panel.

Let me decide how to lean the aircraft. Typical flight I might need to make a few 2 or 3 adjustments to the mixture, no big deal. From T/O, climb, cruise, pattern and touch down there are only a hand full of power settings, and all of them very steady state. If you are willing to monkey with your injectors you can achieve that magic 30F spread (real spread). Also EFI sensor input and just mechanical and installation variation of the engine itself on an air-cooled Lycoming causes power variation between cylinders. A water cooled engine is better for economy because cylinder and piston clearance can be controlled closer. IT does not mean air cooled engine can benifit from EFI or be run LOP, only that there is one less factor in making even power in a water cooled engine.

I mentioned a 4-into-2 cross over exhaust is not good for making "equal power" between cylinders. The better exhaust systems are: 4-into-1 OR 4-into-4 separate pipes. Point is there are so many factors other than the Fuel injection, mechanical or electronic. EFI can make more adjustments for these variations, but you can manually "tune" a mechanical system. All these "OTHER" factors that cause power variation between cylinders. This is why some engines can't be run LOP as easily.

EFI is better but at greater cost and complexity. I know some FADEC designs have a manual reversion but the cost is even more. Again going to more computers and electrical appliances will no doubt marginally improve economy and performance of an aircraft piston engine but at much higher cost and loss of simplicity. "If it works don't.........use your red knob." G

 

[dan]

terminology

...the peak EGT is usually within 15-30F on all cylinders but when one peaks, there can be up to 200F difference in the one that peaks first vs. last...

Exactly! My gripe has more to do with terminology than anything else. People striving to narrow the "EGT spread" rather than trying to get all cylinders to peak simultaneously.

Maybe I'm misinterpreting what people mean by "EGT spread," but to me that term implies the instantaneous difference in EGTs across cylinders, i.e. the difference between the hottest and coldest EGT.

)_( Dan
RV-7 N714D
http://www.rvproject.com

 

[rv6ejguy]

George is correct in saying EGT probe placement is critical to ensure true readings. Differences in depth, location and orientation has been shown to produce fair variations in readings. It is very difficult to be sure that what you see on the gauge is actually true. We often verify with an infrared thermometer gun if there are doubts on an installation. If the plugs are the same color under a magnifier but EGT spread is say 200F, I suspect probe placement as the culprit.

Throttle blade angle has an effect even on some EFI engines due to changes in the manifold airflow. We have also noticed differences in spread as the mixture is changed. We often see differences even within the same model of engine.

The ultimate for testing would be a wideband O2 sensor in each pipe to measure true AFR. Kinda expensive at $1600 for the instrumentation but it would be very interesting...

I have not seen a carbed Lyc that runs well LOP but it could well exist with the right manifold design.

The speed loss with true LOP operation may offset any fuel savings at some point with an atmo engine. With turbos, LOP operation usually involves increasing MP slightly to make up the hp and speed loss. Power loss is only about 5% going from 13.5 AFR to 17 but fuel flow is greatly reduced if the engine will run smoothly and the ignition system will light off this mixture properly. A good EI helps here with higher spark energy and proper timing of the spark for peak cylinder pressure to occur at the optimal piston position to extract all possible energy out of the fuel. With programmable EFI/EI we can vary all this in flight with the autopilot engaged in smooth air and look for a gain in engine rpm and airspeed. Slight ignition timing variations can have big effects also.

In other words, like most experimental testing, you can spend a large portion of your life refining things and testing different ideas. What works on one engine may not work on the next one. I think LOP is one of those topics that fits in the never ending debate section!

 

[gmcjetpilot]

Amazing talents and info on the web

[snip] It is very difficult to be sure that what you see on the gauge is actually true. We often verify with an infrared thermometer gun if there are doubts on an installation. If the plugs are the same color under a magnifier but EGT spread is say 200F, I suspect probe placement as the culprit.

Throttle blade angle has an effect even on some EFI engines due to changes in the manifold airflow. We have also noticed differences in spread as the mixture is changed. We often see differences even within the same model of engine.

The ultimate for testing would be a wideband O2 sensor in each pipe to measure true AFR. Kinda expensive at $1600 for the instrumentation but it would be very interesting...

I have not seen a carbed Lyc that runs well LOP but it could well exist with the right manifold design.

The speed loss with true LOP operation may offset any fuel savings at some point with an atmo engine. With turbos, LOP operation usually involves increasing MP slightly to make up the hp and speed loss. Power loss is only about 5% going from 13.5 AFR to 17 but fuel flow is greatly reduced if the engine will run smoothly and the ignition system will light off this mixture properly. A good EI helps here with higher spark energy and proper timing of the spark for peak cylinder pressure to occur at the optimal piston position to extract all possible energy out of the fuel. With programmable EFI/EI we can vary all this in flight with the autopilot engaged in smooth air and look for a gain in engine rpm and airspeed. Slight ignition timing variations can have big effects also.

One thing that is clear, if you want to go with EFI or do any experimental or custom engine work call rv6ejguy. G

PS, one problem with O2 sensors is they would have very short life with aviation 100LL gas due to lead.

 

[rv6ejguy]

One thing that is clear, if you want to go with EFI or do any experimental or custom engine work call rv6ejguy. G

PS, one problem with O2 sensors is they would have very short life with aviation 100LL gas due to lead.

Thanks for the vote of confidence! We curently use Decalin TCP in non-certified 100LL applications to scavenge the lead. O2 sensor life is now exceeding 100 hours and some other users are reporting in excess of 200 hours. This is also keeping deposits on piston crowns, spark plugs, valves and turbine wheels to a minimum. Safe to carry in the aircraft unlike the Alcor TCP and reasonably priced: www.decalinchemicals.com

One more thing you don't need to worry about with a Lycoming.

 

[osxuser]

Osxuser

There is NO doubt that a properly run Lyc will out run, and out last any auto conversion on the market today, while still being lighter, producing the same or more power, and similer fuel burns.

You have been brainwashed.

