Numerical studies of flame stabilization relevant to gas turbine engines using methane and e-fuels
Time: Thu 2021-11-25 10.00
Subject area: Engineering Mechanics
Doctoral student: Yazhou Shen , Strömningsmekanik och Teknisk Akustik
Opponent: Professor Benoit Fiorina, Ecole Centrale Paris, Frankrike
Supervisor: Assoc. Prof. Christophe Duwig, Processteknologi
The current society undergoes a global energy transformation from fossil fuels to renewable energy. The alternative energy sources to fossil fuels are key factors to accelerate the transition towards a sustainable energy system. Among those, electrofuels (e-fuels) is a promising group that remarkably benefits overall carbon neutrality. However, how to utilize the e-fuels remains challenging. Gas turbines are widely used to convert the chemical bond energy into mechanical power or electricity. In the fuel-lean swirling premixed combustion widely used in current gas turbine engines, issues such as flame instability and pollutant emissions hinder the use of e-fuels. The development of advanced combustion strategies befitting e-fuels is therefore of great importance. Among those, wet combustion is a promising one featuring elevated efficiency and low pollutant emissions. Swirling flame is a challenging topic due to the turbulence-chemistry interaction that governs its dynamics. Numerical simulation is a valuable tool which enables us to gain insight into the details of the physics and chemical kinetics. The present work focuses on the numerical investigation of wet flames using e-fuels, relevant to practical gas turbine applications. Real applications are typically characterised by more complex geometry, and thus a more complicated flow/flame dynamics. By means of Large Eddy Simulations with finite rate chemistry, the high turbulence flow field and flame structure are studied and validated by experimental data. The advanced post-processing tools such as Proper Orthogonal Decomposition (POD) and Chemical Explosive Mode Analysis (CEMA) are performed to extract the featured information. The combination of different analysis methods enhance the understanding of swirling flame dynamics and its relation with flame stabilisation mechanism. The main contributions of this thesis to the field are highlighted as followed. First, an enhanced understanding on the coherent structure in the swirling flame/flow is achieved. In the swirling flow issued from the multi-jet LDI swirler, it is found that the global dynamics are governed by the single and double helical PVC, which is also harmonically associated with the distinctive connection between the outer recirculation zone and the central recirculation zone. In the PRECCINSTA burner, the helical vortex breakdown featured by the triple-helix modes plays an importance role in the combustion dynamics under the quiet conditions. Second, this thesis shows the feasibility of the wet combustion using efuels involving ammonia and methanol. The effect of fuel decomposition and steam addition on the flame characteristics and pollutant v emission are quantitatively studied. A deeper comprehension regarding the associated flame stabilisation mechanism and its coherence with flow dynamics is established. It is found that when flame is distributed, single helix PVC remains dominating the flow and flame dynamics while double helix modes appears due to the reactivity weakening. Meanwhile, autoignition becomes more dominant globally in the ignition process, accompanied by the emergence of high temperature reactions. The improved understandings are expected to guide novel and clean applications of e-fuels in gas turbine engines that are beneficial for the sustainable development of our society.