(555b) Modeling the Combustion of Otto Fuel

Otto Fuel II is a monopropellant that is used in undersea propulsion. It consists of three components: propylene glycol dinitrate, (PGDN), dibutyl sebacate (DBS), and 2-nitrodiphenylamine (NDPA). PGDN is the oxidizer, DBS is added as a plasticizer, and NDPA is serves as a stabilizer. Our modeling results suggest that there are some interesting similarities and differences between monopropellant combustion and large molecular weight transportation fuels. At high temperatures, the decomposition kinetics of the oxidizer is effectively decoupled from the oxidation of the plasticizer, and DBS effectively undergoes pyrolysis and partial oxidation in a high-pressure CH₂O/NO₂/NO bath gas. The stabilizer undergoes a nitrate to nitro conversion, followed by O-NO bond fission to yield a highly stable oxy-diphenylamine radical. This radical recombines to form a large number of polycyclic aromatic amines, which are believed to be responsible for the large amount of carbon deposits that are formed during operation.