Tetra-ethyl lead

[gismo]

My point is.......... there are options out there in case 100LL goes away, which you can bet is going to happen one day. You might need to sharpen up on your fuel comparison numbers too.

But none of the existing "options" will work in my engines (as well as a large number of other "high compression" aircraft engines. I do agree that 100LL's days are numbered for a number of reasons. What specifically would you suggest I "sharpen up" WRT fuel comparison?

 

[N801BH]

But none of the existing "options" will work in my engines (as well as a large number of other "high compression" aircraft engines. I do agree that 100LL's days are numbered for a number of reasons. What specifically would you suggest I "sharpen up" WRT fuel comparison?

In the grand scheme of things your " high compression" engines are not high at all.. For some reason you are convincing yourself that a viable option is not workable... Before I spend my time providing known facts to counter your claim that the fuel I suggested won't work maybe you can enlighten us all on the exact specs on "your engines" ie, bore/stroke/cam profile/overlap/ignition timing/ chts/egts/ and more important your beloved engines 'actual' compression ratio and any boost pressure that elevates that number, and what real numbers that are achieved by that boost.

I eagerly await you answer sir.

Ben.

 

[Trapper John]

I learned it at a flight instructor refresher course back in the 1970s. The instructor was a Lycoming fuels engineer and I took him at his word, since that was his profession. I never ran a chemical test on the fuel and I don't know if you did. I'm not sure I've ever seen a qualitative test procedure for TEL.

Jim

I saw a spec for 80/87. It indicated a maximum TEL content of 0.5g/gal. But it didn't have a minimum TEL content.


Trapper John

 

[poadeleted20]

My plane won't eat anything but 100LL.

What makes you say your engine requires lead? I don't think I know of any piston engine which requires the lead in 100LL and won't run on 100UL avgas which meets the ASTM D-spec.

 

[poadeleted20]

I cant tell you where I saw it... but I saw a statistic stating that 70% of the existing piston fleet could run on lead free gas....

but the 30% that couldnt... was responsible for 70% of the avgas sales by volume... big horsepower, single and multiengine commercial birds that fly every day.

I think you're confusing the 100-octane requirement of those engines with a requirement for lead. Those engines need 100-ocatane fuel, but they don't need the lead. The only reason there's lead in 100LL fuel is up to now that's the only way they could get the fuel to 100 octane, but it appears we're close to clearing that hurdle.

 

[poadeleted20]

The only engine that I know of the was rated for 100/130 is the TSIO-360-KB. in the PA28R-201T. that engine was de-rated to 201 to run 100LL. and will not be able to run 92OUL at that rating.

I don't believe that engine was derated to run 100LL vice 100/130, since they both have the same octane rating. Also, that engine is rated at 200HP, not 201, and AFAIK, always has been.

That said, it will not run as rated on avgas rated at 91-94 octane, and is an example of why they're going for a 100UL here rather than taking the 90-something UL they're using in Eastern Europe.

 

[Cap'n Jack]

I cant tell you where I saw it... but I saw a statistic stating that 70% of the existing piston fleet could run on lead free gas....

but the 30% that couldnt... was responsible for 70% of the avgas sales by volume... big horsepower, single and multiengine commercial birds that fly every day.

Maybe fom an AOPA pub?

It is estimated that approximately 30 percent of the existing GA piston engine fleet uses approximately 70 percent of all 100LL produced. Of those aircraft that use 70 percent of the 100LL produced, most demand the performance that 100LL provides.

References:
http://www.aopa.org/whatsnew/regulatory/regunlead.html 7 Mar 2010
http://www.aopa.org/members/files/pilot/2002/lead0205.html 7 Mar 2010

 

[Clark1961]

I don't believe that engine was derated to run 100LL vice 100/130, since they both have the same octane rating. Also, that engine is rated at 200HP, not 201, and AFAIK, always has been.

Since you're picking nits Ron, the TSIO-360-KB is rated 220 hp maximum output and 200 hp maximum continuous. The KB's fuel system is significantly different from the 200 hp TSIO360's.

The is an STC to upgrade my TSIO-360-FB to 220 hp but I'd have to buy the KB's fuel system.

 

[poadeleted20]

Since you're picking nits Ron, the TSIO-360-KB is rated 220 hp maximum output and 200 hp maximum continuous. The KB's fuel system is significantly different from the 200 hp TSIO360's.

