Research Insights on Hydrogen Peroxide as Film Coolant during the Development of a 200 N Thruster utilizing HIP_11 as Green Hypergolic Propellant

Kurzfassung

Hypergolic storable propellant combinations, which spontaneously ignite upon contact, are commonly used for orbital and attitude control of satellites because do not require external ignition systems and due to their capability to support long mission durations. Conventional hypergolic propellant combinations rely on toxic and carcinogenic substances such as hydrazine and dinitrogen tetroxide. A less toxic alternative is the hypergolic propellant combination HIP_11 developed at the Institute of Space Propulsion at the German Aerospace Center (DLR). The hypergolic propellant combination HIP_11 uses highly concentrated hydrogen peroxide as oxidizer and an ionic liquid based fuel. The hypergolicity of HIP_11 has been demonstrated in drop tests and initial test in engine demonstrators. DLR is currently developing a 200 N thruster utilizing HIP_11 with hydrogen peroxide as film coolant. The present work provides insights on hydrogen peroxide as film coolant as well as the development progress of the 200 N thruster. The literature on film cooling indicates that the combustion chamber pressure, the combustion chamber diameter and thus the contraction ratio of the combustion chamber have a significant influence on the resulting film. The aim of the presented work is to investigate the influence of the mentioned parameters. They are evaluated in hot fire tests using a modular 200 N thruster design. The combustion chamber contraction ratio is varied between 2.5 and 19, the nominal combustion chamber pressure between 3 bar and 22,5 bar, the global mixing ratio between 3.2 and 10 and the film fraction between 0 and 40 % of the total mass flow rate. The tests were conducted at the M11.5 test bench at the Institute of Space Propulsion of the German Aerospace Centre (DLR). It was found that the combustion efficiency is dependent on the mixing ratio of the central injector element. If the combustion chamber contraction ratio is too low and thus the resulting characteristic combustion chamber length is too short, the combustion efficiency drops significantly at high fractions of the film mass flow rate. A plateau in the axial temperature distribution of the combustion chamber wall can be observed. This is linked to the vaporisation of the hydrogen peroxide used as film coolant. The observed boiling temperature depends on the combustion chamber pressure. The boiling plateau at a chamber pressure of 3 bar reaches 156 °C whereas the plateau at 15,2 bar reaches 228 °C. As a result the observed boiling temperatures are above the saturation line of water but below the predictions of the saturation line for pure hydrogen peroxide.