YACT: Octane Rating

[NutBucket]

Taken from: Answers.com

The most important characteristic of petrol is its Research Octane Number (RON) or octane rating, which is a measure of how resistant petrol is to premature detonation (knocking). It is measured relative to a mixture of isooctane (2,2,4-trimethylpentane) and n-heptane. So an 87-octane petrol has the same knock resistance as a mixture of 87% isooctane and 13% n-heptane.

There is another type of Octane, called "Motor Octane Number" (MON), which is a better measure of how the fuel behaves when under load. Its definition is also based on the mixture of isooctane and n-heptane that has the same performance. Depending on the composition of the fuel, the MON of a modern petrol will be about 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the 'headline' octane that would be shown on the pump is the RON: but in the United States and some other countries the headline number is in fact the average of the RON and the MON, sometimes called the "Road Octane Number" or RON. Because of the 10 point difference noted above this means that the octane in the United States will be about 5 points lower than the same fuel elsewhere: 87 octane fuel in the United States would be 92 in Europe.

It is possible for a fuel to have a RON greater than 100. This reflects the fact that isooctane is not the most knock-resistant substance available. Racing fuels, Avgas and LPG typically have octane ratings of 110 or significantly higher.

 

[Stumps]

sound bout right, although LPG in Australia only has a rating of 105, my dad found this out when he rebuilt his motor to suit LPG, with the timing and mixtures spot on the car started to ping under light load and got worse as the load increased, when we investigated we found out that the factory compression ratio of 11:1 was still to high for LPG, when we contacted a few fuel companies to find out why, BP and Shell advised us that the Octane rating for LPG in Australia is really low at 105.

 

[mugs]

What genius gave two different octane ratings the same abbreviation? Thanks for the informative post. I always wondered what the R+M/2 thing meant on the sticker.

 

[Zenmervolt]

Uh, duh?

ZV

 

[NutBucket]

I don't know why the have the same abbreviation but I just know we get piss gas here in Cali...especially premium.

 

[NutBucket]

Originally posted by: Zenmervolt
Uh, duh?

ZV

duh for some people Zen😉

 

[mugs]

Originally posted by: Zenmervolt
Uh, duh?

ZV

Considering that the overwhelming majority of people probably did not know this, isn't that a pretty dumb thing to say?