RON/AKI ((R+M)/2) conversion?

[Jorgeaz]

Please move this if it belongs in another area.

I'd love to know how US gas(petrol) compares with the rest of the world. We use the Anti-knock Index (AKI) to rate our octane, (RON + MON)/2, whereas the rest of the world uses simply RON. I know that AKI understates RON by a bit, but by how much I'm not sure.

Is there a conversion, or rule of thumb, that one can use to compare octane ratings. What does 98 RON compare to in AKI? What does 91 AKI compare to in RON?

[Jorgeaz]

a quick google search yielded 2 sites that were rather informative.

http://www.cheresources.com/greengas.shtml
http://www.adb.org/vehicle-emissions...l.asp?pg=india

an excerpt

Quote:

The anti-knock property of a gasoline is generally expressed as its Octane Number. This number is the percentage by volume of iso-octane (assigned 100 octane) in a blend with n-heptane (assigned zero octane) that matches the knock characteristic of a gasoline sample combusted in a standard engine run under controlled conditions as defined by the American Society for Testing and Materials (ASTM). One set of conditions produces the Research Octane Number ( RON, indicative of normal road performance) and a more severe set of conditions gives the Motor Octane Number (MON, indicative of high speed performance ). Octane numbers quoted in literature usually refer to RON, unless stated otherwise. Generally, it has become practice to label the gasoline with an arithmetic average of both RON and MON ratings (R+M)/2, called the Anti knock Index (AKI). As per the World Wide Fuel Charter (WWFC) , Jan’2000 the proposed specifications are AKI/RON/MON : 86.5/91/82.5.

[sjbartnik]

That article fits with roughly what I've heard and seen in other documents, figure about a 4 point reduction from the RON number to get the U.S. AKI number.

So 91 RON = 87 U.S. and so on.

[noahe]

As I understand it, RON, or Research Octane is measured by laboratory equipement, and MON, or Motor Octane, is tested by running in an engine. The two, RON and MON are averaged to produce the AKI or Anti-Knock-Index also referred to as Pump Octane.

The MINI requires 91 AKI, which correlates to 91 on the pump. Higher octane is fine, although a waste of money. Lower octane will hurt economy with today's sophisticated sensors and electronic ignition timing. Severe knock is unlikely to occur, so you shouldn't damage your engine. But the engine management software can only do so much, before the engine won't fire on the gas you've given it. (Plus, there are warranty issues).

Typically, North American gas is not offered in as high-octane ratings as it is in Europe. But, since higher is not better, unless you have an engine that requires it, we're fine.

What does get us here, is impurities in the gas, specifically sulphur. The sulpher in our gas is very high, and limits the automakers abilities to introduce the best emissions systems, because our gas will just bung them up.

Finally, North American gas contains more non-petrolium additives, such as alcohol (fermented wood), ethanol (fermented corn), and methanol (fermented garbage). These additives are fine, if your car is able to burn them. The MINI, like many other european cars, is not designed to run on the higher quantities of these additives.

Your manual states what the MINI can burn. There are a few more posts like this, that mention gas quality, additives, sulphur quantities, and such... You might want to do a search.

[Jorgeaz]

okay, couple more questions though.

so one could say the readily available 93 AKI octane is ~ 97/98 RON? but this is dependant on MON, is there an equation, other than approx 4pts, one could use?

My understanding was that modern North American gas(petrol) was just about as clean (sulphur free) as Euro gas. I know North American (NA) Diesel is horrible, tons of sulphur, and a big reason why NA doesn't get the good Diesel engines from Europe, among others like lowered fuel costs and market demand.

Are ethanol(alcohol) additives purely a NA phenomenon? They don't do this in Europe?
Also, isn't the relative low proportion(10%) of alcohol irrelevant to engine wear?

better yet, do you know of a site i can visit to get up to speed?

[GordonD]

It is worth noting that while an S will run fine on a variety of octane levels it was optimized to run on 98 RON

I use Sunoco 94 and it seems to be very good.

[noahe]

The approx 4 pts rule is a ballpark. It is dependant on MON. Certain additives can artificially raise the octane rating of a fuel, but an additive is not always as good as an octane level reached by refining. So you could have a high RON with an additive, that still knocks horribly in an actual motor.

North American gas is not as clean (sulphur free) as European gas, on average. Certainly, some premium gasoline in a heavily regulated area, say California, could be better than the worst examples in Europe, but on average, European gas is still many, many times cleaner than what is available across Canada and the USA.

Removing sulphur adds directly to the cost of the fuel, so typically, the premium varieties contain less than regular, and the more fuel costs from state to state, province to province, the less sulphur will be present. But that's not always true either.

Additives are not purely a NA phenominon, however, the most common additive here - Ethanol, is not as popular in Europe. Simply, if European farmers were going to grow millions of hectares of corn, they'd sell it to people as food, rather than convert it into corn alcohol. Certainly the waste by-products of corn (cobs) can make Ethanol, but the entire reason Ethanol is prevalent in gasoline here, is because it was enacted through legislation and laws designed to help the environment.

The proportions of ethanol, methanol and other additives aren't bad for the engine, in fact, in a car designed to burn them, additives are fine, but specifically, ethanol harms the fuel system of vehicles from the more northern climates, with natural or flexible rubber components to their fuel system. These additives can act as a solvent, and lead to dry, brittle cracked parts. Finally, the unburned portions of these fuels act differently in the emmissions systems of vehicles not designed for them.

[noahe]

Quote:

Originally posted by GordonD
It is worth noting that while an S will run fine on a variety of octane levels it was optimized to run on 98 RON

I use Sunoco 94 and it seems to be very good.

