Van's Air Force
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75% power?
- Thread starter David-aviator
- Start date
Unless you have a GAMI spread of zero, it's not possible to take all the peak EGT's at one time hack.
I assume you can download and display your data in tabular format, six simple columns, time hack, four EGTs, and fuel flow? Set up in flight, pull mixture to where you are sure all cylinders are LOP, then creep the mixture forward very slowly (something like 0.1 GPH in 10 seconds) while recording. The tablular data will show all the individual peaks.
Do not use the EFIS/EIS system's peak function.
Of direct value here will be EGT at peak and 11:1 for the single cylinder where the wideband is installed. Yours is installed in a headpipe, or where?
Right. As noted, that would be inaccurate unless your GAMI spread is zero. One to three of the EGT values would be something less than peak. Averaging them would result in a false, low peak value, reducing the difference between "peak" and the 11:1 EGT.
Get tabular data with a very slow mixture sweep as above, then richen to 11:1 on the wideband indication and note EGT of the wideband-equipped cylinder. This assumes the wideband is installed in a single cylinder's headpipe.
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I don't have a wide band on all four , but it is after the "y" on the #1 and #2.
The delta is 147 and 159 respectively. I realize this is not as accurate as it could be if it was on only one, but given all the other variables and how close the numbers are Im confident this is within any margin of error that concerns me.... Heck...Prior to this I was flying with a carburetor and using the "big pull". Both of those egt measurements were taken after the temps were allowed to stabilize. One after finding peak and one after going full rich , which just happens to be 11 to 1. Not sure what a slow advance in mixture would make. I'm not trying to stir any kind of pot here, but it seems, at least as far as my o-360 is concerned, the delta from peak to 11-1 is closer to 150 than 200. Again I have electronic ignition that is certainly advanced at the low manifold pressure I was running, so maybe that's the difference. I'd be happy to provide any other flight data if someone tells me what they would like to see. Also if someone knows the j to K conversion ratio for thermocouples and would like to provide it to me, Savvy says they can fix the CHT issue.
The delta is 147 and 159 respectively. I realize this is not as accurate as it could be if it was on only one, but given all the other variables and how close the numbers are Im confident this is within any margin of error that concerns me.... Heck...Prior to this I was flying with a carburetor and using the "big pull". Both of those egt measurements were taken after the temps were allowed to stabilize. One after finding peak and one after going full rich , which just happens to be 11 to 1. Not sure what a slow advance in mixture would make. I'm not trying to stir any kind of pot here, but it seems, at least as far as my o-360 is concerned, the delta from peak to 11-1 is closer to 150 than 200. Again I have electronic ignition that is certainly advanced at the low manifold pressure I was running, so maybe that's the difference. I'd be happy to provide any other flight data if someone tells me what they would like to see. Also if someone knows the j to K conversion ratio for thermocouples and would like to provide it to me, Savvy says they can fix the CHT issue.
Like I said before, EGT is only a good indication of Stoich near peak (not at peak as we've learned) however even there, AFR varies with the type of fuel- 100LL, Swift, Summer/ Winter E0/ E10 blend Mogas etc. We might be at 14.4 for one type of fuel 15.4 for another- a full point variation.
This is a limitation of this method especially when you throw in changes in ignition timing that may be in play with slight changes in MAP and rpm (FP prop) as you change mixture. You cannot tell with any great precision what AFR might be on different engines on either side of peak. In the end, many people may simply lean to engine roughness and richen slightly to set LOP operation despite and cockpit instrumentation giving additional information. Having multi-probe EGT and WB AFRs just allows us to quantify in some way where mixtures are at. With low GAMI spreads and modern EIs, we may be able to get all the way into the 18s for AFR which is where best efficiency is predicted however the roughness issue will limit leaning no matter what whiz bang gauges we have in the cockpit.
I'd argue that AFR is what matters with regard to what we are trying to achieve and EGT is an indirect method to ballpark AFR since it isn't AFR. This is a reason why today in the modern automotive performance tuning and OEM ECM tuning world, direct AFR measurement is used as the primary tool and EGT as a rather secondary tool. We have the advantage there that individual port flow is usually pretty close due to better design of the entire induction system so cylinder to cylinder AFR variation is generally much smaller than what we'd see on a typical OEM Lycoming.
