Knock Limits "How much better is E85 than E50"

[jodadejss06gt]

Hey guys, I've been toying with the idea of trying to get Manuel to tune for a blend of pump 93 and pump E85 to ~ E50. I remember seeing discussion about E50 before but couldn't remember where and not this in depth.

ONeff = Effective Octane Number

From this thesis done by a student at MIT. Based on the summary(pg.117), it states "ONeff. (chemical) benefit from blending ethanol is non-linear. No benefit beyond ~30-40% ethanol by volume. As seen from the figure, the ONeff of the gasoline-ethanol blend is initially significantly improved with increasing ethanol content up until around 30-40% by volume. Increasing ethanol content further does not improve ONeff any more. What the result is implying is that Ethanol blending provides no antiknock benefit beyond 30-40% by volume, unless it is used in an engine that can realize the charge cooling potential of the fuel.

What I get out of the article: the more ethanol you put into the fuel, the better the charge air cooling benefits, which improve anti-knock properties. However, chemically speaking E85 has very little benefit of anti knock properties over say a mixture of 40% ethanol.

Here is the link to the 134 page article. Some of it is well beyond my understanding!
https://www.google.com/url?sa=t&sour...G1MbGRWeSVL_eg

Page 18 shows the chart of Mixtures and their A/F stoich.
E0 = 14.7
E10 = 14.1
E20 = 13.5
E50 = 11.8
E85 = 9.8
E100 = 9.0

It also shows how much Energy is in the fuel.
Based on my calcs, if you have 30% less energy in E85 than E10, you only have ~ 15% less energy in E50 than E10.

My sole purpose is to extend my tank range on E50 while still being able to lay the hammer down with higher boost on my 11:1 compression engine.

 

[mach828]

It will be challenging to run an e50 mixture every tank.

Extra fuel is closer to 20% (14.1/11.8) = 119.5% more fuel.

Assuming you only run your car to 1/4 tank. You'd need to fill up with 8 gallons of winter e70 and 4 gallons of 91 e10 in order to get e50 with an octane rating ~98. Or with summer e85 it would be 6.5 gallons of e85 and 5.5 gallons of 91 e10.

I may actually try running e50 as well. Guess the only way to tell is to try it and see if you experience some detonation.

 

[jodadejss06gt]

I'd be using 93 only, very easy to get here. I think it would be cool if you don't loose any of the timing characteristics of it and get more range out of the fuel.

 

[CPRsm]

You will lose some timing ability, but not a bunch.

 

[jodadejss06gt]

Dustin, have you tested it out? What do you consider the limits of timing for each?

I'm just going off the article. It doesn't seem like I should based on that. I'm not talking crazy boost either, but possibly up to about 16-18 psi.

 

[CPRsm]

Only tested it on 7-8psi or so. We were trying to extend the stock pump lol. Iirc it was a 2-3 degrees less than he was able to run on pure E85. Didn't push it too hard though

 

[Department Of Boost]

What you will lose is some in cylinder IAT drop with the e50 vs the e85.

 

[jodadejss06gt]

As long as I can run over 10psi, thats about where I'm limited on 93 with my CR.

 

[CPRsm]

Should be fine. We were testing in a coyote w 11-1