General: Leaded Fuel

[100K+]

Just been watching 5th Gear testing 95 Ron fuels V "super unleaded" from Esso,Shell,and BP in a 236BHP Golf

Until recently I have always bought on price,whether that be Branded or Supermarket, with a 50/50 split of both. For the last couple of months I have ran both my T5 and R on Shell V 98RON.

To be honest I did notice a small difference, both cars appeared to be a little quicker on the pick up, but after almost 2,000 miles in both cars I have not seen any increase in MPG, and the performance increase as blended into "the Norm"

5th Gear showed an approx 5BHP gain by using Shell V over the benchmark BP 95RON.

What if anything are other members experiences of using 98RON fuels?
5th Gears conclusions were similar to mine - Yes there is a difference but not sure if its worth the extra cost.

One tech question :- Ok the fuel allows the engine of the car to produce more power, by giving a bigger bang,BUT does the better fuel allow the engine via the electronics to alter its own parameters to produce more power giving a double benifit?? ie alters timing/fueling etc

Cheers

Bob

[Brendan W]

Afaik most if not all modern ecus are constantly feeling for the edge so if a fuel has better knock properties the ecu will exploit them hence differing power outputs. As far as changing fuel goes every time we change our coffee the first cup tastes great.

[owyn]

Octane rating is purely about knock resistance and nothing about calorific value so the gain you get will be a purely boost/timing change. The engines have knock sensors so it'lladvancr everything until it starts to knock.

[Jim314]

Does the owner's manual for UK/EU Volvos say anything about octane rating requirements? The US/Canadian manuals do.

Our manuals state the equivalent* of:

1. Minimum octane rating 90-91 RON

2. Optimum performance with 94 - 95 RON

This suggests that the Volvo engines cannot take advantage of 98 RON.

Two things to note here:

1. The North American Volvos are tuned differently to meet our emissions specifications. My V70 is rated at 168 hp and not 170. The same engine in California tune is even lower in max rated hp.

2. It might be that North American Volvos would do marginally better with 98 RON, but Volvo does not see any benefit in mentioning that because some users will feel compelled to use that if it is mentioned, and the extra expense and trouble will cause dissatisfaction.

*In the US we use the average of RON and MON (motor octane number) called AKI (anti-knock index). The RON is usually 8 units above MON, so AKI is usually about 4 units below RON.

My owner's manual states that Volvo engines are designed for optimum performance with 91 octane AKI and above. The manual further states that the minimum octane rating is 87 AKI.

In my area the grades available are 87, 89, and 93. If I am not pressed for time, I will pump approximately equal volumes of 89 and 93, giving 91. If I am in a hurry, I will usually pump all 93, but sometimes I will pump 89. I can't tell any difference in performance, but then I don't operate at anywhere near max performance. I don't ever use 87, but would of course do so in pinch.

[RM955I]

I buy whatever is cheap....normally 95 and usually supermarket.

My mate is a tanker driver....most of it comes from the same depot. There's a lot of urban myth about 'cheap' supermarket petrol but I use it in my cars and my bikes.

The only time I have used 98 is when I had a 95 Aero where is was specified and did seem to make a difference.

[Jim314]

Originally Posted by owyn

Octane rating is purely about knock resistance and nothing about calorific value so the gain you get will be a purely boost/timing change. The engines have knock sensors so it'lladvancr everything until it starts to knock.

I do not know if it is the case, but it is possible that the super unleaded (RON ~> 97) has a lower heating value than 94 or 95 RON. This would depend on how the petrol is formulated. This could occur if the 98 RON petrol has the same base fuel as the 94 RON, but has a larger amount of the same octane booster, and that booster has a lower heating value than the base petrol.

What I'm imagining is suppose the main octane booster in petrol is ethanol, which we know has a significantly lower heating value than a hydrocarbon.

Ethanol is added to petrol in the US supposedly to give cleaner emissions and to stretch the petroleum by adding a green/renewable domestically produced fuel. (In reality the ethanol mandate is almost entirely a politically motivated subsidy to the US maize producers in key midwestern states.) But ethanol does have a blending octane rating of about 115 AKI, equivalent to ~ 120 RON, and so it is an octane booster.

