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High octane fuel and the truth
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Tsunamix
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Ok Time to put a shoe in this one.
Octane ratings come from a test rig that measures the point in a set test bed engine at which a particular fuel pre-ignites, in comparison to a standard mix of Iso-Octane and Heptane.
91 RON Fuel pre-ignites at the same point as a mix of 91% Iso-Octane and 9% heptane.
All engines from the factory are tuned initially to run on the lowest standard octane fuel available in the country of origin, be it 91 octane, 95, 98 or 2.2 . From their, specif models can be tune with different base fuels in mind, but all will have the ability to be run on the base fuel mixes, somehow. More often by reducing the amount of spark advance to limit pre-ignition.
This very often means that each cars ECU has 2 spark maps. 1 for High octane fuels, and 1 for Standard.
NO-WHERE has flame speed, or anything else been mentioned.
It is interesting to note that Ethanol and methanol share a RON rating when pure of 129, and are frequently added to fuels as an octane booster.
Changing from a 91 Octane fuel to a 98 Octane fuel can have no effect on the engine if the engine does not have a spark map to take advantage of this change.
Other additives in the fuel may affect performance. However a 91 Octane fuel with the performance additives from the very best premium fuels will perform identically to a 98 Octane fuel with the same additives - unless the ECU has the Spark Map to take advantage of it.
This spark map is commonly referred to as the Tune.
Now listen up. this is where you people go wrong.
The ENERGY VALUE of Heptane, per Kg is 44.592 Mj / Kg
The ENERGY VALUE of Iso-Octane, per Kg is 44.374 Mj / Kg
Click Here for Data
The Total maximum energy liberation in burning 1kg of 91 Octane Reference fuel is 44.57238 MJ
The Total maximum energy liberation in burning 1kg of 98 Octane Refernce fuel is 44.58764 MJ
Since the average efficiency of the combustion engine is less than 20%, the difference between the 2 is
0.003052 Mega Joules per Kg . 1 Kg = 1.34228 litres (745g / litre but varies brand and type to type).
So for every Litre you burn, you have an additional .00227374 Mega Joules of energy to play with. This is cut big time by the efficiency of the internal cimbustion engine which is less than 20%.
87 Octane Fuel has 44.4 Mj/Kg, Aviation Petrol (Not kerosene based jet fuel) has 46.8 Mj/Kg.
Picking something like 45.2 as the 91 Octane energy value, by switching to 98 from 91 octane you have about .0002515% more liberated energy to play with (.00227374 / 9.04 - which is the 20% effeciency value of my guesstimated 45.2 MJ figure).
So for all of those that travel additional miles or get better performance from 98 Ron without tuning for it ? I call scientific bullshit.
Word of warning - Theres plenty of chance there are other factors involved than just octane rating. But since this discussion was all about octane ratings to start with....
Octane ratings come from a test rig that measures the point in a set test bed engine at which a particular fuel pre-ignites, in comparison to a standard mix of Iso-Octane and Heptane.
91 RON Fuel pre-ignites at the same point as a mix of 91% Iso-Octane and 9% heptane.
All engines from the factory are tuned initially to run on the lowest standard octane fuel available in the country of origin, be it 91 octane, 95, 98 or 2.2 . From their, specif models can be tune with different base fuels in mind, but all will have the ability to be run on the base fuel mixes, somehow. More often by reducing the amount of spark advance to limit pre-ignition.
This very often means that each cars ECU has 2 spark maps. 1 for High octane fuels, and 1 for Standard.
NO-WHERE has flame speed, or anything else been mentioned.
It is interesting to note that Ethanol and methanol share a RON rating when pure of 129, and are frequently added to fuels as an octane booster.
Changing from a 91 Octane fuel to a 98 Octane fuel can have no effect on the engine if the engine does not have a spark map to take advantage of this change.
Other additives in the fuel may affect performance. However a 91 Octane fuel with the performance additives from the very best premium fuels will perform identically to a 98 Octane fuel with the same additives - unless the ECU has the Spark Map to take advantage of it.
This spark map is commonly referred to as the Tune.
Now listen up. this is where you people go wrong.