The is an STC to upgrade my TSIO-360-KB to 220 hp but I'd have to buy the KB's fuel system.

As long as we're picking nits, the only engines put in the PA28R-201T were the Continental TSIO-360F/FB, not the -KB, and those engines keep their full 200HP rating with 100LL instead of the 100/130 for which they were originally certified. Offhand, I don't know what plane the -KB is in, but I'm still pretty sure its rated power (whatever it happens to be, STC or no) is unaffected by the use of 100LL.

 

[flyersfan31]

What makes you say your engine requires lead? I don't think I know of any piston engine which requires the lead in 100LL and won't run on 100UL avgas which meets the ASTM D-spec.

I didn't say it needed lead. 100LL, 100octane, cripes - do I have to specify the molecular structure? Dammit Ron, I'm a pilot, not chemical engineer!

My engine needs octane, and lots of it, according to engine-type peoples. I gotta go with what they tell me.

 

[poadeleted20]

I didn't say it needed lead. 100LL, 100octane, cripes - do I have to specify the molecular structure?

Here's what you said:

My plane won't eat anything but 100LL.

...and that's not true -- your engine will run fine on 100/130 (which obviously ain't comin' back), as well as on 100 octane unleaded avgas, because...

My engine needs octane, and lots of it, according to engine-type peoples.

...and 100UL will have the same octane as 100LL, so your engine will do fine with that, and the FAA and everyone else in aviation are fighting to make sure that the unleaded replacement for 100LL will meet the 100-octane spec.

 

[flyersfan31]

Here's what you said:
...and that's not true -- your engine will run fine on 100/130 (which obviously ain't comin' back), as well as on 100 octane unleaded avgas, because...
...and 100UL will have the same octane as 100LL, so your engine will do fine with that, and the FAA and everyone else in aviation are fighting to make sure that the unleaded replacement for 100LL will meet the 100-octane spec.

Agh! - I know, I know! I didn't bother to make the distinction between octane and lead. I didn't realize this was a test!

 

[Keane]

Agh! - I know, I know! I didn't bother to make the distinction between octane and lead. I didn't realize this was a test!

Actually, in an attempt to be even more pedantic, your plane doesn't need 'lots of octane', what it really needs is knock resistance in equivalence of pure octane. For example, you could possibly run pure ethanol at 116 AKI, which doesn't contain a single 'octane' molecule.

 

[Cap'n Jack]

Actually, in an attempt to be even more pedantic, your plane doesn't need 'lots of octane', what it really needs is knock resistance in equivalence of pure octane. For example, you could possibly run pure ethanol at 116 AKI, which doesn't contain a single 'octane' molecule.

If you want to play the game properly, the compound you describe as " pure octane" is really a branched pentane. The formal name is 2,2,4-trimethylpentane since the name of the hydrocarbon is formally based on the longest chain length in the molecule. The compound properly named "octane" is a straight-chain C8 molecule. An older name for 2,2,4-trimethylpentane is "isooctane"

Informally, octane as simply being defined as a simple hydrocarbon having 8 carbons and 18 hydrogens, has 25 isomers, including the stereoisomers.

 

[Keane]

If you want to play the game properly, the compound you describe as " pure octane" is really a branched pentane. The formal name is 2,2,4-trimethylpentane since the name of the hydrocarbon is formally based on the longest chain length in the molecule. The compound properly named "octane" is a straight-chain C8 molecule. An older name for 2,2,4-trimethylpentane is "isooctane"

Informally, octane as simply being defined as a simple hydrocarbon having 8 carbons and 18 hydrogens, has 25 isomers, including the stereoisomers.

Consider me out-pedanticized.

 

[flyersfan31]

Actually, in an attempt to be even more pedantic, your plane doesn't need 'lots of octane', what it really needs is knock resistance in equivalence of pure octane. For example, you could possibly run pure ethanol at 116 AKI, which doesn't contain a single 'octane' molecule.

Yes, yes, fine WHATEVER!!!!!!!!!!

UNCLE!!!!!!






My plane needs burny stuff to go vrooom!! Really burny stuff, not just kinda burny stuff, or else it gets broked.

 

[dmccormack]

My plane needs burny stuff to go vrooom!! Really burny stuff, not just kinda burny stuff, or else it gets broked.

Does it have to be liquid burny stuff? How about wood chips?

 

[kevin47881]

Does it have to be liquid burny stuff? How about wood chips?

