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  #61  
Old 06-12-2015, 04:25 PM
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rv6ejguy rv6ejguy is offline
 
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Originally Posted by GEM930 View Post
Not wanting to cause too much of a thread drift.... but... does anyone know approximately how may degrees ROP an O-360 will run full rich? I have an EFI system and can adjust the range of mixture adjustment. I'm seeing around a 275 degree decrease in EGT from peak to full rich. Does this sound about right? I don't remember the the MP, but I was not WOT and at around 4000' on a hot (72 OAT at that altitude) day- if that matters. My fuel flow seems fine at take off and full rich(approx 17 gal/hr). I'm asking because I only have so much range on the mixture adjustment and the leanest I can get is about 35 degrees lean of peak. If the 275 on the rich side is too much, I could off set the entire fuel map to the lean side and be able to run even leaner than 35 degrees. It is still running great at 35 degrees LOP (no sign of stumble) and I'd like to see if it would be more efficient at an even leaner setting. My GAMI spread is less than .3 gal/hour. Additionally, I could increase the fuel flow on the fuel map at high mp settings to maintain the 17 gal/hr for take off. Anyone know???
Yes, you should probably re-map towards the lean side. 275 ROP is very rich (theoretically around 9.5 AFR which should be near the rich misfire range and there is no reason to operate there as power is reduced noticeably and fuel flow is very high. As David said, no reason to run richer than about 11.0 AFR, call that around 150F ROP.
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  #62  
Old 06-12-2015, 05:03 PM
GEM930 GEM930 is offline
 
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Thx Ross!

I was hoping you would chime in! I actually have another question I think you might be able to help with as well, but that would be a huge thread drift. Look for a "mag drop" question with electronic ignition.

GEM
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  #63  
Old 06-13-2015, 07:30 AM
APACHE 56 APACHE 56 is offline
 
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Default Recommend you declare victory

I've been following this post with interest. I see two major things wrong with the methodology and goal.

First is the idea of determining 75% power is impossible to know until DanH comes up with a torque meter (that we can all borrow). Further we don't have a good grasp on propeller efficiency. I think I recall from one of my old flight test manuals the military used a figure of 0.78 as it was too difficult or impossible determine the actual number.

Second is your instrumentation. Did you use a sensitive altimeter, a sensitive air speed indicator. These are flight test calibrated instruments and expensive. Further, was your pitot system on an extended boom out in the free stream mounted on a swivel head? You were within 1% of Vans numbers but I'll bet you error bars are greater than 5%.

I would declare victory.
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  #64  
Old 06-13-2015, 07:44 AM
David-aviator David-aviator is offline
 
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Originally Posted by APACHE 56 View Post
I've been following this post with interest. I see two major things wrong with the methodology and goal.

First is the idea of determining 75% power is impossible to know until DanH comes up with a torque meter (that we can all borrow). Further we don't have a good grasp on propeller efficiency. I think I recall from one of my old flight test manuals the military used a figure of 0.78 as it was too difficult or impossible determine the actual number.

Second is your instrumentation. Did you use a sensitive altimeter, a sensitive air speed indicator. These are flight test calibrated instruments and expensive. Further, was your pitot system on an extended boom out in the free stream mounted on a swivel head? You were within 1% of Vans numbers but I'll bet you error bars are greater than 5%.

I would declare victory.
Thank you Don.
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  #65  
Old 06-13-2015, 09:44 AM
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Originally Posted by David-aviator View Post
EGT range from rich to peak has no relevance, the numbers are only useful when going LOP or ROP for performance.
The standard test for determining if full rich is in fact rich enough is to climb to 24", set 2400 RPM, allow time to stabilize with mixture full rich, record all EGTs, then lean to peak, recording peak value for each EGT in turn. The difference between full rich and peak should 175-225F. Max power centers about 125 ROP, so the 175 end at full rich is preferred if you want the power you paid for.

The above is an upper limit power setting for this test. Data says some angle valve motors will exhibit significant detonation intensity at this setting IF cylinder heat, oil, and intake air temperatures are at their limits. Should be OK with at normal temps (like 375 CHT, 185 oil, and 60F intake), so let it cool off after climb.

