Abstract
The hypergolic interactions between monomethylhydrazine (MMH, CH 3NHNH 2) and various forms of nitric acid were studied by several different experimental techniques. High-speed videos were acquired to visualize the pre-ignition, ignition and post-ignition events when a fuel drop impinged on a pool of nitric acid. A three-stage process was identified in the temperature profiles obtained from drop tests using Al 2O 3 coated fine-wire thermocouples placed in both the liquid-phase and gas-phase regions. The temperature rose rapidly from ambient levels to the boiling point in the first stage, from the boiling point to 280 °C relatively slowly in the second stage and from 280 °C to a flame temperature very rapidly in the third stage. The gaseous species evolved from reactions between MMH and nitric acid in these three stages were probed by a confined-interaction setup, in conjunction with rapid-scan Fourier transform infrared (FTIR) spectroscopy and time-of-flight mass spectrometry (ToFMS). The first stage involved liquid-phase reactions which formed the ionic compound monomethylhydrazinium nitrate (MMH·HNO 3), as well as oxidation products methyl nitrate (CH 3ONO 2), methyl azide (CH 3N 3), N 2O, H 2O and N 2. The second stage involved the formation of an aerosol cloud which was mainly composed of monomethylhydrazinium nitrate. The third stage involved rapid gas-phase reactions leading to ignition. These third-stage reactions were initiated by the thermal decomposition of nitric acid, and the identified species in this stage include H 2O, HONO, CH 3ONO 2, CH 3ONO, CH 3N 3, CH 3OH, CH 3NH 2, CH 4, N 2O, NO, N 2, and small amounts of HNCO, NH 3, HCN and CO 2. Some important pre-ignition reactions are proposed for both liquid and gas phases.
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