Talk:Octane rating

message: I have removed the following sentence from the end of the paragraph.
"A higher octane will burn faster and allow the auto to run more clean."
This is simply not true.  It depends on the chemical composition of the fuel.  Flame front propagation speeds are not goverened by octane.
I'm taking this out! This is so wrong.
"However, premium grades of petrol often contain more energy per litre due to the composition of the fuel as well as increased octane."
This is what people tell themselves to rationalize getting premium fuel when they don't really need it. High octane fuel actually has fewer BTU compared to low octane fuel; thus LESS ENERGY.   —Preceding unsigned comment added by 67.175.221.197 (talk) 03:13, 27 September 2007 (UTC)
thread_title:  Octane 

message: This seems to be a pro-ethanol plug that somebody just decided to place there. It just seems really alone...but that may just be bias talking. — Lunarbunny 20:10, 6 August 2006 (UTC)
thread_title:  Ethanol under ''Knock resistance'' 

message: "On a typical high-rev'ving motorcycle engine, for example, the maximum power occurs at a point where the movements of the intake and exhaust valves are timed in such a way to maximize the compression loading of the cylinder"
I believe this is where the maximum torque occurs.  The maximum torque always occurs at the rpm where the maximum engine efficiency occurs.  And it sounds like this is the point they are talking about.  Does anyone have any ideas, or a reference to where the maximum power information came from?
:: Not necessarily. Motorcycle engines tend to be very primitive.  Maximum power occurs at a specific rpm and is determined by the torque multiplied by the rpm.  But torque is determined by a number of factors which change.  Chief among these is volumetric efficiency which is measured as BMEP (Brake Mean Effective Pressure).  
:: The efficiency of cylinder filling (BMEP), engine friction loss, and the ability of the engine to revolve at a certain speed determines instantaneous power, which is nearly irrelevant to driving performance.  Variable valve timing is now being used to maximize engine performance over a wider range of rpms by varying the torque producing characteristics of the engine to better suit the rpm.
:: Aside from issues of volumetric efficiency, torque is almost exactly a measurement of engine size.  In engine design though, a larger piston is harder to move and will disintegrate at a lower rpm than a smaller piston.  So engine cylinder numbers, rpm, bmep, and friction all provide limits to power output.  In modern engines, power output is almost directly related to the amount of fuel burned.  Note that engines typically have a specific rpm range where specific fuel consumption is the lowest for a given output. This is usually not in the same rpm range as the highest power output.  So engines setup for high power are inefficient.  Variable valve timing helps to compensate somewhat for this.
:: Higher loading of the piston, by definition, also means more friction loss through the rings.  The Miller cycle design of the toyota prius engine is designed to lower friction to a minimum, but is very inefficient.  The Prius is no more efficient than conventional engines that are simply sized correctly for the load. 
:: Motorcycle engines, due to their emphasis on high performance, also won't tolerate lower octane fuels unless they have modern fuel injection.  They are also very high polluting.  The worst polluting engines in use today are the Day and Clerk cycle engines used in motorcycles.  But Harley-Davidson V-Twins are massive polluters due to their primitive hot running designs. Krontach (talk) 09:11, 22 May 2011 (UTC)
thread_title:  Maximum power vs. maximum torque 

message: I have removed the statement "Note: The octane rating of cyclohexane significantly varies form source to source. See for example [3]" since it is wrong and the reference given has no relevant info to confirm the observation.  Cyclohexane is a pure chemical and has the same octane no matter its source; what can vary, like many other blending agents but dramatically for cyclohexane, is its actual octane contribution... depending on the mix of chemicals to which it's being added.
Also note that the "table" which is supposed to appear in this section is misplaced and actually appears later in the article, currently globbed together with the "specific energy" table.  It appears to have moved in the past few days so maybe the author responsible can take care of that.
Scunnerous 04:45, 14 April 2007 (UTC)
thread_title:  Examples of octane ratings 

