Supermarket Petrol - Good Or Not So Good?

[Argento]

ChumpusRex, a question please.

You said "... Higher octane fuel generally tends to have a lower energy content than lower octane fuel ......"

Does "lower energy" mean, less power?

That would be a bad thing, right?

Argento

[ronsis]

yeah... wot he said.....

they've been in bed together for several years actually..... they have been looking after the v-power account etc for years...

ALL v power comes in from Holland...... I know no more.....

Tesco , as I mentioned earlier actually beat shell on the test bench a few years ago.... this was perhaps before the introduction of ethanol as we now have it..so it may not be the case now... but its still good stuff, like all other 99's...

(I like the v-power diesel... lovely smooth clean burner...)

[noby76]

@Argento

Its not the high octane fuel which makes the power its the engine and ECU mapping which makes the power.

as you already aware, a high octane will help keep the engine fuel system and valves burn cleaner due to having more engine cleaning additives. so even if your car does not make power, by using high octane every now and again will help prolong the life of the engine and a clean engine drives smoothly and returns good mpg.

a car can make more power based on mainly two main factors which is high compression ratio and ecu/ignition mapping and the higher compression ratio a car has, the higher octane fuel it may require to function at its best. all high octane fuel is doing is preventing a fuel from igniting early during the compression stroke. the ability of the fuel to hold off longer without self igniting allows a higher compression ratio engine to compress further the air and fuel during compression stroke. and if an engine is able to compress a lot of air and a lot of fuel which takes longer to ignite into a vey small space and ignited with a spark a much more bigger bang(more power) is produced.

so am not sure if ChumpusRex quote about high octane having 'lower energy' meant they take longer to ignite compared to lower octane. this allows for a more compression to be had from the fuel with a high compression ratio engine when put under a lot of stress (high rpm)

[ChumpusRex]

Higher octane fuels tend to be more "dilute", in that 1 litre of fuel, when optimally burned, produces less total heat. However, higher octane fuel has a more controlled, even burn, which allows engines to be more highly tuned; a fuel with an insufficient octane rating has a tendency to "detonate" (spontaneously ignite in an uncontrolled way) before the engine is ready to absorb the energy.

An engine with a more aggressive tune may be able to extract more torque and power from the same amount of combustion, either by optimising the combustion timings (advanced ignition timing), or increasing combustion temperature (higher compression engine design). Or could develop more power simply by forcing more fuel and air into the cylinder (e.g. with a turbocharger)

Things get very complex with fuel formulation. The limiting factor in most car engines, is actually air - the job of the carburettor (in an older car) or ECU (in a modern car) is to measure the amount of air going into the engine, and dispense the correct amount of fuel for optimal combustion (too much air, and the fuel will burn too hot and the piston will melt; too little air, and you waste fuel). Some fuels produce more energy for the same amount of air (the chemistry is a bit complicated, but fuels with more hydrogen in produce more energy from the same amount of air); fuels that produce less energy per litre or air, will give a lower overall power output (all other things, including RON rating being equal). Broadly speaking, traditional high octane fuel components, known as aromatics, need a lot of air for correct burning. That said, pure aromatics were used as formula-1 fuel due to their extreme octane rating, allowing extreme levels of engine tune; clearly in this case, the benefit of the octane was considered more important.

There is another way you can measure how concentrated a fuel is - how much energy per litre of fuel. Some fuels (e.g. ethanol) come with oxygen included. Not only has the oxygen neutralised some of the energy in the carbon/hydrogen, but the oxygen is actually taking up space. 1 litre of ethanol contains about 60% of the energy of 1 litre of petrol; in part because of the bulk of the oxygen. The ECU won't mind - the extra oxygen smuggled into the engine by the ethanol will be detected by the lambda sensor, and the ECU will turn up the flow-rate on the injectors. The car will go just as well, but will be using more fuel. (Oxygen content of petrol is capped at 2.7% by EU law; equivalent to 5% ethanol; and most fuel does contain this using a variety of oxygen containing chemicals). This is more of an issue in the US, where fuels may have between 5 and 15% ethanol, and you will get up to 10% worse MPG on the high ethanol version, because of the extra oxygen bulking up the fuel.

While aromatics are very high octane components, and still concentrated - current regulations are putting the crimp on them. When unleaded first came out, it was something like 35%-40% aromatics. These days, it's limited to 28% by law, because some aromatics are carcinogens, or produce carcinogens when burned. Refiners are increasingly being pushed into using ethanol as an octane booster; but are limited because ethanol is highly corrosive to fuel system materials. This is also a backdoor way of raising fuel taxes, as ethanol is a bulkier fuel - so if fuel duty is paid per litre, more duty ends up getting paid per mile, because 1 litre of ethanol gives fewer miles.

