Spin configurations in Co2FeAl0.4Si0.6 Heusler alloy thin film elements

We determine experimentally the spin structure of half-metallic Co2FeAl0.4Si0.6 Heusler alloy elements using magnetic microscopy. Following magnetic saturation, the dominant magnetic states consist of quasi-uniform configurations, where a strong influence from the magnetocrystalline anisotropy is visible. Heating experiments show the stability of the spin configuration of domain walls in confined geometries up to 800 K. The switching temperature for the transition from transverse to vortex walls in ring elements is found to increase with ring width, an effect attributed to structural changes and consequent changes in magnetic anisotropy, which start to occur in the narrower elements at lower temperatures.Comment: 4 pages, 4 figure

Numerical Analysis of Laser Ignition and Flame Development in a Subscale Combustion Chamber

Methane has never been used as rocket fuel in a flight mission up to now. However, for upper stage engines and long duration scientific missions it can provide beneficial properties compared to the commonly used fuels. Reliable ignition is crucial for the usage of a rocket engine, especially for mission scenarios requiring ignitions at space conditions. Thus, for future use of methane as rocket fuel, detailed knowledge about the flame behavior in methane/oxygen mixtures inside rocket combustion chambers is essential. The goal of this work is to simulate the laser ignition of methane/oxygen-mixtures in an experimental combustion chamber and gain insight in the processes occurring during the ignition phase. Simulations are done using Unsteady Reynolds-averaged Navier-Stokes (URANS) equations. Combustion is modeled using the combined Finite Rate Chemistry/Eddy Dissipation Model (FRC/EDM) and a reduced global four-step chemical reaction mechanism. Simulations are done using a simplified 180°- and the full 3D-geometry of the combustion chamber and injector. The results show sensitivity towards the time of ignition and the geometry used in the simulation

CFD simulation of the ignition of coaxial injected methane and oxygen

The ignition of methane by laser spark in a small combustion chamber has been modelled using CFD-code ANSYS CFX. The numerical simulations were performed in a 2D axisymmetric geometry. Turbulence has been modelled using SST turbulence model while the combustion of methane has been modelled with the help of the combined Eddy Dissipation/Finite Rate Chemistry model and a one-step kinetic mechanism. The numerical results have been compared with the experiments by the pressure inside the combustion chamber. The filling of the combustion chamber with the propellants before the ignition and the stationary combustion in the chamber have been modelled accurately. However the numerical model predicts notably higher pressure peak immediately after the ignition. The reasons of the disagreement with experimental data have been discussed