The Mazda Renesis and 20Bs are lighter (abt 350 lbs firewall forward), significantly more powerful (230/300+HP), far more durable (no measurable wear > 2000 hrs), cheaper to buy ($2500-8000), maintain, and overhaul (<1000), and the fuel burn is very close to comparable HP Lycs.

I can buy a core, and rebuild a lyc for about 12K (IO-360). The another thing is, I've never seen an auto conversion that someone isn't constantly tweaking on to get it to run right. Lycoming is more set it and forget it. And I'm a A&P so I've not been brainwashed, I'm doing the brainwashing... Doesn't anyone miss working on a pre 1970's car with no electronics? Thats the nice part of working on certified lycomings. When something goes wrong, you can find it and fix it, instead of chasing gremlins down wires.

On the other hand, I have an open mind. Show me some actual data on the rotary, and It just might end up in my -7. Alot of the price stuff you quote however, is taking the engine out and having a car guy do the work, or doing it yourself. If you take that same equation and apply it to a Lyc, the same economics apply to overhauling it. Crank, case and cam stay good if you fly every week or so. overhaul the cylinders if you must, but usually a hone and valve grind will do it, clean, paint, and put back together with new gaskets. Mags will need O/H (Unless you have EI on the lyc, which alot of people do). New spark plugs (A set of champions can run the TBO of an engine, I've seen it) harness, and your done. I'm sure it'd cost more than 1000, but not more than 5000 if you do it yourself. It's all a matter of what your able to do yourself that will save you money. Show me data

And Dan, your absolutly right that EGT spread has nothing to do with running LOP, it's all in when they peak. It should be within .5GPH or so as you're leaning. Thats what GAMI's help do. I think about 1/2 of the C177 RG fleet run LOP now thanks to the Cardinal Flyers e-mail digest discussions on it. The egt spread will affect the smoothness of the engine, because it's a gauge of how much fuel/air is being burned. The closer the spread, the smoother the engine.

I'm waiting for someone to come with 9.5:1 pistons for a IO-390, also port and polish job. Maybe get 240+ HP out of one? I know IO-360's that dyno at 230+.

 

[cobra]

Osxuser,
Brainwashed?- YOU said that "NO doubt that a properly run Lyc will out run, and out last any auto conversion on the market today, while still being lighter, producing the same or more power, and similer fuel burns". I disagree- there is a lot of doubt...

Obviously the Lycomming is a proven engine that evolved into a pretty decent powerplant, but IMHO it uses aged technology that has distinct disadvantages compared to newer (better?) designs.

Its biggest plus is that it is an easy bolt-in-and-run solution, its light, produces good torque, and gets decent fuel economy if (manually) tuned correctly. The negs are that it is air-cooled, which require loose tolerences, high wear, and makes it prone to overheating difficulties under continuous high power applictions (some history of broken crankshafts, exhaust valve problems, cracked heads that Ive heard of). Dificulties controlling head heat makes forced induction (turbocharging/supercharging) much more difficult.

The aircraft motors tyically have large (heavy) pistons with long stroke to achieve high torque output. The reciprocatiive stresses (pistons accelerating, decelerating, stop, accelerating, decelerating, stop for each engine revolution) with inherent "hammering" on bearings, valve train, and crankshaft are significant and greatly amplified during high-rpm operation. It is also a low-production certified motor (compared to auto engines) that make the engine and replacement parts expensive, and greatly delay significant mechanical and electrical improvements.

You say you can buy used and rebuild for 12K? As an A&P you must have better sources than the rest of us; typically the "reported" cost is 2-3 times what you mention and the overhaul certainly requires special knowledge and tools.

The Rotary advantages (again my opinion here): the Wankel is a much better aircraft engine than auto- it prefers continouos high rpm operation and is torque-challanged in the idle-to-mid rpm range most important for autos in traffic. The biggest draw involves reliability/durability- the rotary motion does NOT involve reciprocatiive stresses, it is a continual motion that thrives on hi-speed operation (like a turbine). Needed torque is achieved thru gearing, not displacement (which brings weight penalties along for the ride). The triangular rotors exhibit no measurable wear on engine housings or crankshaft bearings after more than 2000 hours high-speed operation. There are only 3 moving parts in a 2-rotor (200+HP) rotary engine, 4 if you include a turbocharger!

Overhaul generally involves replacing several rubber O-rings, cleaning oil deposits (sludge), and replacing the apex seals (cast iron block that contacts the rotor housing)- about $600 for parts (easily obtainable). The overhaul is not difficult and does not require special tools- can be done at home with minimal training.

Downside: rotary seals (O-rings) are damaged by high heat, so adequate oil and water cooling is important. The rotors are cooled only by (crankcase) oil normally- a recommended upgrade involves either mixing oil with fuel or changing the cooling oil to a 2-cycle oil reservoir feed. You will generally have to modify or build your own engine mount, cooling and exhaust systems from automotive parts- several firewall forward sources are being developed.

Upside: durable, light, high power output, active automotive aftermarket, cheap (used RX-7s a good source, low milege from Japan market available for ~1500), very smooth, modern OEM fuel injection and turbocharging available, and several working RV plans/models are available to copy or draw ideas (Tracy Crooks www.rotaryaviation.com is one of the best, with lots of documentation). Another big plus for avaition users- part failures tend to be catastrophic in reciprocating motors- Rotaries generally exhibit reduced power when parts fail- which provide a the chance to fly (slower) to a good site of YOUR chosing.

 

[rv6ejguy]

And Dan, your absolutly right that EGT spread has nothing to do with running LOP, it's all in when they peak. The egt spread will affect the smoothness of the engine, because it's a gauge of how much fuel/air is being burned. The closer the spread, the smoother the engine.

