(-40 °C) storable liquid propellant was considered as the
propulsion source by the NASA Jet Propulsion Laboratory
(JPL) to return samples from the planet Mars. The propellant
combination selected was Monomethylhydrazine (MMH) fuels
and Mixed Oxides of Nitrogen (MON) 25 oxidizers. Different
sized doublet injectors were used to inject the two liquids.
In this study, the basic properties of the sprays were
characterized under cold flow test conditions, thereby
allowing direct comparison of the results to corresponding
hot fire tests. The strategy involved the use of simulants
that met a variety of constraints. The characterization
consisted of visualization for a variety of geometric and
operational conditions. Once these results were reviewed,
a reduced set of conditions was identified for a more detailed
investigation using Planar Laser Induced Fluorescence (PLIF).
The visualization results demonstrated the effects of the
impingement angles, O/F ratio, and the liquid properties
associated with the two temperatures (25 °C and -40 °C).
The visualization indicated that greater impingement angles
improved dispersion. Optimal performance was indicated
at O/F ratios between 2 and 3 for the -40 °C case and at
O/F ratios between 1 and 2 for the 25 °C cases. The PLIF
results were obtained for four select cases at O/F ratios
of 1.6, 2.0, 2.53, and 2.8. The case that demonstrated
superior mixing and performance for the -40 °C case occurred
at O/F = 2.0 (corresponded to Re ratio of 6.35).