Research octane number 91

[Mach1Owner]

I found this in my cars manual, not sure what it means, would it be that that R in (R+M)/2 is 91?

At Least 87AKI (Anti-Knock Index) number (Research octane number 91)

 

[earlyre]

it's a different scale for rating gasoline, used in most of the rest of the world.
http://en.wikipedia.org/wiki/Research_Octane_Number#Measurement_methods
"Research Octane Number (RON)

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.
Motor Octane Number (MON)

There is another type of octane rating, called Motor Octane Number (MON), which is a better measure of how the fuel behaves when under load, as it is determined at 900 rpm engine speed, instead of the 600 rpm for RON.[1] MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON, however there is no direct link between RON and MON. Normally, fuel specifications require both a minimum RON and a minimum MON.[citation needed]
Anti-Knock Index (AKI)

In most countries, including Australia and all of those in Europe[citation needed], the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI, and often written on pumps as (R+M)/2). It may also sometimes be called the Pump Octane Number (PON).
Difference between RON and AKI

Because of the 8 to 10 point difference noted above, the octane rating shown in Canada and the United States is 4 to 5 points lower than the rating shown elsewhere in the world for the same fuel. This difference is known as the fuel's sensitivity,[4] and is not typically published for those countries that use the Anti-Knock Index labelling system."

 

[Boomer]

Interestingly, the RON and MON cannot be too far apart, more than about 8 or so points without some problems occurring relating to engine longevity. This occurred in Germany years ago and resulted in burnt pistons, etc. It is a rare occurence but gasoline formulators are well aware of it. The greater the difference, the higher the sensitivity of the fuel is said to be.

 

[Mach1Owner]

TIL, thanks Gentlemen.

 

[y_p_w]

A fuel of pure iso-octane would have an RON of 100 and an MON of 100. Kind of weird with zero spread, but that's what it is.

The testing is supposed to be the equivalent antiknock performance of a combination of iso-octane and n-heptane. So 91 RON is supposed to be an equivalent performance in the variable compression test with 91% iso-octane and 9% n-heptane. If the number is higher than 100, then there have to be alternate testing techniques.

I've seen some strange claims in my day, including one that the octane rating was a measure of how much octane is present in the fuel, even though it's only in comparison to a reference fuel.

 

[GaleHawkins]

I thought octane was determined by the speed a fuel burnt in the cylinder?

 

[Shannow]

Originally Posted By: GaleHawkins
I thought octane was determined by the speed a fuel burnt in the cylinder?


That's octane 101 on the Interwebs, and it's not right.

It's the resistance of fuels to spontaneously ignite under heat and pressure...once they are ignited by a spark, they burn across the chamber at about the same speed.

Scale is pretty arbitrary, with iso octane (2,2,4 trimethyl pentane, so it's actually quite a compact molecule, and hard to ignite with heat and pressure...sparks do fine) at 100, and N-haptane (7 carbons straight chain), as "zero"...and the fuel being tested being bracketted by an octane/heptane mix 2 percentage points apart defining it's octane.

Zero would, you would think, have no resistance to compression, which isn't the case at all.

Before this test was standardised, fuels had "toluene" numbers

 

[Boomer]

Aromatics, very short chain hydrocarbons (methane through butane) and highly branced alkanes of eight carbons will all have high RON numbers. Methanol and ethanol do as well. Generally, you get a lower yield of these materials from a barrel of oil than just straight chain hydrocarbons of lower octane values. This is why higher octane fuels cost more as a rule. Remeber, higher octane only is needed if you have the higher compression ratios that need it to prevent pinging.

So gasoline is a blend designed to give a reasonable RON to MON spread, meet emissions requirements and the lowest possible costs at the highest possible yields. The best fuel for your vehicle is the one that gives you the lowest cost per mile to drive with little or no noticeable pinging or knock.

 

[GaleHawkins]

Originally Posted By: Shannow
Originally Posted By: GaleHawkins
I thought octane was determined by the speed a fuel burnt in the cylinder?


That's octane 101 on the Interwebs, and it's not right.

It's the resistance of fuels to spontaneously ignite under heat and pressure...once they are ignited by a spark, they burn across the chamber at about the same speed.

