add fds_simple_chemistry.py to readme.md file

Author: drjfloyd

Utilities/Input_File_Tools/README.md

@@ -17,3 +17,8 @@ The script then reads the file called `Template` which is an FDS input file exce
 ## Creating a simple pan using OBST lines
 
 The script `pan_with_lip.py` creates a simple circular pan with a lip. Input your desired dimensions directly in the script.
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+## FDS Simple Chemistry
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+The script `fds_simple_chemistry.py` replicates the internal processing done by FDS when simple chemistry is being used for a `REAC` input. The begining of the script contains inputs for the fuel chemistry, soot and CO yields, ambient conditions, one or two-step chemistry, and if soot should be tracked seperately or as part of product lumped species.  The script outputs stoichiometry, heats of combustion, and EPUMO2 for all reactions and the total reaction; a mass and molar definition, molecular weight, and heat of formation for all lumped species used by the reactions; the fuel specifc heat calculated using gamma; and provides warning messages for EPUMO2 or gamma based fuel specific heat values that are abnormal.
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