Efficiency and Octane of various Gasoline blends from "pure" Gasoline to E85

[Allch Chcar]

It seems I finally found the document that measures thermodynamic efficiency and octane of Ethanol blended fuels and at various compression ratios albeit with three nonstandard ratios. I only wish they had chosen standard and more Static compression ratios such as 10:1 11:1 and 12:1 including one-half points in between. But the study does fix E50 and E85 at certain octane points. I'm not surprised that 85% Ethanol is closer to 95 Octane but that is at Stoichmetric. With Alcohol can simply add more fuel to eliminate knock. Gasoline you need to remove ignition timing AND run pig rich under high load to keep even a respectable level of Static compression ratio.

http://delphi.com/pdf/techpapers/2010-01-0619.pdf

If you have anything to add or comment on please do so but please no politics!

A couple notes regarding this: this document is highly technical, nerdy and funded by the DOE which is gov't funded so put on your tinfoil hats! /endjoke The reason that RF(reformulated ethanol free) Gasoline, HO(high octane) Gasoline, and even 10% Ethanol Gasohol blends were not fully operational at higher than 9.2:1 Static Compression at WOT and other conditions was that the researchers kept the fuel mixture at Stoichometric for the study and that limits the operational range for the fuels. The only variable was ignition advance and as you will notice the E50 and E85 fuels have differing spark advances. They should have used a ratio between 9.2:1 and 11.8:1 for a better example of Gasoline. Please be sure to at least read some of the opening statements before getting too far into the charts and graph results it is a very technical document.

I also want to add:
You may or may not know that EFI Gasoline engines are set to Stoich for cruise speed and light to moderate loads but will change over above 70% load to fuel enrichment mode or Open Loop. This also explains the abnormally high efficiency of the fuels in this study. On my various Forum lurkings I've found that regular cars like the Honda Fit for example; which runs on the lowest octane grade Regular 87(85 at elevations), enters open loop at 70% load and run at almost 11:1 Air:Fuel Ratio in open loop. Generally Peak power for Gasoline is at slightly rich AFRs like 12.5-13:1 while peak TDE is at slightly lean such as 16-18:1. Stoichmetric is the least polluting ratio and (luckily) is a balance between most efficient and most powerful which is why EFI Gasoline engines operates at Stoich throughout most of their operational range excluding Idle.

Aside: This paper was published by the SAE and it was funded by the Department of Energy. I have some respect for the SAE as an organization but I wouldn't and don't know of any bias on their part. They are not a political organization in my humble opinion.
On another note the SAE has done several Ethanol related studies over the last 20 years that the DOE has been funding research on Alcohols as a fuel source.



I'm excited to finally find this document. As you may know anything E85 related from a scientific standpoint is almost nonexistent especially regarding practical matters such as static/dynamic compression ratios or even a very simple thing as it's true octane value. These were RF Gasoline mixtures with "dry" Ethanol blended on site not mysterious E85 pulled from a random Gas station during an unknown time of year.
From a technical standpoint Alcohols makes up for their low energy density by having oxygen which makes it much more resistant to knock and capable of tolerating much higher peak static compression ratios and peak cylinder pressures than unleaded Gasoline is capable of handling.

Looking at this it makes me think of the last 50 years of ICE development and how Automakers were working around the problems of low grade but cheap unleaded Gasoline to deliver engines that would keep people satisfied. With Higher octane fuels such as the Alcohols we could have been pushing the ICE to it's thermodynamic limit instead of limiting ourselves to a cheap and inefficient fuel source.

[gone-ot]

...I wonder who supplied the E85 fuel, because its RON of 101.5 is less than that of the E50 fuel (RON of 101.6), which, technically, is not possible. Pure ethanol (E100) has a RON of 129 and E85 a RON of 105-106, while E50, having more gasoline, should have a RON value closer to E10 than to E85. Typo?

...also, this statement should raise some eyebrows: "* Reported property values for RG and HO are typical values for these products. Actual values of the batch were not measured." ...because, if it's not measured, it's an 'un-controlled' element within the testing protocol.

...as I read it, all they're saying is "...if you've got the octane, you can get more power, if you also have (or can get) the requisite CR."

[tjts1]

Thanks for posting the study. I may try to use some of their timing data on my megasquirted car to try to tune the high load (80-100kpa) areas below 3000rpm at stoich instead of the 12.5-13afr where it is now. I'll probably end up losing a lot of torque because of the conservative timing they're using.

[Allch Chcar]

That's a good point. I only looked at the E85 octane numbers and ignored E50. There is no logical reason that the two mixtures had almost exactly the same octane. The other results are of a large enough different between E50 and E85 that I suspect it may have just been the Octane test that is strange. I've sent them an email to see if there is more to the story.

