GAS: Regular? Premium? Ethanol?

[Tollster]

I'd be curious to know where you got that rule of thumb (sounds like malarky to me). It would suggest that adding oil into the fuel changes the energy content and combustion properties of the fuel itself, but that's not the case for a two stroke. You know how two strokes work and how the oil separates out into lubrication while the energy in the gas goes into combustion. The octane controls the speed of the combustion (slowing it from and explosion into a fast burn). The octane and the oil are independent.

It was not intended as a scientific explanation, but since you are on the subject of malarky, at what point does the dilution of premium with oil make it non flamable in a two stroke, after all, if they are independent as you say?


Gas is dirived from oil, we add it for lubrication, but we also dilute the fuel and everything in the fuel, therefore I will stick by my words you reduced the octane by 2 points or so when adding premix as a general rule.

 

[Bigkrank]

I've been using aviation gas for well over 20 years in all my small engines and two-strokes. Zero problems.

Had a Honda generator that I tried to cheap out on and used 87 10% car gas with stabil, left it sit too long, son did not run it dry last time he used it, cost me a new carb. Never again.

 

[s219]

Do fuel stabilizers like Sta-bil change this equation? I had real problems with stale fuel in my saw until I started using Sta-bil. I don't leave fuel in the saw if I can help it, because of damage to the carburetor, but I store fuel for longer than 6 weeks without apparent problem. Somewhere between 8-12 weeks, I toss whatever is left into my car's gas tank and use it up that way.

I have used Stabil with regular gas for a long time, and do believe it helps. I also use it with the ethanol fuel that I run in my lawn tractor (4-stroke). I do believe Stabil can help with any fuel blend, but it will not offset the unique problems with ethanol (nothing can). So you definitely still want to exercise caution when storing ethanol.

I am good friends with the local Stihl mechanic, who services a lot of chainsaws that develop carb problems due to ethanol. Stihl puts a fuel stabilizer additive in their oil that is like Stabil, and helps extend the shelf life of a gas/oil mix. Sadly, it doesn't solve the problems with ethanol. His dealership hands out a pink flyer with all their equipment, cautioning customers about ethanol issues and that stabilizers only help a little. From what he tells me, the biggest problem is that the ethanol portion separates out, attracts moisture, and eventually you get layers of separated gas, water, and ethanol, where they each start to degrade equipment in different ways.

 

[s219]

when I first started driving, the gas stations had 3 choices, 87, 89with ethanol and 91
what i was told the 89 is 87 plus ethanol. because the ethanol is higher octane than gasoline.

That's probably not true, as octane is separate and independent of the fuel, whether it's gas or ethanol. The gas or ethanol doesn't naturally have octane in it.

What is true is that ethanol contains about 15% less energy per volume than gas. So you really start to lose out when mixing ethanol into gas. It's actually noticeable if you can carefully measure and track MPG on a vehicle.

 

[s219]

It was not intended as a scientific explanation, but since you are on the subject of malarky, at what point does the dilution of premium with oil make it non flamable in a two stroke, after all, if they are independent as you say?

Listen, you can't extrapolate out into extremes and expect the logic to hold (or for me to keep going on with this). Obviously the fuel/oil mix won't work if there is too much oil for the carb to properly atomize everything, or for the fuel/air to ignite and the oil to separate out and lubricate. But that has nothing to do with my point. The point is that the octane is chemically part of the fuel, and the octane sticks with the fuel during the combustion process to control the burn. That is a totally different concept than "mixing" which just combines things in a non-chemical way in a container. The oil and fuel are mixed, and not chemically bonded (they will separate back out if you wait long enough, which is why it's important to shake the mix after it's been sitting a long time). You need to understand that. It's almost like you're saying that mixing vegetable oil and vinegar into salad dressing chemically changes the vinegar, but obviously that's not true -- they simply mix, and can be separated back out.