Which leads to the question: how much wood would a woodchuck chuck if a woodchuck could chuck wood?

 

[Ted]

In the grand scheme of things your " high compression" engines are not high at all.. For some reason you are convincing yourself that a viable option is not workable... Before I spend my time providing known facts to counter your claim that the fuel I suggested won't work maybe you can enlighten us all on the exact specs on "your engines" ie, bore/stroke/cam profile/overlap/ignition timing/ chts/egts/ and more important your beloved engines 'actual' compression ratio and any boost pressure that elevates that number, and what real numbers that are achieved by that boost.

What would these known facts be, and are you stating that there would be no change in required operating limitations or performance for these "higher performance" engines?

Static compression ratios may seem low on aircraft engines, but BMEPs are surprisingly high, moreso than most street cars. In general, people who come from automotive engines seem to think it to be obvious that all aircraft engines can run on lower octane fuel. I've found most of them to be surprised once they actually start getting into detonation testing and see where the real limits exist. Everything is relative.

 

[vontresc]

Does it have to be liquid burny stuff? How about wood chips?

the wood gassifier may add a little too much unneccessary weight.

http://en.wikipedia.org/wiki/Wood_gas_generator

 

[gismo]

In the grand scheme of things your " high compression" engines are not high at all.. For some reason you are convincing yourself that a viable option is not workable... Before I spend my time providing known facts to counter your claim that the fuel I suggested won't work maybe you can enlighten us all on the exact specs on "your engines" ie, bore/stroke/cam profile/overlap/ignition timing/ chts/egts/ and more important your beloved engines 'actual' compression ratio and any boost pressure that elevates that number, and what real numbers that are achieved by that boost.

I eagerly await you answer sir.

Ben.

Bore x Stroke: 5.25 x 4.00 in
Compr ratio: 8.5:1 Normally aspirated
Ign timing: Fixed @ 22 BTDC
Rated HP: 285 @ 2625 RPM

WRT valve timing/overlap my recollection is that there's something like 20° (crank) of overlap but I can't find a reference right now and that could be wrong.

The TCDS for this engine gives a fuel requirement of:

Fuel (minimum grade aviation) 100LL,
100 per ASTM D910 or B95/130CIS

Redline CHT is 460°F but I normally keep cylinder temps at or below 380°F.

EGTs run around 1300°F at full power and 1400-1520°F in cruise flight.

It's my understanding that MON most closely represents the "Lean Octane" rating of gasoline fuel and therefore it will take a MON of 100 for a fuel to be viable as a replacement for 100LL. Other requirements are a fairly low vapor pressure, shelf life in excess of one year, compatibility with artificial and natural rubber plus other materials used in aircraft fuel systems. In addition an avgas replacement has to meet all these requirements when co-mingled with 100LL over a wide range of ratios.

 

[N801BH]

Bore x Stroke: 5.25 x 4.00 in
Compr ratio: 8.5:1 Normally aspirated
Ign timing: Fixed @ 22 BTDC
Rated HP: 285 @ 2625 RPM

WRT valve timing/overlap my recollection is that there's something like 20° (crank) of overlap but I can't find a reference right now and that could be wrong.

The TCDS for this engine gives a fuel requirement of:

Fuel (minimum grade aviation) 100LL,
100 per ASTM D910 or B95/130CIS

Redline CHT is 460°F but I normally keep cylinder temps at or below 380°F.

EGTs run around 1300°F at full power and 1400-1520°F in cruise flight.

It's my understanding that MON most closely represents the "Lean Octane" rating of gasoline fuel and therefore it will take a MON of 100 for a fuel to be viable as a replacement for 100LL. Other requirements are a fairly low vapor pressure, shelf life in excess of one year, compatibility with artificial and natural rubber plus other materials used in aircraft fuel systems. In addition an avgas replacement has to meet all these requirements when co-mingled with 100LL over a wide range of ratios.

Clearly the FAA in their infinate wisdom swings to the ultra conservative side.. 460 f for CHT is darn hot and will promote detonation big time. 22 degrees total advance is so retarded as to ensure a huge margin against detonation too. The drawback is that late of timing also promotes elevated exhaust temps which will eventually soak back into the engine itself thus raising the potential of detonation.. Teds comment on BMEP on large bore motors is correct too as the large surface of the 5 1/4" piston will create a fast rise in BMEP as it comes up to TDC. Your point of the ability of a new fuel to be able to co mingle with existing 100 LL stock is a valid point and one I didn't consider. Personally I would be comfortable with the Sunoco racing fuel in a flat aircooled motor but a 'blend' of both would be an area I would love to be involved in testing. I would think Ted and Lycoming would have been doing extensive testing on alternate fuels. Comments Ted ??

