Method for predicting hypergolic mixture flammability limits: Application for non-ionic liquid based systems

A numerical method is demonstrated in which a simple flame temperature criterion of 2700 K is used to map out flammability diagrams as a function of total mixture pressure and equivalence ratio in the hypergolic system, MMH/NTO/He. The computed results are in good agreement with experimentally determined ignition diagrams for MMH/NTO/He. The method is used to predict the lower and upper hypergolicity limits of other mixtures known to be hypergolic at 298 K and 1 atm. Comparisons between available experimental data (mixing ratios) and calculated limits lead to the conclusion that the present numerical method may allow the screening of other fuel/oxidant systems potentially of interest for spacecraft propulsion as well as for the determination of the range of mixing ratios able to ensure auto-ignitibility (hypergolicity) in combustion devices. In the safety field, the same method allows for the rapid assessment of hazards in terms of hypergolicity.