Here's how you have to look at it. The carb controls flow rate of the gas+oil mix that is combined with air, so it must be adjusted to send the proper amount of gas+oil flow through to the engine such that the independent amount of gas present, combined with air, is correct for proper combustion and performance. The portion of the mix that is gas (with its chemically included octane) and the air it mixes with is what matters for combustion. The oil has been along for the ride up until this point, and it now separates and goes into lubrication (and some of it burns up and goes out the exhaust).

So bottom line, no matter what ratio of gas to oil you add to a two-stroke (in the realm of possibility), as long as the carb is properly adjusted so that the right amount of gas+oil mix passes through to later provide the proper gas+air mix, independent of the oil, then you're OK. The oil is not diluting anything at that point (like octane content) since it has separated back out.

 

[jymbee]

From that video, some very simple, but sound advice:

>>always vigorously shake your fuel mixture imimediately before pouring

Husqvarna: Take the Ethanol Challenge!

 

[Tollster]

Listen, you can't extrapolate out into extremes and expect the logic to hold (or for me to keep going on with this). Obviously the fuel/oil mix won't work if there is too much oil for the carb to properly atomize everything, or for the fuel/air to ignite and the oil to separate out and lubricate. But that has nothing to do with my point. The point is that the octane is chemically part of the fuel, and the octane sticks with the fuel during the combustion process to control the burn. That is a totally different concept than "mixing" which just combines things in a non-chemical way in a container. The oil and fuel are mixed, and not chemically bonded (they will separate back out if you wait long enough, which is why it's important to shake the mix after it's been sitting a long time). You need to understand that. It's almost like you're saying that mixing vegetable oil and vinegar into salad dressing chemically changes the vinegar, but obviously that's not true -- they simply mix, and can be separated back out.

Here's how you have to look at it. The carb controls flow rate of the gas+oil mix that is combined with air, so it must be adjusted to send the proper amount of gas+oil flow through to the engine such that the independent amount of gas present, combined with air, is correct for proper combustion and performance. The portion of the mix that is gas (with its chemically included octane) and the air it mixes with is what matters for combustion. The oil has been along for the ride up until this point, and it now separates and goes into lubrication (and some of it burns up and goes out the exhaust).

So bottom line, no matter what ratio of gasil you add to a two-stroke (in the realm of possibility), as long as the carb is properly adjusted so that the right amount of gas+oil mix passes through to later provide the proper gas+air mix, independent of the oil, then you're OK. The oil is not diluting anything at that point (like octane content) since it has separated back out.

I'll buy that, very nice explanation on the molecular level, well done (some times I just have to call your hand). One more question: Where the h e l l where ya 3 pages ago? (And yes, I will still stick to the 2 point reduction of octane....sorry, due to the combustion area of the cylinder head, and the point that we have diluted the gas with oil. I believe octane ratings where intended for the product undiluted, therefore,I feel once oil is added, we do not get the biggest bang for the buck, just lubrication. )

 

[ruffdog]

BP article about 2-stroke premix

http://www.bp.com/assets/bp_interne...ia/STAGING/local_assets/2_stroke_brochure.pdf

 

[ruffdog]

Airfoolers.com » Premix 101 – 2 schools of thought.

quote: One of the things you should do, is run high octane gas with any two-stroke mix. When all of the two strokes (the old days) were developed, they all used Castrol petroleum oil at a 20:1 ratio and found that 92 octane gas had the octane reduced to 72 with presence of that much oil. Modern oils won’t affect the fuel quite as much, but if you started with 86 or 87 octane regular fuel, you can see where you’ll end with a very low octane mix.

 

[ruffdog]

Another premix item.....does changing premix ratio change the air/fuel mixture? Quote from article: A typical example: you go from a 50:1 ratio to a 20:1 ratio. Your engine will now run leaner, and you値l have to make jetting changes. You値l need bigger (in number) jets because the oil molecules are thicker and the flow rate (the amount coming through the jet) is less.

Aha! The volume of fuel has changed. The oil takes up some volume that the gas used to occupy, so your engine is getting less gas and needs to be richened up.


(We used to do quick jetting changes by changing premix ratios when we were ice racing.)