Ben.

 

[Capt. Geoffrey Thorpe]

Bore x Stroke: 5.25 x 4.00 in
Compr ratio: 8.5:1 Normally aspirated
Ign timing: Fixed @ 22 BTDC
Rated HP: 285 @ 2625 RPM

WRT valve timing/overlap my recollection is that there's something like 20° (crank) of overlap but I can't find a reference right now and that could be wrong.

The TCDS for this engine gives a fuel requirement of:

Fuel (minimum grade aviation) 100LL,
100 per ASTM D910 or B95/130CIS

Redline CHT is 460°F but I normally keep cylinder temps at or below 380°F.

EGTs run around 1300°F at full power and 1400-1520°F in cruise flight.

It's my understanding that MON most closely represents the "Lean Octane" rating of gasoline fuel and therefore it will take a MON of 100 for a fuel to be viable as a replacement for 100LL. Other requirements are a fairly low vapor pressure, shelf life in excess of one year, compatibility with artificial and natural rubber plus other materials used in aircraft fuel systems. In addition an avgas replacement has to meet all these requirements when co-mingled with 100LL over a wide range of ratios.

Swirl and / or tumble (I assume typically not used in aircraft engines) and squish will change the charge motion / mixing during combustion and will have a significant effect on the tendancy to knock. Good luck figuring out how much based on published data for your engine...

A little lead goes a long way. Typically, the knock index of a fuel blend (lead and no lead) will be higher than the average of the two individual fuels.

 

[Ted]

Clearly the FAA in their infinate wisdom swings to the ultra conservative side.. 460 f for CHT is darn hot and will promote detonation big time.

Well, let's look at a few things here. First off, limits are not goals. A lot of people don't seem to understand that. My Jaguar has a coolant temp gauge that actually works (unlike my Ford that has a coolant temp gauge that is processed through the computer to show normal for most temperatures). The engine may have upper limits, but it's well known in that realm that you're a complete idiot if you operate up there, the engine will not like it at all and you will, often times severely, reduce the life of the engine. Even on my big ol' iron block Cummins turbo diesel it was understood that the limits and the proper operating range were different. Why, then, do people take this common sense with their cars and not extrapolate it to their aircraft, which have far more expensive engines? Detonation tests need to be done at the limits, however, because there are times when the engines will operate there. I'm thinking climbing out on a hot day in Phoenix on a plane that has less than optimal cowl designs. Plus a lot of people don't have engine monitors.

22 degrees total advance is so retarded as to ensure a huge margin against detonation too. The drawback is that late of timing also promotes elevated exhaust temps which will eventually soak back into the engine itself thus raising the potential of detonation..

I'm not sure where that comes from. Ignition timing requirements vary on different engines. The goal is to get the peak cylinder pressure in such a time as to maximize the total work performed on the crankshaft. Dynamics come into play here and what the optimal ignition timing is will vary depending on all kinds of different parameters. I've not played with it much in several years, but my recollection on these engines is that you gain almost no power by advancing the timing, but you do decrease your detonation margin significantly. So I wouldn't make a statement like that.

Teds comment on BMEP on large bore motors is correct too as the large surface of the 5 1/4" piston will create a fast rise in BMEP as it comes up to TDC. Your point of the ability of a new fuel to be able to co mingle with existing 100 LL stock is a valid point and one I didn't consider. Personally I would be comfortable with the Sunoco racing fuel in a flat aircooled motor but a 'blend' of both would be an area I would love to be involved in testing.

I'd be careful being comfortable with a fuel on engines that you haven't done extensive detonation testing on. I don't think it's any secret that when you're running engines at low power, low CHTs, etc. that the detonation margins are significantly larger than when you're running high power, high CHTs, etc. One big problem, though, is that the fuel that you use needs to be able to handle all realms of the engine's operation, or else you have to give up performance somewhere and reset your limits. Those places would tend to be takeoff and climb performance, where the power matters the most. Alternately you may be able to get away with higher fuel consumption, but the point is the limits exist for reasons and you can't expect to get a free lunch.