EGT spread certainly does make a big difference in the ability to run LOP effectively. LOP is a general term. Specifically, if #3 cylinder peaks first and you continue to lean, this does not necessarily mean that any of the other cylinders are actually running LOP. Peak EGT simply indicates that stoichiometry has been achieved with the AFR (about 14.7 to 1) in that cylinder when using individual probes. The average carb equipped Lycoming exhibits quite different cylinder to cylinder EGTs, hence likely different AFRs. This is the reason why most carbed Lycs shake like mad if you continue to lean after the last cylinder has peaked, because the first one is now REALLY lean. Injection generally reduces the spread by 2-3 times over carbs so these engines may be leaned significantly more (relatively speaking about all cylinders) and usually show lower fuel flows for the same speeds. My friend with an O-360 RV-6A joked that his Lyc was "4 one cylinder engines flying in close formation" when it came to the EGT spread of 200F.

 

[dan]

Terminology, again

rv6ejguy,

You're referring to "PEAK spread," and I agree that this is the critical factor. For example, my IO-360-A1B6 is balanced to the point where all cylinders reach peak EGT at identical fuel flow, meaning there is no cylinder that reaches peak first. They all peak simultaneously as the mixture is leaned. When one cylinder is 40 LOP, *all* cylinders are 40 LOP. All cylinders are at the same point in the curve at any given mixture setting. That is the condition we strive to achieve to make LOP a safe ordeal.

However! At the moment all of the cylinders peak (simultaneously, I must reiterate) the "EGT spread" is far from zero! That is to say -- the difference between hottest and coldest EGTs at the moment all 4 cylinders peak is about 100F. Even though all cylinders are at the same point in the curve, all cylinders do have significantly different EGT values.

I'm advocating a shift in terminology. I'd like to use the term "PEAK spread" to denote the difference in fuel flow between the first and last cylinders to peak. And we can continue to use the term "EGT spread" to denote temperature difference among cylinders at any given mixture setting.

Or maybe I have my own terminology wrong...if everybody else is using "EGT spread" to mean the difference in fuel flow between first and last cylinders to peak. But...from what I've heard, people aren't using the term that way.

PEAK spread --> get it as close to 0.0 gph as possible for safe LOP

EGT spread --> has no bearing on anything

)_( Dan
RV-7 N714D
http://www.rvproject.com

 

[osxuser]

Dan your a genius

Your right dan. Everyone is still so hung up on temperature, that they don't understand the whole issue. The reason the carbed lyc shakes is because one or more cylinders is making a significantly different amount of power than the others. Because one cylinder just went LOP when the others are still ROP can be a reason. Our C177 is closer than most carb engines so I can get away with a bit of LOP. Powerflow exhaust evens out the peak spread on a carbed lycoming enough to provide LOP operations.

BUT back to topic:

Say we're running ROP and our spread between hottest to coldest is 100?F. As we lean, the hottest one remains hottest, and the coldest one remains coldest, but they all peak at the same time. Running at peak therefore, there still is 100? difference. As we continue to lean, they still remain in the same linear temperature line, and at 150? LOP the spread is still 100? between hottest and coldest. This means that the hottest (we'll say #1) peaked at 1550? and is now running at 1400?, and the coldest (#4) peaked at 1450? and is now running at 1350?. They are still the same distance from peak and therefore it is safe to run the engine this way. This is the PEAK SPREAD that dan CORRECTLY refered too (Zero in the scienario, as normally measured in GPH of Fuel Flow)

The EGT spread (Measured in ? of temperature) is the 100? we refered too above. The main reason that this can matter is smoothness. All probes and gauges being accurate, the temp is the measure of how much HP each cylinder produces. If running LOP the #1 produces 1500? and the rest 1250?, that tells me that #1 is producing significantly more power, which when at this extreme, will cause roughness. The thing is, if that's happening to an engine that peaks all cylinders at the same time, it means that there is a major airflow problem with the engine that should be investigated. Not that there is anything wrong with fuel delivery. But if that happened, in theory it'd happen ROP too, so it'd be an issue that someone should have already been looking into.

So in short, temperature has nothing to do with running LOP. It's all in the peak spread in GPH.

 

[gmcjetpilot]

Perfect world & EGT spread & LOP Ops

Good insight, I learned something, but let's clear a few things up. EGT spread is meaningless and on the other hand it is important to diagnosing engine problems.

Peak EGT: Peak EGT means that you have reached the stochimetric ideal fuel/air mixture where there are just the correct amount of air to fuel molecules to burn, no more or no less of any molecule.

Rich of Peak EGT (ROP): mixture is too rich, un-spent or un-burnt gas is being exhausted and is cooling the combustion. Since the fuel molecules are not burnt they are there to cool and absorbs heat. This rich mixture results in more power, and more fuel usage. However extreme rich condition results in loss of power to the point combustion can't be supported.

Lean of Peak EGT (LOP): mixture is too lean and you have more air than needed. Since less fuel is being burnt there is less heat due to less combustion. This usually results in less power. Running LOP can result in lower temps than peak and less fuel burn, but extreme lean condition can result in combustion no longer being able to be supported.

In an ideal world all cylinder would reach peak EGT at the same mixture setting (ratio of air and fuel), with their respective peak EGT's reached at the exact same time and at the same absolute reading. Variation can cause the ideal mixture ratio to vary between cylinders and thus power varies.

The common practice is we care about the 1st to peak (leanest cylinder) only and we enrichen this leanest cylinder 100F ROP. The rest of the richer cylinders fall where they fall ROP. Since all other cylinders are at 100F ROP or richer they will run cooler. This is safe and produces the most power, with good cooling (from the rich mixture).

What does "EGT Spread" mean. To most it means the difference between the respective Highest and Lowest EGT when the first (leanest) cylinder peaks. That is the classic definition, but as Dan points out it does not mean much. It is relative to something but the absolute magnitude of the spread may not be significant. On the other hand it can be an indirect indication of a problem.

The goal is to have balanced power between cylinders, which usually means the same mixture going into each cylinder. Unfortunately some engines have inherent ?power? imbalanced between cylinders. Some cylinders are stronger than the others (compression, plug gap). When you lean the engine this difference is accentuated and causes rough running (vibration). So even if you have the ideal mixture some cylinders may just make more power. In this case LOP operations are not practical if it shakes too much. ROP operations masks this imbalance.

