Supermarket fuel, false economy..?

[Jody]

I know Super gives me 10% better fuel efficiency than E10 on a 'run' - I'll get 44 mpg over 70 miles on super, or just 40 mpg on E10,. Both still supermarket fuel.

Almost no point in doing it by the time you compensate for difference in cost per litre.

 

[fossyant]

Almost no point in doing it by the time you compensate for difference in cost per litre.

It's about 5% more in cost. (this was pre crazy pries - not bothered since.

 

[Cerdic]

As I understand it, the octane rating relates to the energy contained in a given volume of fuel. So if the octane rating is the same, ie 95 RON, you should get the same mpg.

 

[figbat]

As I understand it, the octane rating relates to the energy contained in a given volume of fuel. So if the octane rating is the same, ie 95 RON, you should get the same mpg.

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.

 

[ebikeerwidnes]

As far as I understand the situation - the fuel economy of supermarket v. branded depends on the car

Some makes are more sensitive than others

more performance brands - like BMW - get more advantages from branded fuels than more family orientated brands

Since 'the great panic' a while ago the ESSO station near me has always been the cheapest so the choice has been easy!

 

[oldwheels]

I used to be a tanker driver, it all comes out of the same pipe.

I knew a tanker driver who drove from the then Esso depot in Bowling [now closed] and he said the same.

 

[Ming the Merciless]

I got some diesel from Tesco and achieved 100 mpg. It was a BOGOF offer

 

[figbat]

As far as I understand the situation - the fuel economy of supermarket v. branded depends on the car

Some makes are more sensitive than others

There is certainly the possibility that some engines can take advantage of higher RON fuels, by the use of dynamic engine mapping combined with knock sensors allowing the ECU to actively find the sweet spot of ignition timing. Some cars only have the ability to retard timing to prevent damaging knock, but not necessarily to advance timing to hunt down best performance - they have a fixed base timing and the ability to retard for safety, so won't see any benefit* from a higher RON.

*there is a case where an older engine may benefit from higher RON, that being if the engine is significantly coked-up. In this case the presence of carbon deposits in the combustion chamber had two impacts: (1) it reduces the volume of the combustion chamber, thereby increasing the compression ratio (and hence increasing the chance of preignition) and (2) the carbon deposits get hot and act like a glow plug, again potentially setting off combustion ahead of the spark timing.

I knew a tanker driver who drove from the then Esso depot in Bowling [now closed] and he said the same.

With respect, the tanker drivers aren't formulating nor blending the fuel. They put this pipe into that nozzle and take it to this station for delivery. Compartmented trucks can make deliveries of different fuels to different forecourts. The formulating and blending which differentiates fuels is confidential and done whether they know it or not.

 

[oldwheels]

There is certainly the possibility that some engines can take advantage of higher RON fuels, by the use of dynamic engine mapping combined with knock sensors allowing the ECU to actively find the sweet spot of ignition timing. Some cars only have the ability to retard timing to prevent damaging knock, but not necessarily to advance timing to hunt down best performance - they have a fixed base timing and the ability to retard for safety, so won't see any benefit* from a higher RON.

*there is a case where an older engine may benefit from higher RON, that being if the engine is significantly coked-up. In this case the presence of carbon deposits in the combustion chamber had two impacts: (1) it reduces the volume of the combustion chamber, thereby increasing the compression ratio (and hence increasing the chance of preignition) and (2) the carbon deposits get hot and act like a glow plug, again potentially setting off combustion ahead of the spark timing.


With respect, the tanker drivers aren't formulating nor blending the fuel. They put this pipe into that nozzle and take it to this station for delivery. Compartmented trucks can make deliveries of different fuels to different forecourts. The formulating and blending which differentiates fuels is confidential and done whether they know it or not.

I presume you work in the fuel industry and therefore know more than I do regarding current practice.
This was some years ago and this guy was not stupid or unobservant so I have no reason not to believe what he told me. Never underestimate the observations of the workers as they often know more than you may expect. I was a general manager of a distillery, maltings, warehouse, workshop and blending bay for nearly 25 years and often got useful insights from my workforce at all levels.

 

[Cerdic]

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.

