Experimental investigations based on a demonstrator unit to analyse the combustion process of a nitrous oxide/ethene premixed green bipropellant
Satellite propulsion systems for orbit- and attitude control mostly operate with Hydrazine as Monopropellant. In respect to the REACH-Regulation there exists a growing demand of propulsion units operating with Green Propellants. Among the different Green Propellants, a very prospective candidate seems to be mixtures of Dinitrogenmonoxide and Carbon Hydrides, also known as Nitrous Oxides Fuel Blends. Within the research for alternative space propellants at the German Aerospace Center (DLR) in Lampoldshausen, a special mixture of Dinitrogenmonoxide and Carbon Hydrides was selected and analysed for further applications in a satellite thruster. The mixture consists of Dinitrogenmonoxide as Oxidizer and Ethene as Fuel. It is a so called premixed Monopropellant, having the advantages of a Bipropellant (high ISP) as well as the advantages of a Monopropellant in respect to the simple propellant tank and feed system. For the design of a thruster operating with this fuel, the aim of DLRs ongoing research activities in this field is the analysis of the whole combustion process as well as the propellant itself. To conduct the combustion and propellant tests a demonstrator unit was designed as well as a tests bench was set up. The demonstrator unit was mounted in the test stand, a measurement and control system was programmed and first tests runs were carried out. The unit consists of an injection and ignition system, several segments to vary the length of the combustion chamber and a nozzle segment. The gaseous Ethene and Nitrous Oxide are mixed in a tube junction of the setup in front of the injection system. The conditioning of the propellant could be realized by different injector systems, an impinging injector, a showerhead injector or a swirl injector for later liquefied gases. To evaluate the heat flux imposed to the combustion chamber wall three thermocouples are implemented in each cylindrical chamber segment, which are positioned at different radial distances to the hot gas side wall surface. The combustion chamber pressure is detected by means of pressure transducers mounted in all segments. The ignition of the Nitrous Oxide/Ethene Fuel could be realized by different ignition systems: A glow plug, an igniter torch using gaseous Hydrogen (H2) and Oxygen (O2) or a spark plug. In a series of tests the occurring chamber pressure, the supply and injection pressure, the wall temperatures and the heat flux on the chamber segments were measured or calculated. During these experiments different N2O/C2H4 mass flow rates as well as varying Oxidizer to Fuel ratios were used. The mass flow rates were adjusted by using several sets of orifices upstream the mixing area in the feeding lines of the test setup. The effective diameter and the corresponding mass flow through the orifices were examined by numerous preliminary tests. To avoid flashback during the test runs a porous material was implemented into the feeding lines upstream of the injector. In addition to the combustion tests, several cold flow tests were carried out. These cold flow tests were used to compare numerical flow simulations of the Nitrous Oxide and Ethene gases with the experimental pressure data.