Supermarket fuel, false economy..?

[neil_merseyside]

I liked the Bob Monkhouse story of how he added fuel to a grumpy hotel owners new car so much so he bragged he was getting lots of mileage per tank, then when he left it alone (drained even) then grumpy wasn't a happy owner, more so when car dealer explained it was impossible to get 100mpg

 

[wafter]

Here's another little snippet that might be of interest. Quite a few years ago a fuel supplier launched a new grade of premium fuel. Over time they started receiving reports of significantly improved fuel economy from customers - well beyond any scientifically-explainable benefit and much more than their own testing had shown, so they investigated. Long story short, it was down to how people 'measure' fuel economy. People were filling their tanks until the nozzle automatically shut off, then driving and when they came to fill up again they'd done far more miles on the tank than previously. It turns out it was because the new fuel formula foamed less during filling, so this allowed more fuel to go into the tank before the nozzle clicked off. People's casual measurement techniques convinced them it was way better than it actually was.

Interesting point; although I guess something that would be accounted for if filling with the same fuel for consecutive tanks..?

 

[gbb]

No, octane rating is not energy content. Octane rating is a measure of resistance to preignition, with a higher number meaning more resistance to preignition, meaning ignition timing can be advanced which can lead to a more complete combustion and hence some performance gain.

Thats right. I suppose more modern cars ECUs can modify the advance automatically when using different RONs, certainly my 2001 Vectra SRI had a 'switch' in the engine compartment , you selected which depending which RON you were using.

 

[Gunk]

I put high octane in my motorbike, only because of the lower Ethanol content, usually V power. Both cars are diesel and I chuck anything in them, I can’t tell any difference between Shell and Asda.

 

[Alex321]

Interesting point; although I guess something that would be accounted for if filling with the same fuel for consecutive tanks..?

Not really. The people who think it is ding so well work on the basis of a "tank full", rather than counting the actual litres/gallons.

And if the tank can be filled fuller each time, each tank will go further.

 

[Arrowfoot]

Next time you see a fuel truck replenishing at a branded garage, why not wait for the driver to finish and ask him. The same RON gets into supermarket station from the same tanker during the run and they come from the same refinery. Ask politely and he may even show you the delivery logs. @Baldy is right

Supermarket don't sell inferior fuel if it i the same RON. Higher the RON, the engine gets better treatment and hence better price.

Slight variations on the higher RON where brands do fuel additives blending for marketing and brand differentiations are more targeted at cleaner engines. Mileage will be within the same zone RON for RON.

Refiners rarely touch the refining process output as prices are volatile and supply comes from all over the World. Refiners biggest issue is sulphur content and to bring it within specs as untreated oil from different fields differs widely

Supermarket fuel is also part of the loss leader bucket such as eggs and milk. Its to draw customers and whack you hard on branded detergents, toothpaste, washing powder and organic and free range products.

If fuel of the same RON differs in performance there would have been comparisons tables run by some brands and consumer organisations.

 

[figbat]

Next time you see a fuel truck replenishing at a branded garage, why not wait for the driver to finish and ask him. The same RON gets into supermarket station from the same tanker during the run and they come from the same refinery. Ask politely and he may even show you the delivery logs. @Baldy is right

Supermarket don't sell inferior fuel if it i the same RON. Higher the RON, the engine gets better treatment and hence better price.

Slight variations on the higher RON where brands do fuel additives blending for marketing and brand differentiations are more targeted at cleaner engines. Mileage will be within the same zone RON for RON.

Refiners rarely touch the refining process output as prices are volatile and supply comes from all over the World. Refiners biggest issue is sulphur content and to bring it within specs as untreated oil from different fields differs widely

Supermarket fuel is also part of the loss leader bucket such as eggs and milk. Its to draw customers and whack you hard on branded detergents, toothpaste, washing powder and organic and free range products.

If fuel of the same RON differs in performance there would have been comparisons tables run by some brands and consumer organisations.

RON is not a measure of quality, it is a measure of resistance to preignition. Yes, all 'regular' road fuel has to be at least 95 RON - there's no specific target for 'premium' fuels so you'll see 97, 98, 99 etc dependent on supplier but a higher RON is not necessarily a higher quality. Petrol must meet BS EN 228, which defines a level of RON and various quality limits (for diesel it's BS EN 590 and cetane number).

Fuel is made up of a base fuel mix, which is refined and blended to hit the RON, and then an additive package. The amount and type of additive varies between brands - there are things like antifoam, stabilisers, ignition improvers, octane improvers, detergents etc but not all brands have all of them or at the same levels. Your tanker driver will not know what additives are in the fuel being delivered.

The base fuel comes from the same refineries, yes - there are only a limited number of them around - plus the requisite amount of ethanol or FAME (petrol or diesel). But the additives come from various suppliers and their formulations are specific and proprietary to each brand.

It's like a cup of coffee - the water is the main thing and comes from the same source, but then you can either spoon some instant granules into it or you can run it through finely ground beans at the correct pressure and temperature for the right amount of time. The water is the same, the coffee is not.

