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What is RON, MON and what do they use in the States? 

Re: RON vs MON
Date:  Fri, 12 Jan 2001 16:13:18 -0800
From:  "PHINNEY,HARRY K (HP-Corvallis,ex1)" <harry_phinney@xxhp.com>
Reply-To:  cbr900@microwave.ph.msstate.edu
To:  "'cbr900@microwave.ph.msstate.edu'" <cbr900@microwave.ph.msstate.edu>

> I thought that we used "research" (engineers calculating octane rating)
> and "method" (actual engine testing, or "reality").

When I was in school (longer ago than I care to ponder) they were termed Research Octane Number (RON) and Motor Octane Number (MON). In the US the posted numbers are indeed the average of the two, and the MON is always significantly lower than the RON. The RON is determined by chemists, and the MON is (or at least was) determined by running the fuel in a standardized engine with an adjustable compression ratio. With the engine running at a standard speed and load the compression ratio is increased until detonation is detectable.
Comparison with other standard fuel results then gives the MON.

Harry Phinney

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What is an Octane Number?
The amount of resistance that a fuel has to detonation. The higher the number, the less likely it is that a particular fuel will detonate in a particular engine. The number is as compared to a standard fuel (not necessarily gasoline)

Octane? Resistance to knock? Compared to what?
Isooctane (C8C18) is the high value reference fuel. It has a knock resistance value of 100 RON.
N-heptane (C7C16) is the low value reference fuel. It is very prone to knock and has a value for 0 RON (zero/naught).
For values above 100 RON, a mixture of isooctane and tetraethyl lead mixed according to DIN 51756 (DIN in at least in most of the world) is used.

How do they raise the knock resistance of a fuel?
In the old days, TetraEthyl Lead (TEL) or TetraMethyl Lead (MEL) was added, with TEL being the most common in the United States. Now, as leaded fuels are not allowed to be sold in many areas, other, generally more expensive and less effective as compared to cost, fuel additives are added. Lead was an extremely effective knock suppressant.

How much lead was in "leaded" fuel?
By law, fuels intended for on road use have been limited in maximum lead content for some time. Maximum lead content was limited to .15 to .33 grams/Liter in the late 1970's.
Lead poisoning causes brain damage. Most fuel has been unleaded for quite some time. People born after the late 70's must be much smarter than the older people.

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