The ENERGY VALUE of Heptane, per Kg is 44.592 Mj / Kg
The ENERGY VALUE of Iso-Octane, per Kg is 44.374 Mj / Kg
Click Here for Data
The Total maximum energy liberation in burning 1kg of 91 Octane Reference fuel is 44.57238 MJ
The Total maximum energy liberation in burning 1kg of 98 Octane Refernce fuel is 44.58764 MJ
Since the average efficiency of the combustion engine is less than 20%, the difference between the 2 is
0.003052 Mega Joules per Kg . 1 Kg = 1.34228 litres (745g / litre but varies brand and type to type).
So for every Litre you burn, you have an additional .00227374 Mega Joules of energy to play with. This is cut big time by the efficiency of the internal cimbustion engine which is less than 20%.
87 Octane Fuel has 44.4 Mj/Kg, Aviation Petrol (Not kerosene based jet fuel) has 46.8 Mj/Kg.
Picking something like 45.2 as the 91 Octane energy value, by switching to 98 from 91 octane you have about .0002515% more liberated energy to play with (.00227374 / 9.04 - which is the 20% effeciency value of my guesstimated 45.2 MJ figure).
So for all of those that travel additional miles or get better performance from 98 Ron without tuning for it ? I call scientific bullshit.
Word of warning - Theres plenty of chance there are other factors involved than just octane rating. But since this discussion was all about octane ratings to start with....
delcowizzid
on holiday
well slower burn helps means you get more force on the pistons down stroke for longer increasing torque theres your fuel saving
vn_v6
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i dont know what you guys are on about but when i put premium in it idles ALOT smoother and its more responsive, there is a difference, and i do feel it when i put my foot down, especialy if i reset the computer after a full tank, argue with me, but in my car atleast, i can feel it
BowTie
Active Member
Why has the argument been narrowed down again to purely to octane ratings.
The OP was adamant that there is NO BENEFIT WHATSOEVER.
Why is it so hard for people to comprehend that the octane rating is not the only difference between the two types of fuels.
The OP was adamant that there is NO BENEFIT WHATSOEVER.
Why is it so hard for people to comprehend that the octane rating is not the only difference between the two types of fuels.
Tsunamix
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I dunno about slower burn Delco.
Slower burn is often more complete for greater completion percentage of burn, but faster burns tend to liberate les sthermal waste during the burn. In the end it doesn't matter if it's slower or faster burn if the energy liberation difference between the 2 is identical.
It's all about converting liquid and gas into a different rapidly expanding gas. The larger and more complete the conversion, the greater the force applied to the piston head.
Slower burn is often more complete for greater completion percentage of burn, but faster burns tend to liberate les sthermal waste during the burn. In the end it doesn't matter if it's slower or faster burn if the energy liberation difference between the 2 is identical.
It's all about converting liquid and gas into a different rapidly expanding gas. The larger and more complete the conversion, the greater the force applied to the piston head.
minux
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As I said earlier, who needs technical mump like Tsunamix copy and pasted.
All I need to know is:
Senator on 91, no skids on take off
Senator on 98 smoky rear window on take off.
All the proof I need that it does make a difference
All I need to know is:
Senator on 91, no skids on take off
Senator on 98 smoky rear window on take off.
All the proof I need that it does make a difference
wraith
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As I said earlier, who needs technical mump like Tsunamix copy and pasted.
All I need to know is:
Senator on 91, no skids on take off
Senator on 98 smoky rear window on take off.
All the proof I need that it does make a difference
Pics or it never happened :whistling
Nanos
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i can only go my experiences.
put 91 in the wagon and the engine will ping and most likely not last long at all.
put 98 in the wagon and no ping and performance is back.
like most have said pinging is directly related to octane rating. so therefore if i use a lower octane fuel i get less performance. higher octane = higher performance and also better km's/100.
the OP did say standard engines. Wonder what his version of standard engine is??
put 91 in the wagon and the engine will ping and most likely not last long at all.
put 98 in the wagon and no ping and performance is back.
like most have said pinging is directly related to octane rating. so therefore if i use a lower octane fuel i get less performance. higher octane = higher performance and also better km's/100.
the OP did say standard engines. Wonder what his version of standard engine is??