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Temperature Estimations in the Near-Flame Field Resulting from Hypergolic Ignition Using Thin Filament Pyrometry

Time-dependent infrared images, temperature profiles, and oxidizer-to-fuel (O/F) mixture ratios are reported for unsteady flames resulting from the hypergolic ignition of a droplet of monomethyl hydrazine (MMH) contacting a small pool of red fuming nitric acid (RFNA). The infrared images of the hypergolic combustion process provide insights into the size, shape, and intensity of the flame ignition, growth, and extinguishment progression. Thin filament pyrometry is used to estimate time-dependent and time-averaged flame temperature profiles across three heights above the propellant contact interface. The flame temperature linearly decreases with distance above the contact interface for the ignition heights (9–19 mm) studied in this work. The flame temperature is largest near the droplet centerline and nonlinearly decreases in the radial direction as the hypergolic combustion products mix with the surrounding nitrogen. A parametric sensitivity analysis is used to show that mixture ratio, gas velocity, and the convective heat transfer coefficient correlation have minimal effect on the flame temperature estimates. A chemical equilibrium optimization analysis indicates that the O/F mixture ratios are smallest near the flame centerline, nonlinearly increase in the radial direction, and asymptotically approach infinity near the edge of the flame. The results provide important data for quantitative comparison with hypergolic ignition models and future studies of alternative hypergolic propellants of practical interest.