Scale is pretty arbitrary, with iso octane (2,2,4 trimethyl pentane, so it's actually quite a compact molecule, and hard to ignite with heat and pressure...sparks do fine) at 100, and N-haptane (7 carbons straight chain), as "zero"...and the fuel being tested being bracketted by an octane/heptane mix 2 percentage points apart defining it's octane.

Zero would, you would think, have no resistance to compression, which isn't the case at all.

Before this test was standardised, fuels had "toluene" numbers


Thanks. It is a little beyond my level of chemistry but does make sense.

After Jay Leno had a Archoil guy on one of his shop videos it got my attention. While they have a full line of products it was their Archoil AR6200/AR7200 (both are same except for labeled use) that got my attention the most.

It is a fuel additive for any type engine it seems and it lowers the start of the burn by 400F but do not know if that impacts the octane rating or not. It does say it lowers the need for premium fuel.

http://www.archoil.com/index.cfm/products/ar6000/ and I got the 4.2 bottle in the mail this week but have not used any yet.

AR6200 tested under the EPA Carbon Balance (CMB), the most accurate and number one test used by the EPA to test fuel mileage and emissions resulted in over 8% improved fuel economy. AR6200 also tested under the SAE J1321 Type ll test resulted in a 8.20% improvment in fuel economy.

AR6200 increases the surface area of fuel droplets to increase the burn rate resulting in a more efficient use of fuel. AR6200 is engineered to lower the ignition point of fuel as much as 400º F therefore modifying the burn at a lower temperature utilizing more BTU’s and providing more energy during the combustion process. This also eliminates black smoke with a major reduction in carbon due to a much higher burn rate. A decrease in fuel usage is realized with added horsepower and torque. AR6200 is for use in all carbon based fuel types including heating oil and bunker fuel, 1 ounce treats 80 gallons of fuel.

AR6200 is used worldwide in every type of application including power plants, ships, mining equipment, fuel storage, fleets, adding needed fuel attributes not added at the additive dispersant location.

AR6200 is also a fuel stabilizer for maintaining fuel not in use for many years. AR6200 is also a polymerization retardant which restores aged fuel. Diesel fuel is estimated at 35% degraded by the time it reaches the filling station.

AR6200 is the only fuel treatment needed to address the major limitations inherent in fuel

AR6200 is nonhazardous and may be air freighted worldwide

AR6200 CMB test are available upon request for fleets, mining and industry

 

[Clevy]

OP

If you own a 2003/2004 ford Mach 1 then you've got a 4v DOHC engine with a 10-1 compression ratio and you require 91 octane fuel.
The automatics came with a 6 bolt cast crank,same as the 2v engines of the same years and the 5 speed came with an 8 bolt forged crank,same as the terminator cobra's.
I know these cars and engines intimately.
The 4v engine does come equipped with a knock sensor however they aren't very reliable and the use of lower octane fuel contributes to the problems encountered in the rear cylinder(number 8).
Use only 91 octane or higher. I built my 2000 into an 04 Mach 1. I know every single connection,wiring harness,etcetera,etc.
If you haven't been using high test you may encounter problems down the road.

 

[Mach1Owner]

Thanks, but the Mach1 was totaled a few weeks ago. I actually used to run it on 89 just fine when I wasn't planning to take it to the track. Even with a Lund dyno tune for 93oct. Ran solid for 10 years.

 

[y_p_w]

Originally Posted By: Shannow

Scale is pretty arbitrary, with iso octane (2,2,4 trimethyl pentane, so it's actually quite a compact molecule, and hard to ignite with heat and pressure...sparks do fine) at 100, and N-haptane (7 carbons straight chain), as "zero"...and the fuel being tested being bracketted by an octane/heptane mix 2 percentage points apart defining it's octane.

Zero would, you would think, have no resistance to compression, which isn't the case at all.

Before this test was standardised, fuels had "toluene" numbers

I'm pretty sure the reference fuels to determine performance were chosen more or less arbitrarily at some point. The other issue is that we're drawn to numbers as if they were some sort of absolute representation. The difference in 91 AKI and 93 AKI are actually pretty substantial - even the small difference doesn't register as such in our minds.

If we were to think of everything in absolute temperature terms, the difference in 10ºC to 32ºC is really 283 degrees Kelvin to 305 degrees Kelvin. May not seem that that much difference, but our bodies and mechanical systems can tell.