See http://en.wikipedia.org/wiki/Gasoline, and http://en.wikipedia.org/wiki/Top_Tie...rgent_Gasoline.

This is just speculation on my part. It could be that the higher octane petrols have a different composition in the petrol base, and it could be that they have the same heating value or even greater heating value than the lower RON petrol (~94 RON). Possibility the aromatic content of super premium is higher than standard. In this case the heating values would be about the same, but the carbon emissions would be higher for the super premium due to the fact that aromatics (e.g. benzene C6H6) have a lower number of hydrogens than aliphatic hydrocarbons (e.g. n-hexane C6H14 or cyclohexane C6H12).

Anybody know?

[owyn]

Originally Posted by Jim314

I do not know if it is the case, but it is possible that the super unleaded (RON ~> 97) has a lower heating value than 94 or 95 RON. This would depend on how the petrol is formulated. This could occur if the 98 RON petrol has the same base fuel as the 94 RON, but has a larger amount of the same octane booster, and that booster has a lower heating value than the base petrol.

What I'm imagining is suppose the main octane booster in petrol is ethanol, which we know has a significantly lower heating value than a hydrocarbon.

Ethanol is added to petrol in the US supposedly to give cleaner emissions and to stretch the petroleum by adding a green/renewable domestically produced fuel. (In reality the ethanol mandate is almost entirely a politically motivated subsidy to the US maize producers in key midwestern states.) But ethanol does have a blending octane rating of about 115 AKI, equivalent to ~ 120 RON, and so it is an octane booster.

This is just speculation on my part. It could be that the higher octane petrols have a different composition in the petrol base, and it could be that they have the same heating value or even greater heating value than the lower RON petrol (~94 RON). Anybody know?

Sorry, I'm not understanding, could be the different nomenclature used here and in the states. All my knowledge is about 4 years old when I did my degree but the uni I went to did specialise in internal combustion so may be able to answer your questions.

[princepugh]

If I remember the 5th Gear test, they also ran a Scooby on SUL and recorded a significant power difference so to cut a long story short, a high performance turbo engine will take advantage of high RON.

Your T5 and R will take advantage to some degree but I doubt it will be as significant because the standard map won't be optimised for it. I bet the owners manual for a Scooby recommends SUL.

Bottom line though - for a performance turbo vehicle SUL will help prevent knock, which has got to be worthwhile in the long run.

[Paddler Ed]

I'm going to wander in here, scribble some irrelevant notes and then leave...

I seem to remember some research done where they said that you needed to allow about 1000-2000miles before the computer reacted to the different fuel.... but that was some years ago, and I can't remember the source...

In Australia we ran an old Mazda van which was noticeably better on 98 than 95, and significantly better than when it was on 91 or E10 (Australian E10 is supposed to be about 94). Admittedly the timing was set towards 98 and LPG as it was dual fuel, but even when it was set to 95 the performance was a bit sketchy... 90kmh when the 90,000kg trucks are coming past at 110kmh is interesting! In fact the cost per km was the same, even allowing for the increased cost in fuel (so there must have been some improvement in fuel economy)

We also had a Land Cruiser with a big old petrol engine, which we always ran on 98 if we could get it, otherwise nothing lower than 95 and upto 100 if we could get it. Unfortunately we didn't run 100 enough to find out if we had any benefit from it.

The 850 we had was fed a diet of 98 (and a minimum of 95) and that seemed to be quite happy on a nice fuel. We ran it on that based on our experience with the van.

[Jim314]

Originally Posted by owyn

Sorry, I'm not understanding, could be the different nomenclature used here and in the states. All my knowledge is about 4 years old when I did my degree but the uni I went to did specialise in internal combustion so may be able to answer your questions.

There could be some differences in nomenclature, but it would advance the discussion if you would elaborate a little on exactly what it is that is not understandable to you.

My formal training in organic chemistry was in the mid 1960s, in the days of leaded petrol, but unleaded was coming. I do remember my instructor saying that oil companies with expertise in aromatics and olefins were better positioned for the coming era of unleaded petrol.