OT: Gasoline Octane in Europe vs. U.S.

[Tommasini53]

Greetings, completely off-topic...but curious about octane levels in gasoline.

I spent a couple weeks driving around Italy last month. I noticed that the octane numbers listed on their gas pumps were way higher than the numbers I see on gasoline in the U.S.

The octane numbers on the Italian pumps were all around "95"

Any Forumites explain why different octane ratings around the globe...are there benefits to higher octane.

It is not like i was driving anything high-performance; it was a Fiat Panda.

[Ken Robb]

there are two (at least) methods of testing and listing octane ratings We average two and list that on our pumps. I don't think that is the case in Europe.

[Ardan MacNessa]

2 different systems of measurement. RON [Research Octane Number] is european and japan... etc, AKI [Anti-Knock Index] is USA. Take any octane in europe and multiply it by .95 for actual rating.

( RON Octane Rating x 0.95 = AKI Octane Rating )
98 RON Octane x 0.95 = 93.1 AKI Octane (US measure)
100 RON Octane x 0.95 = 95 AKI Octane (US measure)

[Ken Robb]

Yeah, what Ardan said.

[Ralph]

2 different systems of measurement. RON [Research Octane Number] is european and japan... etc, AKI [Anti-Knock Index] is USA. Take any octane in europe and multiply it by .95 for actual rating.

( RON Octane Rating x 0.95 = AKI Octane Rating )
98 RON Octane x 0.95 = 93.1 AKI Octane (US measure)
100 RON Octane x 0.95 = 95 AKI Octane (US measure)

Yes....And contrary to what most think....lower octane fuel has more energy content than higher octane fuel. With modern engine controls, most normal passenger cars can use 87, run a relatively hi compression, not preignite, and get better economy with 87 VS 91 (or 93).

Building a race car a different story. But some modern turbo cars (Eco Boost come to mind) can also use 87. CPU pulls a lot of timing though. May not help economy, but one can usually make more power with more timing and more compression, using a high octane fuel, than I lose with the slower burning less volatile 91 or 93. That's why most performance cars still use 91. And BTW....In the US...87 supposed to be same quality as higher octane fuels.....with regard to injector cleaning and intake valves. Tier 1 fuels may burn cleaner....in all octanes. Doubt if burn rate differes much between octanes.

[Ardan MacNessa]

I would use the word "more volatile" for lower octane and I didn't now that about the eco-boost systems. It make a lot of sense as you explained it. In altitude you can see 85 octane USA... Colorado, etc. Where you have less oxygen [higher altitude] you need less fuel or it'll run rich and can run lower octane too.

But I'm more versed in diesels, the only cars I own.

[Ralph]

I would use the word "more volatile" for lower octane and I didn't now that about the eco-boost systems. It make a lot of sense as you explained it. In altitude you can see 85 octane USA... Colorado, etc. Where you have less oxygen [higher altitude] you need less fuel or it'll run rich and can run lower octane too.

But I'm more versed in diesels, the only cars I own.

I prefer the words "more volatile" also when describing 87. You make an interesting point about 85, which I have bought in Colorado. If I were going to be in a gas mileage contest, and could tune engine around use of 85, would use that and not 87. The more volatile the better.....if one can control the combustion....and not get combustion before you want it.

[Ken Robb]

If an engine is designed to run best on high octane fuel that is the fuel that will allow it the most power and MPG. If it has knock sensors to detect preignition(detonation, knocking) its engine control module can probably retard ignition timing enough to prevent engine damage but power and MPG will be reduced. In such a vehicle the driver can decide if he minds the reduction in power and compare the cost-per-mile of each fuel when getting X MPG on high test vs. X-Y MPG burning more of the less expensive regular grade fuel. The lowest cost per mile might even be using a mid-grade.

I want ALL the power I paid for so I always buy premium fuel. In California for sure and probably other states fuel blends vary with the seasons so results of these experiments may also change with the seasons.

