PhD Defence Jesse Hofsteenge | Modelling of low-frequency combustion dynamics in hydrogen-blended flames

Modelling of low-frequency combustion dynamics in hydrogen-blended flames

Jesse Hofsteenge is a PhD student in the Department of Thermal Engineering. Promotors are dr.ir. J.B.W. Kok and prof.dr.ir. A.K. Pozarlik from the Faculty of Engineering Technology.

Industrial combustion systems provide essential process heat across many applications, but the shift toward sustainable energy requires adopting carbon-free fuels such as hydrogen and ammonia. Parts of the combustion system require a redesign when switching to other fuels, when it comes to maintain thermal power, efficiency and emissions. A large challenge in the design of a combustion system is avoiding thermoacoustic instabilities. These instabilities form due to a positive feedback loop between the turbulent fluctuations of heat release rate, which radiate sound waves, and the acoustics of the combustion system cavity.

This thesis focuses on numerically predicting thermoacoustics in industrial atmospheric combustion systems, which operate on larger length and time scales than gas turbines. The goal is to better understand their behavior and develop models to predict stability in new designs. Three systems were studied: a 100 kW lab-scale swirl burner, a 1 MW industrial test furnace, and a 100 MW hot blast stove. Fuel- or airflow-forced simulations were used to determine the Flame Transfer Function (FTF). This function describes the flame's acoustic source due to incoming perturbations. In combination with an acoustic model for the rest of the combustion system, the thermoacoustic stability of the system can be predicted.

Results from the lab burner show how hydrogen addition affects the FTF and stability of methane flames. The simulations of the large furnaces demonstrate that methods developed for small systems scale well to industrial sizes. An alternative FTF retrieval method is also tested. This method can calculate the FTF based on a single steady-state simulation, which makes it a viable burner design tool. Overall, the developed methodology allows accurate and efficient characterization of combustion dynamics, supporting the design of stable, sustainable combustion systems.