Question about ethanol gas in two stroke...

CRkev

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Mar 19, 2004
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So, with pretty much all of our gas in Alabama now having ethanol in it, anybody have any problems? From what I've read online, as long as it's not over 10% ethanol there shouldnt be any problems, but still not preferred if it can be avoided, I might can find some that don't have ethanol but it'll be hard. Any jetting differences with ethanol gas? thanks!!
 

DougTx

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It is not the burning that is the problem

Ethanol is hygroscopic (if that is the word I am tryign to think of) meaning it absorbs water. If you let it sit you will have water in your fuel is most peoples beef I believe.

FWIW
 

CRkev

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Mar 19, 2004
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yeah i've done some reading up on it for my boat. sta-bil has some new marine formula for ethanol gas. I hear in the boat community it's good stuff.
 

ericz103

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Aug 18, 2006
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pretty much all gas around me is 10% and has been for awhile. never had any problems.

There are alot of differences though between ethanol and gas.
burns hotter, asborbs water, doesn't lubricate the same as gas. There alot of info and misinfo out there if you want do some reading up.
 

Rich Rohrich

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ericz103 said:
There alot of info and misinfo out there ....


You mean like this gem? :rotfl:

ericz103 said:
There are alot of differences though between ethanol and gas.
burns hotter

You should have paid more attention in chemistry class. ;)


Back to the original poster's question.

Ethanol based pump fuel is best avoided if possible, but if you have to use it. Consider the following :

- draining the fuel from the tank and the float bowl is a very good idea to avoid water accumulation.
- store the fuel in the smallest sealed containter you can and keep it cool and dry
- test a small sample of your fuel with the oil you use to make sure they mix properly, and stay mixed over time. It's likely they will, but better safe then sorry.
- your fuel mileage will drop compared to standard gas
- your jetting will likely go to the lean side with ethanol based fuel
- it will be harder to jet for good throttle response because ethanol has a fixed boiling point around 173 degrees f and a very high latent heat of vaporization, along with a requiring a different A/F ratio then the rest of the fuel. In short it acts very different then pure gasoline and screws up the fuels distillation curve which can cause jetting issues.
- the octane distribution of ethanol based fuels will be very different than pure gasoline, so it's best to tune on the safe side till you get used to running with ethanol. Two-stroke riders who switch to ethanol based fuels without other changes very often run into knock and detonation issues they never had before.
-older two-strokes can have issues with the solvent properties of ethanol attacking the crank seals and destroying them. This was a real problem in the early 80s when ethanol started first showing up. The current crop of two-strokes don't have these issues.

If you jet really sharp you'll probably see an immediate change in the way the bike runs and will most likely be on the lean side.

If you jet sort of close it may not matter. If you keep in mind it will be a little lean you'll likely be safe.

If anyone is interested in more of the specifics about alcohol as a fuel follow this link to the DRN KnowledgeBase : http://www.dirtrider.net/forums3/showthread.php?t=115212
 
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whenfoxforks-ruled

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And its real important to be at least getting premium for the mx bikes at the pumps, at least! The older enduro, lower compression engines may get away with regular or mid grade. But, there are some mx engines that will not even run on premium! They can start to detonate. Most all mx engines, stock, run fine on premium, from a busy station, from a pump that already had premium ran through the pump hose, and I have never had issues from Amoco or Shell, etc.
 

ericz103

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Aug 18, 2006
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You mean like this gem?


yep, just going off the top of my head, thought that is what I had heard somewhere down the road. Guess thats why I encouraged him to read up on his own.

Chemistry was to long ago for me, but your article did enlighten me.
 

Tom68

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Oct 1, 2007
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Rich Rohrich seems to have it covered. I found a report from South America that claimed because Ethanol absorbs water and also allows the water to mix with petrol a reaction occurs that seriously degrades the octane rating (more moisture lower octane). It will be interesting down here with our V8 supercar series going to an Ethanol blend fuel in there 600HP 5 litre engines, hope they keep an eye on there fuel supply.
 

CRkev

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Mar 19, 2004
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I've read up a good bit on it for my 2 stroke 200 hp boat engine, just wanted some opinions on the dirtbikes. I deliver gasoline for a living so i'm pretty familiar with the characteristics of ethanol etc. I know of 2 people who have burned up their chainsaws in the last year since we started delivering 10% eth blend here in Alabama...thanks guys!
 

rmc_olderthandirt

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Rich Rohrich said:
- the octane distribution of ethanol based fuels will be very different than pure gasoline, so it's best to tune on the safe side till you get used to running with ethanol. Two-stroke riders who switch to ethanol based fuels without other changes very often run into knock and detonation issues they never had before.

I am a little confused by this.

I had always thought that alcohol based fuels had a much higher octane rating than gasoline, which is why it is used for the really top end racing. I suppose that if the refinery was dropping the gasoline portion of the octane because the alcohol was going to bring it back up then you could get into some interesting problems.

What I am 99% sure of is that alcohol burns slower and requires more fuel per a given amount of air to produce the optimum mixture. The slower burn rate translates into ignition timing and the mix rate translates into jetting. So, like Rich said, if you were perfect before, you will be running lean and a little retarded with an alcohol mix.

Rod
 

CRkev

Member
Mar 19, 2004
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ethanol itself is very high octane, cant remember exactly, around 112 I THINK.......when we blend premium, it is 55% prem, 35% reg and 10% eth,
Reg is 90% reg and 10% eth.
I don't know about elsewhere, but here, most of the stores we deliver, the plus is just plain ol reg with 10% eth so people are gettin ripped by paying more for plus at most stores here.