UK spec lexus vehicles prior to 2009 are not supposed to have ANY ethanol in the petrol at all, but the petrol companies expect that 5% (the current EU maximum) will be OK. 2009 and later lexus cars are compatible with 10% ethanol in petrol.

Hope that makes sense. It's not a simple topic.

[Argento]

ChumpusRex, ronsis & noby76, thanks very much for all this.

Things I didn't know about octane rating, ecu and compression rating.

Thanks for that, in particular, noby76

" Hope that makes sense. It's not a simple topic."

You can say that again!

But that's what makes us get out of bed in the morning isn't it?

I'm going to my very quiet room again later to read all this information and advice and inwardly digest!

Argento

[noby76]

Just got been to replace by auto box fluid from a Toyota/Lexus Indie based in Surrey. He also carries out some fuel and engine research work for Denso and Delphi. And I had to take a picture of it. the picture below was his findings when he compared fuel from Tesco and Shell. Both fuels have been let to settle for a week and after re shaking both bottles again in front of me, this is how petrol from Tesco looks like on the right hand side and one from shell on the left hand side. When I got to his garage this morning a customer was just leaving in a T180 diesel Avensis and he confirmed to me the guy had just spent £6000 on his car due to a cracked piston and he also replaced DPF on another customer’s car at a cost of £1500. And he confirmed 60% of all diesel and modern petrol related engine issues are due to Supermarket fuels this guy does not work for Shell, BP, Esso(Mobil,) or Total but confirmed he advises all customers to stay aware from Supermarket fuels. From what I gathered from the discussion we had, he confirmed all fuels sold in EU by law, has to contain a certain percentage of Biofuel and these are fuel derived from plants and other living organisms mainly from farms and over time, parts like fuel tank, injectors, dpf, catalytic convertors etc will start growing these living organisms from these(less additive) fuels resulting in various issues in the engine. He confirmed the fuel additives, cleaning agents, octane boosters added into fuels by Shell, BP, Esso and Total help control these biofuel organisms inside the tank, cylinders, valves, catalyst etc resulting in a smooth running engine, mpg improvement, and longer engine life. He confirmed 90% of his customers who have suffered diesel engine
related issues all used supermarket fuels and advised them to switch to branded fuels and occasionally use higher octane diesel and petrol fuels as well if they want to avoid the issues. As I confirmed this guy does not work for any of these branded oil companies so there is no incentive for him advising
customers to use Shell, BP , Esso over Tesco, ASDA and Sainsbury’s.. I have always been a Shell , Esso man and currently running BP Ultimate and the engine quite likes it so mite stick with it for a while.

[ChumpusRex]

Very interesting photos Noby.

I must say, that I find it hard to believe that that would happen with fresh fuels; but fuel taken from vehicle tanks, definitely. Fuel certainly does go off; the fuel starts forming gums, bacteria and algae can grow in diesel (but not petrol); water (always present in trace amounts) settles to the bottom of the fuel tank and causes the fuel tank to rust, general crap and debris settles to the bottom of the tank, where it stays, etc.

The better fuels do contain additives that help prevent this: gum formation preventers, anti-bacterial/anti-algae chemicals, emulsifiers, and dispersants.

Emulsifiers prevent the water from falling to the bottom of the tank; instead the water mixes with the fuel and just goes through the engine where it is evaporated and comes out with the exhaust. It doesn't build up in the tank of fuel lines, where it can freeze or cause corrosion.

Dispersants do the same sort of thing with general solid crap. Dispersants prevent crap falling to the bottom of the tank, and keep it mixed with the fuel, so that the fuel filter catches it. Collections of crap in the tank can accelerate corrosion and can harbour bacteria, etc.

Diesel suffers worst from fuel quality. One tip, which is opposite to that with petrol, is to avoid filling with diesel at a filling station if you know it has just had a fuel delivery. Diesel fuel from the refinery will contain water. It'll mix in the tanker, and when they pump the tanker out. If you fill up immediately, you'll get a full dose of water which will settle out in your tank. Wait 24 hours before filling, and the water will settle out, and you'll get a clean fill with dry diesel.

Water, while historically, never a problem with petrol, is becoming an issue with the use of ethanol - which will absorb water from the air, and allow water to mix with petrol. The only low ethanol petrol I know of on the market in the UK is Tesco 99.

