Talk:Octane rating

wtfspeak

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

You have a point to the extent that the introduction didn't explain why a normal person would care about octane rating. I have added a sentence which says that high-performance engines need high octane fuels, and that it's got to do with their compression ratio. I have also removed a sentence which effectively duplicates other information and uses some jargon, and I have added the comment (which is buried lower in the article) that higher-octane fuel does not generally help for low-performance engines, as well as some info on how it is defined and tested. For most people, this is all they really need to know. If you have some time and energy to help, read WP:MTAA, and make suggestions or even WP:Be bold and edit the article yourself (but then also be willing to accept that not all your edits will stick!) Especially be careful of "dumbing down" the article, as that is explicitly not recommended by the "MTAA" guideline.

I hope this helps, let us know what you don't understand; maybe we can make some more improvements. --Slashme (talk) 07:02, 31 July 2008 (UTC)[reply]

vandalised ?

"dr.ben elstrott says that methamphetamynes are good for the environment"

what !?? "methamphetamynes" I don't think so ? and who is "dr.ben elstrott"

Thank you for your suggestion! When you feel an article needs improvement, please feel free to make those changes. Wikipedia is a wiki, so anyone can edit almost any article by simply following the Edit this page link at the top. You don't even need to log in (although there are many reasons why you might want to). The Wikipedia community encourages you to be bold in updating pages. Don't worry too much about making honest mistakes — they're likely to be found and corrected quickly. If you're not sure how editing works, check out how to edit a page, or use the sandbox to try out your editing skills. New contributors are always welcome.

Octane

I have removed the following sentance 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)[reply]

Recommended Octane

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)[reply]

_____

11 HP over 280 is about 4%. This is "NOT" huge. This is minor.

Furthermore - the only way you can see this is that the engine can produce slightly more torque at a given RPM. The velocity of the car at a given engine RPM is fixed. This is a function of the gear ratio of the transmission and the rear end. Since this is the case, at any given RPM and consequently velocity of the vehical - there is nothing that suggests that the torque the engine _can_ produce is even needed. IE - the additional "power" the additional octane may confer may not be required.

This can be seen by looking at the lower RPM portions of the curve. In order to conduct this test the amount of power the engine is asked to produce at a given RPM can be scaled back from the maximum then the fuel consumption at this lower power setting can be compared between the various fuels. The cited white paper does not do this.

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. The choking is accomplished by restricting the air flow to the engine (usually by a manifold restriction such as the butterfly value in the intake manifold). Given the amount of air restriction and resultant intake manifold vacuum, the fuel mixture is then optimized for these conditions. Choking the engine by reducing the air flow is exactly the same as reducing the final compression ratio. 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.

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.

Terrell Larson 6 January 2006

_______

A modest suggestion: Seems to me that what this page needs is a definitive statement on whether there are any real benefits - in an engine that accepts both - to using higher-octane fuel. As I understand it, there isn't.

But UK fuel companies are apparently very keen to foster the belief that 98 octane petrol is more powerful, cleaner, and in every way a superior product to 95, and the higher cost is just the price one pays for all this extra wonderfulness.

As far as I'm aware, as long as your engine compression ratio is below the autoignition point of 95 octane fuel, you should receive no advantage at all from 98. Is this the case? If so, this information really deserves to be propagated, because at present many people fork out the extra money - which may be considerable over time - in the firm belief that their engines and their driving will benefit. Those who pocket the price difference, all the way up the line, will be in no hurry to disillusion them.

Indeed, the choice of names for 98-octane fuel, which usually contain superlatives like Ultra- or Super-, reinforce the idea that a fuel that is basically just harder to light is better in every way: after all, 98 is more than 95, isn't it?

Is anyone qualified to confirm this one way or the other? Cdavis999 21:04, 1 March 2007 (UTC)[reply]

This page is a good summary of the above http://www.petrolprices.com/about-fuel.html Paraphrased (talk) 22:59, 19 May 2010 (UTC)[reply]

Change powerful from link to ordinary word

The article contains this passage:

It might seem odd that fuels with higher octane ratings burn less easily, yet are popularly thought of as more powerful.

