Dialcaliper
Well-known member
So I thought I knew the octane ratings of Methanol and Ethanol. Methanol is usually quoted as 114 and Ethanol as having a lower octane.
However I've been looking around, and have been finding that Octane numbers quoted vary incredibly wildly. What seems more interesting though is that most of the reputable sources I have found quote the Octane for Ethanol as being higher than Methanol, not lower. The most common seem to be Ethanol around 113-116, and Methanol around 105-113. Keep in mind these are combined octane numbers. The RON numbers are as high as 123 for Methanol and 129 for Ethanol
What's really been confusing me is that RON is measured at stoichiometric under controlled conditions to reflect low RPM cruise
MON is more equivalent to "aviation lean" - the low rating on the aviation scale, which reflects higher RPM and higher load, but still leaner mixtures.
The aviation "rich" number seems to be an entirely different measure and is the rating at elevated manifold pressures, advanced timing and rich mixtures. This is really the number you care about for alcohol injection under boost, and isn't really reflected in pump gas RON or MON octane numbers.
Now, one advantage of Methanol is that it has a higher density, and takes 30% more energy to vaporize by volume than ethanol, and has a lower boiling point (148 F vs 173F), so the same volume of methanol will cool the intake air better, and is more likely to vaporize fully before it goes into the cylinder. Water of course has a higher boiling point, but the energy taken out by vaporizing it is massively higher than either of those (240% more by volume).
Furthermore, the energy density of Ethanol is 30% higher by volume than Methanol.
This is what prompted my question: IRL switching from Methanol to Ethanol - the cars are producing more power from ethanol vs Meth. MSNBC isn't exactly the most reliable source, but other articles on the same topic seem to agree.
What I'm wondering is, why is Methanol so much more popular than Ethanol for water injection? Are we discounting Ethanol because it doesn't appear to cool the intake as well, even though it is apparently a superior fuel? Is there something I'm missing?
Based on this information, it seems like denatured ethanol from the hardware store (or bulk) would be a better choice for water injection than Methanol. Purity might be an issue, but it can't be any worse than running windshield washer fluid...
Does anyone have experience playing with both?
However I've been looking around, and have been finding that Octane numbers quoted vary incredibly wildly. What seems more interesting though is that most of the reputable sources I have found quote the Octane for Ethanol as being higher than Methanol, not lower. The most common seem to be Ethanol around 113-116, and Methanol around 105-113. Keep in mind these are combined octane numbers. The RON numbers are as high as 123 for Methanol and 129 for Ethanol
What's really been confusing me is that RON is measured at stoichiometric under controlled conditions to reflect low RPM cruise
MON is more equivalent to "aviation lean" - the low rating on the aviation scale, which reflects higher RPM and higher load, but still leaner mixtures.
The aviation "rich" number seems to be an entirely different measure and is the rating at elevated manifold pressures, advanced timing and rich mixtures. This is really the number you care about for alcohol injection under boost, and isn't really reflected in pump gas RON or MON octane numbers.
Now, one advantage of Methanol is that it has a higher density, and takes 30% more energy to vaporize by volume than ethanol, and has a lower boiling point (148 F vs 173F), so the same volume of methanol will cool the intake air better, and is more likely to vaporize fully before it goes into the cylinder. Water of course has a higher boiling point, but the energy taken out by vaporizing it is massively higher than either of those (240% more by volume).
Furthermore, the energy density of Ethanol is 30% higher by volume than Methanol.
This is what prompted my question: IRL switching from Methanol to Ethanol - the cars are producing more power from ethanol vs Meth. MSNBC isn't exactly the most reliable source, but other articles on the same topic seem to agree.
What I'm wondering is, why is Methanol so much more popular than Ethanol for water injection? Are we discounting Ethanol because it doesn't appear to cool the intake as well, even though it is apparently a superior fuel? Is there something I'm missing?
Based on this information, it seems like denatured ethanol from the hardware store (or bulk) would be a better choice for water injection than Methanol. Purity might be an issue, but it can't be any worse than running windshield washer fluid...
Does anyone have experience playing with both?
