Talk:Combustion

I don't think respiration should be included in this page. I thought the definition of "combustion" was rapid oxidation, so by definition there can't be "slow combustion". --Keenanpepper 01:28, 14 Oct 2004 (UTC)

Speed has nothing to do with whether combustion occurs or not, it has to do with what the reactants are. As long as you have a hydrocarbon reacting with oxygen which is creating carbon dioxide, and sometimes carbon monoxide and/or water as well, you have combustion. Respiration is O₂ reacting with the various forms of carbon in an organism, and it creates CO₂ as a result. Therefore, by definition, it is combustion. --BMS 03:47, 16 Dec 2004 (UTC)

Balancing of combustion equation

I think the generalised alkane combustion equation should read:

CxHy + (x+(y/2))02 --> xC02 + (y/2)H20

--81.136.105.66 15:29, 1 Feb 2005 (UTC)

For some reason "Complete combustion" page cannot be edited ... the phraase that says that Iron (III) is an isotope is wrong ... it should refer to an oxidation state of iron

AND JUST WHEN IT HIT ME< GO TO BED

Complete combustion

For some reason "Complete combustion" page cannot be edited by clicking on "edit" button ... the phrase that says that Iron (III) is an isotope is wrong ... it should refer to an oxidation state of iron.

---

I changed it.

Spontaneous Combustion

The spontaneous combustion page disambiguates to this page and this page has a link to spontaneous combustion but neither actually describes what it is or how it works. Which should contain information or should a third page be created?

Factual error

Combustion of a hydrocarbon in oxygen obviously cannot produce any compounds of nitrogen. I think "air" should replace "oxygen".

On an unrelated point, the combustion of CH2S in fluroine is very cute (and should be retained) but probably should not be the first example. Hydrogen burning in oxygen might be more appropriate.

Example

in the example in the intro carbon is made a link in the reaction. Why? It is no more relevant than the other elements. Ozone 00:34, 1 January 2006 (UTC)

Improvements needed

• The "Chemical Equation" section should also include the simple equations for combustion using air and should show Nitrogen as a reactant and as a product. Too many people tend to forget that the combustion product gases include all of the nitrogen in the combustion air. And most combustion in open fires, stoves, ovens, hot water boilers, industrial furnaces and industrial steam generators use combustion air ... not oxygen.

• In the "Combustion temperature" section, I don't understand what is meant by "the heat of combustion (calculated from the fuel's heating value) is used entirely for warming up fuel and gas (e.g. oxygen or air)". That simply is not true or else I have completely misunderstood what it meant to say. The heat of combustion in a stove is used heat the combustion air as well as the surrounding air in an enclosed room or home. The heat of combustion in an oven is used to heat the combustion air and to bake or roast something in the oven. The heat of combustion in a hot water boiler is used to heat the combustion air and the hot water for use in a home or other building. Anywhere from 75 to 90 percent of the heat of combustion in a well-designed industrial furnace or steam generator is transferred into the industrial fluid stream or water being heated and/or vaporized. In other words, some of the heat of combustion, in all of the various heating devices that utilize combustion of a fuel, goes into heating the combustion air but most of the heat of combustion goes into providing heat for some useful purpose. The amount of combustion heat that goes into the heating or vaporizing the fuel itself is a very small part of the combustion heat.

I dont quite get your point. Of course in most cases the heat produced is used for a useful purpose in the end , e.g. like the ones you mentioned. But most often, this heat is taken from the flue gases (that have previously been warmed up by combsustion). And even if not, the text explicitly assumes adiabatic conditions. Academic perhaps, but that's what engineers start off with. --Freeatlast 21:39, 15 April 2006 (UTC)

Perhaps,I can make my point clearer. What the article now says is: The formula that yields this temperature is based on the first law of thermodynamics and takes note of the fact that the heat of combustion (calculated from the fuel's heating value) is used entirely for warming up fuel and gas (e.g. oxygen or air).

The heat of combustion is not calculated from the heating value. They are one and the same thing.

The article does not say that the combustion results in hot flue gases which then provide the useful heating. It says that the heat of combustion is used entirely for warming up the fuel and gas (e.g. oxygen or air). That plainly says that all of the heat goes into warming the fuel and the combustion oxygen or air ...which is simply not correct. The flue gas is not oxygen or air. It is mostly nitrogen, carbon dioxide and water vapor when burning fossil fuels with air (which is about 79% nitrogen). Perhaps if it said "entirely for warming up fuel and the combustion flue gases", then it would be acceptable.

