Is cheaper fuel a false economy?

[ducatilover]

Ive tried both in my XR8 but didnt notice any difference at all.Have always run 98 in the TL.

You got the wrong ute
Just kidding, I haven't seen any differences on the later model XR8 with petrol, early ones (AU3 and earlier) were so bloody slow you can't tell anyway.

What a load of twaddle.

The caloriphic value of all petrols is the same. The higher the compression the more eficient the motor is its called volumetric efficency. You could also say a high compression performance motor makes more HP than a standard low compression motor.

I put the cheapest fuel I can get in all of my vehicles, its all out of spec crap in this country anyway.

Meh, each to their own. You evidently have a late model V8 Dunnydore, I can even explain the different level of power between the fuels with a Dunnydore (not that anyone care, Australian cars are crap)

[Jantar]

What a load of twaddle.

The caloriphic value of all petrols is the same. The higher the compression the more eficient the motor is its called volumetric efficency. You could also say a high compression performance motor makes more HP than a standard low compression motor.

I put the cheapest fuel I can get in all of my vehicles, its all out of spec crap in this country anyway.

What load of twaddle.

Think about why petrol has an octane rating at all. Origionally it was to compare the caloriphic value with a similar quantity of pure octane. Later the rating was modified to reflect the anti-knock properties, but basically the higher octane rating fuel can produce more heat if it is burnt efficiently. More heat means greater combustion pressure and hence more power. But different fuels also have different burn rates and a lower octane fuel with a fast burn rate can produce more heat and hence more combustion pressure than a higher octane fuel with a lower burn rate.

Avgas has a high octane rating, but it also has additives to slow the burn rate and make it suitable for engines that develop peak power at 2500 rpm. Rotax advise that avgas should not be used in their aero engines, just normal mogas. Avgas may be used, but the service interval is halved.

[Old Steve]

its all out of spec crap in this country anyway.

How can you justify that statement.

As someone who has worked over 20 years in the fuels and lubricants industry, for 3 years as the Technical Manager of one of the oil companies and for 8 years in that company's international technical centre, and as as one of the industry team which liaised with the Ministry of Energy and oversaw the technical details of the introduction of unleaded petrol into New Zealand, I've got to disagree with you there.

Octane (and there are two octanes in the petrol spec, Road Octane Number/RON and Motor Octane Number/MON) is only one of about ten or twelve specifications controlling the quality of petrol. There's also esoteric specs like Reid Vapour Pressure which determines the ability of petrol to vaporise so it can burn.

Marsden Point petrol is one of the highest spec petrols in the world. New Zealand petrol specs are based on those used throughout Europe and it was a conscious decision to have 91 and 95 RON petrols with a sensitivity of 10 - that means the MON of 91 petrol is 81 and the MON of 95 petrol is 85. When the spec for 95 ULP was introduced, the oil companies made an undertaking with the MOE that they would supply 96/85 RON/MON petrol for a couple of years even though the spec was 95/85 - this gave motorists time to retune their vehicles for the new 95/85 fuel.

When a tanker brings a load of fuel into a port, either a coastal tanker from Marsden Point or an international tanker, then the petrol goes to all the different company's storage tanks. So I'm a little bemused that people are finding that one brand of the same octane petrol gives superior fuel economy - I think that just emphasises the variability of the testing.

Marsden Point is a refinery that is MON limited, that means that they have to 'give away' RON in order to meet the MON requirement. So often petrol coming out of Marsden Point may have a MON of 85 but a RON of 96, 97 or 98. I think what BP did when they first introduced their 98 petrol (and there is no MOE spec for a 98 RON grade of petrol) was to store any petrol coming from Marsden point which was 98RON/85MON in separate tanks and market it as 98 octane. Don't know if they source their 98 octane petrol from overseas sources specifically as 98RON/88MON now. By the way, Nippon Oil introduced 100 octane petrol in Japan to celebrate their 100 year anniversay, and having that high octane petrol available allowed vehicle manufacturers to produce cars (usually turbo) that required 100 octane petrol - these were Japan only models and have usually been imported into NZ irrespective of the availability of fuel suitable for their engines. When ULP was introduced in New Zealand these vehicles were not in the NZ, their future octane requirements were unknown, and no account was made that in later years vehicles not designed for fuels available in NZ would be imported.

[steve_t]

What a load of twaddle.

The caloriphic value of all petrols is the same.

Don't forget about Gull E10

[Jantar]

.....

When a tanker brings a load of fuel into a port, either a coastal tanker from Marsden Point or an international tanker, then the petrol goes to all the different company's storage tanks. So I'm a little bemused that people are finding that one brand of the same octane petrol gives superior fuel economy - I think that just emphasises the variability of the testing.

