Five diff octane at the pump

I'll wager that they don't have 5 underground tanks

 

Most retailers put in just 2; the 87 and 93. And maybe a 3rd for diesel.

 

Grumble grumble...we used to have 94, but now only 93.

 

Could they have 2 tanks and mix the gasoline at a certain ratio to make the other octanes? Or does gasoline not work like that?

 

Most gasoline stations have 3 underground tanks: regular, midgrade, and premium. The octane ratings vary across the country for each grade. If the location has diesel, there is a 4th tank. The dispenser shown in the photo looks like it came from an old Sunoco location. Those locations had two tanks and the grades were mixed at the dispenser. The proceedure was unreliable and expensive to maintain and for the most part phased out.

 

i stopped to fill fuel at a charlotte,nc station and they had 104 octane at the pump. granted, it was near the race track. had i not been in a rental car, i would of bought some just to see the difference.

 

I believe that this also contributes to the high price due to having to refine many different blends. I would bet if we setteled on just a few fixed blends then we would have refinery capacity and the price would go down. There is a 20 Cent difference from my county vs. the county accross the river due to the different blend requirement. Dumb. Oh well what the hell. Enjoy the ride

 

That is exactly how it is done. There are only two gasoline tanks. Regular and Premium. The Midgrade is a mix of the two.

 

You guys are lucky. 90 is the highest for cars in Alaska. There are two theories:

1. The local companies (Mapco, Tesoro) made 92 and the national ones (Chevron, Shell, etc.) made 92. Local could not compete on price, and the state made a law that no station could sell higher than 90, where the local companies could compete.
2. All of the effort is put towards aviation, and we get the left over for our cars.

Either way, all we get is 90.

 

I also saw an investigative journalism show which explained the distribution system (gasoline pipelines) in the US. It is apparantly just sent in raw batches to several gas terminals, and at that point there was no difference between say Shell or Mobil. At their local terminal they might put in detergents or other additives to make it a little different, but the feedstock was all the same. And IIRC, there were really just two grades in common use. They both went to each city IN THE SAME PIPELINE, just in big "slugs" supposedly carefully separated at each end.

I also was once told an octane theory by a chem-E guy who worked in the refining industry. He claimed that mixing two non-leaded grades to get a mid-grade is not a linear process - i.e. you might not get 90 just because you mixied 92 and 88. His notion was that the presence of even a little of the low grade type molecules could make a car detonate nearly as bad as the low grade itself, as there was no lead additive to mask the presence of these easy-to-detonate type molecules.

I am afraid that we may soon be hunting down 93 octane like a search for the whooping crane or buying AVgas at the airport.

 

Why is there such a big difference with West-Europe? In most countries here you have the choice of 95 or 98 (and sometimes even higher). I always choose 98 for my Impreza as recommended by Subaru (I've heard that in Japan you can find 100 or even 102 on most pumps).
The funny thing is that in Italy, the land of the supercar, I couldn't find a pump with 98!

 

The USA uses the RON+MON/2 scale while Europe and most of the rest of the world uses only RON to measure octane.
http://www.btinternet.com/~madmole/Reference/RONMONPON.html

 

All the refiners have arrangements to buy base gasoline from each other. The additives are added at the local terminal. The "slug" you referred to is called a pig. http://www.ppsa-online.com/about-pigs.php

I think you got this backwards. All the blending charts like this one show a linear relationship for unleaded gasolines. http://www.rockettbrand.com/technicals/documents/BlendingCharts/93OctaneBlendingChart.pdf
The leaded and unleaded mix are non-linear as told to me by a refinery process engineer. You get a bigger boost with the (TEL) of leaded gasoline. Disclaimer: I do not advocate the use of leaded gasoline in street driven automobiles. If caught, you can be fined up to $25k by the Feds.

Here is an updated chart I have posted before. http://www.exxon.com/USA-English/Files/US%20Gasoline%20Map%20100102.pdf
BTW, you people running carbs need to realize that what was appropriate jetting 30 plus years ago might not appropriate today.

 

Or my friend got it backwards - I have no way of knowing, and his real job was to measure the properties of propane as it came out of processing...I would have intuitively put it the way you just did. Especially since they used to just dump in the tetraethyl as needed because it was less expensive than expensive super-refinement on the gas itself.

On another side issue - is this ethanol fixation perhaps a friend in disguise (so long as it is not E85) as it gives a little octane boost?

Final point - what real good is five different octanes (even if the mixing actually was done precisely)? Oh - I am going to have to move up from 91 to 92 because I am just pinging like crazy? Really? Or, more likely IMHO, just a marketing gimmick?

PS - I did not use the term "pig" because I am such a correct and sensitive person.

 

Yep, it was cheaper than what has to be done now. Back in the day, the only difference between Regular Leaded and Premium Leaded was the amount of TEL.

In a way yes. Ethanol was added because it is an oxygenate and helped lower emmisions for EPA compliance. Ethanol adds octane but you didn't see it at the pump because refiner's just lowered the grade of base gasoline to give the same overall octane. Octane=money. You won't get it for free.

I thought it was a P-chop, but apparantly not. http://findarticles.com/p/articles/mi_hb4898/is_200211/ai_n18006329

 

How'd they get away with that? My '03 Lincoln requires 91+ and believe me you don't want to skimp on it. It starts pinggin' all over the place!

Edit: by the way most of the places here in WA have three grades 87, 89, and 92.

 

Thanks for the info.

 

Actually, I find this a very informative discussion.

Thanks!

I recently ran low and had to pull in to a generic station. I've been advised to not use generics as all fuel is not the same. Perhaps someone has additional information, but I suppose it relates to the additives.

CW

 

It also used to relate to the condition of the tanks and equipment. I don't think that's as big a problem anymore since most states have probably mandated new tanks.

 

This is about 10 years old but most of it is still pertinent. http://vettenet.org/octane.html

 

Ok, so I if I read that correctly, it really doesn't matter what goes in the tank as long as I change brands periodically (as the article suggests, every 5K or some lesser interval of at least 1K miles) so I get the maximum benefits of the additives' cleaning power by changing the cleaners.

I'm supposing that there are several reasons why a generic fuel is lower priced, and I'm going to guess that the three single largest reasons are lower additives, marketing and R&D costs.

So, I realize it's a gross oversimplification, but I get the sense that it's OK from that article to use fuel from a "low end" brand for a spell, if one desires.

CW

 

You got it!