With equal airflow, equal fuel flow, equal exhaust flow and equal EGT probe placement/ orientation, we should have near equal EGT in each cylinder and near zero GAMI spread. This is the expectation in the auto engine world and the goal probably achievable through modification in the Lycoming world (flow benched matched components and revised aftermarket intake systems).
Why this is so important in the automotive world is emissions and catalyst performance. We can't have one cylinder at 14 and another at 16 AFR to have ideal catalyst performance. Most people would be staggered if they found out what factors are considered and designed around to achieve the best possible performance on the least amount of fuel and emissions in the automotive world. This advances understanding and raises the bar IMO over what is being done at the OEM level over legacy aircraft engines today.
Granted, aircraft piston engines don't have to worry about emissions (luckily) or operating at continuously varying load and rpm levels like auto engines and they are pretty darn fuel efficient running LOP at steady state cruise but they are a ways from optimal as delivered from the OEM. This is the reason for aftermarket intakes, flow benched cylinders, GAMI injectors and injector restrictors- attempts to correct design/ manufacturing deficiencies present in the OEM product.
I'll say it again, low GAMI spread achieved by changing individual injector flow rate is useful but really a partial patch for the actual cause in the first place. Makes people feel good watching that close alignment but all cylinders are not doing equal work which is what we should really be striving for. People have become fixated on low GAMI spread in the aircraft world with only a few companies (mainly on the race and performance side) tackling the actual problem with better designed and produced components.
As I side note of interest, The one customer who has 1700+ hours on the EFI got 400 hours out of his first WB (4.2 sensor). It was still working fine but he installed a new exhaust system and sensor at the same time. He now has another 300 hours on the second sensor. He burns 100LL exclusively and does not use a lead scavenger chemical. He runs LOP all the time in cruise.
This is a limitation of this method especially when you throw in changes in ignition timing that may be in play with slight changes in MAP and rpm (FP prop) as you change mixture. You cannot tell with any great precision what AFR might be on different engines on either side of peak. In the end, many people may simply lean to engine roughness and richen slightly to set LOP operation despite and cockpit instrumentation giving additional information. Having multi-probe EGT and WB AFRs just allows us to quantify in some way where mixtures are at. With low GAMI spreads and modern EIs, we may be able to get all the way into the 18s for AFR which is where best efficiency is predicted however the roughness issue will limit leaning no matter what whiz bang gauges we have in the cockpit.
I'd argue that AFR is what matters with regard to what we are trying to achieve and EGT is an indirect method to ballpark AFR since it isn't AFR. This is a reason why today in the modern automotive performance tuning and OEM ECM tuning world, direct AFR measurement is used as the primary tool and EGT as a rather secondary tool. We have the advantage there that individual port flow is usually pretty close due to better design of the entire induction system so cylinder to cylinder AFR variation is generally much smaller than what we'd see on a typical OEM Lycoming.
With equal airflow, equal fuel flow, equal exhaust flow and equal EGT probe placement/ orientation, we should have near equal EGT in each cylinder and near zero GAMI spread. This is the expectation in the auto engine world and the goal probably achievable through modification in the Lycoming world (flow benched matched components and revised aftermarket intake systems).
Why this is so important in the automotive world is emissions and catalyst performance. We can't have one cylinder at 14 and another at 16 AFR to have ideal catalyst performance. Most people would be staggered if they found out what factors are considered and designed around to achieve the best possible performance on the least amount of fuel and emissions in the automotive world. This advances understanding and raises the bar IMO over what is being done at the OEM level over legacy aircraft engines today.
Granted, aircraft piston engines don't have to worry about emissions (luckily) or operating at continuously varying load and rpm levels like auto engines and they are pretty darn fuel efficient running LOP at steady state cruise but they are a ways from optimal as delivered from the OEM. This is the reason for aftermarket intakes, flow benched cylinders, GAMI injectors and injector restrictors- attempts to correct design/ manufacturing deficiencies present in the OEM product.
I'll say it again, low GAMI spread achieved by changing individual injector flow rate is useful but really a partial patch for the actual cause in the first place. Makes people feel good watching that close alignment but all cylinders are not doing equal work which is what we should really be striving for. People have become fixated on low GAMI spread in the aircraft world with only a few companies (mainly on the race and performance side) tackling the actual problem with better designed and produced components.
