Detailed mathematical modelling of transient combustion processes

In many cases ignition has a pivotal influence on the flame front development. The multitude of participating hydrodynamical and thermo-chemical processes cover a very large range of time and space scales. These range from several micrometers to the integral scales of several meters. Thus, it makes the accurate modelling of these parameters particularly important. The proposed numerical Adaptive Pseudo Spectral Method can accurately describe the whole range of time and space scales with only limited discretisation parameters. The main application is focused on ignition and on flame propagation in narrow channels, which is accompanied by versatile effects, which are very sensible to system parameters. Additionally, the method is applied to ignition and flame acceleration in unconfined settings. This example proved an extreme scale difference of underlying process, with strong coupling be- tween underlying processes

Numerical model of Co-Electrolysis in Solid Oxide Cells with Ni/Gd-Doped Ceria (CGO) fuel Electrode

The co-electrolysis of atmospheric carbon dioxide with steam is seen as a potential source of synthesis gas. The electrochemically active electrode area on Ni/Gadolinium-doped ceria (CGO) electrodes extends from triple phase boundary (TPB) between Ni, CGO and gas to the double phase boundary (DPB) between CGO and gas. The proposed numerical model of a commercial electrolyser cell aims to reveal main kinetic mechanisms responsible for the electro-reduction at the Ni/CGO fuel electrode. In order to identify main reaction pathways, electrochemical experiments with two types of fuel electrode were performed: porous CGO and mixed Ni/CGO electrode. In this work preliminary results for a mechanism explaining steam electrolysis at the Ni/CGO electrode are presented

2D transient electro-chemical model of steam electrolysis with Ni/Gd-Doped Ceria (CGO) fuel electrode

The advantages of solid oxide electrolysis cells (SOECs), such as high electrical efficiency and long-term stability, make them a promising candidate for conversion of electrical energy into chemical compounds. The presence of the active double phase boundary (DPB) [1] between CGO surface and gas phase in Ni/Gadolinium doped ceria (CGO) electrodes improves the performance compared to other types of Ni/cermet electrodes, where the active area is limited to the triple phase boundary (TPB) between nickel, oxygen ion conducting ceramics and gas phase. Detailed understanding of underlying physical processes within SOEC in general and within the Ni-CGO fuel electrode in particular is crucial for cell optimisation and understanding of cell degradation. In the current study a 2D dynamic multiphase model of a commercial electrolyser cell is presented. The model spatially resolves cell composite layers as well as the gas channels. The following aspects are included: detailed surface kinetics, charge transport, as well as gas transport/conversion in the channels and porous electrodes. The main accent is made on understanding of electro-chemical processes in the fuel electrode. The model is parametrised and validated by electrochemical impedance measurements of an incremental 1 cm² electrolyte-supported symmetrical cell with Ni-CGO electrodes fueled with different compositions of H2, H2O and N2 [2]. A spatial extension of the model and subsequent validation is successfully done for 16 cm² full cells exhibiting lateral temperature and gas concentration gradients. Furthermore, using this cell model as a building block, the development of a transient 2D model of a SOEC short stack will be discussed in this contribution