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RedDevil · 12-22-2013, 07:30 AM

There is someting funny about the effect ethanol has on octane rating.
Ethanol boosts the octane number, so you could take lower grade gasoline, mix it up with ethanol and get a higher grade E10. Right?

Well, maybe not.
According to Wikipedia the octane rating of ethanol is 108.6. Or 89.7 ... What?
First rating is RON. Second is MON. Research Octane Number versus Motor Octane number. Simplified, RON is determined at 600 RPM, MON at 900. Most engines rev higher than that.

Now what does that mean. Most fuels have a higher RON than MON, but the difference is not at large as with ethanol. It may well be that the effect on octane is less than expected, and in some conditions even nonexistent or negative.
If your E10 is cut up with low octane gas no wonder it performs badly.

My experience with ethanol blends is good. My record tank is on German E10, my second and thrird are on hE15. These fuels are officially RON 95, but that is just a legal minimum. The actual RON octane is much higher than that. hE15 is made by taking regular RON 95 and just adding 15% worth of 96% pure ethanol. No doubt the water boosts the octane number even further; there is no ignition point for water vapour, obviously.

You need to know what the properties of any specific blend of E10 is. I suspect there are big differences, ranging from quite bad to quite good.
Commenting on the quality of E10 is like commenting on beer in general. But there are beers I gladly spend a lot on, and some I would not take if they were free. Just sayin

If your local blend of E10 does not work out well it may not be the fault of the 10% ethanol but rather the quality of the gas.
You can find out bij taking the pure stuff and add 10% high grade ethanol to that. If that runs good you know what is to blame.

Chances are you can boost the octane by adding 0.4% of demineralized water to E10. Ethanol is fiercely hygroscopic and will gladly draw it in the mix, unlike pure gasoline. But you need to know that nobody has added some water already, especially whether that was more than 0.4 %.

12-22-2013, 07:30 AM	#32 (permalink)
RedDevil Master EcoWalker Join Date: Dec 2012 Location: Nieuwegein, the Netherlands Posts: 3,998 Red Devil - '11 Honda Insight Elegance Team Honda 90 day: 49.01 mpg (US) Thanks: 1,711 Thanked 2,245 Times in 1,454 Posts	There is someting funny about the effect ethanol has on octane rating. Ethanol boosts the octane number, so you could take lower grade gasoline, mix it up with ethanol and get a higher grade E10. Right? Well, maybe not. According to Wikipedia the octane rating of ethanol is 108.6. Or 89.7 ... What? First rating is RON. Second is MON. Research Octane Number versus Motor Octane number. Simplified, RON is determined at 600 RPM, MON at 900. Most engines rev higher than that. Now what does that mean. Most fuels have a higher RON than MON, but the difference is not at large as with ethanol. It may well be that the effect on octane is less than expected, and in some conditions even nonexistent or negative. If your E10 is cut up with low octane gas no wonder it performs badly. My experience with ethanol blends is good. My record tank is on German E10, my second and thrird are on hE15. These fuels are officially RON 95, but that is just a legal minimum. The actual RON octane is much higher than that. hE15 is made by taking regular RON 95 and just adding 15% worth of 96% pure ethanol. No doubt the water boosts the octane number even further; there is no ignition point for water vapour, obviously. You need to know what the properties of any specific blend of E10 is. I suspect there are big differences, ranging from quite bad to quite good. Commenting on the quality of E10 is like commenting on beer in general. But there are beers I gladly spend a lot on, and some I would not take if they were free. Just sayin If your local blend of E10 does not work out well it may not be the fault of the 10% ethanol but rather the quality of the gas. You can find out bij taking the pure stuff and add 10% high grade ethanol to that. If that runs good you know what is to blame. Chances are you can boost the octane by adding 0.4% of demineralized water to E10. Ethanol is fiercely hygroscopic and will gladly draw it in the mix, unlike pure gasoline. But you need to know that nobody has added some water already, especially whether that was more than 0.4 %. __________________ 2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut. lifetime FE over 0.2 Gmeter or 0.13 Mmile. For confirmation go to people just like you. For education go to people unlike yourself. Last edited by RedDevil; 12-22-2013 at 08:01 AM..