As I side note of interest, The one customer who has 1700+ hours on the EFI got 400 hours out of his first WB (4.2 sensor). It was still working fine but he installed a new exhaust system and sensor at the same time. He now has another 300 hours on the second sensor. He burns 100LL exclusively and does not use a lead scavenger chemical. He runs LOP all the time in cruise.
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David-aviator
Well Known Member
"What do these charts tell you?"
Confusion.
I thought 100 ROP was best for power?
These charts indicate more power at peak EGT than 100 ROP.
Should I be doing power runs at peak EGT to get best TAS?
Confusion.
I thought 100 ROP was best for power?
These charts indicate more power at peak EGT than 100 ROP.
Should I be doing power runs at peak EGT to get best TAS?
brad walton
Well Known Member
So if we have bench flow matched cylinders and change orifices to approuch a 0 GAMI spread, are we adjusting for variance in air flow to individual cylinders or a variance in fuel flow from the spider valve, or both? If both, how can we quantify these variables in a home workshop/hangar environment?
brad walton
Well Known Member
The reason I bring this up is because in the situation where the variance is caused by a difference in airflow between cylinders, there will be a corresponding difference in horsepower each cylinder is producing. But to the extent the difference in restrictor size is necessitated by the pressure from each spider valve outlet, the HP output of the individual cylinders will not be different.
No they don't.
RVbySDI
Well Known Member
What do these charts tell you?
It looks to me that in Fig A-18 the peak EGT for SWIFT is around 1560ish. At that EGT the HP is 197ish. At around 1460ish EGT the HP is 200. That sure looks like best power is around 100 ROP to me on SWIFT fuel. The numbers are slightly different for 100LL but relationally the same.
David-aviator
Well Known Member
Weasel
Well Known Member
First....That someone should have sized the charts with the same range on each parameter.
Second, That with varying fuels, a/f ratio alone would be difficult when determining best power but rich of peak value would be pretty useful.
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The best power EGT relationships are the same (here roughly 100 ROP for either fuel), but the best power AF ratio is very different.
The pilot who sets mixture by reference to EGT would fly either fuel with no change in procedure...find peak, enrich 100, fly fast. Find peak, lean 30, 50, 80, whatever, and fly cheap.
A pilot who sets mixture with a wideband would need to know the appropriate ratios for all fuels he might purchase...assuming accurate FA information gets published. Oh, and things would get really interesting with a mixed fuel load.
Don't blow it off. We've gone a long time with (generally) only one piston aviation fuel on the ramp, that being 100LL. However, the not-so-distant future is likely to include more variety.
That's right....it isn't AFR. So what? On the ROP side all you want is a reliable way to find best power. On the LOP side there is nothing to target.
The pilot who sets mixture by reference to EGT would fly either fuel with no change in procedure...find peak, enrich 100, fly fast. Find peak, lean 30, 50, 80, whatever, and fly cheap.
A pilot who sets mixture with a wideband would need to know the appropriate ratios for all fuels he might purchase...assuming accurate FA information gets published. Oh, and things would get really interesting with a mixed fuel load.
Don't blow it off. We've gone a long time with (generally) only one piston aviation fuel on the ramp, that being 100LL. However, the not-so-distant future is likely to include more variety.
That's right....it isn't AFR. So what? On the ROP side all you want is a reliable way to find best power. On the LOP side there is nothing to target.
rzbill
Well Known Member
Earlier in this thread there were comments about the need for a torque meter.
I had a thought that maybe we don't need an absolute torque meter but rather a method to measure differences in torque from one set of conditions to another.
A measure of average "twist" of the engine relative to the engine mount might give a useful indication.
Just speculating, maybe an LVDT or a simple linear pot, like the flap indicators that are popular here could be hooked up. Or even a liquid filled cylinder and pressure gage.
I had a thought that maybe we don't need an absolute torque meter but rather a method to measure differences in torque from one set of conditions to another.
A measure of average "twist" of the engine relative to the engine mount might give a useful indication.
Just speculating, maybe an LVDT or a simple linear pot, like the flap indicators that are popular here could be hooked up. Or even a liquid filled cylinder and pressure gage.