 

[wafter]

To clarify I'm talking about petrol; no experience of diesel in this regard

 

[cougie uk]

Ah we will miss these conversations when we are all on electric cars.

 

[figbat]

To clarify I'm talking about petrol; no experience of diesel in this regard

Yeah, I guessed that and this is where the conversation usually goes because diesel is not marketed with varying cetane numbers.

Since we're here though, to push the RON thing a bit further - what exactly is it? RON stands for Research Octane Number and is effectively a comparison of how a given fuel compares to pure iso-octane* in terms of resistance to preignition. You'd think you could just run some kind of analysis to determine the composition of the fuel to determine this but RON is actually tested by engine on every batch of fuel. The engine is a variable-compression engine - the compression ratio is gradually increased until preignition is detected. The batch of fuel is run and then compared to mixes of iso-octane (which has a RON of 100) and n-heptane (RON = 0); a RON of 100 means the fuel behaves the same as a 100% iso-octane; 95 RON is the same as 95% iso-octane and 5% n-heptane and so on.

In the USA and other countries they don't use RON - they use AKI (anti-knock index) which is the average of RON and MON. MON is Motor Octane Number and for a given fuel is always lower than its RON. This is due to some differences in how RON and MON are tested in terms of engine speed, intake air temperature, fuel temperature and ignition timing. MON is a more severe test and arguably more relevant to real world driving conditions.

So when someone in the US say "93 octane" and we think "pfft, is that all?!", we're comparing apples with pears. There's no fixed relationship between RON and MON but US 'octane' numbers are typically 3-4 lower than RON.

* chemistry geek fact: iso-octane isn't really octane at all. Octane is, speaking purely from a formal nomenclature POV, a fully-saturated hydrocarbon chain with 8 carbons in it. Iso-octane is a molecule whose longest continuous carbon chain is actually only 5, making it a pentane. It is, in fact, 2,2,4-trimethylpentane which has 8 carbons in total, but not all in a long chain. This is important because it is what's known as a 'branched' hydrocarbon, rather than a linear one. Branched molecules resist preignition much better than linear ones (hence why n-heptane, a linear 7-carbon molecule, has a RON of 0).

 

[figbat]

Ah we will miss these conversations when we are all on electric cars.

There will be premium electrons.

 

[wafter]

Yeah, I guessed that and this is where the conversation usually goes because diesel is not marketed with varying cetane numbers.

Since we're here though, to push the RON thing a bit further - what exactly is it? RON stands for Research Octane Number and is effectively a comparison of how a given fuel compares to pure iso-octane* in terms of resistance to preignition. You'd think you could just run some kind of analysis to determine the composition of the fuel to determine this but RON is actually tested by engine on every batch of fuel. The engine is a variable-compression engine - the compression ratio is gradually increased until preignition is detected. The batch of fuel is run and then compared to mixes of iso-octane (which has a RON of 100) and n-heptane (RON = 0); a RON of 100 means the fuel behaves the same as a 100% iso-octane; 95 RON is the same as 95% iso-octane and 5% n-heptane and so on.

In the USA and other countries they don't use RON - they use AKI (anti-knock index) which is the average of RON and MON. MON is Motor Octane Number and for a given fuel is always lower than its RON. This is due to some differences in how RON and MON are tested in terms of engine speed, intake air temperature, fuel temperature and ignition timing. MON is a more severe test and arguably more relevant to real world driving conditions.

So when someone in the US say "93 octane" and we think "pfft, is that all?!", we're comparing apples with pears. There's no fixed relationship between RON and MON but US 'octane' numbers are typically 3-4 lower than RON.

* chemistry geek fact: iso-octane isn't really octane at all. Octane is, speaking purely from a formal nomenclature POV, a fully-saturated hydrocarbon chain with 8 carbons in it. Iso-octane is a molecule whose longest continuous carbon chain is actually only 5, making it a pentane. It is, in fact, 2,2,4-trimethylpentane which has 8 carbons in total, but not all in a long chain. This is important because it is what's known as a 'branched' hydrocarbon, rather than a linear one. Branched molecules resist preignition much better than linear ones (hence why n-heptane, a linear 7-carbon molecule, has a RON of 0).

Thanks - brings back memories of being taught some of that many years ago and some interesting hours spent in the uni's engine lab

 

[Ming the Merciless]

Ah we will miss these conversations when we are all on electric cars.

Supermarket electrons are sluggish though but

 

[Scottish Scrutineer]

Supermarket electrons are sluggish though but

And have inferior additives

 

[Alex321]

The base fuel comes from the same refineries, yes - there are only a limited number of them around - plus the requisite amount of ethanol or FAME (petrol or diesel). But the additives come from various suppliers and their formulations are specific and proprietary to each brand.

So are you saying that the tanker loads up with fuel at the refinery, then at each filling station, puts in appropriate additives for the brand as they are unloading?

Somehow I don't think so.

Where a tanker only delivers one brand of fuel, yes, it can be the one with the additives for that brand, and will be loaded from a brand specific tank at the refinery.

But arrowfoot above is talking about the situation where one tanker, with one load of fuel, delivers to several different forecourts, some being branded, some being supermarket. In those cases, it is the same fuel going into each forecourt tank.