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)[reply]

Disambiguation link repair - You can help!

In the absence of any objection, I have de-linked as described above. Gerry Ashton 13:58, 31 May 2006 (UTC)[reply]

Ethanol under Knock Resistance

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)[reply]

Maximum Power vs. Maximum Torque

"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)[reply]

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[reply]

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 it's 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)[reply]

Examples of Octane ratings

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)[reply]

Octane Question

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 released per air fuel ratio" ?

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)[reply]

Fuel Octane's Effect on Pollutants emitted

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)[reply]

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)[reply]

Detonation vs. Autoignition

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)[reply]

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)[reply]

Definition of Knock

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)[reply]

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)[reply]

Effects of octane rating

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)[reply]

Octane rating of hydrogen

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)[reply]

Effects of octane rating

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)[reply]

This book disagrees with you: They say that "... knocking tendency depends on the autoignition temperature, ignition lag and flame speed of the air-fuel mixture..." --Slashme (talk) 13:36, 4 September 2008 (UTC)[reply]

I don't think the book disagrees with me. I think the terms used in engineering parlance in that book are being improperly used in the article. For example, auto-ignition is different from pre-ignition. Auto-ignition temperature is the temperature needed to ignite the fuel at a given pressure. Pre-ignition is a mechanic's term, defined as the fuel igniting before the spark plug fires. Auto-ignition temperature is definitely a factor in detonation, and it is a factor in pre-ignition. However, pre-ignition does not necessarily cause detonation, or vice versa. Whoever wrote this article got their words mixed up and it turned out very confusing. I'm going to start making some changes. See what you think. Shreditor (talk) 04:13, 5 September 2008 (UTC)[reply]

Sorry, I didn't express myself clearly enough. When you say "Octane is the measurement of combustion speed at a given pressure and temperature" (I assume you mean "the octane rating of a fuel is ...") that disagrees with what the book says. The octane rating is defined by the knocking tendency of the fuel, which is dependent on more factors than just the flame speed. --Slashme (talk) 05:42, 5 September 2008 (UTC)[reply]

I've taken a look at your edit, and it's very good. I've just done some copy-editing on the prose here and there. One thing that you took out was the comparison with the cetane number. I presume it's because it was just wrong, but can you possibly write a better version? I think it's a natural comparison to make in this article. --Slashme (talk) 06:08, 5 September 2008 (UTC)[reply]

I am not an engineer, nor a chemist. I am a mechanic and I see it from that perspective. As I have understood it from the textbooks I have read, the speed of combustion is the main factor in detonation. If the fuel starts burning too fast, the pressure rises rapidly and the remaining fuel explodes due to shock compression. I could be oversimplifying here. These matters are rarely as simple as one factor causing one effect. If you or someone else can make better sense of the engineering speak and explain it in layman's terms, it would help out the article a lot.

Now, as I understand it, octane rating and cetane rating are not really related. Octane rating measures the fuel's tendency to combust supersonically (explode; detonate). Cetane rating has to do with the fuel's ignition temperature. That is why I removed that section from this article. Shreditor (talk) 18:56, 6 September 2008 (UTC)[reply]

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)[reply]

Usage in Russia

"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)[reply]

Where was that gas station picture taken?

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)[reply]

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)[reply]

star system

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)[reply]

Has anyone considered the effect of increased ignition advance?

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)[reply]

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)[reply]

RON vs. AKI

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! axp_de ^Hello! 17:07, 31 May 2009 (UTC)[reply]

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! axp_de ^Hello! 17:28, 31 May 2009 (UTC)[reply]

Does the table contain RON or AKI values?

I just merged the text from {{Section link}}: required section parameter(s) missing into the table (in section {{Section link}}: required section parameter(s) missing). 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 [1]. 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)[reply]

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[2]. — Sebastian 21:24, 13 July 2009 (UTC)[reply]

how about higher?

The article said that lower octane that engine require will lower performance and efficiencies. How about higher?