Dan?s technique makes sense. Note EGT of the first cylinder to peak, note fuel flow (FF) at 1st to peak, continue to lean until the last cylinder (the richest one) peaks and note (FF). The difference in FF is the indicator or quality of the ?EGT Spread?, meaning the smaller the FF difference from the 1st and last cylinder to peak the better. Even if there was 100F ?spread? it is not significant unless the FF difference is large. However this requires a FF gauge, which even less GA planes have. Although FF probes are more common on experimental aircraft, it is an expensive option. (My EIS-4000 has a $370 FF option, which I do have). Again if the engine shakes like crazy a FF gauge will gain you access to LOP operations.

Unfortunately many Lycoming's will run way too rough past the 1st or 2nd cylinder to peak (uneven power) to make it possible to continue leaning all cylinders out. So no matter if your have Fuel Flow and EGT/CHT probes it is all moot if the engine shakes like crazy. If you can lean all cylinders to peak you are doing real good. If you can't you know what kind of adjustments are needed. Adjustment might mean more than messing with an injector. It might mean porting one cylinder, making spark plug changes/adjustment, exhaust changes or even overhaul a weak cylinder. You are trying to balance power not EGT.

EGT spread is not totally irrelevant when detecting problems. That is why EGT changes relative to the other cylinders indicate a problem: plugged injector, intake leak, compression, burned valve, fouled plug for example. So the change in EGT spread from "normal spread" between cylinders is useful.

For LOP we need to lean the richest cylinder at least 30F LOP. The other cylinders are leaner. Since power falls off quickly lean of peak we need to have the ?spread? close. "Spread means the actual DELTA of each cylinders EGT from its unique peak EGT. All cylinder's must be say be in a spread of 30F-70F LOP, or about a 40F spread. For LOP Ops we care that the richest cylinder is 30F-40F LOP and you have smooth operations. The EGT value of the other leaner cylinders is not important (as long as they are not more than 70F actual LOP).

All these issues are why Lycoming does not recommended LOP operations, because it is hard to get right all the time. They do hint at possible problems or damage with lean operations, but they don?t come out and say it. The fact is heat kills valves and high EGT/CHT is heat. There is more chance that you will screw up and operate a cylinder at peak EGT with LOP operations than with ROP operations. I think LOP operations done well are no problem but not done well, you may have cylinders near peak, which is max heat. Heat is bad for valves, and that is a fact. ROP operations are safer from a pilot workload standpoint and always possible on any engine.

Remember we take 4-channel-EGT/CHT & FF computers as standard equipment. Most GA planes have NO EGT, or one analog Alcor EGT gauge with a no number scale. Running RICH of peak is easier (safer) and will assure smoother operations, where LOP is harder to do well.

This is where the EFI comes in, that RV6ejguy promotes. In real time it can adjust the fuel mixture of each cylinder individually to get them in line with each other. This is also what the FADEC does. With a fixed mechanical FI system or Carb, like Lycoming's have, you have to play around with injectors, flowing cylinders on the bench, plug gaps, timing and exhaust. However is the engine does not have well matched cylinders than EFI may not allow LOP operations.

Bottom line is awareness of what EGT means or does not mean. Dan is right forget EGT "spread", it is NOT an ABSOLUTE VALUE. EGT "spread" is an indirect indication of relative power/mixture between cylinders and diagnosing engine health. The key word is INDIRECT. My be the word should be "INDIRECT EGT SPREAD". G

 

[chuck]

The speed loss with true LOP operation may offset any fuel savings at some point with an atmo engine.

I'm not sure that this is true. The next time I fly I will get some airspeed data to go with my fuel flow/egt/cht data, but suffice it to say that if an aircraft can fly the same speed ROP or LOP it will use less gas in the LOP condition AND it will do so at lower CHT's. Obviously the top speed of the aircraft will be highest with ROP operations since that represents max power.

I noticed on my RV4 (o360, balanced injectors (peak spread = .3gph), dual mags) that when running well lean of peak the EGT's actually began to increase again,while CHT dropped rapidly, engine roughness occurred.

The conclusion that I came to after much headscratching was that I was experiencing incomplete combustion and that the combustion had not completed before the EV opened, thus allowing still burning gasses to pass very close to the EGT sensor. Just a theory but it matches the data. I'm in the midst of setting up EI which 'should' provide a hotter spark w/wider gap to allow better combustion. If this theory is correct I should run smoother longer while LOP.

When complete I will post some numbers.

Chuck

 

[redbeardmark]

LOP ops and EI

This thread on LOP ops has been very educational. Thanks!

Another question: how does EI affect LOP ops? It probably doesn't matter from a FF spread point of view(FF doesn't care what produces the spark). But, does detonation become an issue?

Also, recently while flying XC at altitude, I switched my EI off and ran for a few seconds on the magneto(without adjusting mixture or throttle). All EGT's climbed markedly. The EI manufacturer said that this is normal because the fuel/air mixture is still burning when it leaves the cylinder when running on just the mag, but all of the fuel is burned prior to being expelled when running on EI. So, with EI getting better power output/efficiency AND cooler valves?

 

[rv6ejguy]

The EGT spread (Measured in ? of temperature) is the 100? we refered too above. The main reason that this can matter is smoothness. All probes and gauges being accurate, the temp is the measure of how much HP each cylinder produces. If running LOP the #1 produces 1500? and the rest 1250?, that tells me that #1 is producing significantly more power, which when at this extreme, will cause roughness.

The EGT really has no bearing on how much power a cylinder is producing. This was confirmed from inertial engine dyno testing which can separate individual cylinder torque measurements, combined with logged EGT measurements using low mass thermocouples.

EGT is mainly useful in determining stoichiometry, there are many other variables involved which can alter EGT which have little to do with variations in AFR. The AFR is really what we are interesting and EGT is only an indirect indicator of AFR.