Quote:
Originally Posted by rv6ejguy View Post
As David said, no reason to run richer than about 11.0 AFR, call that around 150F ROP.
Call it around 200 ROP.

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Originally Posted by APACHE 56 View Post
First is the idea of determining 75% power is impossible to know until DanH comes up with a torque meter (that we can all borrow).
You might be amused to know that the idea of a community torque meter was heavily discussed on the old AirSoob BB back in the 90's. The goal was a propshaft extension with a wheatstone bridge strain gauge set, and the necessary electronics to get the signal off the rotating shaft. It would provide torsional vibration information at any RPM, and mean torque for computing HP.

Later I actually did build such a propshaft as part of a redrive designed for a Suzuki...which made 68.4 measured HP.

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  #66  
Old 06-13-2015, 01:45 PM
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Call it around 200 ROP.
This one reason why EGT is not a great relative measure other than at peak EGT (stoich) which is about 14.7 AFR on gasoline (no ethanol added). If your peak was 1600F or 1400F, the degree ROP or LOP is a percentage of that in relation to AFR, not a fixed amount. If you peaked at 1450F, 11 to 1 AFR should theoretically be at around 120-150F ROP, probably not 200.

Many other factors change EGT like CR and ignition timing as well as I've mentioned before. The CR is fixed on a specific engine, timing with an EI could making measurable differences in EGT that you're not aware of. A change of CR on the same engine will change the peak EGT so you'd need to establish some new data in that case.

Want to know AFR, use a wideband, not EGT. EGT is useful to look at cylinder to cylinder AFR spread indirectly but be aware that other small variables may influence this accuracy. When splitting hairs, it's important to know what the experimental error is and don't blindly assume instrumentation is displaying super accurate information.

I've seen rich misfire on different engines as lean as 10.2 AFR (about 87% of peak EGT) and the theoretical max rich point of about 8.8 AFR (about 77% of peak EGT). Most low cost wideband setups can measure 10 to 20 to 1 or 9ish to 18 to 1, depending on scaling and sensor technology type.

There's no good reason to operate an engine close to the rich misfire point at 75% power, especially an atmo one, therefore no good reason to be running 200F ROP on your average Lycoming unless you are running high CR, high IATs and high CHTs on mogas where this would offer less chance of detonation.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 441.0 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi2.htm



Last edited by rv6ejguy : 06-15-2015 at 05:40 PM.
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  #67  
Old 06-14-2015, 10:13 AM
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Originally Posted by rv6ejguy View Post
If you peaked at 1450F, 11 to 1 AFR should theoretically be at around 120-150F ROP, probably not 200.
Data please.

Quote:
Many other factors change EGT like CR and ignition timing as well as I've mentioned before. The CR is fixed on a specific engine, timing with an EI could making measurable differences in EGT that you're not aware of. A change of CR on the same engine will change the peak EGT so you'd need to establish some new data in that case.
So show us some data.

Quote:
Want to know AFR, use a wideband, not EGT.
Right now, leaded fuel apparently makes it necessary to install the wideband sensor very near the exhaust port of a single cylinder, if it is expected to have any lifespan at all. That means the wideband only tells the operator the AF ratio of that individual cylinder.

Quote:
When splitting hairs, it's important to know what the experimental error is and don't blindly assume instrumentation is displaying super accurate information.
Absolutely agree. Tell us why should we assume a wideband meter is accurate, or remains accurate in a leaded fuel environment?

Quote:
There's no good reason to operate an engine close to the rich misfire point at 75% power, especially an atmo one, therefore no good reason to be running 200F ROP on your average Lycoming unless you are running high CR, high IATs and high CHTs on mogas where this would offer less chance of detonation.
Again agree...but nobody said you should operate at 200 ROP at 75%. I posted a standard test to determine if there was enough range of mixture adjustment....or if you have a cylinder with a fuel delivery problem.
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  #68  
Old 06-14-2015, 11:44 AM
David-aviator David-aviator is offline
 
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Originally Posted by DanH View Post

Right now, leaded fuel apparently makes it necessary to install the wideband sensor very near the exhaust port of a single cylinder, if it is expected to have any lifespan at all. That means the wideband only tells the operator the AF ratio of that individual cylinder.

