Pressure Drop Measurement of Porous Materials: Flashback Arrestors for a N2O/C2H4 Premixed Green Propellant

Kurzfassung

For more than 50 years hydrazine (N2H4) has been the most favored monopropellant concerning propulsion of satellites or planetary probes. Due to changing political framework (e.g.the REACH regulation), growing commercial pressure as well as the need for non-toxic alternatives, currently several so called "Green Propellants" for replacing hydrazine are under investigation. The most developed and prospective candidates are energetic ionic liquids e.g. ADN-based (LMP-103S/FLP-106) or HAN-based (AFM-315E) propellants. Furthermore the Green propellants like hydrogen peroxide or mixtures of nitrous oxide with hydrocarbons (e.g. NOFBXTM) can offer signifcant advantages compared to classical hydrazine. Aside with ADN-based monopropellants the German Aerospace Center's Institute of Space Propulsion in Lampoldshausen is carrying out research on a nitrous oxide/ethylene (N2O/C2H4) premixed propellant. The benefits of this propellant (high ISP> 300s and low toxicity) are facing several challenges, for example the need for a proper flashback-arrestor and the high combustion temperature (up to 3300K). DLR set up a test bench and designed a combustor to investigate the combustion and ignition behavior of the N2O/C2H4 mixture. One main task handling a premixed propellant is avoiding flashback at ignition, steady state operation or shutdown of the combustor. To prevent flashback the combustion chambers' injections system is equipped with porous elements. Thus when designing future thrusters or injection systems, knowledge of the pressure drop across the porous materials is indispensable. In this paper pressure drop measurements of five different gases with several porous materials will be shown and discussed. The results are compared to the classical Forchheimer model and an empirical fit with improved accuracy for high speed gas flows will be presented.