Do typical carbed Lys have the same air flow to each cylinder? In most cases, I'd say no due to the intake manifold design.

Do most carbed Lycs have equal AFRs in each cylinder? See above.

Is it possible to get almost equal AFRs in a carbed Lyc? The answer would appear to be yes judging from the comments of some pilots here.

FI whether mechanical or electronic, main advantage is that only dry air, not fuel/air mixture is being conducted by the intake manifold. Air will tend to turn corners which fuel droplets will not. With a poor intake design, FI may not offer equal airflow still, in which case different injector flow rates will be needed to get equal AFRs in each cylinder. This being said, as soon as you have unequal airflow rates to each cylinder, you have unequal mass flow irregardless of AFR. This is what produces unequal power from each cylinder. Charge density has a big effect on flaggregation rates and this will often show up as EGT variations.

In the racing world, we strive to get equal airflow to each cylinder by flow benching each port and runner. This is only part of the story on injected engines as airflow is not steady state. With carbed and mechanically screw type supercharged injected engines with wet compressors, dry flow bench testing may be quite useless. Hence the invention of wet flow benches some even with pulsing capability. These uncover the dynamics of pulsing wet mixture flow, giving true insight into the dynamics and mixture distribution.

While we cannot tune each injector pulse width individually with our EFI system, others do have this capability. While this could equalize AFRs between each cylinder, it cannot correct mass flow differences.

It is interesting to note the different experiences of people here and the success that some are having with carbed Lycs and LOP operation. All this theory is great but perhaps meaningless in the real world where things really count. If it is working on your engine, by all means use it.

The one guy who reported an increase in EGT as he continued to lean well past peak could possibly benefit from an EI or programmable EMS which would increase spark advance at very lean mixtures.

This is a very interesting discussion and shows that we can all learn something from other's experiences. This is such a complex field that one's whole life could be spent experimenting and learning. I've been in this field for 25 years yet have only scratched the surface.

 

[gmcjetpilot]

Hummmm

Another question: how does EI affect LOP ops? It probably doesn't matter from a FF spread point of view (FF doesn't care what produces the spark). But, does detonation become an issue?

[snip] So, with EI getting better power output/efficiency AND cooler valves?

These are good questions. First detonation is an issue when you have early ignition. Detonation is the result of pre-ignition. Pre-ignition is from early timing, bad plug (cracked plug acting as a glow plug), high compression, high temps and poor fuel (low octane). Detonation is a spontaneous combustion of the fuel/air mixture, not in a controlled flame front but an all in one explosion. Pressures and temps can go thru the roof very fast and burn an aluminum piston. The problem in air-cooled aircraft engines is you can't hear it like you hear it in a car, when it "pings."

EI does help make more power, improving combustion, which improves economy in theory. Most report 3% or more fuel economy with an EI. In other words you are burning more or all the fuel with a longer hotter spark and not pushing un-spent gas out the pipes.

With EI are able to burn more fuel and make more power or make the same power with less fuel. EI is a double edge sword and you will run hotter (making more power you will make more heat). So if you have a cooling problem it will aggravate it. Weak ignition can waste fuel. A hot long spark will not cause detonation.

Timing advance of an EI by itself will not cause detonation but can if too much advance is used at too high of a power setting. That is why the timing curve in EI's (P-mag, LS, elctroair) use RPM/MAP to advance timing only below approx 75% power. You could make more power with advanced timing at high power but you would run into possible detonation issues. In aircraft a fixed 25 degrees BTD is uses and is conservative. With EI the timing advance does not happen until you get to below 75% power, where detonation margins are much wider (operating at lower temps and pressures). EI really comes into play on aircraft at high altitudes and lower power settings where the combo of hot spark and timing advance come into play. As the power goes down and you run leaner the flame front goes much slower which calls for timing advance. So with LOP operation timing advance is a plus. Again at low power and lea n mixture there is not enough pressure and temp to cause pre-ignition. Even if the actual timing was too far advanced, at a very low power setting there is not enough fuel or energy to cause damage, in theory. I think the EI limit total advance to about 40 degrees. With high compression pistions you have less detonation margin so timing should not be as aggressive. I know two of the EI make a timing curve for HC pistion engines.

THE EGT RISE PARODOX?
You would think that turning OFF the EI would cause the EGT to drop? In a sense when you turned your EI OFF, you where NOW rich. Even though you had the perfect stoichiometric mixture, the inefficiencies of the combustion chamber with one plug, it was burning late and while going out the exhaust. This flames out the stack effect is an indication of reduced timing and raw fuel going out the pipe. With one plug the flame front is too slow and is still burning thru part of the exhaust cycle. What happened when you turned the MAG off with the EI on? Nothing. With EI the mag is going along for the ride, especially when the EI starts to advance timing.

As far as LOP and EI it can't hurt. As the mixture is leaned the flame front slows down. To have a good hot spark, at the ideal timing can always help. How it affects LOP I am not sure. However if you are LOP you want slightly differnt timing advance than when running rich. A weak ill timed spark is never efficent.
G

 

[cobra]

George,
I think you may have some mistaken ideas mentioned recently- unless there is something truely unique with the Lyc, running it lean of optimum creates a lot more heat than running at optimum. Running it rich lowers the temps, and presumably lowers the egt as well.

Dentonation is caused by several factors, all important: too low octane (fuel burns too fast for design conditions), the biggest factor is HEAT (related to timing and fuel/air ratio), also important is the pressure (affected by compression ratio) in the combustion chamber. Detonation causes early ignition (not caused by it), and it can be compounded by preignition (additional flame front initiated by excessive heat, glowing carbon, etc) which I believe you were referring to.

