Functional Modelling and Simulation of the Off-Design Operation of a Cryogenic Engine

Abstract: The Exploration Company is a French and German start-up that develops and operates Nyx, an orbital vehicle that also has a lunar version. This thesis focuses on the modeling and simulation of the off-design operation of the cryogenic engine of Nyx. The objectives of the thesis are to create a model on EcosimPro that can accurately model the steady state of the engine and its subsystems and to use it to generate the operating off-design domain. First, a state of the art about the particularity of this study is performed. Indeed, the engine is using electrical pumps (e-pump) and is a LOX/methane engine, which is quite new for rocket engines. The state of the art enables to assess the feasibility of such an engine and to emphasize the challenges associated with those new systems. The advantages of using a cycle with e-pumps with regard to other classical cycles are described and their feasibility is confirmed. An example of such cyle is presented, the Rutherford engine, but using RP-1 as propellant. The problematics associated with methane such as the heat transfer deterioration or the pyrolisis are discussed, and the injection role in combustion stability is discussed. It also introduces the simulation software EcosimPro and assesses its capability to model transient phases and steady states of a rocket engine. A first model is created with components coming from the ESPSS library and is used to study the behavior of the engine when throttling is performed. The heat transfer problem between the chamber and the regenerative cooling system is discussed and the correlations used in the model to calculate the heat transfer coecients are described. The performance maps of the pumps and the way they are implemented in ESPSS are presented and the model of the subsystem is validated. The model used in ESPSS to simulate valves is discussed and compared to the theoretical model. The full 1D model is then used to create a simplified model using correlations and a theoretical model of each subsystem in order to save computation time. The engine parameters are scattered in order to take into account discrepancies between the model and the reality and uncertainties in the manufacturing process, in the regulation or in the measurements. A high number of engines are simulated and the operating domains are generated for the point at 100 % thrust. The domains show that the regulation is well performed and that the engine has a high probability of operating near the nominal point and meeting the requirements in terms of performances. It also enables to show that the subsystems are going to be able to operate within the range desined by the design team.