It does.

But one can check EGT activity of all cylinders and get a sense of how helpful a single O2 sensor might be. If the cylinders are peaking near the same fuel flow the single A/F indication will be reasonably accurate and helpful.

Truth is all engines with O2 sensors have a similar issue, one sensor with all the exhaust mixed up in one pipe, you do not know how each cylinder is doing.

I am going with a single EI with A/F ratio sensing because I have a feeling take off power right now is much richer than it needs to be. But I have no way of knowing just how rich it is.

Indications are a sensor mounted near the cylinder in accordance with instructions is immune to O2 build up, have been told one such unit has 400 hours and is ok.
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Last edited by David-aviator : 06-14-2015 at 11:47 AM.
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  #69  
Old 06-14-2015, 06:55 PM
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rv6ejguy rv6ejguy is offline
 
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Dan,

Well I'm looking at a graph here plotting Lambda vs % of peak EGT. 0.75 Lambda (close to 11 AFR) shows about .92 of peak EGT. At 1450F peak, that would be 120F if we rounded to the nearest 5. To be 200 ROP you'd be around 9.8 AFR. Let's get back to David's original idea of looking for best power mixture. That's around 50-75F ROP.

You know as well as anyone that ignition timing changes EGT. With many EIs you have no idea what the MAP and RPM curves are. With a FP prop especially as you pull lean and lose power and rpm, you may also trigger a different amount of total advance, hence making a change in EGT not related to mixture. Humidity effects even slow flame speed and can change EGT. I know you have the texts to look this stuff up. My comment was simply illustrating that under different conditions, the peak EGT value may not always be the same whereas AFR is always AFR.

Where are you getting this info about O2 sensor life from Dan? I had 195 hours on my O2, mounted after the turbo which is 200F colder than the port running on 100% avgas in those days. We have hundreds of people running O2s on aircraft, mounted well downstream. I know of one with over 450 hours on his now. Lots of guys are running mixes of avgas and mogas. As long as they run Decalin, most folks are seeing decent sensor life on 100LL and most have never replaced one running unleaded fuel. We are generally using them for initial tuning anyway and they always last long enough for that purpose, even on 100LL and no Decalin in my experience. You can read some specs if you search the file 57005 Motec. I would recommend changing the sensor at 100 hours when running on 100LL and Decalin and 200-250 hours on mogas due to known issues with sensor drift and aging. Bosch's data documents these effects, which have been reduced with the new 4.9 sensors over the 4.2 sensors.

The PLX WB has a push to test feature as well and an auto warning when data is invalid. Easy to check as you peak in any case, look for 14.7.

Um, why would you want to run at sub 10 to 1 AFRs at any time? You're just sooting stuff up, washing the bores and wasting money.

Pretty much everyone tuning engines today uses WBs, even with heavily leaded race gas (sensor life my be limited in these cases to under 15 hours). Replacement Bosch sensors are around $60 if you toast one, hardly big coin.

I like to use both EGT and WBs for information. I consider them complimentary.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 441.0 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi2.htm



Last edited by rv6ejguy : 06-15-2015 at 05:41 PM.
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  #70  
Old 06-15-2015, 07:09 AM
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Quote:
Originally Posted by rv6ejguy View Post
Well I'm looking at a graph here plotting Lambda vs % of peak EGT.
Can we see it, please?

Quote:
If you peaked at 1450F, 11 to 1 AFR should theoretically be at around 120-150F ROP, probably not 200.
I have a personal interest in the behavior of angle valve cylinder heads, so it's nice to see charts like this one, an IO-540K on the FAA dyno. At 11 AF, EGT is 1320. Peak is 1535, the difference being 215F:



Quote:
Let's get back to David's original idea of looking for best power mixture. That's around 50-75F ROP.
Same chart. Best power (magenta) is 135 ROP. 50 ROP (orange) is somewhat less than best power, and a wee bit into detonation onset given a cylinder at CHT limits

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Last edited by DanH : 06-15-2015 at 02:16 PM.
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