[rePhil]

Some recreational Marine stern drive engines designed for lower octane had the electronics bump the timing until knock is detected then reduce the timing. If the engine does not sense knock it because of higher octane it can default to a lower timing reducing power.
I have no idea if car engines do the same.

[Seramount]

I want ALL the power I paid for so I always buy premium fuel.

premium fuel is not more energetic and doesn't provide more power than lower octane ratings.

octane simply decreases the rate of flame travel in the combustion chamber to avoid pre-ignition in higher-compression engines.

if your car's owner manual doesn't stipulate a requirement for premium and you do not have 'knock' issues, there's no reason to use it.

[Ken Robb]

premium fuel is not more energetic and doesn't provide more power than lower octane ratings.

octane simply decreases the rate of flame travel in the combustion chamber to avoid pre-ignition in higher-compression engines.

if your car's owner manual doesn't stipulate a requirement for premium and you do not have 'knock' issues, there's no reason to use it.

My MINI Cooper S is turbo-charged and designed for premium fuel. It has knock sensors and would "de-tune" itself if I fed it lower octane fuel but I won't do that.

[Ti Designs]

Learn how to crank (it's the automotive version of "learn how to pedal")

You're thinking in absolutes, in the real world conditions change (OK, maybe not in LA...) Detonation is the result of the heat of compression, either from the compression stroke or forced induction, often both. beyond that (and sometimes within that) there are conditions like temperature or humidity. There's nothing that says that systems can't be built to control those conditions, the car makers simply don't want to add that level of complexity. Hmmm, we're now seeing ECU controlled headlights, maybe it's just that the drivers are too stupid...

Just a few ideas:

Nitrous Oxide: Forget what you think you know, nitrous is simply 36% more O2, stored at room temp at 800 PSI. It's stored in a blue bottle with a sticker that says something about "not for highway use", but that sticker comes right off... The heat problem in forced induction comes from the forced part, it's called the heat of compression - let's not get into types of compressors here. Well designed engines will have intercoolers which dissipate that heat to the outside world, but there's a limit to the amount of heat loss you're going to get. A huge intercooler would cause turbo lag, the delay between the turbo spooling and the increase of pressure at the throttle, so the question becomes do you want it cool or do you want it now? Nitrous doesn't bother asking that question, it's boost in a bottle that comes out cold. In most cases nitrous is used as a wet system, a delivery system that adds both fuel and nitrous at the intake. In a forced induction system nitrous can be injected upstream where it would cool the charge and boost the O2 content as it converted to a gas (there's a little issue with injecting liquids past the throttle body with a side draft intake - trust me on that one).

Alternative fuel: Propane has an octane rating somewhere in the 110 range. It can't cool the engine to save it's life, that's not why I'm using it. At higher boost fuel enrichment tends to fail as the injector can only atomize so much fuel. Again, as a gas, propane can be introduced upstream (not too far upstream, you really don't want an intercooler full of propane when you step on the clutch and your bypass valve opens - that could be bad). A little goes a long way...

Water injection: Most car makers have given up on this idea 'cause people just don't get it. Water injection is the reason your car seems to have more power on a cool, damp evening than it does on a hot, dry day. It's using the conversion of a liquid to a gas to remove the heat of vaporization from the intake charge. Ceramic O2 sensors don't much like the idea, but that's another story...

Fuel mixing: Next time you see a guy with a Summit Racing cap go into a paint supply place, ask them why...

[victoryfactory]

Interesting stuff here.
Can anyone explain how the seasonal addition of ethanol affects
power and mileage?
It seem that I get lower MPG and power in the winter.

VF

[Ken Robb]

ethanol has less energy than gasoline(I forget the formula) so the more ethanol in your "gasoline" the less power and mileage you get all other things being equal.
Another factor that will lower MPG in Winter: the "choke" or enrichment system in your carburetor or fuel injection system will be on longer because the engine will take longer to reach normal operating temperature.