For diesel cars, it might be worth thinking about a diesel fuel additive (e.g. Archoil 6200 - this is an additive designed for heating oil and industrial generator fuel tanks, so it contains the various stabilisers listed above, but could probably be used safely for road diesel engines). For petrol engines, you're probably better off using a branded or low ethanol fuel, perhaps with the periodic use of a fuel system additive which contains dispersents and detergents (I use archoil 6400, I bought a bulk pack before I realised that it is primarily a diesel additive, containing diesel friendly additives like octane reducers, and lard; but something like bg44k would probably be better), and if you regularly use ethanol containing fuel, then the occasional use (every 5 fills or so) of a water emulsifier (I use 500 ml of 99.9% isopropanol [easily and cheaply bought off ebay] added to a full tank).

[noby76]

Yes you right there ChumpusRex, both fuels were drained out of customer vehicles.

[dave32]

them pics are unbelievable, ive been using shell for the last month, only there basic diesel, cant say ive noticed a difference but for the sake of 1p more per litre I will stick with it, I do have some archoil 6200 which I use

[normski2]

Whilst it is of interest I would not get too carried away. You can't tell much based on two samples...50 of each would be more relevant.

How old we're the vehicles in question, how old we're the garage tanks? Was one of these from the bottom of a tank before a refill? This could be pinpointing a problem of contamination within one of the vehicles.

I've just had one 'corked' bottle of a chateau sourced Pomerol. It does not mean all bottles from that chateau are dodgy. It was replaced immediately and without question...now that would be a novel step for a fuel supplier to take on board.

Not wishing to throw water on your bonfire at all....but I would say tread warily. Lets see a wider sample and preferably sourced only from outlets and from different tanks.

[ChrisIS200SportTTE]

I don't think the 2 pics are solid proof that supermarket fuels are poorer quality than brand names.

As Normski says what cars were these taking from? One could have been taken from a 1980's Van and the other from a brand new BMW for all we know. Were the tanks full, empty? Is the brown sample from the bottom of a tank?

I like the wine comparison Normski, as a chef I can relate to that :)

[petayV8]

Ive been using Sainsbury's fuel ever since i owned my Lexus so 8 months. Im on my 2nd fill up of BP and it definitely seems smoother, especially at tick over. Not sure about MPG yet

[noby76]

@normski

didn't go into details about asking how old vehicles were, condition of fuel tanks how old the fuel was etc.. but I am happy to pm you the guys number so you can call him for more info about the tests he's carrying out for Denso and Delphi and how many vehicles he has come across with Supermarket fuel problems.

[Argento]

Bh noby76, there's a lot to think about here.

Thank goodness I've not got a diesel!

Is that why they all sound so rough these days? :-)

"over time, parts like fuel tank, injectors, dpf, catalytic convertors etc will start growing these living organisms from these(less additive) fuels resulting in various issues in .."

Things growing in, and water in your fuel system?

Oh boy.

The things the garages don't tell you. ....

noby76 comments are quite plausible IMHO

They would seem to support the horror stories you see regularly see in the press now about suspect dodgy fuels affecting engines I think.

Argento

[ronsis]

that's a bit extreme... never seen fuel old or fresh as dirty as that... whats the vehicle history ?.... diesel and unleaded change colour / odour on a weekly basis. the v power also comes and goes... I really think you should take this with a large pinch of salt. I can agree with almost all of whats been said to a limit, but lets face it... its been going on for years and will continue to do so... as I previously said .... apart from esso....(and 99rons) . all fuel from the southeast at the moment is the same....I personally will continue to go where I know where its came from.

just got back from London -Glasgow.. FUEL DETOX additive and asda fuel... ran fine...51 mpg

Glasgow London esso diesel nothing else, ran fine 49 mpg (both runs full load + 4 bodies 70-80 MPH )

i'm not going to loose any sleep over this one...

[Argento]

" .... apart from esso....(and 99rons) . all fuel from the southeast at the moment is the same.... "

I'm taking good note of this statement.

Thanks again ronsis

Argento

[ronsis]

jfyi... last nights diesel deliveries were extremely yellow... looked like a sample you'd take to the doctors ! smell was ok.. just a lot darker than normal.

[japthree]

How does Tesco's Momentum 99 RON compare to other brand superfuels? It's the cheapest and I get x pence off / litre if I do a big shop at Tesco. I don't ever use standard supermarket fuel but get the Tesco Momentum.

[flotsam]

Momentum 99 is made by Greenergy, whereas Shell seem to blend their own 99 RON forumla for their V-power Nitro+. Shell specify it to be 5% ethanol, but then pretty much all unleaded sold in the UK current does, in order to meet the government's biofuel target. Although Greenergy specify their fuel to contain up to 5% ethanol, their 99 product usually contains less ethanol (usually between 1.5 and 2%). They publish a monthly analysis of their fuels. http://www.greenergy.com/Products_services/test_results/99_octane/99octane_2013.05.pdf

Higher octane fuel generally tends to have a lower energy content than lower octane fuel, but if the ECU is tuned for high RON, then it is possible that you get slightly more performance and slightly better fuel consumption with the higher octane fuel, despite the fact that it is more "dilute". That said, ethanol is much more dilute than "petrol", so a 5% ethanol content will knock about 2% off the energy content of "pure" petrol.

