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This article is written in what I call 'wtfspeak'; to get anything out of it, you need to have some preexisting techincal knowledge. I think it needs to be dumbified for those of us who lack that knowledge. As is, I have no idea what the author is talking about or how it applies to consumers. —Preceding unsigned comment added by 65.113.71.3 ( talk • contribs) 18:25, 30 July 2008
says that methamphetamynes are good for the environment"
what !?? "methamphetamynes" I don't think so ? and who is
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)
Octane refers to Gasoline ONLY. So the statement that Octane refers to a fuel is in error. Krontach ( talk) 08:14, 22 May 2011 (UTC)
Gasoline energy content varies from about 110k BTU to 125k BTU. Adding ethanol, which is mandated, does lower this. Ethanol at 10% lowers mileage by about 2 to 2.5 mpg. Krontach ( talk) 08:49, 22 May 2011 (UTC)
Is the assertion that recommended octane making "a huge difference" adequately supported by the Dinan article? The article is about one test with one model of BMW, one time. It wasn't peer-reviewed or stablished for other cars, other models, or even shown repeatable. -- Mikeblas 16:49, 4 January 2006 (UTC)
In an engine that has active knock control (ignition is advanced or retarded depending on knock sensor feedback) and is knock-limited at full load (the ignition timing cannot be advanced due to knock), an engine can produce more torque with the same amount of fuel due to a increase in the combustion efficiency. Once the ignition timing is advanced to it's optimal point, there are no more thermodynamic benefits to advancing ignition timing. But almost all production engines run very retarded ignition timings at full load due to knock limitations, so an advance is almost always possible. Thus, in an engine with active knock control, a higher octane fuel will lead to increased torque at a given engine speed than if it had lower octane fuel. 198.202.236.129 ( talk) 21:41, 23 August 2010 (UTC)Dan
"The differences in octane between fuels makes little difference in an engine which is performing at below its maximum power for the following simple reasons. In order for the engine at a given RPM to produce less than its maximum horsepower, the engine must be choked."
This is misleading because of the terminology. The term "choked" does not apply here. Choking implies restricting all air. You mean to "throttle" an engine with a "throttle valve". This implies that you add a restriction upstream such that the air pressure after the restriction is lower than ambient.
"Choking the engine by reducing the air flow is exactly the same as reducing the final compression ratio."
No. The geometric compression ratio is calculated by comparing the chamber volume at BDC to the chamber volume at TDC. This doesn't change. You still compress the air (even at a vacuum) at this ratio. You do not change the effective compression ratio this way. This is completely incorrect. One can change the effective expansion ratio or compression ratio with various valve timing techniques, but not with throttling.
"Another way of looking at this is that the average gasoline engine at idle is experiencing air pressures akin to the top of Mount Everest."
But that volume of air (with whatever density you assume) is still being compressed at the compression ratio. That's why it's presented as a ratio, so it can be normalized with whatever pressure you have to start the cycle with.
"To measure an engine's performance at maxium compression ratio when it is normally performing at far less than this limit - and possibly at only 1/3 to 1/2 in fact - leads to a totally incorrect conclusion."
I can't understand what this means. 198.202.236.129 ( talk) 21:51, 23 August 2010 (UTC)Dan
The article contains this passage:
The word powerful was a link to the disambiguation page Power, which lists many possible meanings of 'power'. Since this sentence is describing the way the public misunderstand the meaning of 'powerful', I believe a precise definiton of power would only be a distraction in this context.
I came across this issue while I was disambiguating the Power page. Gerry Ashton 04:57, 26 May 2006 (UTC)
The idea that higher octane is more powerful is supported by all race engines using very high octanes (typically 110). Dac8 ( talk) 13:12, 12 December 2011 (UTC)
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) The idea that higher octane is more powerful is supported by all race cars and boats using around 110 octane. — Preceding unsigned comment added by Dac8 ( talk • contribs) 13:03, 12 December 2011 (UTC)
"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?
--Alex 130.83.244.129 15:55, 14 October 2006 (UTC)
In the article the Btu value of gasoline is compared to other fuels. A question is asked regarding the volume assumed in the comparison; the text states a value of 19,000 Btu for gasoline, but does not specify a volume (in other words, is this per gallon, per liter, or what?)
Various websites indicate gasoline is rated somewhere between 125,000 and 114,000 Btu / gallon
So the article's mention of 19,000 Btu for gasoline does not refer to a gallon volume. I wonder what they were referring to?
