A PREMIXED GREEN PROPELLANT CONSISTING OF N2O AND C2H4: EXPERIMENTAL ANALYSIS OF QUENCHING DIAMETERS TO DESIGN FLASHBACK ARRESTERS

Abstract

Across the world several so-called green propellants for in-space and orbital propulsion are investigated to replace the highly toxic hydrazine. Aside from green alternatives based on ADN and H2O2, the DLR Institute of Space Propulsion examines a premixed propellant consisting of dinitrogen monoxide (N2O) and ethene (C2H4). The mixture called HyNOx (hydrocarbons mixed with nitrous oxide) offers high performance and low toxicity, but due to the premixed state, the danger of flame flashback across the injection system is a major issue. To avoid flashback during operation of a future engine, suitable flashback arresters are needed; thus, the quenching diameters and corresponding quenching Peclet numbers have to be derived. To analyze the quenching diameters, DLR uses an ignition and flashback test setup. The setup consists of two chambers separated by a fitting for capillaries which serve as flashback arresters. Capillaries with diameters between 0.1 and 0.5 mm were examined regarding their ability to quench the flame. Furthermore, one chamber can be equipped with glass windows to record high-speed videos of the flame propagation process. To obtain the critical quenching Peclet number the ignition pressure was consecutively raised until a flame flashback for a given capillary was observed. The quenching Peclet numbers were calculated according to the gas state at ignition. This resulted in critical Peclet numbers between 30 and 40. Additionally, highspeed videos were recorded to analyze the flame propagation speed during the combustion process. The average flame propagation speed was between 33 m/s for an ignition pressure of 0.49 bar and 40 m/s for an ignition pressure of 1 bar.