.....

Some very usefull information in your post. Thank you for that.

Is it the additives that are added at the company's holding tanks that possibly makes a difference? eg Caltex's Techron?

[Flip]

What load of twaddle.

Think about why petrol has an octane rating at all. Origionally it was to compare the caloriphic value with a similar quantity of pure octane. Later the rating was modified to reflect the anti-knock properties, but basically the higher octane rating fuel can produce more heat if it is burnt efficiently. More heat means greater combustion pressure and hence more power. But different fuels also have different burn rates and a lower octane fuel with a fast burn rate can produce more heat and hence more combustion pressure than a higher octane fuel with a lower burn rate.

Avgas has a high octane rating, but it also has additives to slow the burn rate and make it suitable for engines that develop peak power at 2500 rpm. Rotax advise that avgas should not be used in their aero engines, just normal mogas. Avgas may be used, but the service interval is halved.

Na. The higher a motor compresses the mixture before it is burnt the higher the combustion pressure is and the harder the piston is pushed down.Its not heat that pushes your pistons down. In practice more energy can be extracted from the burning mixture by a high compression motor. Its called volumetric efficiency.

Octane is simply speaking the fuels ability not to be ignighted by compression, in general the higher the octane the slower the fuel burns in this case its called FFS or flame front speed not for fuck sake(there are exceptions but all fuels are a shandy). You need a fuel that resists being ignighted by compression to work in a high compression motor without causing it damage.

The caloriphic value of the petrols is all the same. Its just the high octane stuff works best in high compression motors.

AV gas is a bugger of a fuel, it is a high quality relatively narrow cut fuel whose spec goes back to WW2 when nutters put 8 machine guns is 1600 HP V12 airplanes and went out looking to pick a fight with the neighbour hood bully. Its actually a difficult fuel to burn because it contains few small easy to ignite molecules. In many vehicles with single spark systems it misses and backfires and just is just nasty.

When the fuel leaves marsden point it is usually fine. IMHO by the time its been shipped, stored at a terminal, put in a road tanker, dropped in a service station tank it collects dirt and water along the way and is often out of spec by the time the punters get it. Just think what collects in the hoses on the side of a road tanker during a long road trip. Just the free breathing tanks on service stations can put diesel out of spec from atmospheric dirt these days. Much of the imported fuel is brought on the water at a dutch auction, some of the loads recently imported have been out of spec with dissolved water and its been impossible to get out of solution. Why don't service stations run all fuel through a coalessing filter? Why is there also so many failures of common rail diesels in New Zealand?

All those fine black dit particles in the bottom of your fuel tank didn't grow in there by magic!

[Flip]

Don't forget about Gull E10

Ethanol and Methanol are great fuels for race motors. But it is light in energy and big in volume. That extra oxygen molecule is a great boost during combustion. Hippy fuel.

I prefer my Ethanol flavoured.

[Jantar]

.....Its not heat that pushes your pistons down. In practice more energy can be extracted from the burning mixture by a high compression motor. Its called volumetric efficiency. ....

So the Gay-Lussac law doesn't apply in petrol engines?

[GrayWolf]

How can you justify that statement.

As someone who has worked over 20 years in the fuels and lubricants industry, for 3 years as the Technical Manager of one of the oil companies and for 8 years in that company's international technical centre, and as as one of the industry team which liaised with the Ministry of Energy and oversaw the technical details of the introduction of unleaded petrol into New Zealand, I've got to disagree with you there.

Octane (and there are two octanes in the petrol spec, Road Octane Number/RON and Motor Octane Number/MON) is only one of about ten or twelve specifications controlling the quality of petrol. There's also esoteric specs like Reid Vapour Pressure which determines the ability of petrol to vaporise so it can burn.

If our fuel is so good then why is it there is a 'Govt paper' the NZ fuel study 2001, on reducing aromatics etc. We have higher levels of benzine than other countries, MTBE a water pollutant, 25% olefins.... Good quality? Seems not according to that study.