[Ralph]

I believe a better way to say it is....ethanol has less energy than straight gasoline per equal volume. But....if I were building an engine for performance only, and volume of fuel consumption not a consideration, especially if boosted by supercharger or turbo charger, I can make more HP with straight or high concentrations of ethanol than gasoline. You see this in race engines all the time.

And even though ethanol has a much faster burn rate than gasoline, it's so much cheaper than gasoline (could be maybe 50-75 cents a gallon from Brazil.....much more from our subsidized protected ethanol industry), it does save money by using it....or could.

Notice the price of RBOB gasoline (reformulated gasoline blendstock for oxygen blending) on the futures market going across the top of the CNBC screen all day. That's closest futures month before ethanol is blended in, and before taxes, costs to gas stations, profit, etc. It's usually about 80% of retail price or in that vacinity. That extra 10% by volume of ethanol added doesn't cost much.

However....don't want to get into discussion about amount of energy it takes to make, produce, and deliver ethanol for use.

[schneiderrd]

I think there are some misconceptions expressed here.

First of all the volatility (vapor pressure or RVP) is the same in both regular and premium gasoline. The RVP is usually controlled by butane or pentane addition depending on the season.

To use the 0.95 multiplier is not exact as an indication of AKI from RON. RON and MON are measurements taken on two differently configured engines. The engines look the same but the RON engine runs at 600 RPM and the MON engine runs at 900. AKI is an average of the two values. Typically 95 RON and 91 AKI are the same. The 0.95 x RON equation would result in an AKI of 90.3. While that is close to 91, in California, if the Weights and Measures Dept checks the pump and the premium is not 91, the owner had better get out his check book. Actually the AKI is a waste of time and RON is all that is really necessary, but the bureaucrats had to get involved.

Finally, with respect to Ethanol (EtOH), the higher the EtOH concentration, the lower the gas mileage. EtOH is probably the biggest rip off ever perpetrated on the American public. While it does replace some foreign oil imports, it takes more energy to make this stuff than you get out. Also if someone is a tree hugger, if you look at the total carbon foot print of this stuff, it is not very green.

[Mark McM]

Well, maybe that's a bit of hyperbole but ...

Between the Fall of France and the Battle of Britain, England phased in the use of 100 octane gasoline for their fighter planes (Spitfires and Hurricanes). This allowed them to increase the boost on their superchargers to develop significantly more power. Earlier in 1940, when they were using 87 octane fuel, the British planes were barely a match for the Luftwaffe's ME109. With the higher octane fuel their performance exceeded the German fighters (which were still using 87 octane), helping to stem the tide of the battle.

Great Britain itself couldn't produce 100 octane fuel in large enough quantities at the time, but the US had recently ramped up production of this high octane fuel, and most of the fuel used by the British during the battle came from the US.

[carpediemracing]

I thought the Germans were using some carcinogenic super high octane fuel (maybe it was later in the war?). They started using it in F1 for a bit and then the rules changed to specify pump gas.

There's some paint thing... I can't think of the name of it, but it's something like 115 octane. It's used something like 80-85% straight plus 15-20% inert material. Maybe it's the same thing as what the Germans used. I found a bunch of info on a site whose author claimed to be a retired STP chemist or something. He had all sorts of interesting info, octane, advantages, drawbacks. I can't seem to find the stuff that seemed really effective.

There are a surprising number of cars that specify 91 octane fuel. A bunch of Nissans do (I had one), some other cars I looked at do. Honda seems to go with 87. It's not that you get more power if you put 91 in a car that specs 87, it's that your 91-spec car will detune itself a bit to protect its internals if you use 87.

I think in horsepower wars if you spec 91 then you can get better power by being more aggressive with timing, compression, etc., at least without doing as much "engineering". I know that I check that now when I browse cars and I usually eliminate the ones that require 91 (I was recently browsing).