66.123.2.35 21:28, 27 March 2007 (UTC) Rich Flynn
The article is very misleading here and as someone else has hinted could be read as a shameless plug for ethanol motor fuel. The 19,000 BTU figure is approximately correct for a pound of gasoline and is how the specific heat of combustion of fuels is measured in the industry, i.e. in BTU/lb. The figure for the ethanol is obviously not for a pound of ethanol but for its optimal fuel ratio, given the same size of air charge as used for the gasoline, so I figure it's for 12.5/6.5lbs, i.e. ~1.9lbs of ethanol. Macdonaldinho 08:17, 11 April 2007 (UTC)
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)
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.
Energy cannot be released per air fuel ratio!
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)
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)
As a favor to historical reference here, whether the 2nd previous commenter has a shift key or not, he knows what he is talking about regarding autoignition vs detonation. However, the author of the main article does not. Very disappointing.
Autoignition and detonation(knock) are quite independent. Detonation almost always occurs long after ignition. This was Kettering's surprise, not what was stated in the main article.
The effect of autoignition occurring prior to normal ignition is to make combustion conditions more severe later when end gasses form. This is the connection between autoignition and knock. Auto ignition is ignition, just like from a spark plug.
However, if the extra ignition is prior to normal ignition or adds an additional flame front which accelerates combustion, this will cause more end gasses to form earlier on the down stroke and therefore be subjected to higher temperature and pressure. The race of the receding piston to relieve pressure and reduce temperature of the forming end gasses will more likely be lost and the end gasses will detonate.
The main effect of higher octane fuel is that the intermediates, the end gasses, are "nicer" and don't explode so easily. They just keep combusting quitely to H2O and CO2. — Preceding unsigned comment added by 108.38.183.41 ( talk) 10:31, 10 August 2015 (UTC)
I concur strongly with the comments above answering "ThermoDude". The comments are dead-on. The main article was written by a hack, maybe a nice guy, who is simply repeating common misconceptions. Needs to be edited to reduce the common blarney on this point. There is little correlation between self-ignition temperature and octane ratings of various potential fuels. The excellent relevant statements above need to be incorporated into the main article to replace the misconceptions the main article presents on this point.
See gasoline FAQ.
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)
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)
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)
The entire premise of this article is just wrong wrong WRONG... Octane is the measurement of combustion speed at a given pressure and temperature, yet the article repeatedly speaks of the fuel's resistance to pre-ignition, which is just nonsense. This article needs a complete rewrite with verifiable sources. Shreditor ( talk) 05:19, 17 August 2008 (UTC)
its hard to generalize anything about this subject as its just so complex. i think the whole article should be rewritten myself. its my understanding that rate of burning has an influence on tendency to knock but there is no real correlation that can be measured. a good example is that adding TEL to some fuels dose not change the speed at which it burns but greatly inhibits knock. alcohols tend to resist knock and burn slower but many compounds that burn fast are quite knock free. cetane and octane ratings are quite different too, many fuels have a high octane # but also a high cetane # while others don't. —Preceding unsigned comment added by 4.227.193.229 ( talk) 02:19, 14 December 2009 (UTC)
"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)
Found proof that over half of sold petrol in the country is 92 RON. [ [1]] 90.154.71.42 ( talk) 09:38, 20 June 2018 (UTC)
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)
I've seen int the USA at a full service home heating oil comapny's gas station have gasoline in 5 different octanes.
Then a diferent fullservice station, a Sunoco, have 4 different octanes, 87, 89, 91, and 93(or 92?).
