The calculated coefficients match the values given in the FDS example. Images of the stoichiometric calculations using the spreadsheet are shown below. Two readily available tools to calculate “simple chemistry” stoichiometric coefficients are the combustion calculator spreadsheet from Thunderhead or Kristopher Overholt’s online Chemical Equation Balancer. Although we are using two fuels, each fuel is composed only of C, H, O, and N so the “simple chemistry” approach can be used to calculate the coefficients for each individual reaction. The user is responsible for calculating the stoichiometric coefficients given in the above reactions. In this example, air has been simplified to consist of only oxygen and nitrogen. The other species are sub-species used to define the tracked species. In the FDS calculation, only the two fuels, air, and the two products will be tracked. Similarly, wood is defined by the chemical formula and the reaction has a soot yield and a yield of. In the example, polyurethane is defined by the chemical formula and the combustion reaction has a soot yield and a yield of. The Section 13.2.2 example shows how to model two simultaneously burning fuels, polyurethane and wood. For multiple reactions, you must specify the gas species and stoichiometry of the reactions. The “simple chemistry” approach can only be used in FDS when there is a single mixing controlled reaction. PyroSim supports the “simple chemistry” combustion model in FDS that considers a single fuel species composed of, ,, and that reacts with in one mixing-controlled step to form, ,, , and. This post references that example frequently and readers are encouraged to have both documents available while working through this post. In the FDS User Guide, Section 13.2.2 “Complex Stoichiometry”, an example is given that demonstrates how to accomplish this using FDS directly. To use multiple-fuel reactions in an FDS simulation, it is necessary to specify the gas species and stoichiometry of the reactions. This post demonstrates how to perform a multiple-fuel simulation using PyroSim. For simulations requiring multiple fuel species, a few extra steps are required. PyroSim’s design assumes that most users want to use FDS with a single-fuel, “simple chemistry” combustion model. The post Complex Stoichiometry in PyroSim updates and replaces the contents of this post. PyroSim 2018.2 now supports complex stoichiometry in the user interface.
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