Editing Combustion (section)

====Complete====
[[File:Methane-combustion.svg|thumb|The combustion of [[methane]], a [[hydrocarbon]]]]
In complete combustion, the reactant burns in oxygen and produces a limited number of products. When a [[hydrocarbon]] burns in oxygen, the reaction will primarily yield carbon dioxide and water. When elements are burned, the products are primarily the most common oxides. Carbon will yield [[carbon dioxide]], sulfur will yield [[sulfur dioxide]], and iron will yield [[iron(III) oxide]]. Nitrogen is not considered to be a combustible substance when oxygen is the [[Oxidizing agent|oxidant]]. Still, small amounts of various nitrogen oxides (commonly designated [[NOx|{{chem|NO|''x''}}]] species) form when the air is the oxidative.

Combustion is not necessarily favorable to the maximum degree of oxidation, and it can be temperature-dependent. For example, [[sulfur trioxide]] is not produced quantitatively by the combustion of sulfur. {{NOx}} species appear in significant amounts above about {{convert|2800|F|C}}, and more is produced at higher temperatures. The amount of {{NOx}} is also a function of oxygen excess.<ref name="NOx formation">[http://www.alentecinc.com/papers/NOx/The%20formation%20of%20NOx_files/The%20formation%20of%20NOx.htm The formation of NOx]. Alentecinc.com. Retrieved on 2010-09-28.</ref>

In most industrial applications and in [[fire]]s, [[air]] is the source of oxygen ({{chem|O|2}}). In the air, each mole of oxygen is mixed with approximately {{val|3.71|ul=mol}} of nitrogen. Nitrogen does not take part in combustion, but at high temperatures, some nitrogen will be converted to [[NOx#Thermal|{{chem|NO|''x''}}]] (mostly [[Nitric oxide|{{chem|NO}}]], with much smaller amounts of [[Nitrogen dioxide|{{chem|NO|2}}]]). On the other hand, when there is insufficient oxygen to combust the fuel completely, some fuel carbon is converted to [[carbon monoxide]], and some of the hydrogens remain unreacted. A complete set of equations for the combustion of a hydrocarbon in the air, therefore, requires an additional calculation for the distribution of oxygen between the carbon and hydrogen in the fuel.

The amount of air required for complete combustion is known as the "theoretical air" or "stoichiometric air".<ref>{{cite report |url=https://books.google.com/books?id=jqkXAAAAYAAJ&pg=RA1-PA26R |title=Central Boiler Plants |year=1989 |page=Glossary 26 |publisher=US Department of the Army |id=TM 5-650}}</ref> The amount of air above this value actually needed for optimal combustion is known as the "excess air", and can vary from 5% for a natural gas boiler, to 40% for [[anthracite]] coal, to 300% for a [[gas turbine]].<ref>{{cite web |title=Engineering Toolbox: Optimal Combustion Processes - Fuel vs. Excess Air |url=https://www.engineeringtoolbox.com/fuels-combustion-efficiency-d_167.html |access-date=15 May 2023 |date=2003 }}</ref>