Ah, fair enough! You learn something new every day and all that…

 

[figbat]

I presume you work in the fuel industry and therefore know more than I do regarding current practice.
This was some years ago and this guy was not stupid or unobservant so I have no reason not to believe what he told me. Never underestimate the observations of the workers as they often know more than you may expect. I was a general manager of a distillery, maltings, warehouse, workshop and blending bay for nearly 25 years and often got useful insights from my workforce at all levels.

I do work in the industry, although I’ll admit my area of experience and expertise is lubricants, but the fuels R&D people are just next door and I socialise with them, as well as staying informed on all such things.

I don’t doubt that some workers [sic] are well-informed but there is plenty they simply won’t have access to because it is, as I said, confidential.

The refrain “my mate drives tankers and they all use the same fuel” comes up every time this conversation happens and is often used as a proxy for “all fuel is the same regardless of where you buy it”. That simply isn’t true.

 

[Badger_Boom]

The refrain “my mate drives tankers and they all use the same fuel” comes up every time this conversation happens and is often used as a proxy for “all fuel is the same regardless of where you buy it”. That simply isn’t true.

That's as maybe, but a lot of "supermarket fuel is the devils liquid" believers seem to think it's somehow injurious to their engines, but when it has to comply with a legally defined minimum standard then it can't be significantly 'worse' than bog standard branded fuel.

 

[figbat]

That's as maybe, but a lot of "supermarket fuel is the devils liquid" believers seem to think it's somehow injurious to their engines, but when it has to comply with a legally defined minimum standard then it can't be significantly 'worse' than bog standard branded fuel.

You’re right - there is a minimum standard to meet and all road fuels must meet it. That’s not to say that some fuels don't go beyond the minimum though. I liken this to a high jump round - to pass you have to clear the bar, but a sneak over the bar with a wobble is the same result as clearing the bar with inches of clear air.

 

[wafter]

Cheers guys - evidently a contentious subject!

A military pal of mine (and they use a lot of fuel) had done lots of training on stuff like this and he told me that supermarket fuel wasn't as good as the pricier branded stuff.
I'm sure the AA or Which could do proper tests and give us the best per mile but I guess prices change all the time so it's instantly out of date.

Miles per lite / gallon remains a valid basis for comparison though

You need a much more scientific study to determine what improvement, if any, you are seeing. 10% in the world of fuel economy savings is HUGE - car makers will have your arm off for a 1% improvement. Fuel economy is notoriously tricky to evaluate under anything but the cleanest scientific conditions - there are myriad factors that impact it such as weather, traffic, topography, tyre pressure, wheel alignment, tyre condition, vehicle load, accessory use, barometric pressure and - biggest of all - the driver. No matter how consistent you think you are driving, you are not. In fuel and oil testing laboratories all of these variables are eliminated and a robot does the driving and improvements in fractions of a % are a good result.

That said, I see no reason why a 'better' fuel shouldn't give you some benefits, which can be incremental over time as fuel systems get cleaned up, injectors get more efficient etc.

Thanks - while I agree in principle, I'd counter that with the fact that all my driving's very samey in terms of route, traffic etc and that the trends are pretty stark - previous six tanks on supermarket fuel gave 42-48mpg (with the ability to call them to an extent based on the driving experience and ambient conditions etc), while the last two tanks with branded stuff both gave convincingly over 50mpg.

I'd not considered the injector cleaning angle - perhaps it might be interesting to run a tank of supermarket fuel through the car now it's had some better stuff through it and see what the economy's like - potentially giving the best of both worlds through alternating the type used.

As far as I understand the situation - the fuel economy of supermarket v. branded depends on the car

Some makes are more sensitive than others

more performance brands - like BMW - get more advantages from branded fuels than more family orientated brands

Since 'the great panic' a while ago the ESSO station near me has always been the cheapest so the choice has been easy!

That'd be the ability of a vehicle to adjust to different octane ratings as figbat's explained. I'd expect that beyond that there are also fuel qualities that affect its burn characteristics and thus efficiency.

That's as maybe, but a lot of "supermarket fuel is the devils liquid" believers seem to think it's somehow injurious to their engines, but when it has to comply with a legally defined minimum standard then it can't be significantly 'worse' than bog standard branded fuel.

Tbh I'd agree with figbat on this one (who seems to be owning this thread ) - just because something meets a minimum standard doesn't mean that superior alternatives can't offer better performance.

 

[figbat]

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.