Detonation is defined as a flame front that moves at, or faster, than the speed of sound, which creates a pressure spike (shock wave) that you often hear as a metallic knock. The shock wave creates pressures many times higher than normal burn rates, high enough to deform tear metal and break parts (often valves or rods). That pressure spike forces all the remaining fuel to burn instantaneously (explosion). If the pressure spike strikes the piston before it reaches TDC, all of that energy drives the piston, thru the almost vertical connecting rod, into the rod and main bearings and works against the normal crankshaft rotation. Normally the peak pressure is timed to arrive after TDC, which forces the piston downward and turns the crankshaft. In addition, excessive heat is geneated by detonation that often melts aluminum pistons.

In short, if you control heat, you control detonation. You control heat by setting a safe fuel air mix (rich of optimum), set ignition timing at a safe point (generally a bit before optimum), and by removing heat effectively (cooling system).

 

[gmcjetpilot]

Pre-ignition results in Detonation, not the other way around

George,
I think you may have some mistaken ideas mentioned recently- unless there is something truly unique with the Lyc, running it lean of optimum creates a lot more heat than running at optimum. Running it rich lowers the temps, and presumably lowers the EGT as well.

No I am not mistaken, read the previous post where he turned his single EI off in cruise, was running off one magneto, which caused his EGT's to rise, NOT DROP. This was the post I was addressing which also asked questions about (EI) electronic ignition and the affect it has on detonation and LOP operations.

The reasons for the EGT increase were due to overly rich mixture (fuel could not be burnt fast enough or soon enough due to poor single spark on one side of large piston). With the EI on, a hotter and earlier spark allowed him to run a richer mixture and make more power. The higher EGT was after the EI was turned off, raw gas was being burned in the pipes and not in the combustion chamber, inefficient to be sure. I understand the concept of rich mixture "cools" but why does turning off the EI cause an EGT ride? (Extreme rich condition and retarded timing); Dropping the advance of the EI off and going just to the fixed 25 degree timing of a Magneto (late timing) was what caused the EGT increase. At the lower power setting at cruise the flame front was so slow it was still burning when the exhaust valve was opening. That was one part of my post. The second part was addressing the affect EI has detonation and LOP Ops.

My explanation about "Flame front propagation" and detonation was general and accurate in explaining the roll of timing advance in economy and power. As power goes down or mixture is leaned the flame front slows down and you need earlier timing. That is why the fixed magneto timing of 25 degrees is so inefficient at low power settings. However it is clever that 25 degrees is simple and works well over a wide range of power settings. It also illustrates how narrow a power band we operate in with an aircraft engine.

Detonation is caused by pre-ignition (not the other way around). People don't understand detonation, it is a definition only not a cause, mechanism or reason, it is the result of pre-ignition only, period.) Detonation means just that, detonation: a sudden, spontaneous, un-controlled explosion.

Obviously if the EI provides timing is too far advanced (pre-ignition) at high power (high temp/pressure), boom, you can get detonation. However EI uses very conservative timing advance of fixed 25 degrees until 75% power and slowly advances to about 40 degrees at a vary low power.

Detonation is caused by several factors, all-important: too low octane (fuel burns too fast for design conditions), the biggest factor is HEAT (related to timing and fuel/air ratio), also important is the pressure (affected by compression ratio) in the combustion chamber. Detonation causes early ignition (not caused by it), and it can be compounded by pre-ignition (additional flame front initiated by excessive heat, glowing carbon, etc) which I believe you were referring to.

I is like spins, you CAN'T spin unless you stall first. Same with detonation, pre-ignition comes first before detonation. You state, "it can be compounded by pre-ignition". No, No, No, No , No, Pre-ignition comes first, not detonation. Detonation is a by-product of pre-ignition. Detonation describes the affect of combustion happing abruptly, that is all, that is it, nothing more. Detonation is not a cause or mechanism, it is just a definition of the type of combustion you have. YOU MUST HAVE PRE-IGNITION TO HAVE DETONATION. To say detonation causes pre-ignition is like the putting the cart-before-the-horse, or pre-flight you airplane while it is cruise flight.

I mention all the typical factors of pre-ignition, which in turns leads to detonation. Octane is only one and not the common reason for low compression aircraft engines running Avgas. I would reference Sacramento Sky Ranch Engineering manual, Lycoming and Continental.

Detonation is defined as a flame front that moves at, or faster, than the speed of sound, which creates a pressure spike (shock wave) that you often hear as a metallic knock. The shock wave creates pressures many times higher than normal burn rates, high enough to deform tear metal and break parts (often valves or rods). That pressure spike forces all the remaining fuel to burn instantaneously (explosion). If the pressure spike strikes the piston before it reaches TDC, all of that energy drives the piston, thru the almost vertical connecting rod, into the rod and main bearings and works against the normal crankshaft rotation. Normally the peak pressure is timed to arrive after TDC, which forces the piston downward and turns the crankshaft. In addition, excessive heat is generated by detonation that often melts aluminum pistons.

TRUE and that is what I said, spontaneous combustion all at once. Since the mechanism is pre-ignition and the combustion happens much faster and more abruptly than it is earlier, by definition detonation is early.

In short, if you control heat, you control detonation. You control heat by setting a safe fuel air mix (rich of optimum), set ignition timing at a safe point (generally a bit before optimum), and by removing heat effectively (cooling system).

True, but it is heat and pressure. Not sure what "set ignition timing at a safe point, bit before optimum" means, but I think you ment after optimum. Again if you understand pre-ignition you will understand what causes detonation. Detonation does not just happen, it needs the right ingredients. True, better cooling increases detonation margins. In low RPM, high torque, low compression aircraft piston engines air-cooling is adequate. Water-cooling is better, but most builders do not want to carry the extra burden (weight, installation, drag) of water-cooling in their aircraft when it is not needed. However there is a product called "cool jugs", which is water cooled cylinders for the Lycoming, making it sound like a car engine on the test stand. Amazing how quite the mechanical noise is reduced on a test stand when you wrap the suck, squeeze, bang, blow end of the engine in water. However all the prop and wind noise still does not make it quite. So do Subaru and Mazda guys fly with out headsets? Rotary engines are even louder than a Lycoming. So much for water cooling. G

 

[Tandem46]

I agree with George on this one, pre-ignition definitely comes before detonation, not the other way around.