Your Ford engine can make 300 hp out of 302 cubic inches without any sort of detonation concerns. It also has liquid cooling (lower combustion chamber temps), does it at a higher RPM with lower BMEPs (lower propensity to detonation), and I would highly suspect higher SFCs (lower efficiency). That higher SFC thing is a big deal. I have found that when most people give aircraft engines a close look with an open mind, they are generally impressed with just how well they do their jobs. Perfect? Of course not, but they're pretty darn good at what they do. My point is to be careful with assumptions on what fuels you can just put in and use without any issues. As you know, it's a more complicated subject.

I would think Ted and Lycoming would have been doing extensive testing on alternate fuels. Comments Ted ??

Last summer at Osh we had a seminar on fuels. If we repeat it this year, I'd suggest attending, there is a lot of useful information there.

 

[Capt. Geoffrey Thorpe]

(unlike my Ford that has a coolant temp gauge that is processed through the computer to show normal for most temperatures).

For the record, that came from either Toyota or Honda (I forget which) - they found that customers have "more confidence" in their vehicle if the "gauges" stay in the middle and don't move. Also it improved their "quality" statistics.

 

[N801BH]

Ted.. We are both on the same page and mostly agree on all the topics.. I am coming from a pretty extensive racing, R&D and machining background. You are coming from a manufacturing( Lycoming) background. MY objective is to maximize internal engine performance, you guys @ Lycoming are into supplying engines with the least amount of warranty work, ie, broken cranks, burnt pistons, burnt valves, cracked cylinders, broken rings and the list goes on and on. I fully understand the dynamics of internal combustion engines, in fact for a while in a previous life I had a pretty elaborate R&D company complete with a in house dyno. I have probably blown up more motors for customers on purpose to see what will fail then 99% of the guys reading this have changed oil on. From Lyc's point of view 22` of timing is a VERY conservative setting and my bet is it is determined by getting the motor out of warranty more then it is for obtaining maximum cylinder pressures.

As for my motor,,, I am always pushing the envelope and thats why I built an experimental..

Motor is a 302, stroked to 347 cu in. All Aluminum
10.4-1 compression flat top pistons
roller cam, roller lifters and it even has roller cam bearings.
timed to 34 degrees total advance, yeah, that is very conservative too.
I have advanced it to 39` for 100LL and no signs of detonation. 36 for 91 octane auto fuel, same results.
Plane has been tested to 17,995 msl on straight 100LL, on 91 auto fuel and also on 91 auto fuel with 10% ethanol. Ran perfect in all tests.
takeoff rpm is 4500, cruise at 2900-3100 rpm.
EGT @ takeoff is 1700 f +
cruise @ 1550 f
TB coating on piston heads, combustion chambers and exhaust ports.
BSFC is alot better then you suggest.

I am not arguing sir... Just pointing out my past life experiences and what is currently working for me in my unique situation.. YMMV.

Ps..Sunoco has gone through extensive testing on their no lead racing fuel and I am confident of its potential. With that said I am sure they could 'reformulate' it to achieve a higher octane rating without too much difficultly. Would they want to deal with all the nay sayers is another question, and quite frankly with all the pessimests I have seen come to the forefront that in itself would detract from any viable fuel company to attempt to venture into the aircraft no lead market. Just my .02 cents worth. Good luck to all you guys/gals who will have to deal with this issue

Tailwinds .

Ben
www.haaspowerair.com

 

[Ted]

Ted.. We are both on the same page and mostly agree on all the topics.. I am coming from a pretty extensive racing, R&D and machining background. You are coming from a manufacturing( Lycoming) background. MY objective is to maximize internal engine performance, you guys @ Lycoming are into supplying engines with the least amount of warranty work, ie, broken cranks, burnt pistons, burnt valves, cracked cylinders, broken rings and the list goes on and on. I fully understand the dynamics of internal combustion engines, in fact for a while in a previous life I had a pretty elaborate R&D company complete with a in house dyno. I have probably blown up more motors for customers on purpose to see what will fail then 99% of the guys reading this have changed oil on.

And was your background working on racing engines or street engines that were expected to last 100,000 miles without issue? I would also defend the stance that no street motor has to run at as high a duty cycle for as many hours as an aircraft engine is expected to.

From Lyc's point of view 22` of timing is a VERY conservative setting and my bet is it is determined by getting the motor out of warranty more then it is for obtaining maximum cylinder pressures.

