Regarding the research on alternatives for monopropellant hydrazine, several so called green propellants are currently under investigation or qualification. Aside others, the DLR Institute of Space Propulsion investigates a N 2 O/C 2 H 4 premixed green propellant. During the research activities, flashback from the rocket combustion chamber into the feeding system has been identified as a major challenge when using the propellant mixture. This paper shows the results of ignition experiments conducted in a cylindrical, optical accessible ignition chamber. During the ignition and flame propagation process, pressure, temperature and high-speed video data were collected. The high speed video data were used to analyze the flame propagation speed. The obtained propagation speed was about 20 m/s at ignition, while during further propagation of the flame speeds of up to 120 m/s were measured. Additionally, two different porous materials as flame arresting elements were tested: Porous stainless steel and porous bronze material. For both materials Peclet numbers for flashback were derived. The critical Peclet number for the sintered bronze material was around 20, while for the sintered stainless steel the critical Peclet number seems to be larger than 40. Due to the test results, sintered porous materials seem to be suitable as flashback arresters.
A theoretical screening and experimental characterization of the hypergolicy of different ionic liquids in combination with highly concentrated hydrogen peroxide was conducted. The aim of the investigation was to find a possible alternative hypergolic bipropellant, which substitutes the commonly used hypergolic propellant combinations of hydrazines and dinitrogen tetraoxide.Highly concentrated hydrogen peroxide was chosen as 'green' oxidizer, ionic liquids were chosen as alternative fuels. Ionic liquids offer very low vapor pressures compared to common fuels and this allows simplified handling procedures. The theoretical screening focused on commercially available ionic liquids. Criteria for the selection of ionic liquids included density, melting point, viscosity and theoretical performance calculations. By means of these results 1-butyl-3methylimidazolium acetate (BMIM Ac) was chosen for further investigation. Pure BMIM Ac was tested with the so-called drop test method and did not show a hypergolic behavior with hydrogen peroxide. Hence catalytic transition metals like acetate salts were dissolved in the ionic liquid .With different concentrations of copper (II) acetate hypergolic ignition was archived. The ignition delay time is in the order of several 100 milliseconds.
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