Fuel octane ratings and Engine damage

[HenryDorsetCase]

https://www.stuff.co.nz/motoring/115903134/driver-put-wrong-grade-petrol-into-her-car-loses-compensation-bid


I didnt think the 4% (or so) difference in octane rating would make enough of a difference to lunch a motor - especially a modern motor with knock sensors and so forth.

My understanding of detonation is that the fuel spontaneously combusts in pockets in the combustion chamber before the main fuel charge is ignited by the spark plug.... causing uncontrolled pressure and thus causing damage to an engine.

Fascinated if anyone has any insight.... also whether I should be running my street bikes on 95 - I've always used 91 because it seems to run OK on it.....

[BadSarah]

It was my understanding that a vehicle designed for 95 would run poorly and be less efficient on 91. I was also given to believe that higher octane can damage parts of fuel systems, particularly if it has a higher level of ethanol in the fuel mix.

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[SaferRides]

Not a good idea to run a Euro car on NZ 95, let alone 91, but the knock sensor should have prevented any damage.

No responsible dealer should be selling used import VW's anyway.

[george formby]

Not a good idea to run a Euro car on NZ 95, let alone 91, but the knock sensor should have prevented any damage.

No responsible dealer should be selling used import VW's anyway.

Why do you say that?

[onearmedbandit]

I've had first hand experience with many of the aforementioned vehicles, and continued use of 91 will kill these engines. Especially the Highline model with the 1.4TSi twin-charge engine (super and turbocharged). I'm not in the slightest surprised her engine was damaged.

[onearmedbandit]

No responsible dealer should be selling used import VW's anyway.

Ignorance 101.

[Laava]

Not a good idea to run a Euro car on NZ 95, let alone 91, but the knock sensor should have prevented any damage.

No responsible dealer should be selling used import VW's anyway.

So what should you run it on? Given that 98 is not commonly available.

[onearmedbandit]

So what should you run it on? Given that 98 is not commonly available.

95 is perfectly fine. From someone that has sold in excess of 400 Golf models plus numerous other Euro’s, and who also runs a modified GTi that puts out 150% of its original power on 95 all day long.

[Laava]

That's what I would have thought...

[pritch]

My import is supposed to be run on 100 Octane but...

The manuals for my bikes recommended 95, so 95 it was. The Triumph manual specifies 95RON and I believe that's what we have.

Used to put 95 in the moped too, didn't want any less power than the poor little thing was capable of producing.

[HenryDorsetCase]

My import is supposed to be run on 100 Octane but...

The manuals for my bikes recommended 95, so 95 it was. The Triumph manual specifies 95RON and I believe that's what we have.

Used to put 95 in the moped too, didn't want any less power than the poor little thing was capable of producing.

Errrrrr. Read the manual you say? Shit, I never thought of that. Fuck.

wonder if my rings and pistons are crumbling as we speak?

[onearmedbandit]

My import is supposed to be run on 100 Octane but...

.

What car is that?

[Temporary-Kiwi]

octane ratings are an indicator of what you get out of the pump, I once talked to a tanker driver, he said that a delivery could be diluted up to 6% by an alternate fuel.
so that 91oct might have a few % of diesel in it !
I've had detonation troubles caused by various things in modified engines, mostly in my xr650r, once I went over 12:1 comp ratio it won't run on 91oct without protesting
, I went around the south island on it , the mtr in super mortard eng spec , I fitted a lead adding device , it ran ok on 95 Oct, but still didn't like 91.
most bikes sold in nz, will happily run on 91oct when std, but big-bore hi-comp singles are susceptible more than most

[Honest Andy]

Ignorance 101.

The real ignorance was the driver who kept running a car that must have been pinking like hell!

[OddDuck]

https://www.stuff.co.nz/motoring/115903134/driver-put-wrong-grade-petrol-into-her-car-loses-compensation-bid


I didnt think the 4% (or so) difference in octane rating would make enough of a difference to lunch a motor - especially a modern motor with knock sensors and so forth.

My understanding of detonation is that the fuel spontaneously combusts in pockets in the combustion chamber before the main fuel charge is ignited by the spark plug.... causing uncontrolled pressure and thus causing damage to an engine.

Fascinated if anyone has any insight.... also whether I should be running my street bikes on 95 - I've always used 91 because it seems to run OK on it.....

Octane rating is a weird beast. Have a look at the wiki page: https://en.wikipedia.org/wiki/Octane_rating

Basically there are two reference fuels and a specified test engine (of unusual geometry) which set the scale. One fuel has a knock rating of 0, the other a knock rating of 100 (by definition), it isn't linked to any absolute values of pressure, temperature etc. It's an arbitrary scale, but it's repeatable and so it's fit for purpose.

