Octane around the world
 

I was reading some old posts on the fuel types being purchased. I noticed that a number of X5 owners were even buying <90 octane fuel for their cars.

It got me thinking if octane levels vary from country to country. Here in Australia we have:

Standard ULP - 91/92 octane
Premium - 95 octane
Ultra Premium - 98 octane
Ultimate Premium (with 5% ethanol) - 100 octane

Is that different to the rest of the world?

We don't really get past 93 here, occasionally one might come across 94..

Oz,
In most of the states we have:
-"Regular" unleaded at 87 Octane
-"Mid Grade" unleaded at 89 "
-"Premium" or "Super" unleaded at 91-93/94 octane, depending upon state/area.

There are some racing fuels available and of course, diesel.

Cheers from the Northern Hemisphere Colonies!
BR,mD

There is a Sunoco gas station near me, just south of Philly that supposedly has "260 GT Unleaded" rated at 100 octane. There are also Purple Sunocos around the US that sell "racing fuel" not intended for street use but I have to imagine people use it for street cars all the time. I think the Sunoco Purple dealers sell unleaded fuel rated at over 105 octane.

I've never seen anything past 91 octane here in Canada.
It would be nice to try some 100oct.

most stations in canada only carry a maximum of 91 octane (petro-can, esso, shell) I believe the only company that sells gasoline over 91 octane is sunoco, which has ultra 94

I believe different countries use different numbers to rate their octane. There's a "octane research number" and a "octane knock index" (or something like that. The research number is always higher. I remember reading this in the manual that came in our LS400 when we got it back in 91. If I'm not mistaken, an octane research number of 98 equals 91 "knock index" octane. The numbers we see here in the US are the latter. On the other hand, it's the other way around in Taiwan, so while people think they're getting 98 octane, they're actually getting 91 :confused:

from http://www.sizes.com/units/octane_number.htm


A rating of a gasoline in terms of its propensity to cause knocking.
Gasoline is not a chemical compound; it is a mixture of many different compounds.
By 1882, experimenters noted that spark ignition internal combustion engines knocked more on some gasolines than on others. Ideally, when the spark ignites the fuel-air mixture in the cylinder of a gasoline engine, the flame front spreads out smoothly from the spark into the unburned part of the mixture, giving a gradually increasing push to the piston. However, as the flame front spreads, the hot products of combustion behind the flame front compress the unburned part of the fuel-air mixture. Compressing a gas raises its temperature. Radiation from the burning fuel can also raise the temperature of the unburned fuel. The unburned fuel-air mixture can be heated so much that some of the hydrocarbons in it reach their ignition temperature and ignite all at once–explosively, causing knock. Knock can destroy engines.
To select a way of rating the propensity of a gasoline to cause knocking, a Cooperative Fuel Research Committee was set up in 1927 comprising representatives of the American Petroleum Institute, the American Manufacturers Assn., the National Bureau of Standards, and the Society of Automotive Engineers. A single-cylinder engine with a variable compression ratio had been built by John Campbell at General Motors. Graham Edgar at the Ethyl Corporation prepared samples of various pure hydrocarbons. including normal heptane distilled from the sap of the Jeffrey Pine. The engine enabled researchers to burn mixtures of Edgar's pure hydrocarbons while varying the compression, to see at what point knock occurred.
In 1929, T. A. Boyd proposed to the committee that a variable-compression engine be the basis for rating gasolines. Some committee members felt that such an engine would be too complicated for routine use, but the Waukesha Engine Company volunteered to build a prototype. By 1931 Waukesha was able to display its engine at a meeting of the American Petroleum Institute; skeptics were persuaded and thousands of the engines were subsequently built. (In fact, in 1980 the American Society of Mechanical Engineers designated the engine an “engineering landmark.”)
In the committee’s opinion, no one test was able to give a rating useful over the whole range of operating conditions, and so two methods were defined: the Motor Method (ASTM d 357) and the Research Method (ASTM d 908). Both methods are based on comparing the performance of the gasoline being tested with the performance of a mixture of 2,2,4, trimethyl pentane (also called iso-octane) and normal heptane. The octane number is the percentage of iso-octane in that mixture whose performance (in regard to knocking) is the same as that of the gasoline under test. For example, if the performance of the gasoline under test is the same as that of a mixture of 80% 2,2,4,trimethyl pentane and 20% normal heptane, the gasoline is 80 octane. Octane numbers above 100 are found by extrapolation.
The two test methods give different results, and the difference in the results differs from gasoline to gasoline. As a broad generalization, the motor method captures the gasoline's performance at high engine speeds and loads, and the research method at low speeds. The octane rating on American gasoline pumps is usually the average of the research and motor octane numbers, which is sometimes called the anti-knock index. In Europe, pumps have traditionally displayed the research octane number.
Fuel is just one of many factors affecting whether an engine will knock. Consequently in any particular engine gasolines with the same octane number but from different blenders may perform differently: one may cause knock and the other may not. Similarly a gasoline that causes knock in one engine model may not in another. This is not proof that the octane rating was inaccurate.

So, in plain words; will 89oct make our x's knock?
Does anyone use anything below 91oct?

Yes, I accidentally put 87 in once and putting a load on the engine at low RPMs (read: anything more than 1/4 throttle at low RPMs) caused TERRIBLE knocking. With 91, I only occasionally get slight knocking under load with 1/2 throttle or more I'd say.

In CA the highest oct i see is 91, in NJ is 93, the X gets the 93, but with these prices sometimes I feel like putting 89.