Simulation of bi-propellant reaction control thrusters based on nitrous oxide and hydrocarbons

Kurzfassung

In order to replace hydrazin-driven reaction control systems widely used on satellites, a number of promising alternatives are under developments, that are usually referred to as ``green propellants''. In recent years many thrusters and propulsion hardware has been developed, as e.g. by the German Aerospace Center [4] or by Politecnico di Milano [2]. One promising candidate [3] is the bi-propellant combination of nitrous oxide and hydrocarbons. This is the focus of this investigation as this propellant choice is investigated by several groups. First commercial thrusters have been build e.g. by Dawn Aerospace. One advantage of this fuel/oxidizer combination is that the both gases are self-pressurant and it can be as well used as mono-propellants at a lower specific impulse (ISP). This is an advantage for the design of the propulsion system on satellites. The focus of previous publications was mostly on the development of the the propulsion characteristics as well as raising the technology readiness level of such green-propellant thruster systems. Limited work was spent until now on setting up a detailed numerical model other than characterizing the thruster and raising the ISP of the thruster, as e.g. in [3]. Still missing is a detailed simulation model which would allow the simulation of steady-state and transient operating conditions, i.e. during startup and shutdown. Due to the preferred usage as reaction control thrusters, its operation characterized by small impulse bits with potential non-optimal conditions during the transient phases. This might raise potential issues due to contamination concerns on many planetary missions. A first experimental study at DLR [1] using a propene - nitrous oxide thruster of Dawn Aerospace showed potential contamination effects especially during the startup and shutdown of the thruster. This supports the necessity of having a numerical model of the green-propellant thruster available to simulate the transient phases. In this contribution we describe a numerical model for a representative small-scale reaction thruster developed in Lampoldshausen [4] based on ethane and nitrous oxide as fluid combination. The numerical model is derived from the choice of suitable kinetic reaction mechanisms to the application of this model using a simulation of the combustion chamber including the nozzle at ambient conditions. Results for the choice of suitable reaction mechanisms as well as steady-state thruster computations will be presented. The numerical model will be developed further towards transient operation conditions for which contamination effects potentially will play a significant role. [1] Leonie Johanna Buntrock, Martin Grabe, and Holger Fischer. Contamination assessment of a freely expanding green propellant thruster plume. In IOP Conference Series: Materials Science and Engineering, volume 1287, page 012004. IOP Publishing, 2023. [2] Stefania Carlotti and Filippo Maggi. Evaluating new liquid storable bipropellants: Safety and performance assessments. Aerospace, 9(10):561, 2022. [3] Lukas Werling and Patrick Bätz. Parameters influencing the characteristic exhaust velocity of a nitrous oxide/ethene green propellant. Journal of Propulsion and Power, 38(2):254--266, 2022. [4] Lukas Werling, Felix Lauck, Julian Dobusch, Marc Andre Gritzka, Vincent Stratmann, Florian Merz, Till Hörger, Philipp Jan Teuffel, and Luca Braune. From lampoldshausen to space: Dlr spin-off inspacepropulsion technologies and the development status of green propellant thrusters based on h2o2 and n2o. 2023.