ENGINEERING AND CFD

Researchers at the Chair of Turbomachinery and Flight Propulsion (LTF) at the Technical University Munich numerically investigate flow and combustion in rocket engines using “green” propellants. The current focus involves researching methane/oxygen as a propellant combination, promising to be a good replacement for the commonly used hydrazine, offering good performance, storability, and handling qualities, while also being significantly less toxic. The goal of the project is an improved understanding of the relevant physical processes and a reliable prediction of thermal loads on the combustor. The numerical analysis is accompanied by experimental work conducted at the LTF and integrated into the SFB/TRR-40 (Technological Foundations for the Design of Thermally and Mechanically Highly Loaded Components of Future Space Transportation Systems) funded by the DFG (Deutsche Forschungsgemeinschaft). For the investigation, high-fidelity numerical models are employed to accurately predict the complex underlying turbulence and combustion chemistry. These models are computationally expensive and demand the use of high-performance computer systems.

Resonance Ignition Investigation

While the combination of methane and oxygen has a number of advantages compared to traditional propellants, all “green” bipropellants have the disadvantage of requiring a dedicated ignition system. This is a severe drawback for in-space propulsion applications where reliable ignition has to be ensured over the entire lifetime of the vehicle, often in excess of ten years. Therefore, the LTF investigates resonance ignition methods for integration into a novel methane/oxygen thruster.

In these passive devices, pressurized gas is used for generating oscillating compression shocks and expansion waves, generating heat through irreversible processes. Although the experimental setup is comparatively simple, the fundamental processes influencing and maintaining resonance and heat generation are not well understood. By combining experimental and numerical investigations, these processes were identified and explained, leading to the implementation of models able to predict the performance of resonance ignition devices. With this knowledge, various means of optimization were established with the goal to realize a complete ignition system for integration into a methane/oxygen rocket engine [1].

Rocket Combustor Investigations

The accurate prediction of the heat load on a rocket combustor is essential for the layout of the thermal management system as well as predicting the engine’s lifetime. Investigations of heat transfer characteristics of new propellant combinations are still ongoing. Modelling challenges include combustion and heat release, turbulence and turbulence-chemistry interaction as well as multi-injector flame interaction and flame-wall interaction phenomena, therefore posing a complex multiphysics problem.

Numerical investigations help to acquire insight into the dominating physical processes, but newly developed models need to be validated by experimental results. Figure 2 shows the temperature field predicted for the 7-element lab-scale combustor, which is under numerical and experimental investigation within the SFB/TRR-40. The contour of the stoichiometric mixture fraction is shown in the plot demonstrating individually closed flames for each injector and therefore indicating a weak flame-flame interaction [2].