The most significant changes proposed to the petrol specifications include:
Progressively reducing maximum benzene levels from 4.2% to 1% by volume.
Benzene is a known carcinogen. Our allowable limits are high compared to other international standards.
Progressively reducing maximum sulphur levels from 500 parts per million (ppm) to 50 ppm.
This amendment will codify current practice and facilitate the introduction of advanced engine technologies.
Prohibiting the use of MTBE in petrol with a contamination limit of 1% by volume.
MTBE mixes readily with water and has been known to taint groundwater at very low concentrations.
This has led to its ban in parts of the United States.
Allowing ethanol blends up to 10%, subject to a testing and approval process.
Currently ethanol blends are not provided for. Many countries allow ethanol blends. A precautionary approach is
proposed to ensure ethanol blended petrol meets New Zealand motoring requirements.
Prohibiting the addition of MMT (manganese).
This is not currently used. The automotive industry strongly opposes it as an additive.
Specifying and progressively reducing maximum levels of olefins from 25% by volume to 18%.
Olefin levels are currently not regulated. Olefins contribute to smog forming emissions and formation of toxic dienes.
Reducing maximum aromatics level in regular grade petrol to 40% by volume and progressively reducing maximum
aromatics level in premium grade petrol from 48% to 42% by volume.
This is a means of limiting exhaust emissions of hydrocarbons.
Reducing maximum lead levels from 13 mg/litre to 5 mg/litre.

http://www.dieselduck.ca/library/05%...el%20Study.pdf

[neels]

Have played this game myself, and in very unscientific testing found that the vw golf costs less to run on 95/98 than on 91, even though 91 meets the minimum requirements.

The manuals for the peugeot, ducati and drz all point me in the direction of 95/98 due to compression ratios, so I just pay the extra few cents and rely on supermarket coupons to prevent me from declaring bankruptcy

[steve_t]

Have played this game myself, and in very unscientific testing found that the vw golf costs less to run on 95/98 than on 91, even though 91 meets the minimum requirements.

The manuals for the peugeot, ducati and drz all point me in the direction of 95/98 due to compression ratios, so I just pay the extra few cents and rely on supermarket coupons to prevent me from declaring bankruptcy

I think with many performance cars, the engines can alter the spark advance sufficiently to to extract more power from each unit of petrol. I don't think it's specifically due to compression ratio but obviously timing will be retarded if knock is detected with using a low octane petrol and pre-detonation occurs.

[avgas]

Why is there also so many failures of common rail diesels in New Zealand?

Sulphur on 4 of mine. This is due to how they cut the diesel though. NZ diesel is shit in NZ though - but petrol is pretty bloody good.

We also seem to get the shit models of engine here too. Usually made in some crap country like spain.

The other element of high failure rate of CRD's in NZ, the most common one........is much simpler. The owner.
- No understanding of glowplugs.
- No understanding of how imperative air quality is to diesels (yes its more important that for petrol).
- No understanding that diesels in NZ need servicing twice as often as anywhere else due to our unique environment. They really should change factory specifications in NZ..........but they don't.

[Old Steve]

Flip: "Why is there also so many failures of common rail diesels in New Zealand?"

Uh, I thought we were talking about petrol. Yes, water will damage common rail diesels severely. However I think NZ diesel is now the equivalent of the European standard E5 (?) and that's a pretty high standard. Water is a contaminant and comes from many sources. Service Stations dip their tanks regularly and record the precense or abcense of water in the tank bottom. Dirt too is a contaminant but will usually settle out at the bottom of storage tanks and be drained off, thats why the oil companies allow a settling time after discharge of a shipment.

But overall, the specification for diesel in NZ is very high, up with European specs. It's contamination is another matter. Boy, I've seen some horribly contaminated diesel samples - mainly from farmers' tanks which can be left nearly empty for long periods while the inside rusts then filled and used immediately so the rust/dirt goes straight into the vehicle tank. Then it's a case of "bad" diesel, not diesel with dirt in it.

GreyWolf: I left NZ in 2002 just when the MOE raised that discussion on petrol specs. I think all those issues you have listed have been addressed in the eleven years since that paper. These specs are a living document, they have changed as engine and pollution controls have developed.

Benzene levels are a bit of a problem, benzene contributes higher octane to a petrol so low benzene fuel is dearer to produce. The additive company that sells lead additive started a campaign about the benzene content of petrol when the introduction of unleaded was being discussed. They also raised concerns about valve seat wear too, but this is only a problem in cast iron engines with no hardened valve seats that run for extended time at high power and high engine speed - like the tractors plowing those huge wheat fields in the US mid-west. Or a local example would be an old Holden V8 hauling a heavy boat on a trailer at over the speed limit from Auckland to Wellington and back continuously.

Nothing has been done about sulphur levels. However I'm sure that SULFUR levels have been reduced as you pointed out (sorry, a bit pedantic of me there!). IUPAC (International Union of Chemists and Pharmacists) have stipulated that the spelling is "sulfur" (and "aluminium" too, though the US don't accept this and still use aluminum) so the NZ spec should refer to sulfur. In accordance with developments in European specs the level of sulfur in NZ petrol will have been reduced.