The Octane values for RF Gasoline and High Octane Gasoline are commonly accepted and well published numbers. RF Gasoline is a very common and regulated product. The only variables I can think of between Gas stations excluding water content(which is regulated) are the aromatics, dye, and detergents. All three are variables that may not be large factors for Octane.

Alcohols have oxygen in them which reduces their energy density but also means they can tolerate much higher Octane than Petroleum products. Pure Ethanol is 120-130 RON. Gasoline was mixed with lead in the 60's to increase it's Octane but was later banned in the US due to Lead being toxic, even more so than Gasoline. Other than adding Lead there are no cheap options for improving the Octane of Gasoline that I am aware of.

Edit: Okay I already found it.
"It is interesting to note that the blending response of RON
and MON as a function of ethanol content is highly nonlinear.
There is a substantial octane improvement between
RG and E10, and between E10 and E50. However, between
E50 and E85 there is very little difference in either RON or
MON. It is well-established that properties of ethanolgasoline
blends, such as Reid vapor pressure, do have nonlinear
responses [4]. Surprisingly, the authors have been
unable to find RON and MON measurements as a function of
ethanol content that either support or refute these results."

It looks like the link for the source is restricted.

[Allch Chcar]

I feel very silly now , I had to amend my email by rephrasing the question 10 minutes after I sent it .

But @ Old Tele Man, to answer your question regarding where they got their Gasoline octane numbers from:

"A total of 5 fuels are investigated in this study: regular
gasoline (RG), high octane gasoline (HO), and ethanol blends
of 10% (E10), 50% (E50), and 85% (E85). Both RG and HO
are emissions certification gasolines from Chevron Phillips
Chemical Company LLC (CPChem) with product names
UTG-91 and UTG-96, respectively."

I need to go back and reread the whole document page for page now. Not that it bothers me . I can only imagine what other little tidbits I missed skimming through it.

Originally Posted by tjts1

Thanks for posting the study. I may try to use some of their timing data on my megasquirted car to try to tune the high load (80-100kpa) areas below 3000rpm at stoich instead of the 12.5-13afr where it is now. I'll probably end up losing a lot of torque because of the conservative timing they're using.

Sounds like fun . Wish I could help/watch. Probably more watching than helping, I've never tuned an ECU before.

I'm still very impressed by them running Stoich for WOT at such a low RPM. But the Engine is a research converted Ecotec to a one cylinder with completely variable valve timing, not exactly your mom's neon .

[tjts1]

Originally Posted by Allch Chcar

I'm still very impressed by them running Stoich for WOT at such a low RPM. But the Engine is a research converted Ecotec to a one cylinder with completely variable valve timing, not exactly your mom's neon .

I think the direct injection has a lot to with it. But they were injecting the fuel during the intake stroke, not the compression stroke which how normal DI engines function.

Also did anybody else catch the bit about the way they blended regular 87 octane gasoline with ethanol to get a 90.8 octane E10 mix The real E10 you get at the pump uses sub 87 octane gasoline specifically designed to be blended with ethanol, the end result of which is an 87 octane E10 mix. I don't think their E10 test is representative of the real world. They even admitted to it. Their RG results are more representative of what you and I would see with pump E10.

[Allch Chcar]

Spec blending to get 87 octane is mentioned.
Actually that was the part of Fuel Methodology that I do remember reading:

"The decision to use RG as the blend stock for ethanol
blending, rather than HO, was based on real-world trends in
that ethanol is unlikely to be blended with high-octane
gasoline. As fuel ethanol consumption increases in the US,
there is a trend away from splash-blends toward matchblends,
which use a blendstock for oxygenate blending
(BOB). In splash-blending, ethanol is mixed with a finished
in-spec gasoline, whereas with match blending the ethanol is
blended with a BOB that is formulated for the specific
purpose of ethanol blending. One of the intended purposes of
BOB is to reduce evaporative emissions by reducing the
vapor pressure of ethanol fuel blends. Importantly, since
ethanol also acts as an octane improver, the octane number of
BOB doesn't need to be as high as conventional finished
gasoline to meet market specs. Because producing a high
octane product is more expensive for refiners, the BOB
blendstock is likely to be of a lower octane than conventional
gasoline. Thus, the ethanol fuels for this study were blended
with the lower-octane gasoline."

It doesn't mention mixing with a lower Octane Gasoline so maybe they just used regular 87? If anything I would imagine this blending stock would be 85 Octane or so.

[tjts1]

Originally Posted by Allch Chcar

It doesn't mention mixing with a lower Octane Gasoline so maybe they just used regular 87? If anything I would imagine this blending stock would be 85 Octane or so.

Yes, their E10 blend is made from 90% RG (87 octane) and 10% ethanol with a 90.5 total octane (R+M/2). Our real world E10 is 87 total octane.

Ethanol blends are prepared by splash blending in-house
using RG and denatured fuel-grade ethanol blendstock
(E100), also from CPChem.