Experimentelle Untersuchung von Detonations- und Flammensperren für einen vorgemischten, grünen Raketentreibstoff aus Lachgas (N2O) und Ethen (C2H4) Experimental investigation of detonation and flame arrestors used for a premixed, green propellant consisting of nitrous oxide (N2O) and ethylene (C2H4)

Kurzfassung

Hydrazine is one of the major propellants for attitude and orbital control systems in spacecrafts. The handling of hydrazine is difficult due to its high toxicity. There are political efforts in Europe to restrict the use of hydrazine (REACH-Regulation). For this reason, research for environmentally friendly, alternative propellants is conducted. One of those so called “Green Propellants” is a mixture consisting of nitrous oxide (N2O) and ethylene (C2H4), which is under experimental investigation at the Institute for Space Propulsion of the German Aerospace Center (DLR) in Lampoldshausen. In future application, the propellant is intended to be stored premixed and liquefied in a tank combining the advantages of mono and bipropellants. A specific risk of such premixed fuel-oxidizer-mixtures is flashback into the propellant feeding lines. In this case, the flame could flash back into the tank. Such an event would be fatal for the propulsion system of a spacecraft and its whole mission. A particular effort must be made to prevent the occurrence of flashback. This thesis looks at the theoretical models of flame propagation and flashback. Based on this examination and previous experimental test results possible flame arrestors are chosen for further investigations. The flame arrestors consist of porous sintered metal. To investigate their properties, an ignition test bench was built. The test setup consists of two chambers: a cylindrical ignition chamber and a secondary chamber. The cambers are connected and the flame arrestor can be placed in between them. Ignition tests were conducted at a constant oxidizer to fuel ratio and variation of the initial pressure. A selection of the tests was recorded by high-speed camera. The gained data is analyzed, illustrated and discussed. It is shown, that there are porous materials with small pore sizes, for example the GKN’s SIKA-B 30 or SIKA-R 200 from a length longer 10.5 mm and with a diameter of 12.45 mm, can prevent flashback to an initial pressure of 4 bar. Furthermore, experiments were conducted on the quenching ability of orifices with a diameter of 0.3 and 0.5 mm. The critical Peclet numbers at our initial conditions are in the order of 30. High-speed recordings of the ignition show, that the flame in the ignition chamber propagates laminar and the maximum expansion speed of the flame tip is in the order of 60 to 70 m/s. The maximum expansion speed is combined by the laminar burning rate of the flame and a velocity induced by the expansion of the combustion products.