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-   -   100LL Future and Engine Purchase Concerns (https://vansairforce.net/community/showthread.php?t=163606)

mjanduda 08-28-2018 04:41 PM

Quote:

Originally Posted by rv6ejguy (Post 1284298)
Computer controlled fuel and spark has lots to do with it too. At least we can add those parts to help out the old Lyc these days. We can retard the spark at high MAP to avoid detonation and re-advance when MAP is lower to gain back the power and efficiency. Can't do that with mags.

Back to the first question in this thread:
You think by using modern ignition systems you can use MOGAS on an IO-390 without engine modifications and without losing lots of power or lifetime?

rv6ejguy 08-28-2018 06:54 PM

Quote:

Originally Posted by mjanduda (Post 1284302)
Back to the first question in this thread:
You think by using modern ignition systems you can use MOGAS on an IO-390 without engine modifications and without losing lots of power or lifetime?

Yes. 390s are base timed at 20 degrees already which is conservative. The 8.7 CR is not too high. Once the MAP drops below about 27 inches, you should be able to run the full 20 degrees on 91 octane. You might give up 5-7hp running 18 degrees at SL. No negative impact on engine life.

BMC_Dave 08-29-2018 12:04 AM

Quote:

Originally Posted by rv6ejguy (Post 1284320)
Yes. 390s are base timed at 20 degrees already which is conservative. The 8.7 CR is not too high. Once the MAP drops below about 27 inches, you should be able to run the full 20 degrees on 91 octane. You might give up 5-7hp running 18 degrees at SL. No negative impact on engine life.

How about 87E10 in a IO-540 with 7.2:1? :O

rv6ejguy 08-29-2018 04:09 AM

Quote:

Originally Posted by BMC_Dave (Post 1284365)
How about 87E10 in a IO-540 with 7.2:1? :O

Same thing applies, reduce total timing down to 20ish at sea level MAPs, by 25 inches, I'd think you could be back up to 24-25 degrees total. Would cost you a few ponies at SL vs. 91 octane. You'd have to weigh the cost vs. power de-rating of the two fuels.

F1R 08-29-2018 06:20 AM

Have a look at this
 
Quote:

Originally Posted by BMC_Dave (Post 1284365)
How about 87E10 in a IO-540 with 7.2:1? :O

https://youtu.be/K46IJV0Lg24?t=8s

Here is an STC'd $12,000 water injection system for IO 520 Continentals
If you watch the first 2 minutes you will see the MP and CHT values the system starts flowing at. Mostly at take off power settings with MOGAS

A slightly different tool to address pre ignition / detonation that lets you maintain high MP and normal advance for rated HP output.

jacoby 08-29-2018 08:06 AM

Quote:

Originally Posted by Mudfly (Post 1284297)
This is from the Shell link I listed on post 1. (Avgas Fact and Future).
Is this relative to mjanduda's question? Last paragraph mainly.

"Octane rating is a measure of how resistant a fuel is to detonation or "pinking"; the higher the Octane rating, the more the fuel / air mixture can be compressed without detonation happening. To make this clear, octane rating is not a measure of the amount energy in the fuel, but is a measure of its resistance to detonation.

The advantage or higher octane fuels is that a higher compression ratio or supercharging ratio can be used, which then leads to a higher engine cycle efficiency, which in turn means more power output for a given fuel burn. However, to confuse things further, there are four principal ways to measure Octane rating, RON, MON, Lean Mixture and Rich Mixture ratings.

Road fuels tend to be measured on a RON scale, for which unleaded fuels tend to be 95 - 98 RON but are only 85 - 87 MON. Avgas is measured on Lean Mixture (similar to MON) but also has a Rich Mixture Octane rating.

The Lean Mixture rating is 100 octane (15 octane higher than the comparable 85 MON for unleaded Mogas) but Avgas also has a Rich Mixture rating of 130 which allows higher supercharger boost pressures to be used without detonation occurring. This is particularly a problem when using high power settings at low altitude, for example during take off.