71.58.198.190 (
talk)
00:21, 7 November 2011 (UTC)
Prior to the switch to unleaded there was afaict a star system used to rate the knock resistance of petrol in the UK. Afaict all grades except four star gradually dissapeared (and four star was eventually replaced by LRP) as unleaded (which wasn't rated on the star system) came in. Anyone got any further information on this system. Plugwash ( talk) 22:15, 22 December 2008 (UTC)
Under this system one star was the lowest grade, 2 star was 92 octane, 3 star 95 octane, 4 star 98 octane and 5 star 101 octane. — Preceding unsigned comment added by 78.144.90.52 ( talk) 01:41, 4 August 2011 (UTC)
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)
This is incorrect on several points. Yes, there is a sweet spot for ignition timing called "maximum timing for best torque" (MBT). But the idea behind ignition advance is not to place peak cylinder pressure at TDC. The optimal location of peak pressure is somewhere around 12 deg aTDC for most engines...roughly. It is absolutely true that most engines have active knock control which retards or advances timing as necessary dependant on knock sensor feedback. Most engines at full load (WOT) have a heavily retarded ignition timing, much later than optimal. So, with active knock control an engine will run more advanced relative to the very retarded WOT timing with higher octane fuel. This increases combustion efficiency and thus increases torque at any specific engine speed that the ignition is knock-limited. So, effectively speaking, yes, a higher octane fuel can increase the specific power output of an engine (or prevents it from being derated with a lower octane fuel). This is especially true for our European brethren, who can often be found driving turbocharged vehicles, which are often knock-limited at full load conditions. The action of retarding timing by the knock control is indeed a "safety feature", but that safety is at the expense of combustion efficiency. So preventing that loss of efficiency effectively allows one to run higher output. If you run more advanced timing closer to optimal (MBT) timing the engine produces higher temperatures in-cylinder during combustion. Higher in-cylinder combustion temperatures lead to increased thermodynamic efficiency. This is a thermodynamic principle. 198.202.236.129 ( talk) 21:26, 23 August 2010 (UTC)Dan
The "safety feature" of a knock sensor is only part of it. There is a level of detonation that can be detected by knock sensors that does not significantly damage the engine. By using knock detection, the engine computer is able to st the spark advance at an optimum level, at least as far as detonation is concerned. Presumably the "sweet spot" is fixed, so increasing the octane rating beyond that needed to allow the engine to run a this "sweet spot" would not provide performance benefits. - unitacx 4-aug-2016. — Preceding unsigned comment added by Unitacx ( talk • contribs) 03:32, 5 August 2016 (UTC)
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! axpde Hello! 17:07, 31 May 2009 (UTC)
P.S.: I just redid the definiton section and added an own section just for explaining the difference. All other occurances should be redundant now and can be safely deleted! axpde Hello! 17:28, 31 May 2009 (UTC)
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 [2]. 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)
I should add that the statement "Most of these ratings are given as 'AKI' ratings", which has been there prior to the edit I cite above, was itself added without any justification [3]. — Sebastian 21:24, 13 July 2009 (UTC)
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)
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)
Why would altitude have any impact on knock behaviour of an engine. James 80.176.88.36 ( talk) 22:40, 4 July 2011 (UTC)
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)
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) Why is there only speculation and amateur short term test results? Dac8 ( talk) 13:17, 12 December 2011 (UTC)
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)
Why this section was removed?
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)
Why this section removed?
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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)
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)
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)
§ Examples has an {{ Excessive examples}} 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? @ Stifle: 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)
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This article is written in what I call 'wtfspeak'; to get anything out of it, you need to have some preexisting techincal knowledge. I think it needs to be dumbified for those of us who lack that knowledge. As is, I have no idea what the author is talking about or how it applies to consumers. —Preceding unsigned comment added by 65.113.71.3 ( talk • contribs) 18:25, 30 July 2008
says that methamphetamynes are good for the environment"
what !?? "methamphetamynes" I don't think so ? and who is
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)
Octane refers to Gasoline ONLY. So the statement that Octane refers to a fuel is in error. Krontach ( talk) 08:14, 22 May 2011 (UTC)
Gasoline energy content varies from about 110k BTU to 125k BTU. Adding ethanol, which is mandated, does lower this. Ethanol at 10% lowers mileage by about 2 to 2.5 mpg. Krontach ( talk) 08:49, 22 May 2011 (UTC)
Is the assertion that recommended octane making "a huge difference" adequately supported by the Dinan article? The article is about one test with one model of BMW, one time. It wasn't peer-reviewed or stablished for other cars, other models, or even shown repeatable. -- Mikeblas 16:49, 4 January 2006 (UTC)
In an engine that has active knock control (ignition is advanced or retarded depending on knock sensor feedback) and is knock-limited at full load (the ignition timing cannot be advanced due to knock), an engine can produce more torque with the same amount of fuel due to a increase in the combustion efficiency. Once the ignition timing is advanced to it's optimal point, there are no more thermodynamic benefits to advancing ignition timing. But almost all production engines run very retarded ignition timings at full load due to knock limitations, so an advance is almost always possible. Thus, in an engine with active knock control, a higher octane fuel will lead to increased torque at a given engine speed than if it had lower octane fuel. 198.202.236.129 ( talk) 21:41, 23 August 2010 (UTC)Dan
"The differences in octane between fuels makes little difference in an engine which is performing at below its maximum power for the following simple reasons. In order for the engine at a given RPM to produce less than its maximum horsepower, the engine must be choked."
This is misleading because of the terminology. The term "choked" does not apply here. Choking implies restricting all air. You mean to "throttle" an engine with a "throttle valve". This implies that you add a restriction upstream such that the air pressure after the restriction is lower than ambient.
"Choking the engine by reducing the air flow is exactly the same as reducing the final compression ratio."