message: Removed the question: [Can someone please determine the correct unit for this measurement?  Does the gasoline release 19,000 BTU per cycle, per gallon, or what.  It is tough to determine whether ethanol is actually being proven to be a better fuel in this article].
It should be in the discussion, not in the article.
:: Gasoline, developed first in 1908 by the United States Navy, has undergone decades of improvement.  Originally you had to go to your local apothecary with your hygrometer and measure the specific density of your fuel to make sure it would run in your engine.  The first filling station was built in Detroit in 1910 after the Navy created the specification for gasoline.
:: By 1912 all the known reserves of crude oil from which gasoline could be made were known to be running out.  Charles F. Kettering of Dayton Engineering Laboratories (Delco) was given the task of finding a way to boost the compression ratio of Otto engines.  At that time 6 to 1 was about all that an engine could run at prior to destruction.  Kettering put two of his assistants to work studying Kerosene (which had NEVER been able to be used as a motor fuel). His belief was that the reason engines blew up using kerosene was that the fuel did not burn totally and was continuing to burn in the exhaust causing a melt down, broken rods, pistons, valves, guides, etc. etc.
:: What was found instead was Pre-Ignition.  Ethanol is much less likely to pre-ignite.  But it has less heat energy.  Ethanol is bio-degradable, carbon neutral.  From the standpoint of whether humans will poison themselves to death with soot, CO, CO2, NOS, H2S etc. etc. Ethanol is preferable to preserve life on the planet.  Otherwise gasoline is a better fuel for high power and to preserve the petroleum monopolies that keep us all permanently indebted to heat our uninsulated homes and to drive our inefficient vehicles.
:: Gasoline is good for the Oil Monopoly.  —Preceding unsigned comment added by Krontach (talk • contribs) 09:24, 22 May 2011 (UTC)
thread_title:  Octane question 

message: Energy cannot be released per air fuel ratio!
* energy per kg of fuel (values mentioned by factor 10 too low!)
* energy per kg of air (most propable case for these values)
:I agree, this doesn't make much sense to me...The energy_density article shows ethanol having a much lower energy density than gasoline (30 and 46, respectively), so I'd like to know how these figures are calculated.  While I agree that due to running a richer mixture "the net energy released per cycle is higher", this doesn't translate to an increased net energy of ethanol.  Mattjm 22:16, 15 November 2007 (UTC)
thread_title:  "Energy released per air fuel ratio"? 

message: I was wondering whether higher or lower octane fuels emit more pollants as a result of combustion (and why). If you have any idea please let me know.
199.159.108.208 17:23, 5 July 2007 (UTC)
replies: text: I can't see why it would make a difference with the possible exception of when the engine is actually knocking, but even then... —Ben FrantzDale (talk) 00:36, 18 April 2008 (UTC)
thread_title:  Fuel octane's effect on pollutants emitted 

message: I just raised this complaint on gasoline and figured I'd check if it came from here.  This article repeated uses the terms "detonation" and "autoignition" interchangeably, which is incorrect.  Detonation is not the correct term. A detonation is a premixed flame wave structure which is self-sustaining through the coupling of a shock front and subsequent heat release. There is no wave structure in knock. I think the correct term is autoignition, referring to the phenomenon of a fuel/air premixture which self-ignites due to high ambient temperatures and pressures, and should be made to be consistent throughout the article. Unless someone else wants to argue that point, I'll make the change in a week or so. Thermodude 16:52, 10 July 2007 (UTC)
replies: text: detonation is actually the correct term. it is easy to prove as well, an engine running on fuel such as methanol can be made to auto ignite very easily without knocking. "knock" is quite audible and can be detected with a microphone type pick up while pre ignition or auto ignition makes nearly no sound at all. it is mealy a dull "thud" if it can be heard. the knocking sound is the result of the fuel exploding rather than burning. this happens well after combustion has started, during the period where the pressures and temperatures are highest. its a bit like comparing gunpowder to high explosives, normal burning vs knocking. indeed there are many fuels with high octane ratings that have extremely poor resistance to auto ignition, methyl ethyl ketone is one fine example. one reason i think the two are grouped together is that they often accompany each other. an engine that starts to knock can over heat the spark plug and start to preignite. this has killed countless methanol engines. i intend to edit this article to be accurate but will not until i have better data.  —Preceding unsigned comment added by 4.227.193.229 (talk) 02:07, 14 December 2009 (UTC)
replies: text: Haven't found the shift key on the keyboard yet, have we, archyl?—QuicksilverT @ 03:55, 24 September 2010 (UTC)
thread_title:  Detonation vs. autoignition 