As you can see TEL in Avgas makes a significant difference to the octane rating and without it Octane ratings would be back down to 80 - 85 Lean Mixture - the level for road fuels - instead of 100 / 130. This is not a problem for most typical modern normally aspirated engines as their compression ratios are quite modest and detonation would not be a problem with 80 - 85 Lean Mixture Octane fuel."

1 - "pinking" should be "pinging"
2 - road fuels in the US are rated in AKI not RON. AKI is (RON+MON)/2. You'll see that formula shown on pumps

rv6ejguy 08-29-2018 08:16 AM

Quote:

Originally Posted by jacoby (Post 1284411)
1 - "pinking" should be "pinging"
2 - road fuels in the US are rated in AKI not RON. AKI is (RON+MON)/2. You'll see that formula shown on pumps

Likely from Shell UK where the term used is "pinking" and also where they rate their road fuels differently than North America.

In any case, under 9 to 1 Lycomings can safely use 91 AKI with proper timing adjustments and care with AFRs. Under 7.5 CRs ones can run on 87 AKI with the same care.

The Swift UL avgas is higher octane and certainly suitable as well.

The "universal" UL avgas, when it's introduced, is likely to be similar in octane rating to the current 100LL so as not to have to derate the current turbocharged engines too far, if at all.

jacoby 08-29-2018 08:32 AM

Quote:

Originally Posted by rv6ejguy (Post 1284413)
Likely from Shell UK where the term used is "pinking" and also where they rate their road fuels differently than North America.

In any case, under 9 to 1 Lycomings can safely use 91 AKI with proper timing adjustments and care with AFRs. Under 7.5 CRs ones can run on 87 AKI with the same care.

The Swift UL avgas is higher octane and certainly suitable as well.

The "universal" UL avgas, when it's introduced, is likely to be similar in octane rating to the current 100LL so as not to have to derate the current turbocharged engines too far, if at all.

"pinking" is a new one to me! I thought it was a typo. Shell UK would also explain the use of RON. The link was to shell.com though that could be their international site.

Has anyone tried to use in-tank pumps with EFI? You'd nearly eliminate the vapor lock issues (pretty hard to vapor lock at 2-3 bar), extend pump life, and have automatic redundancy.

BMC_Dave 08-29-2018 09:35 AM

Quote:

Originally Posted by F1R (Post 1284385)
https://youtu.be/K46IJV0Lg24?t=8s

Here is an STC'd $12,000 water injection system for IO 520 Continentals
If you watch the first 2 minutes you will see the MP and CHT values the system starts flowing at. Mostly at take off power settings with MOGAS

A slightly different tool to address pre ignition / detonation that lets you maintain high MP and normal advance for rated HP output.

Huh, that's interesting thanks for the link!

Quote:

Originally Posted by rv6ejguy (Post 1284371)
Same thing applies, reduce total timing down to 20ish at sea level MAPs, by 25 inches, I'd think you could be back up to 24-25 degrees total. Would cost you a few ponies at SL vs. 91 octane. You'd have to weigh the cost vs. power de-rating of the two fuels.

Awesome. With most options away from home being 100LL would one need two configurations or could you run those settings for higher octanes as well?

rv6ejguy 08-29-2018 09:41 AM

Quote:

Originally Posted by jacoby (Post 1284419)
"pinking" is a new one to me! I thought it was a typo. Shell UK would also explain the use of RON. The link was to shell.com though that could be their international site.

Has anyone tried to use in-tank pumps with EFI? You'd nearly eliminate the vapor lock issues (pretty hard to vapor lock at 2-3 bar), extend pump life, and have automatic redundancy.

If an in tank pump fails, you can't access the fuel in that tank. The current pump life is excellent and vapor lock hasn't been an issue if proper location and plumbing practices are followed.

We strongly recommend that people use what's been proven over a half million flight hours with regards to the EFI fuel system if you don't want surprises or to be on a test program to validate a new design.


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