Numerical Simulations of a Research Thruster operating with N2O/C2H4 and Comparison to Experimental Data
Creators: name:  L. WERLING 
name:   N. PERAKIS 
name:   A. BACHMANN 
name:   T. METHLING 
name:   C. JANZER 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: PROPULSION PHYSICS
FUTURE FUELS

description: Since decades the highly toxic hydrazine is used as propellant for in-space propulsion. During the last years several non-toxic alternatives so called green propellants - were developed. One promising replacement for hydrazine are mono- and bipropellants consisting of nitrous oxide and one or more fuels. The German Aerospace Center (DLR) investigates a propellant consisting of nitrous oxide and ethane in premixed monopropellant configuration as well as conventional bipropellant. In the frame of the research activities several experimental thrusters were developed. The thrusters were used to analyse the heat fluxes to the chamber walls and to evaluate the combustion efficiency depending on parameters as the mixture ratio, chamber pressure or chamber length. Furthermore, a regenerative cooling system for the thruster was developed and successfully tested. In parallel to the experimental work, reaction mechanisms for the combustion of N2O/C2H4 and N2O/C2H6 were developed by DLRs Institute of Combustion Technology. The mechanism for N2O/C2H6 is also capable to model the N2O/C2H4 combustion, this allows direct comparison of both mechanisms. The reaction mechanisms were used to design appropriate flame arresters for the monopropellant operation, to derive laminar flame speeds and are finally used to simulated the whole combustion process inside the rocket combustor. To model the combustion process, the commercial CFD solver Ansys Fluent was used. In sum 3 different basic configurations were simulated: 1) The reaction of premixed N2O/C2H4 by employing the N2O/C2H4 mechanisms in a first combustor, 2) the reaction of premixed N2O/C2H4 by using the N2O/C2H6 mechanisms and 3) the reaction of premixed N2O/C2H6 in a second combustor utilizing the N2O/C2H6 mechanism. As for all cases a large experimental database is available, the results of the simulations could directly be compared to the experimental results. To evaluate the precision and quality of the simulations, the numerical and experimental results for the chamber pressure, thrust and wall heat flux were considered. Two different reaction models were used to simulate the reaction of N2O/C2H4 in the rocket combustion chamber: The Eddy-Dissipation-Concept (EDC) and the Finite-Rate model. Using the EDC, the experimental data of the experiment could not be reproduced. In numerous cases the reaction zone left the combustor during the iterations. Whereas with the Finite-Rate model, the deviation of the simulation from the experiment were in a reasonable range below 1,5 % for the chamber pressure. Furthermore, the use of different turbulence models was evaluated. Several operating points of the thruster were evaluated and could all be reproduced by the CFD-simulations. Special interest lay in the experimental wall heat flux, which was calculated by using a so-called inverse method. By means of the temperature data within the corresponding chamber segment, the wall heat flux was calculated. Due to a high axial heat flux and insufficient temperature data, the wall heat flux could not be calculated for every experiment. In summary, the simulations could capture the experimental heat fluxes with good agreement and the deviations were in the order of 10 %. Based on the obtained findings, the combustion of N2O/C2H6 in a second combustion chamber was simulated. Due to chemical effects in the hereby used reaction mechanism, the simulation only converged by using a transient simulation. The results of these simulations were also in good agreement with the experimental data. The final paper will describe and discuss the obtained results with the different reaction mechanisms and combustors. Furthermore, information about the used solution process and an appropriate model selection will be given.