Detonation: yes, pockets of the fuel go bang in advance of the flame front, leading to a massive rise in pressure and heat in the cylinder since the detonation happens so quickly. Really bad detonation will be the main charge going off before the spark bubble has a chance to propagate.

From reading the Stuff article, it sounds like they were going cheap to save those precious bucks... yeah didn't work very well I guess. On that note, apparently the hypermilers (people who keep notebooks of $ vs km) have been finding that for a given octane rating, it's actually the most expensive fuel per litre that gives you the most km's per buck... something to do with the calorific value of the fuel blend. Not all 95 is equal.

[SaferRides]

Not a good idea to run a Euro car on NZ 95, let alone 91, but the knock sensor should have prevented any damage.

No responsible dealer should be selling used import VW's anyway.
I should have put a smiley after the 2nd comment.

To be fair, Marsden Point 95 is better fuel than it used to be, but every vehicle I've had that required 95 has run better on 98.

[F5 Dave]

Errrrrr. Read the manual you say? Shit, I never thought of that. Fuck.

wonder if my rings and pistons are crumbling as we speak?
Stop panicking. My Tiger speced for 95. Actually the previous owner had the pistons replaced as they broke. Not sure if he ran 91 but I suspect so. I put a label on the cap for next owner.

675 is speced for 91.

In NZ was use, , , erm either RON or MON, but they differ slightly. 100 octane is like AV gas so no road vehicle will spec that. Think US use the queer high number system.

[Mike.Gayner]

I've had first hand experience with many of the aforementioned vehicles, and continued use of 91 will kill these engines. Especially the Highline model with the 1.4TSi twin-charge engine (super and turbocharged). I'm not in the slightest surprised her engine was damaged.

That's exactly the model in question, too.

http://www.nzlii.org/cgi-bin/sinodisp/nz/cases/NZMVDT/2019/177.html


The vehicle is a 2010 Volkswagen Golf TSI which has a 1.4 litre petrol engine.

[F5 Dave]

Oh no my tyres cut out. I wasn't told they needed air in them.

And my ice cream melted when I left it in the car.

[HenryDorsetCase]

Oh no my tyres cut out. I wasn't told they needed air in them.

And my ice cream melted when I left it in the car.

Honestly, ice cream is one of my favourite foods. No wonder I am so fat.

[TheDemonLord]

Speaking of Melting etc.

I'm not sure if this is due to different Octane ratings, but I remember something about incorrect fuel causing parts of the engine to run much cooler than they should, due to the difference in energy required to vaporise the liquid into a gas for a combustion.

[HenryDorsetCase]

aH-lDh3rVFQ



https://www.youtube.com/watch?v=aH-lDh3rVFQ

Here is a clear explanation with examples of pre-ignition and detonation. From the damage described to the VW Golf in the news article it sounds like it was detonation.

My VW Golf mad mate ran/runs all his on 98.

[F5 Dave]

Speaking of Melting etc.

I'm not sure if this is due to different Octane ratings, but I remember something about incorrect fuel causing parts of the engine to run much cooler than they should, due to the difference in energy required to vaporise the liquid into a gas for a combustion.



That's a snippet of no mixed with perhaps methanol stories which are in no way relevant. So just no

Maybe also confused with the light gasses that evaporate quickest . These really help starting a cold engine. Old gas may make it hard to start some engines.

Gas stations have measures to try stave off this loss of light gasses . Usually tall pipes at the side, but you dont always see them.these days.

[F5 Dave]

Most people think pistons are pushed down by carefully timed explosions.
They are not. There is a fire lit which very quickly burns to increase the temperature and thus via Boyles law the pressure.

If there were explosions it would destroy the engine components. And indeed detonation is just that with the end gasses.

[TheDemonLord]

That's a snippet of no mixed with perhaps methanol stories which are in no way relevant. So just no

Maybe also confused with the light gases that evaporate quickest . These really help starting a cold engine. Old gas may make it hard to start some engines.

Hairy Muff, Now that you mention Methanol - that does ring a bell.

[Motu]

aH-lDh3rVFQ




Here is a clear explanation with examples of pre-ignition and detonation. From the damage described to the VW Golf in the news article it sounds like it was detonation..

Detonation will shatter rings...and detonation is post ignition, not pre ignition. The knock sensor will retard ignition timing to control pre ignition, but post ignition is a bit harder to control. I will run my Euro car on Gull 98 for a trip when it is the same price as 91 in town, and get better fuel economy, but around town driving makes no difference. If I damage the engine in my $500 car, I will have to replace it with a $600 car.

[spanner spinner]

This ruling makes a change, usually it's the dealer who gets to pay for the customer's ignorance. I have worked in the automotive industry for many years and have seen many disputes where the customer is proven to be in the wrong as in this case be due to some feeble excuse from the customer the ruling goes against the dealer.