Please re-read the following:

I've not played with it much in several years, but my recollection on these engines is that you gain almost no power by advancing the timing, but you do decrease your detonation margin significantly. So I wouldn't make a statement like that.

I will have to disagree with your statement that 22 degrees of timing is very conservative on these engines. I do not consider it to be conservative, I consider it to be an appropriate setting. Although 22 degree timing is a Continental number, Lycomings are generally 20-25 degrees.

As for my motor,,, I am always pushing the envelope and thats why I built an experimental..

Motor is a 302, stroked to 347 cu in. All Aluminum
10.4-1 compression flat top pistons
roller cam, roller lifters and it even has roller cam bearings.
timed to 34 degrees total advance, yeah, that is very conservative too.
I have advanced it to 39` for 100LL and no signs of detonation. 36 for 91 octane auto fuel, same results.
Plane has been tested to 17,995 msl on straight 100LL, on 91 auto fuel and also on 91 auto fuel with 10% ethanol. Ran perfect in all tests.
takeoff rpm is 4500, cruise at 2900-3100 rpm.
EGT @ takeoff is 1700 f +
cruise @ 1550 f
TB coating on piston heads, combustion chambers and exhaust ports
BSFC is alot better then you suggest.

And your engine sounds built the way that I would build an automotive engine for aircraft use, but I'd also ask what your BSFC is. I would definitely believe that you're running at a better BSFC than most people with engines like yours are, so I'd be curious to see how close it gets to actual aircraft engines.

I am not arguing sir... Just pointing out my past life experiences and what is currently working for me in my unique situation.. YMMV.

And I don't think I've said anything that suggests that your setup isn't working or that I'm arguing with anything about your setup. But, as you pointed out, this is working for you in your unique situation, and your engine is very different than an aircraft engine for a number of reasons. So, what you find to be conservative on engines you have tested may or may not be conservative on the engines we're discussing here.

Ps..Sunoco has gone through extensive testing on their no lead racing fuel and I am confident of its potential. With that said I am sure they could 'reformulate' it to achieve a higher octane rating without too much difficultly. Would they want to deal with all the nay sayers is another question, and quite frankly with all the pessimests I have seen come to the forefront that in itself would detract from any viable fuel company to attempt to venture into the aircraft no lead market. Just my .02 cents worth. Good luck to all you guys/gals who will have to deal with this issue.

And for experimentals there are a lot more options that you can work with (with associated risks) than for certified aircraft. The issue is more complex for certified production aircraft than most people seem to think.

As you know, Ben, I really like what you've done and have a lot of respect for it. I know you've got a lot of engine experience, but I have found time and time again that automotive engine experience has a few differences from aviation engines. The laws of physics are obviously the same, but the specific execution is slightly different.

 

[Dan Thomas]

From Lyc's point of view 22` of timing is a VERY conservative setting and my bet is it is determined by getting the motor out of warranty more then it is for obtaining maximum cylinder pressures.



Motor is a 302, stroked to 347 cu in. All Aluminum
10.4-1 compression flat top pistons
roller cam, roller lifters and it even has roller cam bearings.
timed to 34 degrees total advance, yeah, that is very conservative too.
I have advanced it to 39` for 100LL and no signs of detonation. 36 for 91 octane auto fuel, same results.
Plane has been tested to 17,995 msl on straight 100LL, on 91 auto fuel and also on 91 auto fuel with 10% ethanol. Ran perfect in all tests.
takeoff rpm is 4500, cruise at 2900-3100 rpm.
EGT @ takeoff is 1700 f +
cruise @ 1550 f
TB coating on piston heads, combustion chambers and exhaust ports.
BSFC is alot better then you suggest.

I presume, from the RPMs you give, that this isn't a direct-drive setup. Apples to oranges.

Aircraft engines run much slower that redrive auto engines, so that detonation has much more time to set in. The auto engines' high RPM requires more advanced timing since the piston reached TDC so much more quickly. They also have much smaller cylinders, typically with shorter strokes as well, so that normal combustion is completed much sooner and detonation has less time to start. Measurements on the combustion pressures have been taken in aircraft engines and the timing is predicated on those findings.