message: I was reading this article as a n00b and the term 'knock' doesn't mean anything to me. Can anyone create a stub and link it? Jddriessen (talk) 13:34, 29 January 2008 (UTC)
replies: text: The article already exists, and is rather more than a stub. :-) Indeed, it's already linked to in the introduction. Angus Lepper(T, C, D) 14:56, 29 January 2008 (UTC)
thread_title:  Definition of knock 

message: The sentence "It might seem odd that fuels with higher octane ratings explode less easily and are therefore more powerful." was simply incorrect, so I changed it to read "It might seem odd that fuels with higher octane ratings explode less easily and can therefore be used in more powerful engines."
The whole section needs a re-write, however.  It's disjointed and confusing. --Slashme (talk) 07:29, 31 July 2008 (UTC)
thread_title:  Effects of octane rating 

message: Maybe this article will have a good reference to the octane rating of pure hydrogen as fuel.  Does someone here have access to it? --Slashme (talk) 07:34, 31 July 2008 (UTC)
replies: text: I don't have the specifics on Hydrogen but I can tell you it requires that ignition timing be AFTER TDC due to it's burning so fast.  I don't believe Hydrogen will ever be a viable fuel due to the necessity to compress it to about 10,000 psi to get a decent range out of it. Krontach (talk) 09:28, 22 May 2011 (UTC)
thread_title:  Octane rating of hydrogen 

message: "In Russia and CIS countries 80 RON (76 MON) is the minimum available, the standard is 92 RON, however, the most used type is 95 RON."
I dare say this is incorrect. Most people actually use 92, particularly so outside Moscow; 95 is generally considered above average. 98 is also available here and there, but is very rarely used. -- int19h (talk) 20:24, 30 November 2008 (UTC)
thread_title:  Usage in Russia 

message: I'm kind of an anthro-dork, and I found it really interesting.  I've been all over the US and have never seen anything like that.
Sit booboo sit (talk) 11:06, 6 December 2008 (UTC)
replies: text: Hmmm... There has been a recent discussion about this photograph on the Wikimedia Commons. One people thinks this photograph is photoshopped. I completely agree with him: the labels "Plus" are roughly made and added, so is also at least one of labels at the bottom of the image. -- Basilus (talk) 15:16, 2 March 2010 (UTC)
thread_title:  Where was that gas station picture taken? 

message: Most modern engines use a knock sensor to control ignition advance. Using a higher-than-necessary octane fuel will allow the engine to use a more aggressive ignition advance than if the minimum octane fuel were used. Therefore, using a higher octane fuel can increase power, especially at high engine speeds at high throttle. Is this correct?
On the other hand, use of an increased ignition advance will probably increase total wear on engine parts - since the combustion will be started earlier, the average amount of downward force on the piston will be greater during end of the compression stroke. Does this increased friction overwhelm the benefit of increased ignition advance (assuming a normal compression ratio which does not require high octane)?  —Preceding unsigned comment added by 66.235.43.99 (talk) 13:08, 20 March 2009 (UTC)
replies: text: I don't think your logic is correct. There is a sweet spot for ignition timing, and advancing it more than the engine was designed for isn't going to produce more power. The idea behind ignition advance is to give the fuel time to burn so the cylinder pressure goes as high as it's going to go right as the piston passes top-dead-center. This produces maximum power. For cars that feature a knock sensor which causes the computer to retard the timing, this is only a safety feature designed to keep detonation from damaging the engine. The only way to produce more power with a given engine displacement is to increase the compression ratio or add forced induction, or increase the maximum RPM. Any of these modifications may require a higher octane fuel to prevent detonation, but using high octane fuel without any modifications is not going to increase power. Shreditor (talk) 06:04, 30 March 2009 (UTC)
thread_title:  Has anyone considered the effect of increased ignition advance? 