In reading both my manual and Sunoco's leaflets on their Ethanol Enhanced fuels, I discovered that the MINI requires:

Quote:

Fuels containing up to and including 10% ethanol or other oxygenates with up to 2.8% oxygen by weight (i.e. 15% MTBE or 3% methanol plus an equivalent amount of co solvent) will not void the applicable warranties with respect to defects in materials or workmanship.

However, the Sunoco Leaflet stated that their Ethanol Enhanced fuels contained a minimum of 10% Ethanol.

So, if the car's maximum, is their minimum, Sunoco gas is only acceptable some of the time.

[HarryHBMCC]

Australia at least also runs with ethanol blends and in fact a bill is before the house right now to increase the maximum allowable from 10% to 25% which is a problem as most cars, including the MINI, state that up to 10% is OK but no more. Whether it is forced to say so for gov't reasons or not I don't know but supposedly anything up to 10% ethanol is OK for the MINI. Other locations also likely include some ethanol as it is cheaper than gasoline and there is tons of corn rotting in silos right now.

As for 91 being the minimum and anything above it being a waste, my empirical testing says otherwise. My MINI Cooper doesn't run as well on 91 as it does on 92 or higher. Perhaps it is coincidence and the rough running is the result of something else about the 91 octane gas I've tried (both Shell and Petro Canada Premium grade) but for now I believe my car runs smoothest on 92 or higher. Some 91 octane gases give slightly higher mileage but especially in the upper part of the RPM band the car runs noticably better on 92-94 -- I think it is more powerful too but that could be my imagination and my butt dyno lying to me.

Harry

[GordonD]

Noahe

that's why i hate to read manuals they tell you things you would rather not know- thankfully it doesn't say that using 10% + enthinol will void the warrenty.

I did think that many (most?) Canadian fuels were mixed with ethynol in the winter for easier starting/avoid gas line freezing etc

[noahe]

Quote:

Originally posted by HarryIndiBlue
As for 91 being the minimum and anything above it being a waste, my empirical testing says otherwise.

Well, that's another good point. The standard line, is that anything above what the manufacturer states the car requires, is a waste of money.

Octane is an anti-knock agent. Knocking is caused by pre-ignition of one or more cylinders due to heat and compression (not spark). One cylinder exploding when it shouldn't, causes a great deal of stress on the engine, and consequently can shorten it's life. But, modern engine timing is adaptive, and electronic. Meaning it can advance or retard the spark timing to make sure this does not happen. So now, due to electronics, your 104 octane car, can run on 88, although it gets lousy power and mileage.

So, at some point the manufacturer states what the engine should run at, to make the engine efficient, powerful and reliable in hot or cold weather, and thick or thin air.

If the engine management can adapt to crappy gas, then certainly it can adapt to good gas. That's what your butt-o-meter is telling you. When you put in higher octane fuel, the car can adapt to the better fuel, and make more power. But only to an extent. The design of the engine determines the maximum compression of the engine, and more octance cannot make more power beyond this.

But, in certain conditions, more octane will allow for more power.

But usually, on average, across all conditions, more than the recommended octane is a waste.

[HarryHBMCC]

Remember that knocking is dependent on air pressure. I assume that, as you say, they take the normal range of air temperature and pressure into account when recommending a 91 octane rating but it seems to me like they have erred a little on the low side and at least 92 or 93 is required to really get the best out of it.

Are you sure that >10% ethanol is even allowed in Ontario right now? Most pumps say "up to 10%" and they mean exactly 10% as it is cheaper than gas by volume. I didn't think it was legal to put more than 10% in but I could be wrong. We'd better hope that 10% is OK as it will be required to have 5% ethanol in Ontario by 2007 and 10% in all gas by 2010 unless I'm remembering the regulations incorrectly.

Harry

[noahe]

Quote:

Originally posted by HarryIndiBlue
Remember that knocking is dependent on air pressure. I assume that, as you say, they take the normal range of air temperature and pressure into account when recommending a 91 octane rating but it seems to me like they have erred a little on the low side and at least 92 or 93 is required to really get the best out of it.

Are you sure that >10% ethanol is even allowed in Ontario right now? Most pumps say "up to 10%" and they mean exactly 10% as it is cheaper than gas by volume. I didn't think it was legal to put more than 10% in but I could be wrong. We'd better hope that 10% is OK as it will be required to have 5% ethanol in Ontario by 2007 and 10% in all gas by 2010 unless I'm remembering the regulations incorrectly.

Harry

You're right, all manufacturers set their cars conservatively, or else the car might do something funny, like not start on a cold morning, (eek.) or not run in the mountains. So, in our currently cold, oxygen rich, relatively low altitude conditions, more octane will be more fun.

I'm not sure if there's a max allowable limit on Ethanol. Makes sense if there was. I just was erring of the side of caution, if Sunoco says it puts in 10% minimum. If they're also legislated to 10% max, then it's not much of a selling feature in the pamphlet.

Also avoid Petro Can's "Tactrol" additive. They will not disclose what it is, or how much they put in their gas.

There is a thread on Canadian Gasoline on MINI2, where I detailed my findings and opinions.

[Jorgeaz]

Thanks for the info.

I pretty much stick to the BP/Amoco "clear ultimate" 93AKI. maybe it has lower sulphur (being clear), maybe it doesn't.

[MaximumPDA]

Here is a great page on fuel:

http://www.76.com/cgi-bin/b2cpt01/sc...1&catoid=-8318