From Chapter 2

The simplest alkane is methane, CH4. Methane is the major component of natural gas. It is shaped like a tetrahedron, with a carbon atom in the center and hydrogen atoms at each corner.

When carbon-based fuels burn, the products of complete combustion are carbon dioxide (CO2) and water. The secret to balancing hydrocarbon combustion equations is to first balance the carbons. For the burning of methane (the major component of natural gas), this is simple because there is one carbon atom on each side of the equation. However,

CH4 + O2 → CO2 + H2O

is not balanced with respect to hydrogen (four reactant atoms but only two product atoms), nor is it balanced with respect to oxygen (two reactant atoms
but three product atoms). The hydrogen can be balanced by doubling the water, as in CH4 + O2 → CO2 + 2H2O, but this still leaves an oxygen deficiency (two reactant atoms but four product atoms). Doubling the oxygen in the reactants balances the equation:

CH4 + 2O2 CO2 + 2H2O

Because air is only one-fifth oxygen (actually, it is 20.95% by volume, but for our purposes, 20% is close enough and easier to use), it can be seen that 10 volumes of air are required for each volume of methane burned.

The chemical equation describing the combustion of the simplest organic fuel, methane, is only slightly more complicated.
In this case, one volume of methane combines with two volumes of oxygen to produce two volumes of water vapor and one volume of carbon dioxide:
CH4 + 2O2  2H2O + CO2

As simple as this reaction seems, it has been studied in some detail to understand all the intermediate steps that can, and usually do, take place. For example, if there is insufficient oxygen, burning methane, usually encountered as
burning natural gas, will produce carbon monoxide:
CH4 + 1.5O2  2H2O + CO or 2 CH4 + 3O2  4H2O + 2CO

I'll send you a copy of Chapter 2 offline, but only if you buy the book, available at www.firesciientist.com