This may be helpful when talking about regional differences in fuel and engine tuning. Sometimes someone will pop in and say US fuel is of lower quality compared to EU. As always it's the details which matter
Octane conversion chart US vs EU
- Thread starter BMWTurboDzl
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This may be helpful when talking about regional differences in fuel and engine tuning. Sometimes someone will pop in and say US fuel is of lower quality compared to EU. As always it's the details which matter
The lowesr grade we get is 95 RON, it's also the most commonly sold.
I'm sure some countries in europe sell lower grades, but never seen them.
So we could say the lowest grade sold in the US is lower octane, but octane and quality aren't the same thing...
I'm sure some countries in europe sell lower grades, but never seen them.
So we could say the lowest grade sold in the US is lower octane, but octane and quality aren't the same thing...
This is certainly useful as a guide, but I'm not sure it's completely accurate.
I'd have to dig up my notes, but from an undergrad class now years ago where we discussed a lot about fuel blending and the chemistries that lead to different octane ratings, I seem to recall that the nature of the fuel components(i.e. alkane, aromatic, alcohol, ether, etc) can change the relationship between ROM and MON. At the fuel testing lab we visited, they had standard engines for both RON and MON, and would blend their own standards from isooctane(100 in both standards by definition), n-heptane(0 in both standards by definition), toluene(121 RON, 107 MON per Wiki) and ethanol(108.6/89.7). I may have the exact components wrong, but that's the general idea.
Both numbers certainly have their place, and there's no perfect way to categorize fuel, but to my mind the MON is more of a "real world" number given that, in general, engines don't vary their compression as in RON(I know VVT can change dynamic compression, but it's also a relatively recent development) but variable ignition timing has been used, well, since the beginning of practical gasoline engines.
I know that's a lot of rambling, but the take-away from it is that I don't think you can really compare RON and AKI directly without knowing the exact composition of the fuel. It's probably good enough to say, for example, 87 AKI/92 RON as a minimum, especially now that cars can pull ignition timing at least to a point as needed if something is off. I know almost nothing about, for example, seasonal variations in European gasoline blends. IIRC, we use butane(94/90.1 for n-butane, 102/97.6 for isobutane) in winter blends...
On the whole, too, in my mind using the US AKI((R+M)/2) is probably the best balance of approaches, but I'm sure there are arguments for both.
Of course I'd welcome one of the actual pretroleum engineers on here to weigh in on this-I'm just a chemist with an interest but no practical research experience in this field.
BTW, Wiki gives a nice summary of RON, MON, and AKI numbers for a whole bunch of specific compounds
https://en.wikipedia.org/wiki/Octane_rating
I'd have to dig up my notes, but from an undergrad class now years ago where we discussed a lot about fuel blending and the chemistries that lead to different octane ratings, I seem to recall that the nature of the fuel components(i.e. alkane, aromatic, alcohol, ether, etc) can change the relationship between ROM and MON. At the fuel testing lab we visited, they had standard engines for both RON and MON, and would blend their own standards from isooctane(100 in both standards by definition), n-heptane(0 in both standards by definition), toluene(121 RON, 107 MON per Wiki) and ethanol(108.6/89.7). I may have the exact components wrong, but that's the general idea.
Both numbers certainly have their place, and there's no perfect way to categorize fuel, but to my mind the MON is more of a "real world" number given that, in general, engines don't vary their compression as in RON(I know VVT can change dynamic compression, but it's also a relatively recent development) but variable ignition timing has been used, well, since the beginning of practical gasoline engines.
I know that's a lot of rambling, but the take-away from it is that I don't think you can really compare RON and AKI directly without knowing the exact composition of the fuel. It's probably good enough to say, for example, 87 AKI/92 RON as a minimum, especially now that cars can pull ignition timing at least to a point as needed if something is off. I know almost nothing about, for example, seasonal variations in European gasoline blends. IIRC, we use butane(94/90.1 for n-butane, 102/97.6 for isobutane) in winter blends...
On the whole, too, in my mind using the US AKI((R+M)/2) is probably the best balance of approaches, but I'm sure there are arguments for both.
Of course I'd welcome one of the actual pretroleum engineers on here to weigh in on this-I'm just a chemist with an interest but no practical research experience in this field.
BTW, Wiki gives a nice summary of RON, MON, and AKI numbers for a whole bunch of specific compounds
https://en.wikipedia.org/wiki/Octane_rating
Quality of fuel has nothing to do with it's octane rating.
Agree but I've found that when it comes up they're actually talking about differences in octane.
Yep. MON is always lower than RON, how much lower varies and is called "sensitivity".
True, MON is closer to a real-world result, measured at higher RPM and temperature. This is when pre-ignition is most likely, and when the engine actually needs the octane.
Agreed
So the conversion chart in the OP is over-simplified because the conversion is not a fixed ratio, but depends on sensitivity, which varies depending on the gasoline & octane additives used.
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