As mentioned earlier, detonation occurs ahead of the normal flame front as the pressure and therefore temperatures are rising and the complex, detonation-resistant fuel molecules begin to break down into simpler, autoignitable forms. This takes time, and the auto engine offers far less time than the aircraft engine for this to happen. The lower-octane rated fuels will run fine even when pushed in the auto engine, but will cause serious damage if we try to make them work in some aircraft engines.

Dan

 

[dmccormack]

This question is posed to all the engine experts who have responded so far:

What is the order of design priority for airplane engines? And how does lead/lead free fuel affect these design paramters?

• Efficiency
• Power output (per lb of mass)
• Longevity
• Maintainability (ease of access, remove & replace, etc)

 

[Capt. Geoffrey Thorpe]

This question is posed to all the engine experts who have responded so far:


What is the order of design priority for airplane engines? And how does lead/lead free fuel affect these design paramters?

• Efficiency
• Power output (per lb of mass)
• Longevity
• Maintainability (ease of access, remove & replace, etc)

dunno how the airplane engine company prioritizes, but lead or not lead is much less improtant than knock resistance ("octane"). (Note, any number larger than 100 is, by definition, not an "octane" number)

Increasing knock resistance lets you run higher compression (all other things (and there are a LOT of other things) being equal) which will increase efficiency and power.

Lead has some plusses and minuses for maintainance / longevity - Lead tends to foul plugs but valve seats need to be a better material for no lead (depends somewhat on engine speed range and cam profiles and...)

 

[N801BH]

I presume, from the RPMs you give, that this isn't a direct-drive setup. Apples to oranges.

Aircraft engines run much slower that redrive auto engines, so that detonation has much more time to set in. The auto engines' high RPM requires more advanced timing since the piston reached TDC so much more quickly. They also have much smaller cylinders, typically with shorter strokes as well, so that normal combustion is completed much sooner and detonation has less time to start. Measurements on the combustion pressures have been taken in aircraft engines and the timing is predicated on those findings.

As mentioned earlier, detonation occurs ahead of the normal flame front as the pressure and therefore temperatures are rising and the complex, detonation-resistant fuel molecules begin to break down into simpler, autoignitable forms. This takes time, and the auto engine offers far less time than the aircraft engine for this to happen. The lower-octane rated fuels will run fine even when pushed in the auto engine, but will cause serious damage if we try to make them work in some aircraft engines.

Dan

We are all thinking the same here with a few differences..

My motor is a redrive set up 1.43-1 so you observations is correct. But I am wondering about your apples to oranges comment.

As far as I know a GIO motor, that is one that has a reduction drive included in it has the exact same fuel requirments as a ungeared motor.. I am incorrect there?

 

[dmccormack]

As far as I know a GIO motor, that is one that has a reduction drive included in it has the exact same fuel requirments as a ungeared motor.. I am incorrect there?

The numbers for Lycoming's original Geared-Drive a/c motor (GO-145)would support that assumption.

The Lycoming site has this interesting tidbit:

Igor Sikorsky flew the first successful helicopter powered by a 65-horsepower GO-145

65 horsepower helicopter??? Wow!!!

 

[Ted]

As far as I know a GIO motor, that is one that has a reduction drive included in it has the exact same fuel requirments as a ungeared motor.. I am incorrect there?

You are correct, but even geared engines are still running significantly lower speeds than yours. I believe GTSIO and TIGO engines are in the 3400-3600 RPM range at rated. However they're geared to allow them to produce more power than their non-geared counterparts as a rule. So, the GTSIO-520s and TIGO-541s were producing 375-450 hp. That's taking the same BMEPs, cylinder pressures, etc. as the non-geared turbocharged engines, but since each cylinder ends up producing more power, you have more heat, which then means it's more difficult to cool.

I don't know how much power you're making, but you are running naturally aspirated. I seem to recall you telling me something in the 300 hp range at some point. So, let's say that puts you at comparable to some sort of naturally aspirated Lycoming or Continental 6-cylinder. While you may be running around 2/3 the displacement for that same power, you're also doing it at double the RPM.

 

[N801BH]

Not double the rpm.. I turn it 4400-4500 on take off for maybe 20 seconds. Then I lay the prop into it and bring the motor down to 3300 or so. That makes the motors you stated are revving higher then mine in cruise, or about the same. The difference is they are 550 cu in, mine is alot smaller in displacement and at 437 lbs complete, ie, fliuds, prop, redrive, exhaust etc. It is about half the weight of those geared aircraft engines. I have only had it down close to sea level once,, that was at OSH last year.. Full throttle gave me 24 gph, up here at 6700 asl I can get 17 gph or so. With my thermal barrier coatings = TBC, my BSFC is around .37.