Reg with 10% eth is actually plus(89 octane) so we're kinda getting a bargain in that respect, if you wanna look at it like that........eth gas sux, no mileage, evaporates fast, attracts water like crazy, the eth can seperate from the gas and settle to the bottom of the tank, then you get a big dose of eth which is bad on most engines unless they're e85 engines.

We cant even drop eth gas if there is over 1/2 inch water in the tank. before we started eth we could drop gas with up to 4 inches of water in a tank, because the pickup is usually about 10-14 inches up from the bottom of the tank. the water will mix with eth gas where it will hardly mix with straight gas, and if it does it seperates very quickly and sinks back to the bottom. it'll stay mixed with eth gas for a long time before settling.
 

Rich Rohrich

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The problem with that approach using American fuels is the octane raising components are not evenly distributed throughout the distillation curve of the fuel. So if you use water to pull the ethanol out of the fuel (which you can never do completely) you will be left with an incredibly low octane fuel with a gaping hole in the middle of the distillation curve due to ethanol being a single boiling point component. It would be very difficult to get a proper running fuel curve if you just removed the ethanol.

With the ethanol in the fuel it's tendency to attract water will complicate things if it's left in an unsealed container in high humidity areas.
 

Okiewan

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I was going to post the same thing, but Rich beat me to it.

LOL
 

Rich Rohrich

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I am a little confused by this.

I had always thought that alcohol based fuels had a much higher octane rating than gasoline, which is why it is used for the really top end racing. I suppose that if the refinery was dropping the gasoline portion of the octane because the alcohol was going to bring it back up then you could get into some interesting problems.

What I am 99% sure of is that alcohol burns slower and requires more fuel per a given amount of air to produce the optimum mixture. The slower burn rate translates into ignition timing and the mix rate translates into jetting. So, like Rich said, if you were perfect before, you will be running lean and a little retarded with an alcohol mix.

Rod

Rod - The opposite actually happens in terms of laminar flame speed. As the percentage of alcohol increases in the mix with hydrocarbon fuels the flame speed actually increases slightly, but for our purposes it isn't enough to matter in my experience. Pure alcohol may burn at a different rate than a hydrocarbon based fuel, but I don't have enough experience switching a specific engine combination from hydrocarbon fuel to pure alcohol to be able to offer anything concrete.

You are correct that alcohol in it's pure state has some really useful characteristics as an ultra-high performance fuel and it certainly has different jetting requirements. I wrote an article a while back on just that subject. I'll see if Okie can re-link it from the DRN Archives.


In the meantime if anyone is interested in more info on the subject (assuming you haven't nodded off already :) ) Here's are a couple of papers that you can read for free online that go into great detail on the subject.

SAE Paper 2008-01-1591
Characteristics of Ethanol, Butanol, Iso-Octane and Gasoline Sprays and Combustion from a Multi-Hole Injector in a DISI Engine
J. Serras-Pereira and P.G. Aleiferis University College London, UK D. Richardson and S. Wallace Jaguar Advanced Powertrain Engineering, Coventry, UK

Laminar Flame Characteristics of C1–C5 Primary Alcohol-Isooctane Blends at Elevated Temperature
Qianqian Li *, Wu Jin and Zuohua Huang *
 
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jaguar

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Well here in South America my 100cc two stroke had detonation (or was it pre-ignition) problems due to a little higher compression (only 150psi cranking) when I was using gas with 25% ethanol. It was jetted too lean also. Now the cranking psi is down to 135 and it's jetted right on and I use gas that's had the ethanol taken out of it (by me using the water method) and I've had no more detonation problems. Keep in mind it gets as hot as the Arizona desert here. So if the water method lowers octane then it hasn't lowered it too much for my application. I should test for octane level though just to satisfy curiosity.
If it's true that the water method doesn't get all the alcohol then it's an extremely small amount it isn't catching because if you do the water method twice on the same gas, the second time doesn't show a measurable amount of alcohol trapped by the water.
 

jaguar

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from Gasoline Octane and E10 Ethanol Blend Fuels
"When E10 gas phase-separates (high octane ethanol drops to the bottom of the tank with water), the upper tank layer octane typically drops 2.5 points. E.G. 87 octane gas purchased now becomes sub-octane 84.5 gasoline.
Testing a fuel sample from tank bottom for alcohol percent will confirm gas contaminated with water, and is not safe for use. After phase-separation upper tank layer typically drops from 10% ethanol to 0-2%.
Fuel that tests greater than 10% alcohol is "bad" and should not be used in conventional engines. Some motors (airplanes and certain marine engines) can NOT use fuel that contains alcohol."

Funny that they say over 10% is bad because the 25% ethanol gas (from Brasil) is almost the only type of gas available here. I think it is only OK for engines designed to use it but probably most of the vehicles here are only made to handle E10 gas.

I wonder if that 80% reduction of ethanol is only for the phase separation of small amounts of water due to humidity. It's quite a different thing to vigorously mix in 25% water to bond to the alcohol..
 

Rich Rohrich

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Assuming for the sake of discussion that the separation only causes a 2.5 point drop in octane the type of point drop is significant for our purposes. Two points in MON octane have a distinctly different impact on high performance engines (especially two-strokes) than the same drop in RON. It would be interesting to see how changes like this play out in a real world environment.
 
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