I'm not sure what has happened about MTBE, this is a compound often added to US fuel in those listed polluted cities where oxygenated petrol is specified. The fuel specs are not environmental specs, the use of petrol is in itself a pollutant isn't it. I can't recall that MTBE was ever used in NZ petrol but at the time the specs were first developed it was included as a fall back - mainly to allow fuel to be sourced from refineries which used MTBE I think. Ethanol inclusion was not included in the original ULP specs, but I think this has been altered. I'm certain that this has been altered as Gull include 10% in their product. Ethanol is a problem as it is also hydrophilic, dissolves readily with water, so if there is water in the bottom of the tank the ethanol drops out of the petrol into the water, octane of the petrol decreases slightly. BTW< Do you know how to get rid of water from the bottom of your vehicle tank? Pour some propyl alcohol (some service stations actually sell it) into the tank, and the water dissolves in the propyl alcohol which remains in suspension in the petrol.

You're right about MMT which is an octane improver, I don't recall it ever being used in NZ and I think that it was only included in the spec for petrol at the MOE's insistance or as a fall back in case octane enhancement was ever needed. I think the oil companies oppose it's use as well. The specs for ULP were first laid down in the early 90s and some specs were set because the industry and MOE were not certain how or where NZ's fuel would be supplied from.

Olefins are hydrocarbons with double bonds in them, they tend to produce gums and varnishes which block carburettors and injectors. NZ petrol has very low levels of olefins, Marsden Point petrol especially. I remember back in the late 80s or early 90s when I supervised sending some petrol (800 L I think) to California to have it tested against the BMW fuel additive cleanliness test (the petrol landed in San Fransisco the day before the earthquake, the location of the shipment was unknown for weeks). BMW actually rang the additive company to ask what they had supplied as the test was the best they'd ever seen - and that was down to the low level of olefins in Marsden Point fuel. The level of olefins in petrol is a cost decision, and I think the level in NZ petrol specs may have been reduced.

Aromatics are mainly benzene, the reduction in this level follows the reduction in benzene levels.

The level of lead in unleaded petrol has definitely been reduced. Note that the description of petrol is UNLEADED, not lead free. That means that lead has not been deliberately added to the petrol. NZ had a leaded petrol distribution system for many years so there is still the possibility of infintesimal contamination from tanks and pipes. I think that even aviation gasoline has had it's lead level reduced as an aviation LL (low lead) gasoline is available, I think it's 35 mg/L down from 85 mg/L - don't quote me on that though.

On other matters. Yes the alcohols are great for race engines. The fact that they are already oxigenated (ie. partly burnt) means that a larger volume/mass has to be used to generate the same power. In the Indy cars raced at Surfers in the 90s they were using 2.3 times the volume of alcohol compared to what the engine would use if petrol was the fuel. Alcohol also has advantages because of it's evaporative cooling, more energy is required to evaporate it so it cools the engine more therefore smaller cooling systems are needed, the car is lighter. In some extreme cases engines running on alcohol do not even have a cooling system fitted.

Regarding petrol additives, I only fill up at Caltex because their petrol includes the Techron additive. These additives keep the intake system clean, whether it's carburetted or injected. They reduce carbon build up on the back of the inlet valves which can absorb fuel on start-up (making starting harder) then release the fuel as they warm up (producing rough running). As well they keep the pintle of the fuel injector clean ensuring an even and correct spray of petrol from the injector - this can give better fuel economy or higher power output compared to an engine with restricted injectors.

[Akzle]

fascinating

[Flip]

Until Caltex tells me what Techron is, its just witches brew and is being added for marketing purposes. From time to time I do add a squirt of valve master to my petrol powered vehicles. It was originally marketed as a fuel system detergent. The dose rate to prevent VSR is a lot higher than needed to clean fuel deposits.

I have a 50 n brass gause strainer under the fill cap on my bike, it collects a lot of rubbish from the fuel stations before it blocks my fuel filter.

Farm tanks are not the fuel companies problem, if I had a couple of 250k tractors I would run my fuel through a nappy-coalessor and the tank would have a propper filter/PV vent on it, the issue I have with diesel fuel here is the seven sisters knew that the euro regs were comming and have done almost nothing to bring their retail and distribution fuel handeling equipment up to spec. As a result much of the fuel is being contaminated and is a major contributing factor fucking up a lot of vehicles fuel systems, I personally won't be buying another diesel vehicle until the retail fuel quality improves.

The topic was, is cheap fuel cost effective? I say yes it is.