No. The geometric compression ratio is calculated by comparing the chamber volume at BDC to the chamber volume at TDC. This doesn't change. You still compress the air (even at a vacuum) at this ratio. You do not change the effective compression ratio this way. This is completely incorrect. One can change the effective expansion ratio or compression ratio with various valve timing techniques, but not with throttling.
"Another way of looking at this is that the average gasoline engine at idle is experiencing air pressures akin to the top of Mount Everest."
But that volume of air (with whatever density you assume) is still being compressed at the compression ratio. That's why it's presented as a ratio, so it can be normalized with whatever pressure you have to start the cycle with.
"To measure an engine's performance at maxium compression ratio when it is normally performing at far less than this limit - and possibly at only 1/3 to 1/2 in fact - leads to a totally incorrect conclusion."
I can't understand what this means. 198.202.236.129 ( talk) 21:51, 23 August 2010 (UTC)Dan
The article contains this passage:
The word powerful was a link to the disambiguation page Power, which lists many possible meanings of 'power'. Since this sentence is describing the way the public misunderstand the meaning of 'powerful', I believe a precise definiton of power would only be a distraction in this context.
I came across this issue while I was disambiguating the Power page. Gerry Ashton 04:57, 26 May 2006 (UTC)
The idea that higher octane is more powerful is supported by all race engines using very high octanes (typically 110). Dac8 ( talk) 13:12, 12 December 2011 (UTC)
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) The idea that higher octane is more powerful is supported by all race cars and boats using around 110 octane. — Preceding unsigned comment added by Dac8 ( talk • contribs) 13:03, 12 December 2011 (UTC)
"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?
--Alex 130.83.244.129 15:55, 14 October 2006 (UTC)
In the article the Btu value of gasoline is compared to other fuels. A question is asked regarding the volume assumed in the comparison; the text states a value of 19,000 Btu for gasoline, but does not specify a volume (in other words, is this per gallon, per liter, or what?)
Various websites indicate gasoline is rated somewhere between 125,000 and 114,000 Btu / gallon
So the article's mention of 19,000 Btu for gasoline does not refer to a gallon volume. I wonder what they were referring to?
66.123.2.35 21:28, 27 March 2007 (UTC) Rich Flynn
The article is very misleading here and as someone else has hinted could be read as a shameless plug for ethanol motor fuel. The 19,000 BTU figure is approximately correct for a pound of gasoline and is how the specific heat of combustion of fuels is measured in the industry, i.e. in BTU/lb. The figure for the ethanol is obviously not for a pound of ethanol but for its optimal fuel ratio, given the same size of air charge as used for the gasoline, so I figure it's for 12.5/6.5lbs, i.e. ~1.9lbs of ethanol. Macdonaldinho 08:17, 11 April 2007 (UTC)
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)
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.
Energy cannot be released per air fuel ratio!
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)
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)
As a favor to historical reference here, whether the 2nd previous commenter has a shift key or not, he knows what he is talking about regarding autoignition vs detonation. However, the author of the main article does not. Very disappointing.
Autoignition and detonation(knock) are quite independent. Detonation almost always occurs long after ignition. This was Kettering's surprise, not what was stated in the main article.
The effect of autoignition occurring prior to normal ignition is to make combustion conditions more severe later when end gasses form. This is the connection between autoignition and knock. Auto ignition is ignition, just like from a spark plug.
However, if the extra ignition is prior to normal ignition or adds an additional flame front which accelerates combustion, this will cause more end gasses to form earlier on the down stroke and therefore be subjected to higher temperature and pressure. The race of the receding piston to relieve pressure and reduce temperature of the forming end gasses will more likely be lost and the end gasses will detonate.
The main effect of higher octane fuel is that the intermediates, the end gasses, are "nicer" and don't explode so easily. They just keep combusting quitely to H2O and CO2. — Preceding unsigned comment added by 108.38.183.41 ( talk) 10:31, 10 August 2015 (UTC)
I concur strongly with the comments above answering "ThermoDude". The comments are dead-on. The main article was written by a hack, maybe a nice guy, who is simply repeating common misconceptions. Needs to be edited to reduce the common blarney on this point. There is little correlation between self-ignition temperature and octane ratings of various potential fuels. The excellent relevant statements above need to be incorporated into the main article to replace the misconceptions the main article presents on this point.
See gasoline FAQ.
