Talk:Octane rating

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"

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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.

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]

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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

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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]

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)

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]

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]