What is the difference between a complete and incomplete combustion reaction?

Nov 7, 2015

Typically complete and incomplete combustion relates to the combustion of hydrocarbons. Here, complete combustion indicates that carbon dioxide is the sole oxidation product; incomplete combustion means otherwise.

Explanation:

We can take octane as our exemplar:

${C}_{8} {H}_{18} \left(g\right) + \frac{25}{2} {O}_{2} \left(g\right) \rightarrow 8 C {O}_{2} \left(g\right) + 9 {H}_{2} O \left(g\right)$

Is the above equation balanced? Don't trust my arithmetic! Here, all the hydrocarbon reactant ends up as carbon dioxide product; the carbon in the hydrocarbon is completely combusted to $C {O}_{2}$. Under the conditions of a ICE or diesel fuel engine, combustion would be incomplete, and some products of incomplete combustion, $C O$, or particulate $C$, would result. I can represent this by the following reaction:

${C}_{8} {H}_{18} \left(g\right) + 11 {O}_{2} \left(g\right) \rightarrow 6 C {O}_{2} \left(g\right) + C O \left(g\right) + C \left(s\right) + 9 {H}_{2} O \left(g\right)$

Again, is this balanced? Why or why not? Of course the products would have to be analyzed in order to see the effectiveness of combustion; this is simply a representation.