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)
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)
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)
The entire premise of this article is just wrong wrong WRONG... Octane is the measurement of combustion speed at a given pressure and temperature, yet the article repeatedly speaks of the fuel's resistance to pre-ignition, which is just nonsense. This article needs a complete rewrite with verifiable sources. Shreditor ( talk) 05:19, 17 August 2008 (UTC)
its hard to generalize anything about this subject as its just so complex. i think the whole article should be rewritten myself. its my understanding that rate of burning has an influence on tendency to knock but there is no real correlation that can be measured. a good example is that adding TEL to some fuels dose not change the speed at which it burns but greatly inhibits knock. alcohols tend to resist knock and burn slower but many compounds that burn fast are quite knock free. cetane and octane ratings are quite different too, many fuels have a high octane # but also a high cetane # while others don't. —Preceding unsigned comment added by 4.227.193.229 ( talk) 02:19, 14 December 2009 (UTC)
"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)
Found proof that over half of sold petrol in the country is 92 RON. [ [1]] 90.154.71.42 ( talk) 09:38, 20 June 2018 (UTC)
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)
I've seen int the USA at a full service home heating oil comapny's gas station have gasoline in 5 different octanes.
Then a diferent fullservice station, a Sunoco, have 4 different octanes, 87, 89, 91, and 93(or 92?).
71.58.198.190 (
talk)
00:21, 7 November 2011 (UTC)
Prior to the switch to unleaded there was afaict a star system used to rate the knock resistance of petrol in the UK. Afaict all grades except four star gradually dissapeared (and four star was eventually replaced by LRP) as unleaded (which wasn't rated on the star system) came in. Anyone got any further information on this system. Plugwash ( talk) 22:15, 22 December 2008 (UTC)
Under this system one star was the lowest grade, 2 star was 92 octane, 3 star 95 octane, 4 star 98 octane and 5 star 101 octane. — Preceding unsigned comment added by 78.144.90.52 ( talk) 01:41, 4 August 2011 (UTC)
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)
This is incorrect on several points. Yes, there is a sweet spot for ignition timing called "maximum timing for best torque" (MBT). But the idea behind ignition advance is not to place peak cylinder pressure at TDC. The optimal location of peak pressure is somewhere around 12 deg aTDC for most engines...roughly. It is absolutely true that most engines have active knock control which retards or advances timing as necessary dependant on knock sensor feedback. Most engines at full load (WOT) have a heavily retarded ignition timing, much later than optimal. So, with active knock control an engine will run more advanced relative to the very retarded WOT timing with higher octane fuel. This increases combustion efficiency and thus increases torque at any specific engine speed that the ignition is knock-limited. So, effectively speaking, yes, a higher octane fuel can increase the specific power output of an engine (or prevents it from being derated with a lower octane fuel). This is especially true for our European brethren, who can often be found driving turbocharged vehicles, which are often knock-limited at full load conditions. The action of retarding timing by the knock control is indeed a "safety feature", but that safety is at the expense of combustion efficiency. So preventing that loss of efficiency effectively allows one to run higher output. If you run more advanced timing closer to optimal (MBT) timing the engine produces higher temperatures in-cylinder during combustion. Higher in-cylinder combustion temperatures lead to increased thermodynamic efficiency. This is a thermodynamic principle. 198.202.236.129 ( talk) 21:26, 23 August 2010 (UTC)Dan
The "safety feature" of a knock sensor is only part of it. There is a level of detonation that can be detected by knock sensors that does not significantly damage the engine. By using knock detection, the engine computer is able to st the spark advance at an optimum level, at least as far as detonation is concerned. Presumably the "sweet spot" is fixed, so increasing the octane rating beyond that needed to allow the engine to run a this "sweet spot" would not provide performance benefits. - unitacx 4-aug-2016. — Preceding unsigned comment added by Unitacx ( talk • contribs) 03:32, 5 August 2016 (UTC)
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! axpde Hello! 17:07, 31 May 2009 (UTC)
P.S.: I just redid the definiton section and added an own section just for explaining the difference. All other occurances should be redundant now and can be safely deleted! axpde Hello! 17:28, 31 May 2009 (UTC)
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 [2]. 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)
I should add that the statement "Most of these ratings are given as 'AKI' ratings", which has been there prior to the edit I cite above, was itself added without any justification [3]. — Sebastian 21:24, 13 July 2009 (UTC)
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)
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)
Why would altitude have any impact on knock behaviour of an engine. James 80.176.88.36 ( talk) 22:40, 4 July 2011 (UTC)
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)
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) Why is there only speculation and amateur short term test results? Dac8 ( talk) 13:17, 12 December 2011 (UTC)
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)
Why this section was removed?
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)
Why this section removed?
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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)
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)
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)
§ Examples has an {{ Excessive examples}} 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? @ Stifle: 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)