message: This article explains the difference between the "Researched octane number" and the "Anti-knock index" at least three times at different places. IMHO one time is sufficient for one aritcle! axpdeHello! 17:07, 31 May 2009 (UTC)
thread_title:  RON vs. AKI 

message: I just merged the text from Difference between RON and AKI into the table (in section Examples of octane ratings). It seemed to me the values referred to MON, but then I noticed that the text before the table says "the following table ... gives the 'AKI' ratings." I'm not sure if we can trust that sentence. It has been changed in February 2008 without any justification . I am now deleting this sentence, which has become obsolete since the new table contains a column for each. I assume that all existing values were in fact MON values, and I am keeping them in the MON column. But because the change has been around for one and a half years, I am not sure if my assumption is correct. In particular, there is a risk that values that may have been added after the sentence changed are in fact AKI values. — Sebastian 18:45, 13 July 2009 (UTC)
thread_title:  Does the table contain RON or AKI values? 

message: The article said that lower octane that engine require will lower performance and efficiencies. How about higher?  —Preceding unsigned comment added by Kelvin1704 (talk • contribs) 09:48, 5 June 2010 (UTC)
replies: text:  It's like penicillin.  If you reach a certain amount it does the job.  Beyond that there is no further effect. Krontach (talk) 09:32, 22 May 2011 (UTC)
thread_title:  How about higher? 

message: I am trying to find an octane/altitude/ combustion coefficient relative to petrol powered electrical generators in order to establish what percentage mixture of European '95 & '98 RON fuels would compensate for reduction in air density. If a petrol generator designed to run on '95 runs on pure '98 there is a risk of knocking but would the appropriate percentage mixture give better performance without risk of dammage to the motor?—Preceding unsigned comment added by 193.252.53.93 (talk) 13:39, 28 October 2010 (UTC)
replies: text:  Because the lower oxygen content of the air in higher altitudes can influence the air/fuel-ratio in the engine, making the mixture richer. Well, it really influences the oxygen/fuel-ratio, but that's what is important.  — Preceding unsigned comment added by 190.193.215.167 (talk) 18:21, 20 June 2015 (UTC)
replies: text: I'd like if someone knowledgeable would add information about the relation between recommended octane number and altitude to the main article (it's not there right now). In the Lake Tahoe area, at , some gas stations sell 85 Octane gasoline, which is not really available at sea level in California. 173.164.203.189 (talk) 20:37, 20 September 2016 (UTC)
thread_title: Octane/Altitude/Combustion Coefficient

message: I think it's very important to outline octane index (OI) here. It's a key parameter in describing knock in S.I. engines. A higher RON doesn't automatically mean better resistance to knock at all. It's quite possible to have a RON 100 fuel knock well before a RON 95 fuel.
The actual performance of a fuel in on-the-road terms of knocking performance is the OI which is determined as follows. OI = RON - KS, where S is the fuel sensitivity (RON - MON) and K is a weighting factor dependant on each engine and operating condition. When the RON MON tests were conceived in the 30s carburettor engines required far higher intake temperatures than we see today. As compression ratios and intake pressures have increased and intake temperatures have decreased, the value of K has gone from 1.0 to values < 0 in the most modern engines. With negative K values for modern engines it is clear to see that a higher RON can be worse for modern engines with GDI and FI technologies.
Please see the SAE paper "The Shift in Relevance of Fuel RON and MON to Knock Onset in Modern SI Engines Over the Last 70 Years" for more details.  — Preceding unsigned comment added by Gtconway (talk • contribs) 13:42, 29 June 2011 (UTC)
thread_title:  Octane Index and Relevance to RON/MON tests 

message: With a stated boiling point of 125 C then surely octane is a liquid and NOT a gas as the opening sentence says...
Could I also suggest that editors refer to "Internal Combustion Engine Fundamentals" by Heywood. There is a whole chapter on knock and this page could certainly use some input from there. James 80.176.88.36 (talk) 22:38, 4 July 2011 (UTC)
thread_title:  Since when was octane a gas?? 

