Combustion instabilities in single and multi-flame systems

Gas turbine engines are an integral part of the global energy production and infrastructure. The ability to rapidly scale their power output makes them an attractive partner to intermittent renewable energy sources, meaning they are likely to retain their importance throughout the energy transition. They are also widely used for propulsion, with their high power to weight ratio, and their fuels’ energy to weight ratio making them difficult to replace for long distance transportation. There has long been a focus to reduce the emission of pollutants such as nitrous oxides (NOx) from gas turbines, but the impending climate crisis means there is a growing need to also eliminate the emission of carbon dioxide (CO2). One promising method of achieving this is to switch from hydrocarbon-based fuels such as natural gas (mainly composed of methane – CH4), to fuel blends composed of increasing proportions of carbon-free fuels such as hydrogen (H2) and ammonia (NH3). However, switching to these fuels is challenging due to substantially different fuel properties. Designing future gas turbine systems that can operate in a fuel-flexible manner, accepting a wide variety of alternative carbon-free fuels is not straightforward, and hindered by our incomplete understanding of these fuels and some important phenomena which occur during their use, including flame stabilization, combustion instabilities, and harmful emissions. In this talk recent experimental work on thermoacoustic instabilities in single flames and annular combustors will be presented, with an emphasis on the careful excitation of modes of interest, and the effects of realistic boundary conditions. Work will also be presented from a simple axially staged combustor, in which the concept of flexible fueling is briefly explored.