As a chemical engineer for over 40 years, I have often calculated adiabatic combustion temperatures so I know full well what adiabatic means. And by the way, adiabatic combustion temperature is much more commonly referred to as adiabatic flame temperature. - mbeychok 01:08, 16 April 2006 (UTC)

• Again in the "Combustion temperature" section, there is no mention of the fact that almost all the various heating devices mentioned above do not operate at stoichiometric conditions. Instead, almost all of them use a certain amount of excess combustion air (i.e., air in excess of the stoichiometric amount) so as to obtain more complete combustion but not so much that the combustion flue gases will fail to comply with governmentally regulated NOx emission limits. There is also no mention that excess combustion air affects the adiabatic combustion temperature. My calculated adiabatic temperatures are:
  • 1800 °C for a typical coal using 20% excess combustion air in a typical power plant
  • 2030 °C for a typical oil using 15% excess combustion air in a typical industrial furnace such as used in oil refineries
  • 1900 °C for a typical natural gas using 12% combustion air in a typical industrial furnace such as used in oil refineries

I don't think we have an oversight here, since the stoichiometric air ratio is mentioned as an influencing factor. But I do agree that you can expound on this issue, especially pointing out the influence of process parameters (such as the air ratio) on certain emissions (I generally think the article could have more to say on emissions). --Freeatlast 21:39, 15 April 2006 (UTC)

In general, writing equations for combustion with oxygen rather than air , neglecting to mention excess combustion air being much more prevalent than stoichiometric combustion, saying that the heat of combustion is calculated from the heating value, and saying that all of the heat of combustion goes into warming the fuel and the combustion air ... all struck me as being as being significant oversights that need revision. I am sure that most experienced engineers would agree with me._ mbeychok 01:08, 16 April 2006 (UTC)

All of the above are significant oversights and should be taken into consideration to improve the science of this article. After all, we should not just define the word "combustion" as if it were an abstraction. We should also focus on the real world uses and applications of combustion. Please excuse me if I sound as if I am preaching. - mbeychok 06:54, 7 April 2006 (UTC)

You seem to be missing the engineering examples in this arcticle (don't mistake that for flaunted science). To explain combustion it makes sense to start abstract as done throughout this article but you may want to add a new engineering section "Practical purposes" (e.g.) and link to other wiki articles. For instance the section "See also" contains a subsection "Machines" which might as well be included directly into such an engineering section --Freeatlast 21:39, 15 April 2006 (UTC)

No, I am not missing having some practical examples included in the article. What I have pointed out are simply incorrect statements as well as oversights. - mbeychok 01:08, 16 April 2006 (UTC)

Re. the whole of the above section.

- Re. technical terms: I'm not entirely confident with the English specialised terms. In particular I wasnt aware that heat of combustion and heating value are the same thing (which explains some previous irritation). Also, if adiabatic flame temperature is the only correct term, we should remove reference to adiabatic combustion temperature. Feel free to correct.

- Re. flue gases: I'm not statisfied with the mention of warming fuel and flue gas in this context. We should either concentrate on heating up the input side of the process (fuel and combustion gas be it air or oxygen) or the output side (combustion products i.e. flue gas plus uncombusted plus ash etc.) but not both. Right now, it's mixed reference (to fuel and flue gas) and just confuses (since flue gas contains combusted fuel). I think it's more straightforward to say "is used entirely for heating the fuel and combustion gases". Of course in this analysis the combustion gas (e.g. air) is only warmed up after combustion has taken place (i.e. when a certain part of it is no longer what it used to be e.g. air). But what is really meant is that the heat capacity equivalent of the input air has been taken out of that released during the combustion process. That's why I think it's fair to say that the combustion heat is used to heat fuel and cobustin gases. Comments?

Freeatlast, I think we are finally both on the same page. If you will read the revisons, most of which I made last night, you will see that I changed that warm up sentence to read "the heat of combustion is used entirely for heating the fuel, the combustion air or oxygen, and the combustion product gases (commonly referred to as the flue gas)". That is exactly what a rigorous calculation of the adiabatic combustion temperature involves.

Please note that "flue gases" and "combustion product gases" have the same meaning in almost all cases. If it is an open fire, of course one would use "combustion gases" rather than "flue gases". For stoves, boilers, ovens, furnaces, fired heaters, etc., either term may be used because the combustion gases usually exit through a flue gas stack or chimney.

As far as terminolgy is concerned, we must all learn to understand each others language. I see no problem with using either or both "adiabatic combustion temperature" or "adiabatic flame temperature", "combustion gases" or "flue gases", "heat of combustion" or "heating value" or "caloric value", "air-fuel ratio" or "Lambda" or "percent excess combustion air", etc. ... as long as the article clearly spells out the alternative terminologies, which is part of what I also included last night. In other words, I don't think we should indicate in any way that there is only one prescribed terminology to be used. I think it is part of our duty towards readers of the article to educate them on that point. Another way of putting it is that chemists, engineers, physicists, etc. all have their own commonly used terminology and all are equally valid. Cheers, - mbeychok 21:59, 16 April 2006 (UTC)

Formation of formaldehyde

Formaldehyde says that it can be formed by incomplete combustion. What kind of reaction would result in formaldehyde? Just taking a wild stab in the dark with methane:

$CH_{4}+O_{2}\to H_{2}CO+H_{2}O+heat$

I have no idea if that's a valid reaction but the elements at least are equal on both sides... Cburnett 05:02, 11 April 2006 (UTC)

Combustion Analysis ?

In the short section called "Combustion Analysis", it is defined as the determination of the compounds created by combustion. Though, I added a link to a page called "Combustion Analysis" regarding -mainly- the application of exhaust fume analysis to the determination of combustion efficiency. We have here two different fields related to the same term: theory of chemistry and empirical thermal engineering. Does anyone can help to get an agreement on the definitions ?