message: According to the definition, the octane number is the percentage of iso-octane in a mixture with n-heptane. How are octane numbers greater than 100 defined?  — Preceding unsigned comment added by Thalb2000 (talk • contribs) 10:39, 21 December 2011 (UTC)
replies: text: Well I am not expert, but here goes. 100% iso-octane has an octane number of 100, but the scale is not really about the iso-octane content but performance that is like isooctane.  Some other fuels are even better than iso-octane in terms of resisting pre-ignition.  Apparently toluene is one such species.  So if you load up with toluene, you get better performance.  --Smokefoot (talk) 11:35, 21 December 2011 (UTC)
thread_title:  Octane numbers greater than 100 

message: Why this section was removed? 
*Hydrogen does not fit well into the normal definitions of octane number. It has a very high RON and a low MON,[16] so that it has low knock resistance in practice,[17] due to its low ignition energy (primarily due to its low dissociation energy) and extremely high flame speed. These traits are highly desirable in rocket engines, but undesirable in Otto-cycle engines. However, as a minor blending component (e.g. in a bi-fuel vehicle), hydrogen raises overall knock resistance. Flame speed is limited by the rest of the component species; hydrogen may reduce knock because of its high thermal conductivity  — Preceding unsigned comment added by 87.110.181.186 (talk) 16:13, 18 June 2012 (UTC)
thread_title:  Hydrogen MON 

message: This is not the UK version of Wiki is it?  Take out all the "petrol" jargon and save it for the .uk site.  — Preceding unsigned comment added by 173.218.135.200 (talk) 01:55, 21 October 2014 (UTC)
replies: text: Nor is it the US version. It is the English-language version. GrindtXX (talk) 07:53, 21 October 2014 (UTC)
thread_title:  Petrol V. Gasoline 

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I have just modified 12 external links on Octane rating. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
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thread_title:  External links modified 

message: No real information in the article about how octane affects fuel consumption, whether it’s cost effective to pay for higher octane fuel, and of course, how higher octane improves performance in high end vehicles.  Please can the technical people address these questions in the article IN PLAIN ENGLISH.  Thank you 122.106.196.62 (talk) 10:58, 3 July 2019 (UTC)
thread_title:  Not useful - please update  

message: I don’t have the technical knowledge to know how to correctly resolve this, but the last sentence of a graf (the third, perhaps?) reads “Using gasoline with lower octane may cause engine knocking (pre-ignition).” Engine knocking is a link to the appropriate article, which says that knocking and pre-ignition are different things. Can this be clarified somehow? Claudia (talk) 14:59, 26 March 2022 (UTC)
thread_title:  knock vs. pre-ignition? 

message: According to https://archive.dhakatribune.com/bangladesh/power-energy/2021/01/18/bsti-for-allowing-import-of-downgraded-petrol petrol sold in Bangladesh is now 89 Octane, not 80 as stated here. 195.213.169.183 (talk) 16:37, 2 February 2023 (UTC)
thread_title:  Regional variations 

message: § Examples has an  template, indicating that it "contains indiscriminate, excessive, or irrelevant examples", but no clarification as to why it was added.  What would be needed to fix this?  Was it added because it contains too many irrelevant examples of specific brands of fuel, too many chemical compounds, or because the list is too long in general?  Would splitting the list into two tables (chemical compounds / specific fuel brands) help?   Could you clarify this?
This talk section may also be used to discuss that template, which edits need to be made, and whether it can be removed (once changes have been made, or if the template is deemend unneeded). —Cousteau (talk) 20:21, 2 July 2023 (UTC)
replies: text: Yes, the point was that having lists of brands and countries is probably excessive. I would remove the specific brand references altogether or severely trim it. Stifle (talk) 08:05, 4 July 2023 (UTC)
thread_title:  "Excessive examples" template