Cobra, you say "I think you may have some mistaken ideas mentioned recently- unless there is something truely unique with the Lyc, running it lean of optimum creates a lot more heat than running at optimum. Running it rich lowers the temps, and presumably lowers the egt as well."

This can be misleading. It only holds true up to peak, but them after that all temps drop dramatically. When I run my IO-360 RV-7 LOP all my CHT's and oil temp drop way down. Matter of fact, during the winter sometimes I can't run LOP because the darn thing is too cool. Of course I'm talking cruise here, < than 75%. I'm always full rich on takeoff, at least at or near sea level.


Tobin

 

[rv6ejguy]

George,
I think you may have some mistaken ideas mentioned recently- unless there is something truely unique with the Lyc, running it lean of optimum creates a lot more heat than running at optimum. Running it rich lowers the temps, and presumably lowers the egt as well.

Dentonation is caused by several factors, all important: too low octane (fuel burns too fast for design conditions), the biggest factor is HEAT (related to timing and fuel/air ratio), also important is the pressure (affected by compression ratio) in the combustion chamber. Detonation causes early ignition (not caused by it), and it can be compounded by preignition (additional flame front initiated by excessive heat, glowing carbon, etc) which I believe you were referring to.

Detonation is defined as a flame front that moves at, or faster, than the speed of sound, which creates a pressure spike (shock wave) that you often hear as a metallic knock. The shock wave creates pressures many times higher than normal burn rates, high enough to deform tear metal and break parts (often valves or rods). That pressure spike forces all the remaining fuel to burn instantaneously (explosion). If the pressure spike strikes the piston before it reaches TDC, all of that energy drives the piston, thru the almost vertical connecting rod, into the rod and main bearings and works against the normal crankshaft rotation. Normally the peak pressure is timed to arrive after TDC, which forces the piston downward and turns the crankshaft. In addition, excessive heat is geneated by detonation that often melts aluminum pistons.

In short, if you control heat, you control detonation. You control heat by setting a safe fuel air mix (rich of optimum), set ignition timing at a safe point (generally a bit before optimum), and by removing heat effectively (cooling system).

Running LOP reduces EGT and CHTs. The excess of air cools the EGT, the lower energy content of the lean charge reduces the CHT.

Detonation does not cause early ignition. Detonation or knock is defined as a form of combustion which involves too rapid a rate of energy release producing excessive temperatures and pressures, adversely affecting the conversion of chemical energy into useful work. Detonation usually involves ignition and literal explosion of the end gases, these being the gases not in contact with the initial spark or the progressing flame front.

Detonation almost never melts anything but causes broken ring lands and blown head gaskets primarily. Pre-ignition melts holes in the piston crowns and removes the spark plug electrodes.

Heat has a lot to do with the initiation of pre-ignition but little to do with detonation which is a rate pressure rise related issue. Pre-ignition can cause detonation but not vice versa.

LOP operation is a viable mode for many aircraft engines. The Wright turbo compound engines were designed for this mode and to this day had some of the lowest SFCs of any piston Otto cycle engine.

 

[gmcjetpilot]

Thank you teacher

Detonation almost never melts anything but causes broken ring lands and blown head gaskets primarily. Pre-ignition melts holes in the piston crowns and removes the spark plug electrodes.

[snip]

LOP operation is a viable mode for many aircraft engines. The Wright turbo compound engines were designed for this mode and to this day had some of the lowest SFCs of any piston Otto cycle engine.

Learning is fun. Thanks for the info. G

Here are some cool pictures:
http://www.cancutter.com/photogallery/engine/index3.html
http://www.sacskyranch.com/eng180.htm
http://www.sacskyranch.com/deton.htm

 

[cobra]

I think we have a semantics problem here. Preignition is normally defined as the early burning of the fuel due to hot spots in the combustion chamber. I believe it is being used here in reference to any early initiation of the charge.

Detonation has a very specific meaning which comes from the explosives industry used by physicists/chemists. Detonation references the (supersonic) speed of the flame front; it is often measured by the amount of deformation of a test slug because the pressure rises so fast during detonation. It is also possible to have a slower "detonative-type" event, called a conflagruration, which also builds pressure slower and to a lesser peak.

I still have to disagree. Preignition does not necessarily cause detonation, but detonation can cause preiginition depending when the event occurs in relationship to the crankshaft throw location. An engine can run just fine (albeit with low power) with preignition- dieseling comes to mind (engine runs with key turned off).

Where preiginition gets dangerous is when it starts a second flame front on the other side of the combustion chamber- when the two fronts meet, detonation can result if there is enough heat or pressure present to initiate a pressure spike and posssibly detonation.

It is easy to force detonation without preignition (depending on your definition)- just reduce the fuel octane rating, increase the compression ratio, go excessively lean, or increase combustion pressures with a supercharger for example and hold everything else (spark timing) the same. If the mixture fires too early, detonation becomes a preignition, because of its relationship to the crankshaft.

The heat and pressure from detonation can and is involved in melting holes in aluminum pistons, especially when running very lean; it also breaks valves, head gaskets, and ring lands as mentioned. It happens quite often at the racetrack.

George, I was referring to an earlier post in reference to lean mixture:
Lean of Peak EGT (LOP): mixture is too lean and you have more air than needed. Since less fuel is being burnt there is less heat due to less combustion. This usually results in less power. Running LOP can result in lower temps than peak and less fuel burn, but extreme lean condition can result in combustion no longer being able to be supported.

 

[rv6ejguy]

I think we have a semantics problem here. Preignition is normally defined as the early burning of the fuel due to hot spots in the combustion chamber. I believe it is being used here in reference to any early initiation of the charge.

Detonation has a very specific meaning which comes from the explosives industry used by physicists/chemists. Detonation references the (supersonic) speed of the flame front; it is often measured by the amount of deformation of a test slug because the pressure rises so fast during detonation. It is also possible to have a slower "detonative-type" event, called a conflagruration, which also builds pressure slower and to a lesser peak.

