This problem considers the combustion of methane in air, as a function of air:fuel ratio and temperature, as a model of an industrial boiler. The goal is to calculate the equiibrium species distribution and the temperature of the product gase. This is accomplished by calculating the equilibrium composition as a function of temperature and simultaneously calculating the enthalpy change from the initial fuel at a specified initial temperature.

If all the heat produced by the combustion is available to heat the product gas (there are no heat losses to the environment), then the final temperature is called the adiabatic flame temperature. A simplified version of such a calculation is typically made in an introductory thermodynamics course, by assuming the combustion reaction takes place in a stoichiometric amount of O₂, according to
CH₄ + 2O₂ = CO₂ + 2 H₂O

The example problem included in all versions of EQS4WIN explores the results of a more accurate calculation for such a problem in two ways. First, complete combustion is not assumed, and the full equilibrium composition and enthalpy change is calculated as a function of temperature. Second, the air:fuel ratio is varied to examine the effects of this quantity on the final results. In all, a total of 44 species are included in the calculation. An important consequence of this is the availability of the composition of the product gas. Environmental aspects of this are considered in the Environmental Chemistry example appearing next on the list of Example Applications.