Looking at the figures from my IS250's ECU, which generally only gets fed 95, the ECU does claim to have knocked a couple of degrees off the ignition timing, so it may actually be tuned for 98. I might run a few tanks of 99 and see if the ECU advances the timing, or whether the Euro-spec ECU comes pre-set to the less aggressive timing.

Neither fuel company are particularly forthcoming with regards to their additive package. Shell are obviously aggressively marketing their Nitro+ additive, which is said to be puchased from the additive company lubrizol. However, only an insider would really know, because I doubt that Shell publish what's in it or where it comes from. It wouldn't surprise me if Greenergy buy from the same additive supplier, even if it's not the same product. That said, you can't blame shell from promoting their new additive - a state-of-the art additive may only add 0.05 - 0.1p/l to the cost of the fuel, but can command a price premium of 3p/l (nice profit if you can get it).

Oh, and Greenergy and Shell have recently announced a Joint Venture with regard to revamping a major refinery - wouldn't surprise me if there's a lot of "cross-pollnation" in terms of sharing fuel blends. That said, Greenergy already supply most supermarkets with fuel, as well as many Esso stations.

Suprised!

I've tried Momentum and the engine (compression ratio 10.5:1) though smooth feels underpowered. Sainsbury's super unleaded (which was 97RON last I looked) feels much livelier.

Ethanol has a RON of 102 meaning you can compress it that much more before it self ignites (known as "knocking" or "pinking") and it has less energy; it expands less when ignited. Perhaps the Sainsbury's petrol I've been using has next to no ethanol!!!

[Silver Arrow]

There have been loads of tests on this in the past by journo's and the differences are very marginal. It's all clever marketing, a few more octanes (or cetanes) and they charge you a fortune for it. You won't notice the difference in normal driving, I'm pretty sure. It's a placebo thing.

I've used Sainsbury's for years in lots of cars, never had a problem, never had gummed up injectors, never had failed an MOT for crappy emissions. Some cars have covered massive mileages, no problems related to fuels.

[is200 Newbie]

Took a trip to Scotland at the weekend and thought I would just see what I could get out of the tank on the way back. Filled up at ASDA as I thought I would get through the full tank in the journey and I don't mind filling up now and then with supermarket juice.

Trip started of with the range stating 360 miles on a full tank - windscreen wipers and lights were used off and on for most of the journey and with the radio/CD on. Cruise set to 70 for most of the journey.

Picture shows distance travelled at 329 with the remaining range in the tank left at 133, total = 462 but I reckon on a longer trip then this could stretch to almost 500 miles. Thought that was pretty good for the car.

Might put Shell fuel in next time to compare the results

[ChumpusRex]

I've set a new MPG record after filling with Momentum 99. Never got anywhere this before. Probably weather related, warmer air makes a big difference to air resistance. However, the denser, low ethanol fuel probably contributed (the Greenergy 99 RON weighs 750 grams per litre, but regular 95 RON weighs 730 grams per litre). The problem is that there are so many factors, it's near impossible to do a fair test.

220 mile run from a full tank.

[Silver Arrow]

I think the differences are very marginal. Loads of tests done by journo's, none are that conclusive. If I drive at 60, with cruise, my GS250 will deliver that sort of MPG on Sainsbury's petrol, Reg low sulfur 95 ron.

[ChumpusRex]

I've now done some testing with both Asda petrol (95 RON) and Shell V-power Nitro plus (99 RON), while monitoring the ECU.

On 99 RON, the ECU has recalibrated to a significantly more aggressive tune with about 4-5 degrees of extra ignition timing advance, compared to 95 RON.

The ECU has also adjusted the fuel injection by reducing the fuel delivery for a given amount of throttle opening (by about 2%).

Although not really scientific, I haven't really noticed a definite change in fuel consumption - maybe I get about an extra 5%, but it's marginal; I don't think I could reliably detect a change in fuel consumption of less than about 10-15% because of differences in weather conditions, road conditions, driving style, etc.

For information, I've enclosed a copy of the ECU data. The light blue trace is the ignition timing, red is the knock feedback timing adjustment, dark blue is engine speed and green is mass air flow. Top trace is on 99 RON, and bottom is on 95 RON.

[noby76]

so on a more powerful engines like turbo or a higher compression ratio engine by using higher RON fuels is like getting extra free power due to ignition timign advance.. i noticed on your test, the V power kept ignition timing at its peak for longer which equates to free power without having effect on consumption , how much free power all depends on engine tune of course.