 

[Ted]

The naturally aspirated 540s, 580s, 520s, and 550s are what are most comparable to yours, not the turbocharged and geared engines. In that case, takeoff RPM for the 540s and 580s are 2700 RPM, and then cruise typically between 2200 and 2400 RPM, depending on what power setting you want to run. So, your takeoff RPM is double, and then cruise RPM is in the 30-50% higher range, with your displacement in the 30-40% smaller range. So that makes sense.

An 0.37 BSFC is extremely impressive, beating just about any aircraft engine that I've seen even at its most efficient in cruise. I'd ask how that was measured, and at what power setting and mixture setting. Typical naturally aspirated Lycomings have about an 0.50 at best power and 0.40 at best economy, but those are very rough and depend on the specific engine.

I'm enjoying this information exchange.

 

[N801BH]

My.37 number is based on best economy.. WFO on take off is in the .42-.43 range.. One thing us in the experimental side can enjoy is trying cutting edge stuff. The Thermal Barrier Coatings are the road to the future and let me achieve that TE= thermal efficiency. Now when the real smart guys/gals engineers can perfect durable ceramics for internal engine parts then we will all see a dramatic decrease in fuel burn. Until then the homebuilt guys can experiment. Too bad the certified motors can't take advantage of those 'trick' but very functional coatings..

Tailwinds.

Ben.

 

[Dan Thomas]

You are correct, but even geared engines are still running significantly lower speeds than yours. I believe GTSIO and TIGO engines are in the 3400-3600 RPM range at rated. However they're geared to allow them to produce more power than their non-geared counterparts as a rule. So, the GTSIO-520s and TIGO-541s were producing 375-450 hp. That's taking the same BMEPs, cylinder pressures, etc. as the non-geared turbocharged engines, but since each cylinder ends up producing more power, you have more heat, which then means it's more difficult to cool.

And the geared aircraft engine still has much larger cylinders than the auto engine, so there's still more time for detonation to occur.

Dan

 

[N801BH]

And the geared aircraft engine still has much larger cylinders than the auto engine, so there's still more time for detonation to occur.

Dan

Time. ??

Now I am confused, the geared aircraft engine has a 4" stroke, mine is 3.400. Both engines are running about the same rpm at cruise,, 3300 or so. The aircraft engine has a higher piston speed because of the longer stroke. Higher speed means a shorter time for detonation to manifest itself... Now, I can see the fact that a larger combustion area can have a harder time creating a proper flame front which can lead to 'knock',,, but time ? Maybe you know something I don't.

 

[Capt. Geoffrey Thorpe]

Time. ??

Now I am confused, the geared aircraft engine has a 4" stroke, mine is 3.400. Both engines are running about the same rpm at cruise,, 3300 or so. The aircraft engine has a higher piston speed because of the longer stroke. Higher speed means a shorter time for detonation to manifest itself... Now, I can see the fact that a larger combustion area can have a harder time creating a proper flame front which can lead to 'knock',,, but time ? Maybe you know something I don't.

A larger bore tends to promote knocking because it takes the flame front longer to reach the walls. More time for the HC chains to disassociate. More time for heat transfer.

A more open chamber tends to promote knock for the same reason.

Lack of squish - ditto.

Less swirl or tumble, same.

Time is a big factor. Taylor and Taylor - Chapter 6 IIRC.

 

[Dan Thomas]

Time. ??

Now I am confused, the geared aircraft engine has a 4" stroke, mine is 3.400. Both engines are running about the same rpm at cruise,, 3300 or so. The aircraft engine has a higher piston speed because of the longer stroke. Higher speed means a shorter time for detonation to manifest itself... Now, I can see the fact that a larger combustion area can have a harder time creating a proper flame front which can lead to 'knock',,, but time ? Maybe you know something I don't.

That geared engine also has a bore of 5.25", while yours has a bore of 4". In terms of area, and therefore flame front travel time, the 520 cylinder takes longer to burn. With two sparkplugs this is reduced somewhat. A Lycoming 540 has a bore and stroke of 5.125" and 4.325". There are 541 cubic inches in six cylinders, or 90 cubes per cylinder, while your engine has about 43 cubes per, which would take a lot less time to consume, I'd think.

Dan