I still have to disagree. Preignition does not necessarily cause detonation, but detonation can cause preiginition depending when the event occurs in relationship to the crankshaft throw location. An engine can run just fine (albeit with low power) with preignition- dieseling comes to mind (engine runs with key turned off).

Where preiginition gets dangerous is when it starts a second flame front on the other side of the combustion chamber- when the two fronts meet, detonation can result if there is enough heat or pressure present to initiate a pressure spike and posssibly detonation.

It is easy to force detonation without preignition- just reduce the fuel octane rating, increase the compression ratio, go excessively lean, or increase combustion pressures with a supercharger for example and hold everything else (spark timing) the same. If the mixture fires too early, detonation becomes a preignition, because of its relationship to the crankshaft.

The heat and pressure from detonation can and is involved in melting holes in aluminum pistons, especially when running very lean; it also breaks valves, head gaskets, and ring lands as mentioned. It happens quite often at the racetrack.

Pre-ignition is just as the name implies- ignition BEFORE spark initiation. Hot spots are not the only cause of pre-ignition. All that has to happen is that the charge reaches auto ignition temperature. The Merlins at Reno running up to 145 inches will run just fine with the mags turned off just as a Top Fuel drag engine will. The boost and charge temps are so high in these engines and everything so finely balanced, that the mixture lights off anyway as the piston approaches TDC. Part Otto cycle, part Diesel cycle. As such detonation can NEVER cause PRE-ignition by definition.

If you want to get really technical, observations by Miller, Hugonot and Becker back in the '40s supported by NACA high speed combustion chamber photography found six different types of auto ignition and three different types of spark knock. These studies showed that some types of knock do not need pre-ignition as an initiator but were set up by different vibratory frequencies within the burning gas. The speed of sound varies as the square root of the temperature. As temperatures and pressures vary widely during the cycle, many possibilities exist for setting up shock waves within the mixture, both burning and not burning. In severe, high frequency knock, the speed of the wave front has been measured at around 6800 fps.

Pre-ignition is dangerous in itself without multiple flame fronts. Remember that pre-ignition is PRIOR to spark discharge. Because the piston is still coming up the bore and chamber volume is decreasing, the liberation of heat is sped up because combustion rates increase with increasing charge density. Peak heat release and peak cylinder pressures occur prior to the optimal 15-20 ATDC. Now the energy (heat) goes into compressing the piston and rod without doing much useful work. Piston gets REALLY hot, really fast. Pre-ignition failure modes of parts are completely different from detonation failures and often confused or lumped together as one mode by many lay people.

The reason that detonation never causes heat/ melting failures is that the event is over in about 0.25 milliseconds and, like a flash fire, has no time to transfer heat to the parts. Detonation will shatter ring lands and crack pistons and spit out head gaskets due to the very high pressure spikes, but never melt a piston.

Combustion and knock studies done in 1999 in Australia using a Toyota 3S-FE engine and Motec EMS confirmed much earlier studies and also showed that mixture stength was a minor factor in detonation. These studies continued to be ignored by auto racers in general who have many wild, unsubstantiated theories about AFRs, best power and detonation/ pre-ignition.

 

[cobra]

Pre-ignition is just as the name implies- ignition BEFORE spark initiation. Hot spots are not the only cause of pre-ignition. All that has to happen is that the charge reaches auto ignition temperature. The Merlins at Reno running up to 145 inches will run just fine with the mags turned off just as a Top Fuel drag engine will. The boost and charge temps are so high in these engines and everything so finely balanced, that the mixture lights off anyway as the piston approaches TDC. Part Otto cycle, part Diesel cycle. As such detonation can NEVER cause PRE-ignition by definition

If detonation occurs before the spark, isnt it also defined as a preignition, by your definition? The difference is probably best explained by the pressure levels generated.

Good point about autoignition temp- the scientific/chemical explination of the point I was trying to make regarding heat as the real source of detonation. The other factors cause heat and set the stage for detonation.


The reason that detonation never causes heat/ melting failures is that the event is over in about 0.25 milliseconds and, like a flash fire, has no time to transfer heat to the parts. Detonation will shatter ring lands and crack pistons and spit out head gaskets due to the very high pressure spikes, but never melt a piston.

This makes good sense. The damage Ive seen at the track is probably the result of BOTH preignition AND detonation (as suggested before). The shock wave pushes right thru and burns the preignition heat-softened pistons (the weakest mechanical point in the combustion chamber). The damage generally follows heavy knocking (detonation) at full boost in a hot motor, and almost always when the motor was run too lean with too much spark advance.

Ive heard of some engine designs that attempt to use detonation as the normal event, mostly using exotic combustion chamber shapes, to get a lot more power and efficiency out of a motor. As far as I know, none have been successful yet- probably because of difficulties getting the piston timing correct. It should work in theory.

 

[rv6ejguy]

The big difference between detonation and pre-ignition is that detonation always involves the end gases and pressure wave initiation after a conventional or pre ignition event.

Certainly you can have both pre-ignition and detonation happening together. See what a piston looks like here after this: http://www.sdsefi.com/meltdown.htm

Miller's evidence and the testing in Oz conclusively showed a loss in power with detonation events and the thermodynamics of such experiments don't support hp gains by operating under detonation with Otto cycle engine.

 

[rv6ejguy]

I think the last question here which was on topic was whether LOP ops risked detonation. The answer is likley no at the cruise power settings recommended by Lycoming when using 100LL, standard magneto timing and stock compression ratios. Even turboed Lycs are not likely to encounter this due to the low boost pressures in cruise. 100LL is pretty good stuff. I've run road racing Toyota engines on it, 10 to 1 CR, 60 inches and 35 degrees of timing for 3 seasons. The engine was bulletproof. 200 hp/ liter specific output (that would be 720hp on an O-360)